U.S. patent application number 10/697399 was filed with the patent office on 2004-08-19 for methods of optimizing antibody variable region binding affinity.
Invention is credited to Huse, William D., Marquis, David, Smith, Eric, Vasserot, Alain P., Watkins, Jeffry D..
Application Number | 20040162413 10/697399 |
Document ID | / |
Family ID | 26856186 |
Filed Date | 2004-08-19 |
United States Patent
Application |
20040162413 |
Kind Code |
A1 |
Watkins, Jeffry D. ; et
al. |
August 19, 2004 |
Methods of optimizing antibody variable region binding affinity
Abstract
The present invention provides optimized heteromeric variable
region binding fragments and antibodies comprising optimized
heteromeric variable region binding fragments. Preferably, the
optimized heteromeric variable region binding fragments exhibit
optimized activity compared to donor heteromeric variable regions
and have unvaried human frameworks. The present invention also
provides methods of making the optimized heteromeric variable
region binding fragments.
Inventors: |
Watkins, Jeffry D.;
(Encinitas, CA) ; Huse, William D.; (Del Mar,
CA) ; Vasserot, Alain P.; (Carlsbad, CA) ;
Marquis, David; (Encinitas, CA) ; Smith, Eric;
(San Diego, CA) |
Correspondence
Address: |
Jason R. Bond
MEDLEN & CARROLL, LLP
Suite 350
101 Howard Street
San Francisco
CA
94105
US
|
Family ID: |
26856186 |
Appl. No.: |
10/697399 |
Filed: |
October 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10697399 |
Oct 30, 2003 |
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10110141 |
Oct 29, 2002 |
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10110141 |
Oct 29, 2002 |
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PCT/US00/28435 |
Oct 13, 2000 |
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10110141 |
Oct 29, 2002 |
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09434870 |
Nov 4, 1999 |
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10697399 |
Oct 30, 2003 |
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09434870 |
Nov 4, 1999 |
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60159689 |
Oct 14, 1999 |
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60159689 |
Oct 14, 1999 |
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Current U.S.
Class: |
530/387.3 ;
435/328 |
Current CPC
Class: |
C07K 16/465 20130101;
C07K 2317/55 20130101; C07K 2317/24 20130101; C07K 2317/56
20130101; C07K 16/00 20130101; C07K 16/464 20130101; C07K 2317/92
20130101; C07K 16/2878 20130101; C07K 16/36 20130101 |
Class at
Publication: |
530/387.3 ;
435/328 |
International
Class: |
C07K 016/44; C12N
005/06 |
Claims
What is claimed is:
1. A heteromeric variable region having higher antigen binding
affinity than a donor heteromeric variable region, wherein said
donor heteromeric variable region comprises three light chain donor
CDRs and three heavy chain donor CDRs, and wherein said heteromeric
variable region comprises: a) a light chain altered variable region
comprising; i) four unvaried human germline light chain framework
regions, wherein three of said four unvaried human germline light
chain framework regions are from a human kappa light chain gene
selected from the group consisting of: A11, A17, A18, A19, A20,
A27, A30, L1, L11, L12, L2, L5, L6, L8, O12, O2, and O8; and ii)
three light chain altered variable region CDRs, wherein at least
one of said three light chain altered variable region CDRs is a
light chain donor CDR variant, and wherein said light chain donor
CDR variant comprises a different amino acid at only one, two,
three or four positions compared to one of said three light chain
donor CDRs, and b) a heavy chain altered variable region
comprising; i) four unvaried human germline heavy chain framework
regions, wherein three of the four unvaried human germline heavy
chain framework regions are from a human heavy chain gene selected
from the group consisting of: VH2-5, VH2-26, VH2-70, VH3-20,
VH3-72, VH1-46, VH3-9, VH3-66, VH3-74, VH4-31, VH1-18, VH1-69,
VH3-7, VH3-11, VH3-15, VH3-21, VH3-23, VH3-30, VH3-48, VH4-39,
VH4-59, and VH5-51; and, ii) three heavy chain altered variable
region CDRs, wherein at least one of said three heavy chain altered
variable region CDRs is a heavy chain donor CDR variant, and
wherein said heavy chain donor CDR variant comprises a different
amino acid at only one, two, three, or four positions compared to
one of said three heavy chain donor CDRs.
2. The heteromeric variable region of claim 1, wherein one of said
three light chain altered variable region CDRs is identical to one
of said three light chain donor CDRs.
3. The heteromeric variable region of claim 1, wherein two of said
three light chain altered variable region CDRs are each identical
to one of said three light chain donor CDRs.
4. The heteromeric variable region of claim 1, wherein one of said
three heavy chain altered variable region CDRs is identical to one
of said three heavy chain donor CDRs.
5. The heteromeric variable region of claim 1, wherein two of said
three heavy chain altered variable region CDRs are each identical
to one of said three light chain donor CDRs.
6. The heteromeric variable region of claim 1, wherein at least two
of said three light chain altered variable region CDRs are light
chain donor CDR variants.
7. The heteromeric variable region of claim 1, wherein three of
said three light chain altered variable region CDRs are light chain
donor CDR variants.
8. The heteromeric variable region of claim 1, wherein at least two
of said three heavy chain altered variable region CDRs are heavy
chain donor CDR variants.
9. The heteromeric variable region of claim 1, wherein three of
said three heavy chain altered variable region CDRs are heavy chain
donor CDR variants.
10. The heteromeric variable region of claim 1, wherein said donor
heteromeric variable region is murine.
11. The heteromeric variable region of claim 1, wherein said higher
antigen binding affinity is at least 2-fold higher than the
affinity of said donor heteromeric variable region.
12. The heteromeric variable region of claim 1, wherein said higher
antigen binding affinity is at least 3-fold higher than the
affinity of said donor heteromeric variable region.
13. A method of expressing a heteromeric variable region having
higher antigen binding affinity than a donor heteromeric variable
region, wherein said donor heteromeric variable region comprises
three light chain donor CDRs and three heavy chain donor CDRs, and
wherein said method comprises; a) providing; i) a first
oligonucleotide encoding an altered light chain variable region,
wherein said altered light chain variable region comprises: A) four
unvaried human germline light chain framework regions, wherein
three of said four unvaried human germline light chain framework
regions are from a human kappa light chain gene selected from the
group consisting of: A11, A17, A18, A19, A20, A27, A30, L1, L11,
L12, L2, L5, L6, L8, O12, O2, and O8; and B) three light chain
altered variable region CDRs, wherein at least one of said three
light chain altered variable region CDRs is a light chain donor CDR
variant, and wherein said light chain donor CDR variant comprises a
different amino acid at only one, two, three or four positions
compared to one of said three light chain donor CDRs, and ii) a
second oligonucleotide encoding an altered heavy chain variable
region, wherein said altered heavy chain variable region comprises;
A) four unvaried human germline heavy chain framework regions,
wherein three of the four unvaried human germline heavy chain
framework regions are from a human heavy chain gene selected from
the group consisting of: VH2-5, VH2-26, VH2-70, VH3-20, VH3-72,
VH1-46, VH3-9, VH3-66, VH3-74, VH4-31, VH1-18, VH1-69, VH3-7,
VH3-11, VH3-15, VH3-21, VH3-23, VH3-30, VH3-48, VH4-39, VH4-59, and
VH5-51; and B) three heavy chain altered variable region CDRs,
wherein at least one of said three heavy chain altered variable
region CDRs is a heavy chain donor CDR variant, and wherein said
heavy chain donor CDR variant comprises a different amino acid at
only one, two, three, or four positions compared to one of said
heavy chain donor CDRs, and b) expressing said first and second
oligonucleotides under conditions such that a heteromeric variable
region binding fragment is generated that exhibits higher antigen
binding affinity than said donor heteromeric variable region.
14. The method of claim 13, wherein said expressing is
coexpressing.
15. The method of claim 13, wherein said higher antigen binding
affinity is at least 2-fold higher than the affinity of said donor
heteromeric variable region.
16. The method of claim 13, wherein said higher antigen binding
affinity is at least 3-fold higher than the affinity of said donor
heteromeric variable region.
17. A method of expressing a heteromeric variable region having
higher antigen binding affinity than a donor heteromeric variable
region, wherein said donor heteromeric variable region comprises
three light chain donor CDRs and three heavy chain donor CDRs, said
method comprising; a) providing; i) first oligonucleotides encoding
four unvaried human germline light chain framework regions, wherein
three of said four unvaried human germline light chain framework
regions are from a human kappa light chain gene selected from the
group consisting of: A11, A17, A18, A19, A20, A27, A30, L1, L11,
L12, L2, L5, L6, L8, O12, O2, and O8; ii) a population of second
oligonucleotides encoding: A) first light chain CDRs, wherein said
first light chain CDRs comprise donor CDR variants, wherein said
donor CDR variants comprise a different amino acid at only one,
two, three or four positions compared to one of said three light
chain donor CDRs, B) second light chain CDRs, wherein said second
light chain CDRs encode each of said three light chain donor CDRs;
iii) third oligonucleotides encoding four unvaried human germline
heavy chain framework regions, wherein three of the four unvaried
human germline heavy chain framework regions are from a human heavy
chain gene selected from the group consisting of: VH2-5, VH2-26,
VH2-70, VH3-20, VH3-72, VH1-46, VH3-9, VH3-66, VH3-74, VH4-31,
VH1-18, VH1-69, VH3-7, VH3-11, VH3-15, VH3-21, VH3-23, VH3-30,
VH3-48, VH4-39, VH4-59, and and VH5-51; and iv) a population of
fourth oligonucleotides encoding: A) first heavy chain CDRs,
wherein said first heavy chain CDRs comprise donor CDR variants,
wherein said donor CDR variants comprise a different amino acid at
only one, two, three or four positions compared to one of said
three heavy chain donor CDRs, and B) second heavy chain CDRs,
wherein said second heavy chain CDRs encode each of said three
heavy chain donor CDRs; b) mixing said first oligonucleotides and
said population of second oligoncucleotides such that a population
of fifth oligonucleotides encoding light chain variable regions is
generated, wherein at least one of said light chain variable
regions encoded by said population of fifth oligonucleotides
comprises i) an unvaried human germline light chain framework, and
ii) at least one light chain donor CDR variant; c) mixing said
third oligonucleotides and said population of fourth
oligonucleotides such that a population of sixth oligonucleotides
encoding heavy chain variable regions is generated, wherein at
least one of said heavy chain variable regions encoded by said
population of sixth oligonucleotides comprises; i) an unvaried
human germline heavy chain framework, and ii) at least one heavy
chain donor CDR variant; and d) expressing said fifth and sixth
populations of oligonucleotides to produce combinations of
heteromeric variable region binding fragments.
18. The method of claim 17, further comprising step e) identifying
at least one heteromeric variable region having higher antigen
binding affinity than said donor heteromeric variable region.
19. The method of claim 17, wherein said unvaried human germline
light chain framework regions comprises FR1, FR2, FR3 and FR4
regions configured to hybridize to said light chain donor CDRs and
said light chain donor CDR variants such that said population of
fifth oligonucleotides encoding light chain variable regions is
generated.
20. The method of claim 17, wherein said unvaried human germline
heavy chain framework regions comprises FR1, FR2, FR3 and FR4
regions configured to hybridize to said heavy chain donor CDRs and
said heavy chain donor CDR variants such that said population of
fifth oligonucleotides encoding heavy chain variable regions is
generated.
Description
[0001] The present Application is a Continuation-in-part of U.S.
application Ser. No. 10/110,141, filed Apr. 9, 2002, which is a
U.S. National Stage Entry of International Application Serial
Number PCT/US00/28435 filed Oct. 13, 2000, which is a
Continuation-in-part of both U.S. application Ser. No. 09/434,870,
filed Nov. 4, 1999, and U.S. Provisional Application Serial No.
60/159,689, filed Oct. 14, 1999. The present Application is also a
Continuation-in-part of U.S. application Ser. No. 09/434,870, filed
Nov. 4, 1999, which claims priority to U.S. Provisional Application
60/159,689, filed Oct. 14, 1999.
FIELD OF THE INVENTION
[0002] The present invention provides optimized heteromeric
variable region binding fragments and antibodies comprising
optimized heteromeric variable region binding fragments.
Preferably, the optimized heteromeric variable region binding
fragments exhibit optimized activity compared to donor heteromeric
variable regions and have unvaried human frameworks. The present
invention also provides methods of making the optimized heteromeric
variable region binding fragments.
BACKGROUND OF THE INVENTION
[0003] The war on cancer is entering its third decade and recent
years have shown tremendous progress in the understanding of cancer
development and progression yet there has been only marginal
decreases in death rates from most types of cancer. Standard
chemotherapy and radiation therapy generally involve treatment with
therapeutic agents that impact not only cancer cells but other
highly proliferative cells of the body, often leading to
debilitating side effects. Thus, it is desirable to identify
therapeutic agents with a higher degree of specificity for the
carcinogenic lesion.
[0004] The discovery of monoclonal antibodies (mAbs) in the 1970's
provided great hope for the reality of creating therapeutic
molecules with high specificity. Antibodies that bind to tumor
antigens would provide specific targeting agents for cancer
therapy. However, while the development of monoclonal antibodies
has provided a valuable diagnostic reagent, certain limitations
restrict their use as therapeutic entities.
[0005] A limitation encountered when attempts are made to use mAbs
as therapeutic agents is that since mAbs are developed in non-human
species, usually mouse, they elicit an immune response in human
patients. Chimeric antibodies join the variable region of the
non-human species, which confers binding activity, to a human
constant region. However, the chimeric antibody is often still
immunogenic and it is therefore necessary to further modify the
variable region.
[0006] One modification is the grafting of
complementarity-determining regions, (CDRs) which in part antigen
binding onto a human antibody variable framework. However, this
approach is imperfect because CDR grafting often diminishes the
binding activity of the resulting humanized mAb. Attempts to regain
binding activity require laborious, step-wise procedures which have
been pursued essentially by a trial and error type of approach. For
example, one difficulty in regaining binding affinity is because it
is difficult to predict which framework residues serve a critical
role in maintaining antigen binding affinity and specificity.
Consequently, while antibody humanization methods that rely on
structural and homology data are used, the complexity that arises
from the large number of framework residues potentially involved in
binding activity has prevented success.
[0007] Combinatorial methods have been applied to restore binding
affinity, however, these methods require sequential rounds of
mutagenesis and affinity selection that can both be laborious and
unpredictable.
[0008] Thus, there exists a need for efficient and reliable methods
for producing human monoclonal antibodies which exhibit comparable
or enhanced binding affinities to their non-human counterparts. The
present invention satisfies this need and provides related
advantages as well.
SUMMARY OF THE INVENTION
[0009] The present invention provides optimized heteromeric
variable region binding fragments and antibodies comprising
optimized heteromeric variable region binding fragments.
Preferably, the optimized heteromeric variable region binding
fragments exhibit optimized activity compared to donor heteromeric
variable regions and have unvaried human frameworks. The present
invention also provides methods of making the optimized heteromeric
variable region binding fragments.
[0010] In some embodiments, the present invention provides an
optimized heteromeric variable region (e.g. that may or may not be
part of a full antibody other molecule) having an optimized
activity such as higher antigen binding affinity than a donor
heteromeric variable region, wherein the donor heteromeric variable
region comprises three light chain donor CDRs, and wherein the
optimized heteromeric variable region comprises: a) a light chain
altered variable region comprising; i) four unvaried (e.g.,
unvaried human, bovine, canine, feline, porcine, etc.) germline
light chain framework regions, and ii) three light chain altered
variable region CDRs, wherein at least one of the three light chain
altered variable region CDRs is a light chain donor CDR variant,
and wherein the light chain donor CDR variant comprises a different
amino acid at only one, two, three or four positions compared to
one of the three light chain donor CDRs (e.g. the at least one
light chain donor CDR variant is identical to one of the light
chain donor CDRs except for one, two, three or four amino acid
differences). In further embodiments, the optimized heteromeric
variable region comprises a heavy chain variable region. In certain
embodiments, three of the four unvaried human germline light chain
framework regions are from a human kappa light chain gene selected
from the group consisting of: A11, A17, A18, A19, A20, A27, A30,
L1, L11, L12, L2, L5, L6, L8, O12, O2, and O8.
[0011] In other embodiments, the present invention provides an
optimized heteromeric variable region (e.g. that may or may not be
part of a full antibody other molecule) having an optimized
activity, such as higher antigen binding affinity than a donor
heteromeric variable region, wherein the donor heteromeric variable
region comprises three heavy chain donor CDRs, and wherein the
optimized heteromeric variable region comprises: a) a heavy chain
altered variable region comprising; i) four unvaried (e.g.,
unvaried human, bovine, canine, feline, porcine, etc.) germline
heavy chain framework regions, and ii) three heavy chain altered
variable region CDRs, wherein at least one of the three heavy chain
altered variable region CDRs is a heavy chain donor CDR variant,
and wherein the heavy chain donor CDR variant comprises a different
amino acid at only one, two, three or four positions compared to
one of the three heavy chain donor CDRs (e.g. the at least one
heavy chain donor CDR variant is identical to one of the heavy
chain donor CDRs except for one, two, three or four amino acid
differences). In further embodiments, the optimized heteromeric
variable region comprises a light chain variable region. In other
embodiments, three of the four unvaried human germline heavy chain
framework regions are from a human heavy chain gene selected from
the group consisting of: VH2-5, VH2-26, VH2-70, VH3-20, VH3-72,
VH1-46, VH3-9, VH3-66, VH3-74, VH4-31, VH1-18, VH1-69, VH3-7,
VH3-11, VH3-15, VH3-21, VH3-23, VH3-30, VH3-48, VH4-39, VH4-59, and
VH5-51.
[0012] In additional embodiments, the present invention provides an
optimized heteromeric variable region (e.g. that may or may not be
part of a full antibody molecule) having an optimized activity such
as higher antigen binding affinity than a donor heteromeric
variable region, wherein the donor heteromeric variable region
comprises three light chain donor CDRs and three heavy chain donor
CDRs, and wherein the optimized heteromeric variable region
comprises: a) a light chain altered variable region comprising; i)
four unvaried (e.g., unvaried human, bovine, canine, feline,
porcine, etc.) germline light chain framework regions, and ii)
three light chain altered variable region CDRs, wherein at least
one of the three light chain altered variable region CDRs is a
light chain donor CDR variant, and wherein the light chain donor
CDR variant comprises a different amino acid at only one, two,
three or four positions compared to one of the three light chain
donor CDRs, and b) a heavy chain altered variable region
comprising; i) four unvaried (e.g., unvaried human, bovine, canine,
feline, porcine, etc.) gernline heavy chain framework regions, and
ii) three heavy chain altered variable region CDRs, wherein at
least one of the three heavy chain altered variable region CDRs is
a heavy chain donor CDR variant, and wherein the heavy chain donor
CDR variant comprises a different amino acid at only one, two,
three, or four positions compared to one of the three heavy chain
donor CDRs.
[0013] In certain embodiments, three of the four unvaried germline
light chain framework regions (e.g. FRL1, FRL2, and FRL3) are from
a human kappa light chain gene selected from the group consisting
of: A11, A17, A18, A19, A20, A27, A30, L1, L11, L12, L2, L5, L6,
L8, O12, O2, and O8. In other embodiments, three of the four
unvaried human germline heavy chain framework regions (e.g. FRH1,
FRH2, and FRH3) are from a human heavy chain gene selected from the
group consisting of: VH2-5, VH2-26, VH2-70, VH3-20, VH3-72, VH1-46,
VH3-9, VH3-66, VH3-74, VH4-31, VH1-18, VH1-69, VH3-7, VH3-11,
VH3-15, VH3-21, VH3-23, VH3-30, VH3-48, VH4-39, VH4-59, and VH5-51.
In some embodiments, the optimized heteromeric variable region
binding fragment is capable of binding von Willebrand Factor (vWF)
or other protein involved with human disease.
[0014] In additional embodiments, the present invention provides an
antibody comprising an optimized heteromeric variable region with
optimized activity such as having higher antigen binding affinity
than a donor heteromeric variable region, wherein the donor
heteromeric variable region comprises three light chain donor CDRs
and three heavy chain donor CDRs, and wherein the optimized
heteromeric variable region comprises: a) a light chain altered
variable region comprising; i) four unvaried (e.g., unvaried human,
bovine, canine, feline, porcine, etc.) germline light chain
framework regions, and ii) three light chain altered variable
region CDRs, wherein at least one of the three light chain altered
variable region CDRs is a light chain donor CDR variant, and
wherein the light chain donor CDR variant comprises a different
amino acid at only one, two, three or four positions compared to
one of the three light chain donor CDRs, and b) a heavy chain
altered variable region comprising; i) four unvaried (e.g.,
unvaried human, bovine, canine, feline, porcine, etc.) germline
heavy chain framework regions, and ii) three heavy chain altered
variable region CDRs, wherein at least one of the three heavy chain
altered variable region CDRs is a heavy chain donor CDR variant,
and wherein the heavy chain donor CDR variant comprises a different
amino acid at only one, two, three, or four positions compared to
one of the three heavy chain donor CDRs. In some embodiments, the
antibody further comprises a C.sub.L region and a C.sub.1 region.
In other embodiments, the antibody further comprises an Fc region.
In certain embodiments, the antibody further comprises a second
heteromeric variable region binding fragment (e.g. an optimized
heteromeric variable region binding fragment). In certain
embodiments, the donor heteromeric variable region is non-human
(e.g. rat, mouse, monkey, etc.) and the unvaried light and heavy
chain frameworks are human.
[0015] In some embodiments, the present invention provides methods
of expressing a heteromeric variable region (which may or may not
be part of a larger molecule such an antibody) with optimized
activity such as having higher antigen binding affinity than a
donor heteromeric variable region, wherein the donor heteromeric
variable region comprises three light chain donor CDRs and three
heavy chain donor CDRs, and wherein the method comprises; a)
providing; i) a first oligonucleotide encoding an altered light
chain variable region, wherein the altered light chain variable
region comprises: A) four unvaried human germline light chain
framework regions, wherein three of the four unvaried human
germline light chain framework regions are from a human kappa light
chain gene selected from the group consisting of: A11, A17, A18,
A19, A20, A27, A30, L1, L11, L12, L2, L5, L6, L8, O12, O2, and O8;
and B) three light chain altered variable region CDRs, wherein at
least one of the three light chain altered variable region CDRs is
a light chain donor CDR variant, and wherein the light chain donor
CDR variant comprises a different amino acid at only one, two,
three or four positions compared to one of the three light chain
donor CDRs, and ii) a second oligonucleotide encoding an altered
heavy chain variable region, wherein the altered heavy chain
variable region comprises; A) four unvaried human germline heavy
chain framework regions, wherein three of the four unvaried human
germline heavy chain framework regions are from a human heavy chain
gene selected from the group consisting of: VH2-5, VH2-26, VH2-70,
VH3-20, VH3-72, VH1-46, VH3-9, VH3-66, VH3-74, VH4-31, VH1-18,
VH1-69, VH3-7, VH3-11, VH3-15, VH3-21, VH3-23, VH3-30, VH3-48,
VH4-39, VH4-59, and VH5-51; and B) three heavy chain altered
variable region CDRs, wherein at least one of the three heavy chain
altered variable region CDRs is a heavy chain donor CDR variant,
and wherein the heavy chain donor CDR variant comprises a different
amino acid at only one, two, three, or four positions compared to
one of the heavy chain donor CDRs, and b) expressing the first and
second oligonucleotides under conditions such that a heteromeric
variable region binding fragment is generated that exhibits higher
antigen binding affinity than the donor heteromeric variable
region.
[0016] In additional embodiments, the present invention provides
methods of expressing a heteromeric variable region having higher
antigen binding affinity (or other optimized activity) than a donor
heteromeric variable region, wherein the donor heteromeric variable
region comprises three light chain donor CDRs and three heavy chain
donor CDRs, the method comprising; a) providing; i) first
oligonucleotides encoding four unvaried human germline light chain
framework regions, wherein three of the four unvaried human
germline light chain framework regions are from a human kappa light
chain gene selected from the group consisting of: A11, A17, A18,
A19, A20, A27, A30, L1, L11, L12, L2, L5, L6, L8, O12, O2, and O8;
ii) a population of second oligonucleotides encoding: A) first
light chain CDRs, wherein the first light chain CDRs comprise donor
CDR variants, wherein the donor CDR variants comprise a different
amino acid at only one, two, three or four positions compared to
one of the three light chain donor CDRs, B) second light chain
CDRs, wherein the second light chain CDRs encode each of the three
light chain donor CDRs; iii) third oligonucleotides encoding four
unvaried human germline heavy chain framework regions, wherein
three of the four unvaried human germline heavy chain framework
regions are from a human heavy chain gene selected from the group
consisting of: VH2-5, VH2-26, VH2-70, VH3-20, VH3-72, VH1-46,
VH3-9, VH3-66, VH3-74, VH4-31, VH1-18, VH1-69, VH3-7, VH3-11,
VH3-15, VH3-21, VH3-23, VH3-30, VH3-48, VH4-39, VH4-59, and VH5-51;
and iv) a population of fourth oligonucleotides encoding: A) first
heavy chain CDRs, wherein the first heavy chain CDRs comprise donor
CDR variants, wherein the donor CDR variants comprise a different
amino acid at only one, two, three or four positions compared to
one of the three heavy chain donor CDRs, and B) second heavy chain
CDRs, wherein the second heavy chain CDRs encode each of the three
heavy chain donor CDRs; b) mixing the first oligonucleotides and
the population of second oligoncucleotides such that a population
of fifth oligonucleotides encoding light chain variable regions is
generated, wherein at least one of the light chain variable regions
encoded by the population of fifth oligonucleotides comprises i) an
unvaried human germline light chain framework, and ii) at least one
light chain donor CDR variant; c) mixing the third oligonucleotides
and the population of fourth oligonucleotides such that a
population of sixth oligonucleotides encoding heavy chain variable
regions is generated, wherein at least one of the heavy chain
variable regions encoded by the population of sixth
oligonucleotides comprises; i) an unvaried human germline heavy
chain framework, and ii) at least one heavy chain donor CDR
variant; and d) expressing the fifth and sixth populations of
oligonucleotides to produce combinations of heteromeric variable
region binding fragments. In other embodiments, the method further
comprises step e) identifying at least one heteromeric variable
region having higher antigen binding affinity than the donor
heteromeric variable region.
[0017] In some embodiments, the unvaried human germline light chain
framework regions comprises FR1, FR2, FR3 and FR4 regions
configured to hybridize to the light chain donor CDRs and the light
chain donor CDR variants such that the population of fifth
oligonucleotides encoding light chain variable regions is
generated. In other embodiments, the unvaried human germline heavy
chain framework regions comprise FR1, FR2, FR3 and FR4 regions
configured to hybridize to the heavy chain donor CDRs and the heavy
chain donor CDR variants such that the population of fifth
oligonucleotides encoding heavy chain variable regions is
generated.
[0018] In other embodiments, one of the three light chain altered
variable region CDRs is identical to one of the three light chain
donor CDRs. In some embodiments, two of the three light chain
altered variable region CDRs are each identical to one of the three
light chain donor CDRs. In certain embodiments, one of the three
heavy chain altered variable region CDRs is identical to one of the
three heavy chain donor CDRs. In additional embodiments, two of the
three heavy chain altered variable region CDRs are each identical
to one of the three light chain donor CDRs. In certain embodiments,
at least two of the three light chain altered variable region CDRs
are light chain donor CDR variants. In other embodiments, three of
the three light chain altered variable region CDRs are light chain
donor CDR variants. In some embodiments, at least two of the three
heavy chain altered variable region CDRs are heavy chain donor CDR
variants. In yet other embodiments, three of the three heavy chain
altered variable region CDRs are heavy chain donor CDR variants. In
certain embodiments, the donor heteromeric variable region is
murine.
[0019] In other embodiments, the higher antigen binding affinity is
at least 2-fold higher antigen binding affinity (e.g. about 2-3
fold higher or about 2-20 fold higher). In particular embodiments,
the higher antigen binding affinity is 3-fold higher antigen
binding affinity. In certain embodiments, the higher antigen
binding affinity is at least: 5-fold higher, 8-fold higher, or
10-fold higher. In other embodiments, the higher antigen binding
affinity is at least 12-fold, 15-fold, 20-fold, 25-fold, 50-fold,
100-fold, or 1000-fold higher (e.g. 10-50 fold or 20-500 fold
higher).
[0020] In some embodiments, the optimized activity is an increased
association rate (k.sub.on) for an antigen (e.g. 2-fold to 50-fold
increased association rate compared to the donor). In certain
embodiments, the optimized activity is a decreased disassociation
rate (k.sub.off) for an antigen (e.g. a 2-fold, 50-fold, 100-fold,
500-fold or 100-fold decrease in disassociation rate compared to
the donor). In particular embodiments, the optimized activity is
selected from higher binding affinity, increased/decreased
association rate, or increased/decreased disassociation rate--all
as compared to the donor. In other embodiments, the optimized
activity is an increased or decreased catalytic rate,
disassociation constant or association constant (e.g. for a
catalytic heteromeric variable region) as compared to the donor
heteromeric variable region.
[0021] In some embodiments, the donor CDRs and the altered variable
region CDRs are as defined by Chothia. In other embodiments, the
donor CDRs and the altered variable region CDRs are as defined by
Kabat. In particular embodiments, the donor CDRs and the altered
variable region CDRs are as defined by MacCallum. In preferred
embodiments, the donor CDRs and the altered variable region CDRs
are as defined by the combined definitions of Kabat and Chothia. In
other preferred embodiments, the donor and altered variable region
CDRs are as defined by Kabat, except CDRH1 is defined by the
combined definition of Kabat and Chothia.
[0022] In certain embodiments, three of the four unvaried human
germline light chain framework regions are LFR1, LFR2, and LFR3 all
of which are from the same human germline light chain variable
region gene. In other embodiments, three of the four unvaried human
germline heavy chain framework regions are HFR1, HFR2, and HFR3 all
of which are from the same human germline heavy chain variable
region gene.
[0023] In certain embodiments, the present invention provides
heteromeric variable region binding fragments and antibodies that
are able to bind to human von Willebrand factor (vWF) and comprise
an unvaried human framework. In particular embodiments, the
unvaried human framework is a human germline framework.
[0024] In some embodiments, the present invention provides
compositions comprising a vWF binding molecule (or nucleic acid
sequence encoding a vWF binding molecule), wherein the vWF binding
molecule comprises: a) a light chain variable region, or a portion
of a light chain variable region, wherein the light chain variable
region (or the portion) comprises; i) a CDRL1 amino acid sequence
as shown in SEQ ID NO:9. In certain embodiments, the vWF binding
molecule has a CDRL2 amino acid sequence selected from SEQ ID
NO:11, 13, 15, 17, 19, and 21. In further embodiments, the vWF
binding molecule has a CDRL3 amino acid sequence as shown in SEQ ID
NO:23.
[0025] In certain embodiments, the present invention provides
compositions comprising a heavy chain variable region (or portion
thereof), or a nucleic acid sequence (or portion thereof) encoding
a heavy chain variable region, wherein the heavy chain variable
region (or portion thereof) comprises: a) a CDRH1 amino acid
sequence as shown in SEQ ID NO:25. In other embodiments, the heavy
chain variable region comprises a CDRH2a amino acid sequence
selected from the group consisting of SEQ ID NO:27, 29, or 31. In
some embodiments, the heavy chain variable region comprises a
CDRH2b anino acid sequence selected from the group consisting of
SEQ ID NO:33, 35, 37, 39, and 41. In further embodiments, the heavy
chain variable region comprises a CDRH3 amino acid sequence
selected from the group consisting of SEQ ID NO:43, 45, 47, and
49.
[0026] In some embodiments, the present invention provides
compositions comprising a nucleic acid molecule encoding a light
chain variable region of a vWF binding molecule, wherein the
nucleic acid molecule comprises a CDRL1 nucleic acid sequence as
shown in SEQ ID NO:10 or a nucleic acid sequence encoding the same
peptide as SEQ ID NO:10 (e.g., due to the degeneracy of the genetic
code, many nucleic acid sequences may be constructed that code for
the same peptide as encoded by SEQ ID NO:10; this same principle is
true for the sequences described below as well). In certain
embodiments, the vWF binding molecule has a CDRL2 nucleic acid
sequence selected from SEQ ID NO:12, 14, 16, 18, 20, and 22, or a
nucleic acid sequence encoding the same peptides as SEQ ID NOs:12,
14, 16, 18, 20, or 22. In further embodiments, the vWF binding
molecule has a CDRL3 amino acid sequence as shown in SEQ ID NO:24,
or a nucleic acid sequence encoding the same peptide as SEQ ID
NO:24.
[0027] In certain embodiments, the present invention provides
compositions comprising a nucleic acid sequence (or portion
thereof) encoding a heavy chain variable region, wherein the heavy
chain variable region (or portion thereof) comprises: a) a CDRH1
nucleic acid sequence as shown in SEQ ID NO:26. In other
embodiments, the present invention provides a nucleic acid sequence
encoding a CDRH2a as shown in SEQ ID NO:28, 30, or 32. In some
embodiments, the present invention provides a nucleic acid sequence
encoding a CDRH2b as shown in SEQ ID NO:34, 36, 38, 40, and 42. In
further embodiments, the present invention provides a CDRH3 as
shown in SEQ ID NO:44, 46, 48, and 50.
[0028] In some embodiments, the present invention provides a
peptide comprising at least two (or at least three or four) CDRs
selected from the group consisting of SEQ ID NO:9, 11, 13, 15, 17,
19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, and 49.
In certain embodiments, the light and/or heavy chain variable
region comprises a portion of a framework (e.g. containing 2 or 3
subregions, such as FR2 and FR3). In some embodiments, the light
and/or heavy chain variable region comprises a filly human
framework. In other embodiments, the light and/or heavy chain
variable region comprise a human germline framework.
[0029] In some embodiments, the vWF binding molecule comprises an
antibody or antibody fragment (e.g., Fv, Fab, etc.). In particular
embodiments, the vWF binding molecule comprises the C1 Fv or Fab.
In other embodiments, the vWF binding molecule comprises the C4 Fv
or Fab. In additional embodiments, the vWF binding molecule
comprises an Fv or Fab selected from the group consisting of C7,
C8, C9, and C4-4.
[0030] In certain embodiments, the vWF binding molecule is
contained within a host cell (e.g. eukaryotic, or prokaryotic host
cell). In other embodiments, the nucleic acid sequence encoding the
light and/or heavy chain is contained within a plasmid or other
expression vector.
[0031] In some embodiments, the present invention provides methods
of inhibiting the binding of vWF to the GPIb protein comprising: a)
providing; i) a subject, and ii) a composition, wherein the
composition comprises a vWF binding molecule of the present
invention (e.g. acting as an anti-thrombotic agent); and b)
administering the composition to the subject. In certain
embodiments, the administering inhibits RIPA (ristocetin-induced
platelet aggregation), BIPA (botrocetin-induced platelet
aggregation), or SIPA (shear stress-induced platelet
aggregation)--type reactions in human patients. In other
embodiments, the present invention provides methods of treating a
disease comprising: a) providing; i) a subject with symptoms of the
disease, and ii) a composition, wherein the composition comprises
the vWF binding molecules of the present invention; and b)
administering the composition to the subject such that the symptoms
are reduced or eliminated. In particular embodiments, the vWF
binding molecules are applied to prevent or treat diseases relevant
to platelet adhesion and aggregation, including, but not limited
to, the treatment of transient cerebral ischemic attack, unstable
angina pectoris, cerebral infarction, myocardial infarction, and
peripheral arterial occlusive disease, prevention of reocclusion
after PTCA and occlusion of coronary artery by-pass graft, and for
the treatment of coronary artery valve replacement and essential
thrombocythemia.
[0032] In some embodiments, amino acid modification(s) are
introduced into the CH2 domain of an Fc region of a vWF binding
molecule or any of the binding molecules (e.g. antibodies)
disclosed herein. Useful amino acid positions for modification in
order to generate a variant IgG Fc region with altered Fc gamma
receptor (FcyR) binding affinity or activity include any one or
more of the following amino acid positions: 268, 269, 270, 272,
276, 278, 280, 283, 285, 286, 289, 290, 292, 293, 294, 295, 296,
298, 300 301, 303, 305, 307, 309, 331, 332, 333, 334, 335, 337,
338, 340, 360, 373, 376, 416, 419, 430, 434, 435, 437, 438 or 439
of the Fc region of a binding molecule of the present invention. In
preferred embodiments, the parent Fc region used as the template to
generate such variants comprises a human IgG Fc region. In some
embodiments, to generate an Fc region variant with reduced binding
to the FcyR one may introduce an amino acid modification at any one
or more of the following amino acid positions: 252, 254, 265, 268,
269, 270, 272, 278, 289, 292, 293, 294, 295, 296, 298, 300, 301,
303, 322, 324, 327, 329, 332, 333, 335, 338, 340, 373, 376, 382,
388, 389, 414, 416, 419, 434, 435, 437, 438 or 439 of the Fc region
of a vWF, or other type of, binding molecule. In particular
embodiments, Fc region variants with improved binding to one or
more FcyRs may also be made. Such Fc region variants may comprise
an amino acid modification at any one or more of the following
amino acid positions: 280, 283, 285, 286, 290, 294, 295, 298, 300,
301, 305, 307, 309, 312, 315, 331, 332, 333, 334, 337, 340, 360,
378, 398 or 430 of the Fc region of a binding molecule as disclosed
herein. In certain embodiments, the amino acid modification is
Y300I.
[0033] In other embodiments, the amino acid modification is Y300L.
In some embodiments, the amino acid modification is Q295K or Q295L.
In certain embodiments, the amino acid modification is E294N. In
other embodiments, the amino acid modification at position 296 is
Y296P. In some embodiments, the amino acid modification at position
298 is S298P. In other embodiments, the amino acid modification is
S289N, S298P, S298V or S298D. In certain embodiments, the vWF
binding molecule, or other type of binding molecules (e.g.
heteromeric variable regions) comprises a heavy chain constant
region mutation. In other embodiments, the binding molecule
comprises a heavy chain constant region with a mutation selected
from D280H and K290S. Additional Fc mutations or changes in Fc
glycosylation are described in U.S. Pat. No. 6,528,624; WO0042072;
U.S. Pat. No. 5,648,260; U.S. Pat. No. 6,180,377; WO0179299;
WO9958572; WO9823289; WO8907142; U.S. Pat. No. 5,834,597; U.S. Pat.
No. 6,602,684; WO9858964; and WO9730087; all of which are herein
incorporated by reference.
[0034] Alternatively or additionally, it may be useful to combine
amino acid modifications with one or more further amino acid
modifications that alter C1q binding and/or the complement
dependent cytotoxicity function of the Fc region of a binding
molecule as disclosed herein. The starting polypeptide of
particular interest may be one that binds to C1q and displays
complement dependent cytotoxicity (CDC). Amino acid substitutions
described herein may serve to alter the ability of the starting
polypeptide to bind to C1q and/or modify its complement dependent
cytotoxicity function (e.g., to reduce and preferably abolish these
effector functions). However, polypeptides comprising substitutions
at one or more of the described positions with improved C1q binding
and/or complement dependent cytotoxicity (CDC) function are
contemplated herein. For example, the starting polypeptide may be
unable to bind C1q and/or mediate CDC and may be modified according
to the teachings herein such that it acquires these further
effector functions. Moreover, polypeptides with pre-existing C1q
binding activity, optionally further having the ability to mediate
CDC may be modified such that one or both of these activities are
enhanced. Amino acid modifications that alter C1q and/or modify its
complement dependent cytotoxicity function are described, for
example, in WO0042072, which is hereby incorporated by
reference.
[0035] One type of amino acid substitution serves to alter the
glycosylation pattern of the Fc region of a binding molecule. This
may be achieved, for example, by deleting one or more glycosylation
site(s) found in the polypeptide, and/or adding one or more
glycosylation sites that are not present in the polypeptide.
Glycosylation of an Fc region is typically either N-linked or
O-linked. N-linked refers to the attachment of the carbohydrate
moiety to the side chain of an asparagine residue. The peptide
sequences asparagine-X-serine and asparagine-X-threonine, where X
is any amino acid except proline, are the recognition sequences for
enzymatic attachment of the carbohydrate moiety to the asparagine
side chain. Thus, the presence of either of these peptide sequences
in a polypeptide creates a potential glycosylation site. O-linked
glycosylation refers to the attachment of one of the sugars
N-aceylgalactosamine, galactose, or xylose to a hydroxyamino acid,
most commonly serine or threonine, although 5-hydroxyproline or
5-hydroxylysine may also be used.
[0036] Addition of glycosylation sites to the Fc region of a
binding molecule (e.g. heteromeric variable region) is conveniently
accomplished by altering the amino acid sequence such that it
contains one or more of the above-described tripeptide sequences
(for N-linked glycosylation sites). An exemplary glycosylation
variant has an amino acid substitution of residue Asn 297 of the
heavy chain. The alteration may also be made by the addition of, or
substitution by, one or more serine or threonine residues to the
sequence of the original polypeptide (for O-linked glycosylation
sites).
[0037] In certain embodiments, the binding molecules of the present
invention are expressed in cells that express
beta(1,4)-N-acetylglucosami- nyltransferase III (GnT III), such
that GnT III adds GlcNAc to the binding molecules. Methods for
producing binding molecules in such a fashion are provided in
WO9954342, WO03011878, patent publication 20030003097A1, and Umana
et al., Nature Biotechnology, 17:176-180, February 1999; all of
which are herein specifically incorporated by reference in their
entireties.
[0038] In certain embodiments, the present invention provides kits
comprising: a) a binding molecule of the present invention (e.g.
heteromeric variable region); and b) instructions for using the
binding molecule to treat a disease in a subject or instructions
for employing the binding molecule for scientific research or
diagnostic purposes (e.g., for performing ELISA assays, etc.). In
some embodiments, the present invention provides cell lines stably
or transiently transfected with nucleic acid sequences encoding the
binding molecules of the present invention.
[0039] In some embodiments, the present invention provides methods
of conferring donor CDR binding affinity onto an antibody acceptor
variable region framework, comprising: (a) constructing a
population of altered antibody variable region encoding nucleic
acids, the population comprising encoding nucleic acids for an
acceptor variable region framework containing a plurality of
different amino acids at one or more acceptor framework region
amino acid positions and donor CDRs containing a plurality of
different amino acids at one or more donor CDR amino acid
positions; (b) expressing the population of altered variable region
encoding nucleic acids, and (c) identifying one or more altered
variable regions having binding affinity substantially the same or
greater than the donor CDR variable region.
[0040] In certain embodiments, the one or more altered variable
regions are identified by comparing the relative binding of the
altered variable regions to the donor CDR variable region. In other
embodiments, the one or more altered variable regions are
identified by measuring the binding affinity of the altered
variable regions. In particular embodiments, the one or more
altered variable regions are identified by measuring the
association rate (kon) or disassociation rate (koff) of the altered
variable regions. In additional embodiments, the acceptor variable
region framework is a heavy chain variable region framework. In
other embodiments, the acceptor variable region framework is a
light chain variable region framework. In some embodiments, the
framework amino acid positions are located in framework region 1,
framework region 2, framework region 3 or framework region 4. In
particular embodiments, the donor CDR amino acid positions is
located in CDR1, CDR2 or CDR3.
[0041] In particular embodiments, the one or more amino acid
positions in the acceptor framework region is selected by
differences in amino acid identity between corresponding positions
in donor and acceptor framework regions. In further embodiments,
the one or more amino acid positions in the acceptor framework
region is selected as being a canonical framework residue. In other
embodiments, the one or more amino acid positions in the acceptor
framework region is selected as being exposed to solvent. In some
embodiments, the one or more amino acid positions in the acceptor
framework region is selected by a characteristic within the group
consisting of being proximal to a CDR, predicted to contact the
opposite domain in the VL-VH interface, lack of relatedness to the
donor framework amino acid position at that position and predicted
to modulate CDR activity.
[0042] In certain embodiments, the one or more amino acid positions
in the donor CDR is selected as being a CDR residue as defined by
Kabat. In some embodiments, the altered variable regions are
coexpressed with a light chain variable region. In additional
embodiments, the altered variable region is coexpressed with a
heavy chain variable region.
[0043] In some embodiments, the present invention provides methods
of simultaneously grafting and optimizing the binding affinity of a
variable region binding fragment, comprising: (a) constructing a
population of altered heavy chain variable region encoding nucleic
acids comprising an acceptor variable region framework containing
donor CDRs and a plurality of different amino acids at one or more
framework region and CDR amino acid positions; (b) constructing a
population of altered light chain variable region encoding nucleic
acids comprising an acceptor variable region framework containing
donor CDRs and a plurality of different amino acids at one or more
framework regions and CDR amino acid positions; (c) coexpressing
the populations of heavy and light chain variable region encoding
nucleic acids to produce diverse combinations of heteromeric
variable region binding fragments, and (d) identifying one or more
heteromeric variable region binding fragments having affinity
substantially the same or greater than the donor CDR heteromeric
variable region binding fragment.
[0044] In certain embodiments, the one or more heteromeric variable
region binding fragments are identified by comparing the relative
binding of the heteromeric variable region binding fragments to the
donor CDR heteromeric variable region binding fragment. In some
embodiments, the one or more heteromeric variable region binding
fragments are identified by measuring the binding affinity of the
heteromeric variable region binding fragments. In particular
embodiments, the one or more heteromeric variable region binding
fragments are identified by measuring the association rate (kon) or
disassociation rate (koff) of the heteromeric variable region
binding fragments. In further embodiments, the framework amino acid
positions are located in framework region 1, framework region 2,
framework region 3 or framework region 4. In other embodiments, the
donor CDR amino acid positions is located in CDR1, CDR2 or
CDR3.
[0045] In certain embodiments, the one or more amino acid positions
in the acceptor framework region is selected by differences in
amino acid identity between corresponding positions in donor and
acceptor framework regions. In other embodiments, the one or more
amino acid positions in the acceptor framework region is selected
as being a canonical framework residue. In particular embodiments,
the one or more amino acid positions in the acceptor framework
region is selected as being exposed to solvent. In other
embodiments, the one or more amino acid positions in the acceptor
framework region is selected by a characteristic within the group
consisting of being proximal to a CDR, predicted to contact the
opposite domain in the VL-VH interface, lack of relatedness to the
donor framework amino acid position at that position and predicted
to modulate CDR activity. In some embodiments, the one or more
amino acid positions in the donor CDR is selected as being a CDR
residue as defined by Kabat.
[0046] In particular embodiments, the present invention provides
methods of optimizing the binding affinity of an antibody variable
region, comprising: (a) constructing a population of antibody
variable region encoding nucleic acids from a parent variable
region encoding nucleic acid, the population comprising two or more
CDRs containing a plurality of different amino acids at one or more
CDR amino acid positions; (b) expressing the population of variable
region encoding nucleic acids, and (c) identifying one or more
variable regions having binding affinity substantially the same or
greater than the parent variable region.
[0047] In some embodiments, the one or more variable regions are
identified by comparing the relative binding of the variable
regions to the parent variable region. In other embodiments, the
one or more variable regions are identified by measuring the
binding affinity of the variable regions. In certain embodiments,
the one or more variable regions are identified by measuring the
association rate (kon) or disassociation rate (koff) of the
variable regions. In other embodiments, the variable region is a
heavy chain variable region. In some embodiments, the variable
region is a light chain variable region.
[0048] In particular embodiments, the two or more CDRs are selected
from the group consisting of CDR1, CDR2 or CDR3. In some
embodiments, the one or more amino acid positions in the two or
more CDRs is selected as being a CDR residue as defined by Kabat.
In other embodiments, the variable regions are coexpressed with a
light chain variable region. In certain embodiments, the variable
regions are coexpressed with a heavy chain variable region. In
particular embodiments, the antibody variable region is selected
from the group consisting of native, grafted, altered and optimized
variable regions.
[0049] In some embodiments, the present invention provides methods
of optimizing the activity of a catalytic antibody variable region,
comprising: (a) constructing a population of heavy chain variable
region encoding nucleic acids from a parent heavy chain variable
region encoding nucleic acid, the population comprising two or more
CDRs containing a plurality of different amino acids at one or more
CDR amino acid positions; (b) constructing a population of light
chain variable region encoding nucleic acids from a parent light
chain variable region encoding nucleic acid, the population
comprising two or more CDRs containing a plurality of different
amino acids at one or more CDR amino acid positions; (c)
coexpressing the population of heavy and light chain variable
region encoding nucleic acids containing the two or more CDRs
having the plurality of different amino acids at one or more CDR
positions to produce diverse combinations of heteromeric variable
region catalytic fragments, and (d) identifying one or more
heteromeric variable regions having optimized catalytic activity
compared to the parent catalytic antibody variable region.
[0050] In other embodiments, the one or more heteromeric variable
regions are identified by comparing the relative catalytic activity
of the heteromeric variable regions to the parent variable region.
In some embodiments, the one or more heteromeric variable regions
are identified by measuring a substrate association rate (kon), a
substrate disassociation rate (koff), substrate binding affinity, a
transition state binding affinity, a turnover rate or a Km. In
particular embodiments, the two or more CDRs are selected from the
group consisting of CDR1, CDR2 and CDR3. In certain embodiments,
the one or more amino acid positions in the two or more CDRs is
selected as being a CDR residue as defined by Kabat.
[0051] The invention provides a method of conferring donor CDR
binding affinity onto an antibody acceptor variable region
framework. The method consists of: (a) constructing a population of
altered antibody variable region encoding nucleic acids, said
population comprising encoding nucleic acids for an acceptor
variable region framework containing a plurality of different amino
acids at one or more acceptor framework region amino acid positions
and donor CDRs containing a plurality of different amino acids at
one or more donor CDR amino acid positions; (b) expressing said
population of altered variable region encoding nucleic acids, and
(c) identifying one or more altered variable regions having binding
affinity substantially the same or greater than the donor CDR
variable region. The acceptor variable region framework can be a
heavy or light chain variable region framework and the populations
of heavy and light chain altered variable regions can be expressed
alone to identify heavy or light chains having binding affinity
substantially the same or greater than the donor CDR variable
region. The populations of heavy and light chains additionally can
be coexpressed to identify heteromeric altered variable region
binding fragments. The invention also provides a method of
simultaneously grafting and optimizing the binding affinity of a
variable region binding fragment. The method consists of: (a)
constructing a population of altered heavy chain variable region
encoding nucleic acids comprising an acceptor variable region
framework containing donor CDRs and a plurality of different amino
acids at one or more framework region and CDR amino acid positions;
(b) constructing a population of altered light chain variable
region encoding nucleic acids comprising an acceptor variable
region framework containing donor CDRs and a plurality of different
amino acids at one or more framework regions and CDR amino acid
positions; (c) coexpressing said populations of heavy and light
chain variable region encoding nucleic acids to produce diverse
combinations of heteromeric variable region binding fragments, and
(d) identifying one or more heteromeric variable region binding
fragments having affinity substantially the same or greater than
the donor CDR heteromeric variable region binding fragment. A
method of optimizing the binding affinity of an antibody variable
region is also provided. The method consists of: (a) constructing a
population of antibody variable region encoding nucleic acids, said
population comprising two or more CDRs containing a plurality of
different amino acids at one or more CDR amino acid positions; (b)
expressing said population of variable region encoding nucleic
acids, and (c) identifying one or more variable regions having
binding affinity substantially the same or greater than the donor
CDR variable region. The variable region populations can be heavy
or light chains and can be expressed as individual populations or
they can be coexpressed to produce heteromeric variable region
binding fragments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 (SEQ ID NO:s 1-4) shows the alignment of anti-CD40
variable region and human template amino acid sequences.
[0053] FIG. 2 shows binding reactivity of humanized anti-CD40
variants.
[0054] FIG. 3 shows molecular modeling of anti-CD40 variant
CW43.
[0055] FIG. 4 shows a comparison of the quantitation of murine
framework residues in active variants from two libraries.
[0056] FIG. 5 shows an alignment of NMC-4 with human genrline
sequences. Vertical lines denote differences in sequences. The work
of Kabat was used to number residues and define CDR's (underlined)
with the exception of CDR-H1 with used Kabat and Chothia residues
combined.
[0057] FIG. 6 shows the results of a vWF ELISA with the
combinatorial clones described in Example 2.
DEFINITIONS
[0058] To facilitate an understanding of the invention, a number of
terms are defined below.
[0059] As used herein, the term "CDR" or "complementarity
determining region" is intended to mean the non-contiguous antigen
combining sites found within the variable region of both heavy and
light chain polypeptides. These particular regions have been
described by Kabat et al., J. Biol. Chem. 252, 6609-6616 (1977) and
Kabat et al., Sequences of protein of immunological interest.
(1991), and by Chothia et al., J. Mol. Biol. 196:901-917 (1987) and
by MacCallum et al., J. Mol. Biol. 262:732-745 (1996) where the
definitions include overlapping or subsets of amino acid residues
when compared against each other. Nevertheless, application of
either definition to refer to a CDR of an antibody or grafted
antibodies or variants thereof is intended to be within the scope
of the term as defined and used herein. The amino acid residues
which encompass the CDRs as defined by each of the above cited
references are set forth below in Table 1 as a comparison.
1TABLE 1 CDR Definitions Kabat(1) Chothia(2) MacCallum(3) VH CDR1
31-35 26-32 30-35 VH CDR2 50-65 53-55 47-58 VH CDR3 95-102 96-101
93-101 VL CDR1 24-34 26-32 30-36 VL CDR2 50-56 50-52 46-55 VL CDR3
89-97 91-96 89-96 (1)Residue numbering follows the nomenclature of
Kabat et al., supra (2)Residue numbering follows the nomenclature
of Chothia et al., supra (3)Residue numbering follows the
nomenclature of MacCallum et al., supra
[0060] As used herein, the term "framework" when used in reference
to an antibody variable region is entered to mean all amino acid
residues outside the CDR regions within the variable region of an
antibody. Therefore, a variable region framework is between about
100-120 amino acids in length but is intended to reference only
those amino acids outside of the CDRs.
[0061] As used herein, the term "framework region" is intended to
mean each domain of the framework that is separated by the CDRs.
Therefore, for the specific example of a heavy chain variable
region and for the CDRs as defined by Kabat et al., framework
region 1 corresponds to the domain of the variable region
encompassing amino acids 1-30; region 2 corresponds to the domain
of the variable region encompassing amino acids 36-49; region 3
corresponds to the domain of the variable region encompassing amino
acids 66-94, and region 4 corresponds to the domain of the variable
region from amino acids 103 to the end of the variable region. The
framework regions for the light chain are similarly separated by
each of the light claim variable region CDRs. Similarly, using the
definition of CDRs by Chothia et al. or McCallum et al. the
framework region boundaries are separated by the respective CDR
termini as described above.
[0062] As used herein,the term "donor" is intended to mean a parent
antibody molecule or fragment thereof from which a portion is
derived from, given or contributes to another antibody molecule or
fragment thereof so as to confer either a structural or functional
characteristic of the parent molecule onto the receiving molecule.
For the specific example of CDR grafting, the parent molecule from
which the grafted CDRs are derived is a donor molecule. The donor
CDRs confer binding affinity of the parent molecule onto the
receiving molecule. It should be understood that a donor molecule
does not have to be from a different species as the receiving
molecule of fragment thereof. Instead, it is sufficient that the
donor is a separate and distinct molecule.
[0063] As used herein, the term "acceptor" is intended to mean an
antibody molecule or fragment thereof which is to receive the
donated portion from the parent or donor antibody molecule or
fragment thereof. An acceptor antibody molecule or fragment thereof
is therefore imparted with the structural or functional
characteristic of the donated portion of the parent molecule. For
the specific example of CDR grafting, the receiving molecule for
which the CDRs are grafted is an acceptor molecule. The acceptor
antibody molecule or fragment is imparted with the binding affinity
of the donor CDRs or parent molecule. As with a donor molecule, it
is understood that an acceptor molecule does not have to be from a
different species as the donor.
[0064] A "variable region" when used in reference to an antibody or
a heavy or light chain thereof is intended to mean the amino
terminal portion of an antibody which confers antigen binding onto
the molecule and which is not the constant region. The term is
intended to include functional fragments thereof which maintain
some of all of the binding function of the whole variable region.
Therefore, the term "heteromeric variable region binding fragments"
is intended to mean at least one heavy chain variable region and at
least one light chain variable regions or functional fragments
thereof assembled into a heteromeric complex. Heteromeric variable
region binding fragments include, for example, functional fragments
such as Fab, F(ab)2, Fv, single chain Fv (scFv) and the like. Such
functional fragments are well known to those skilled in the art.
Accordingly, the use of these terms in describing functional
fragments of a heteromeric variable region is intended to
correspond to the definitions well known to those skilled in the
art. Such terms are described in, for example, Harlow and Lane,
Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, New
York (1989); Molec. Biology and Biotechnology: A Comprehensive Desk
Reference (Myers, R. A. (ed.), New York: VCH Publisher, Inc.);
Huston et al., Cell Biophysics, 22:189-224 (1993); Pluckthun and
Skerra, Meth. Enzymol., 178:497-515 (1989) and in Day, E. D.,
Advanced Immunochemistry, Second Ed., Wiley-Liss, Inc., New York,
N.Y. (1990).
[0065] As used herein, the term "population" is intended to refer
to a group of two or more different molecules. A population can be
as large as the number of individual molecules currently available
to the user or able to be made by one skilled in the art.
Populations can be as small as 2-4 molecules or as large as
10.sup.13 molecules. An example where a small population can be
useful is where one wishes to optimize binding affinity of a
variable region or of heteromeric binding fragments by compiling
beneficial differences from a small number of parent molecules
having similar binding affinity into a single variable binding
fragment species. An example of where large populations, including
as large as 10.sup.8 or greater different molecules, can be desired
is where all possible combinations of amino acids differences
between donor and acceptor at all positions within a variable
region are to be generated in order to obtain maximum diversity and
increase the efficiency of compiling beneficial changes. In some
embodiments, populations are between about 5 and 10 different
species as well as up to hundreds or thousands of different
species. The populations can be diverse or redundant depending on
the intent and needs of the user. Those skilled in the art will
know what size and diversity of a population is suitable for a
particular application.
[0066] As used herein, the term "altered" when used in reference to
an antibody variable region is intended to mean a heavy or light
chain variable region that contains one or more amino acid changes
in a framework region, a CDR or both compared to the parent amino
acid sequence at the changed position. Where an altered variable
region is derived from or composed of different donor and acceptor
regions, the changed amino acid residues within the altered species
are to be compared to their respective amino acid positions within
the parent donor and acceptor regions. For example, a variable
region containing donor CDRs grafted into an acceptor framework and
containing one or more amino acid changes within the framework
regions and one or more amino acid changes within the CDRs will
have amino acids residues at the changed framework region positions
different than the residues at the comparable positions in the
acceptor framework. Similarly, such an altered variable region will
have amino acid residues at the changed CDR positions different
than the residues at the comparable positions in the donor
CDRs.
[0067] As used herein, the term "nucleic acid" or "nucleic acids"
is intended to mean a single- or double-stranded DNA or RNA
molecule. A nucleic acid molecule of the invention can be of
linear, circular or branched configuration, and can represent
either the sense or antisense strand, or both, of a native nucleic
acid molecule. The term also is intended to include nucleic acid
molecules of both synthetic and natural origin. A nucleic acid
molecule of natural origin can be derived from any animal, such as
a human, non-human primate, mouse, rat, rabbit, bovine, porcine,
ovine, canine, feline, or amphibian, or from a lower eukaryote,
such as Drosophila, C. elegans or yeast. A synthetic nucleic acid
includes, for example, chemical and enzymatic synthesis. The term
"nucleic acid" or "nucleic acids" is similarly intended to include
analogues of natural nucleotides which have similar functional
properties as the referenced nucleic acid and which can be utilized
in a manner similar to naturally occurring nucleotides and
nucleosides.
[0068] As used herein, the term "coexpressing" is intended to mean
the expression of two or more molecules by the same cell. The
coexpressed molecules can be polypeptides or encoding nucleic
acids. The coexpression can be, for example, constitutive or
inducible. Such nucleic acid sequences can also be expressed
simultaneously or, alternatively, regulated independently. Various
combinations of these modes of coexpression can additionally be
used depending on the number and intended use of the variable
region encoding nucleic acids. The term is intended to include the
coexpression of members originating from different populations in
the same cell. For example, populations of molecules can be
coexpressed where single or multiple different species from two or
more populations are expressed in the same cell. A specific example
includes the coexpression of heavy and light chain variable region
populations where at least one member from each population is
expressed together in the same cell to produce a library of cells
coexpressing different species of heteromers variable region
binding fragments. Populations which can be coexpressed can be as
small as 2 different species within each population. Additionally,
the number of molecules coexpressed from different populations also
can be as large as 10.sup.8 or greater, such as in the case where
multiple amino acid position changes of multiple framework regions
or CDRs in both heavy and light chain antibody variable region.
populations are produced and coexpressed. Numerous different sized
populations of encoding nucleic acids in between the above ranges
and greater can also be coexpressed. Those skilled in the art know,
or can determine, what modes of coexpression can be used to achieve
a particular goal or satisfy a desired need.
[0069] As used herein, the term "identifying" is intended to mean
detecting by a qualitative or quantitative means, a variable region
or altered variable of the invention by functional or biochemical
properties, including, for example, binding affinity of catalytic
activity.
[0070] As used herein the term "binding affinity" is intended to
mean the strength of a binding interaction and therefore includes
both the actual binding affinity as well as the apparent binding
affinity. The actual binding affinity is a ratio of the association
rate over the disassociation rate. Therefore, conferring or
optimizing binding affinity includes altering either or both of
these components to achieve the desired level of binding affinity.
The apparent affinity can include, for example, the avidity of the
interaction. For example, a bivalent heteromeric variable region
binding fragment can exhibit altered or optimized binding affinity
due to its valency.
[0071] As used herein, the term "optimizing" when used in reference
to a variable region or a functional fragment thereof is intended
to mean that the binding affinity of the variable region has been
modified compared to the binding affinity of a parent variable
region or a donor variable region. A variable region exhibiting
optimized activity can exhibit, for example, higher affinity or
lower affinity binding, or increased or decreased association or
dissociation rates compared to an unaltered variable region.
A,variable region exhibiting optimized activity also can exhibit
increased stability such as increased half-life in a particular
organism. For example, an antibody activity can be optimized to
increase stability by decreasing susceptibility to proteolysis. An
antibody exhibiting optimized activity also can exhibit lower
affinity binding, including decreased association rates or
increased dissociation rates, if desired. An optimized variable
region exhibiting lower affinity binding is useful, for example,
for penetrating a solid tumor. In contrast to a higher affinity
variable region, which would bind to the peripheral regions of the
tumor but would be unable to penetrate to the inner regions of the
tumor due to its high affinity, a lower affinity variable region
would be advantageous for penetrating the inner regions of the
tumor. As with optimization of binding affinities above,
optimization of a catalytic variable region can be, for example,
increased or decreased catalytic rates, disassociation constants or
association constants.
[0072] As used herein, the term "substantially the same" when used
in reference to binding affinity is intended to mean similar or
identical binding affinities where one molecule has a binding
affinity constant that is similar to another molecule within the
experimental variability of the affinity measurement. The
experimental variability of the binding affinity measurement is
dependent upon the specific assay used and is known to those
skilled in the art.
DETAILED DESCRIPTION OF THE INVENTION
[0073] The invention is directed to a method of conferring donor
CDR binding affinity onto an antibody acceptor variable region
framework. The method effectively combines CDR grafting procedures
and affinity reacquisition of the grafted variable region into a
single step. The methods of the invention also are applicable for
affinity maturation of an antibody variable region. The affinity
maturation process can be substituted for, or combined with the
affinity reacquisition function when being performed during a CDR
grafting procedure. Alternatively, the affinity maturation
procedure can be performed independently from CDR grafting
procedures to optimize the binding affinity of variable region, or
an antibody. An advantage of combining grafting and affinity
reacquisition procedures, or affinity maturation, is the avoidance
of time consuming, step-wise procedures to generate a grafted
variable region, or antibody, which retains sufficient binding
affinity for therapeutic utility. Therefore, therapeutic antibodies
can be generated rapidly and efficiently using the methods of the
invention. Such advantages beneficially increase the availability
and choice of useful therapeutics for human diseases as well as
decrease the cost to the developer and ultimately to the
consumer.
[0074] In one embodiment, the invention is directed to methods of
producing grafted heavy and light chain variable regions having
similar or better binding affinity as the CDR donor variable
region. When coexpressed, the grafted heavy and light chain
variable regions assemble into variable region binding fragments
having similar or better binding affinity as the donor antibody or
variable region binding fragments thereof. The grafting is
accomplished by generating a diverse library of CDR grafted
variable region fragments and then screening the library for
binding activity similar or better than the binding activity of the
donor. A diverse library is generated by selecting acceptor
framework positions that differ at the corresponding position
compared to the donor framework and making a library population
containing of all possible amino acid residue changes at each of
those positions together with all possible amino acid residue
changes at each position within the CDRs of the variable region.
The grafting is accomplished by splicing a population of encoding
nucleic acids for the donor CDR containing species representing all
possible amino acid residues at each CDR position into a population
of encoding nucleic acids for an antibody acceptor variable region
framework which contains species representing all possible amino
acid residue changes at the selected framework positions. The
resultant population encodes the authentic donor and acceptor
framework amino acid sequences as well as all possible combinations
and permutations of these sequences with each of the 20 naturally
occurring amino acids at the changed positions.
[0075] In another embodiment, the invention is directed to methods
of producing grafted heavy and light chain variable regions, and
heteromeric binding fragments thereof, having similar or better
binding affinity as the CDR donor variable region. As described
above, the grafting is accomplished by generating a diverse library
of CDR grafted variable region fragments and then screening the
library for binding activity similar or better than the binding
activity of the donor. However, the diverse library is generated by
selecting acceptor framework positions that are predicted to affect
CDR binding affinity and making a library population containing of
all possible amino acid residue changes at each of those positions
or subsets of the selected amino acid positions together with all
possible amino acid residue changes at each position within the
CDRs of the variable region, or subsets of CDR positions. The
grafting is accomplished by splicing a population of encoding
nucleic acids for the donor CDR containing the selected position
changes into a population of encoding nucleic acids for an antibody
acceptor variable region framework which contains the selected
position changes.
[0076] In yet another embodiment, the invention is directed to the
optimization of binding affinity of an antibody variable region.
The optimization is accomplished by generating a library of
variable regions which contain all possible amino acid residue
changes at each amino acid position within two or more CDRs. When
expressed and screened for binding activity, the variable region,
or heavy and light chain heteromeric binding fragments, those
species within the population are selected that contain increased
or decreased binding activity compared to the parent molecule as
optimal binders. Libraries containing subsets, representing less
than all amino acid positions within the CDRs, can similarly be
generated and screened for selecting optimal binding variable
regions and heteromeric binding fragments thereof.
[0077] The invention provides a method for conferring donor CDR
binding affinity onto an antibody acceptor variable region
framework. The method consists of: (a) constructing a population of
altered antibody variable region encoding nucleic acids, the
population consisting of encoding nucleic acids for an acceptor
variable region framework containing a plurality of different amino
acids at one or more acceptor framework region amino acid positions
and donor CDRs containing a plurality of different amino acids at
one or more donor CDR amino acid positions; (b) expressing the
population of altered variable region encoding nucleic acids, and
(c) identifying one or more altered variable regions having binding
affinity substantially the same or greater than the donor CDR
variable region.
[0078] The process of producing human antibody forms from nonhuman
species involves recombinantly splicing CDRs from a nonhuman donor
antibody into a human acceptor framework region to confer binding
activity onto the resultant grafted antibody, or variable region
binding fragment thereof. The process of grafting, referred to as
the procedure for splicing CDRs into a framework, while
mechanically simple it almost always results in a grafted antibody
that exhibits a substantial loss in binding affinity. Although
donor and acceptor variable regions are structurally similar, the
process nevertheless combines CDR binding domains with a
heterologous acceptor region, resulting in a conformationally
imperfect setting for the binding residues of the grafted antibody.
Therefore, once the CDR-grafted antibody, or variable region
binding fragment is made, it requires subsequent rounds of
molecular engineering to reacquire binding affinity comparable to
the donor antibody. The present invention combines these steps such
that CDR grafting and binding reacquisition occur in a single
simultaneous procedure. The method is also applicable to optimizing
the binding affinity of an antibody, or variable region binding
fragment simultaneous with CDR grafting and to optimizing an
antibody or variable region binding fragment in a single procedure
without including the CDR grafting process.
[0079] The methods of the invention confer or impart donor CDR
binding affinity onto an antibody acceptor variable region
framework in a procedure which achieves grafting of donor CDRs and
affinity reacquisition in a simultaneous process. The methods
similarly can be used, either alone or in combination with CDR
grafting, to modify or optimize the binding affinity of a variable
region. The methods for conferring donor CDR binding affinity onto
an acceptor variable region are applicable to both heavy and light
chain variable regions and as such can be used to simultaneous
graft and optimize the binding affinity of an antibody variable
region.
[0080] The methods for conferring donor CDR binding affinity onto a
variable region involve identifying the relevant amino acid
positions in the acceptor framework that are known or predicted to
influence a CDR conformation, or that are known or predicted to
influence the spacial context of amino acid side chains within the
CDR that participate in binding, and then generate a population of
altered variable region species that incorporate a plurality of
different amino acid residues at those positions. For example, the
different amino acid residues at those positions can be
incorporated either randomly or with a predetermined bias and can
include all of the twenty naturally occurring amino acid residues
at each of the relevant positions. Subsets, including less than all
of the naturally occurring amino acids can additionally be chosen
for incorporation at the relevant framework positions. Including a
plurality of different amino acid residues at each of the relevant
framework positions ensures that there will be at least one species
within the population that will have framework changes which allows
the CDRs to reacquire their donor binding affinity in the context
of the acceptor framework variable region.
[0081] In addition to the framework changes at selected amino acid
positions, the CDRs also are altered to contain a plurality of
different amino acid residue changes at all or selected positions
within the donor CDRs. For example, random or biased incorporation
of the twenty naturally occurring amino acid residues, or
preselected subsets, are also introduced into the donor CDRs to
produce a diverse population of CDR species. Including a diverse
population of different CDR variant species ensures that beneficial
changes in the framework positions are not neutralized by a
conformationally incompatible residue in a donor CDR. Inclusion of
CDR variant species into the diverse population of variable regions
also allows for the generation of variant species that exhibit
optimized binding affinity for a predetermined antigen.
[0082] The resultant population of CDR grafted variable regions
described above will therefore contain, at the relevant framework
positions and at the selected CDR positions, a species
corresponding to the authentic parent amino acid residue at each
position as well as a diverse number of different species which
correspond to the possible combinations and permutations of the
authentic parent amino acid residues together with the variant
residues at each of the relevant framework and selected CDR
positions. Such a diverse population of CDR grafted variable
regions are screened for an altered variable region species which
retains donor CDR binding activity, or optimized binding
activity.
[0083] One advantage of the methods of the invention is that they
do not limit the choice of acceptor variable regions applicable, or
expected to be successful, for receiving CDRs from the donor
molecule. For example, when choosing an acceptor region it can be
desirable, or in some circumstances even required, to select an
acceptor that is closely similar to the variable region amino acid
sequence harboring the donor CDRs because the CDR conformation in
the grafted variable region will likely be more similar to that of
the donor. However, selecting similar framework region sequences
between the donor and acceptor variable regions still does not
provide which residues, out of the differences, actually play a
role in CDR binding affinity of the grafted variable region.
Selection of similar acceptor frameworks therefore only limits the
number of possible residues which to investigate in order to
reacquire binding affinity onto the grafted variable region. The
methods of the invention circumvent this problem by producing a
library of all possible or relevant changes in the acceptor
framework, and then screening those variable regions, or
heteromeric binding fragments thereof for species that maintain or
exhibit increased binging affinity compared to the donor molecule.
Therefore, the applicability is not preconditioned on the
availability or search for an acceptor framework variable region
similar to that of the donor.
[0084] Selection of the relevant framework amino acid positions to
alter can depend on a variety of criteria well known to those
skilled it the art. As described above, one criteria for selecting
relevant framework amino acids to change can be the relative
differences in amino acid framework residues between the donor and
acceptor molecules. Selection of relevant framework positions to
alter using this approach is simple and has the advantage of
avoiding any subjective bias in residue determination or any
inherent bias in CDR binding affinity contribution by the residue.
Criteria other than relatedness of amino acid residues can be used
for selecting relevant framework positions to alter. Such criteria
can be used in combination with, or alternative to the selection of
framework positions having divergent amino acid residues. These
additional criteria are described further and similarly are well
known to those skilled in the art.
[0085] Another criteria which can be used for determining the
relevant amino acid positions to change can be, for example,
selection of framework residues that are known to be important, or
contribute to CDR conformation. For example, canonical framework
residues play such a role in CDR conformation or structure. Such
residues can be considered to be relevant to change for a variety
of reasons, including for example, their new context of being
associated with heterologous CDR sequences in the grafted variable
region. Targeting of a canonical framework residue as a relevant
position to change can identify a more compatible amino acid
residue in context with its associated donor CDR sequence.
Additionally, targeting of canonical residues can allow for the
identification of residues at these positions that absorb
detrimental effects to CDR structure from residues located
elsewhere in the framework region.
[0086] The frequency of an amino acid residue at a particular
framework position is another criteria which can be used for
selecting relevant framework amino acid positions to change. For
example, comparison of the selected framework with other framework
sequences within its subfamily can reveal residues that occur at
minor frequencies at a particular position or positions. Such
positions harboring less abundant residues are similarly applicable
for selection as a position to alter in the acceptor variable
region framework.
[0087] The relevant amino acid positions to change also can be
selected, for example, based on proximity to a CDR. In certain
contexts, such residues can participate in CDR conformation or
antigen binding. Moreover, this criteria can similarly be used to
prioritize relevant positions selected by other criteria described
herein. Therefore, differentiating between residues proximal and
distal to one or more CDRs is an efficient way to reduce the number
of relevant positions to change using the methods of the
invention.
[0088] Other criteria for selecting relevant amino acid framework
positions to alter include, for example, residues that are known or
predicted to reside in three-dimensional space near the antigen-CDR
interface or predicted to modulate CDR activity. Similarly,
framework residues that are known or predicted to contact opposite
domain of the heavy (VH) and light (VL) chain variable region
interface. Such framework positions can effect the conformation or
affinity of a CDR by modulating the CDR binding pocket, antigen
interaction or the VH and VL interaction. Therefore, selection of
these amino acid positions as relevant for construction of the
diverse population to screen can beneficially identify framework
changes which replace residues having detrimental effects on CDR
conformation or absorb detrimental effects of residues occurring
elsewhere in the framework.
[0089] Finally, other framework residues that can be selected for
alteration include amino acid positions that are inaccessible to
solvent. Such residues are generally buried in the variable region
and therefore capable of influencing the conformation of the CDR or
VH and VL interactions. Solvent accessibility can be predicted, for
example, from the relative hydrophobicity of the environment
created by the amino acid side chains of the polypeptide or by
known three-dimensional structural data.
[0090] In addition to selecting the relevant framework positions,
the method of conferring donor CDR binding affinity onto an
antibody acceptor variable region framework also incorporates
changes in the donor CDR amino acid positions. As with selecting
the relevant framework positions to change, there is similarly a
range of possible changes that can be made in the donor CDR
positions. Some or all of the possible changes that can be selected
for change can be introduced into the population of grafted donor
CDRs to practice the methods of the invention.
[0091] One approach is to change all amino acid positions along a
CDR by replacement at each position with, for example, all twenty
naturally occurring amino acids. The replacement of each position
can occur in the context of other donor CDR amino acid positions so
that a significant portion of the CDR maintains the authentic donor
CDR sequence, and therefore, the binding affinity of the donor CDR.
For example, an acceptor variable region framework targeted for
relevant amino acid positions changes as described previously, can
be targeted for grafting with a population of CDRs containing
single position replacements at each position within the CDRs.
Similarly, an acceptor variable region framework can be targeted
for grafting with a population of CDRs containing more than one
position changed to incorporate all twenty amino acid residues, or
a fractional subset, at each set of positions within the CDRs. For
example, all possible sets of changes corresponding to two, three
or four or more amino acid positions within a CDR can be targeted
for introduction into a population of CDRs for grafting into an
acceptor variable region framework.
[0092] Single amino acid position changes are generated at each
position without altering the remaining amino acid positions within
the CDR. A population of single position changes will contain at
each position the varied amino acid residues, incorporated either
randomly or with a biased frequency, while leaving the remaining
positions as donor CDR residues. For the specific example of a ten
residue CDR, the population will contain species having the first,
second and third, continued through the tenth CDR residue,
individually randomized or represented by a biased frequency of
incorporated amino acid residues while the remaining non-varied
positions represent the donor CDR amino acid residues. For the
specific example described above, these non-varied positions would
correspond to positions 2-10; 1,3-10; 1,2,4-10, continued through
positions 1-9, respectively. Therefore, the resultant population
will contain species that represent all single position
changes.
[0093] Similarly, double, triple and quadruple amino acid position
changes can be generated for each set of positions without altering
the remain amino acid positions within the CDR. For example, a
population of double position changes will contain at each set of
two positions the varied amino acid residues while leaving the
remaining positions as donor CDR residues. The sets will correspond
to, for example, positions 1 and 2, 1 and 3, 1 and 4, through the
set corresponding to the first and last position of the CDR. The
population will also contain sets corresponding to positions 2 and
3, 2 and 4, 2 and 5, through the set corresponding to the second an
last position of the CDR. Likewise, the population will contain
sets of double position changes corresponding to all pairs of
position changes beginning with position three of the CDR. Similar
pairs of position changes are made with the remaining sets CDR
amino acid positions. Therefore, the population will contain
species that represent all pairwise combinations of amino acid
position changes. In a simialar fashion, populations corresponding
to sets of changes representing all triple and quadruplet changes
along a CDR can similarly be targeted for grafting into the
variable region frameworks using the methods of the invention.
[0094] The above populations of CDR variant species can be targeted
for any or all of the CDRs which constitute the binding pocket of a
variable region. Therefore, an acceptor variable region framework
targeted for relevant amino acid positions changes as described
previously, can be targeted for the simultaneous incorporation of
donor CDR variant populations at one, two or all three recipient
CDR locations. The choice of which CDR or the number of CDRs to
target with amino acid position changes will depend on, for
example, if a full CDR grafting into an acceptor is desired or
whether the method is being performed for optimization of binding
affinity. Many grafting procedures will generally employ the
grafting of all three CDRs, where at least one of the CDRs will
contain amino acid positions changes. Generally however, all of the
donor CDRs will be populations containing amino acid position
changes. Converesly, and as described further below, optimization
procedures can employ CDR variant populations corresponding to any
or all of the CDRs within a variable region.
[0095] Another approach for selecting donor CDR amino acids to
change for conferring donor CDR binding affinity onto an antibody
acceptor variable region framework is to select known or readily
identifiable CDR positions that are highly variable. For example,
the variable region CDR 3 is generally highly variable due to
genetic recombination. This region therefore can be selectively
targeted for amino acid position changes during grafting procedures
to ensure binding affinity reacquisition or augmentation when made
together with relevant acceptor variable framework changes as
described previously.
[0096] In contrast, CDR residues that appear conserved or have been
empirically determined to be non-mutable by functional criteria
will generally be avoided when selecting residues in the CDR to
target for change. It should be noted however, that apparent
non-mutable residues can nevertheless be successfully changed using
the methods of the invention because the populations of altered
variable regions contain from a few to many amino acid position
changes in both the framework regions and in the CDR regions. As
such, the CDR grafted variable regions identified by binding
affinity are a result of the all the changes and therefore, all the
interactions of residues introduced into a particular species.
Therefore, suboptimal residues incorporated at, for example, an
apparent non-mutable position can be counteracted and even
augmented by amino acid substitutions elsewhere in the framework
regions or in other CDRs.
[0097] Similarly, because the methods of the invention for CDR
grafting, affinity reacquisition and affinity optimization employ
the production and screening of diverse populations of variable
region species generated from an acceptor framework and donor CDR
variants, there are numerous effects on binding affinity that will
occur due to the combined interactions of two or more amino acid
changes within a single variable region species. For example, the
affect of amino acid changes in either a framework region or CDR
that are inherently beneficial can be masked or neutralized due to
surrounding authentic parent residues or due to their context in a
heterologous region of a grafted antibody. However, second site
changes in the surrounding residues or the heterologous regions can
unveil the beneficial characteristics of the latent residue or
residues. Such second site changes can occur, for example, in both
proximal and distal heterologous or homologous region
sequences.
[0098] For example, if the beneficial residue is in a grafted CDR
region, the proximal heterologous sequences would be the adjacent
framework regions whereas distal heterologous regions would be
framework regions separated by an adjacent CDR. In this specific
example, a proximal homologous region would be the surrounding
residues within the grafted CDR harboring the beneficial change
whereas the remaining CDRs are examples of distal homologous
regions. By analogy, the opposite would be true for an inherently
beneficial residue in a framework region. Specifically, proximal
homologous region sequences would be located in the same framework
region and distal homologous sequences would be in any of the other
framework regions. Proximal heterologous region sequences would be
in the adjacent CDR or CDRs whereas nonadjacent CDRs constitute
distal heterologous region sequences. Such second site effects can
occur, for example, through the translation of conformational
changes to the CDR binding pocket or to the framework regions.
[0099] Other effects on binding affinity that will occur due to the
combined interactions of two or more amino acid changes within a
single variable region species include, for example, the
neutralization or augmentation of inherently detrimental changes
and the augmentation of beneficial amino acid changes or the
augmentation of parent residues. As with the unveiling of
beneficial changes and the ability to counteract changes in
apparently non-mutable residues, the neutralization and
augmentation of amino acid changes within the grafted CDRs or
framework region by second site changes can occur, for example, by
imparting or translating conformational changes from the second
site changes to the CDR binding pocket or to the framework regions.
The second site changes can occur in any of the framework regions,
including for example, framework regions 1 through 4 as well as in
any of the three CDR regions. An advantage of the methods of the
invention is that no prior information is required to assess which
amino acid positions or changes can be inherently beneficial or
detrimental, or which positions or changes can be further augmented
by second site changes. Instead, by selecting relevant amino acid
positions or subsets thereof in the acceptor variable region
framework and CDRs, and generating a diverse population containing
amino acid variants at these positions, combinations of beneficial
changes occurring at the selected positions will be identified by
screening for increased or optimized binding affinity of the CDR
graft variable region. Such beneficial combinations will include
the unveiling of inherently beneficial residues, neutralization of
inherently detrimental residues and the augmentation of parent
residues or functionally neutral changes.
[0100] Following selection of relevant amino acid positions in the
framework regions and in the donor CDRs as described previously,
amino acid changes at some or all of the selected positions are
incorporated into encoding nucleic acids for the acceptor variable
region framework and donor CDRs, respectively. Simultaneous with
incorporating the encoding amino acid changes at the selected
positions, the encoding nucleic acids sequences for each of the
donor CDRs, including selected changes, are also incorporated into
the acceptor variable region framework encoding nucleic acid to
generate a population of altered variable region encoding nucleic
acids.
[0101] An altered variable region of the invention will contain at
least one framework position which variably incorporates different
amino acid residues and at least one CDR position which variably
incorporates different amino acid residues as described previously.
The variability at any or all of the altered positions can range
from a few to a plurality of different amino acid residues,
including all twenty naturally occurring amino acids or functional
equivalents and analogues thereof. The different species of the
altered variable region containing the variable amino acid residues
at one or more positions within the framework and CDR regions will
make up the population for which to screen for an altered variable
region having binding affinity substantially the same or greater
than the donor CDR variable region.
[0102] Selection of the number and location of the amino acid
positions to vary is flexible and can depend on the intended use
and desired efficiency for identification of the altered variable
region having substantially the same or greater binding affinity
compared to the donor variable region. In this regard, the greater
the number of changes that are incorporated into a altered variable
region population, the more efficient it is to identify at least
one species that exhibits substantially the same or greater binding
affinity as the donor. Alternatively, where the user has empirical
or actual data to the affect that certain amino acid residues or
positions contribute disproportionally to binding affinity, then it
can be desirable to produce a limited population of altered
variable regions which focuses on changes within or around those
identified residues or positions.
[0103] For example, if CDR grafted variable regions are desired, a
large, diverse population of altered variable regions can include
all the non-identical framework region positions between the donor
and acceptor framework and all single CDR amino acid position
changes. Alternatively, a population of intermediate diversity can
include subsets, for example, of only the proximal non-identical
framework positions to be incorporated together with all single CDR
amino acid position changes. The diversity of the above populations
can be further increased by, for example, additionally including
all pairwise CDR amino acid position changes. In contrast,
populations focusing on predetermined residues or positions which
incorporate variant residues at as few as one framework and one CDR
amino acid position can similarly be constructed for screening and
identification of an altered antibody variable region of the
invention. As with the above populations, the diversity of such
focused populations can be further increased by additionally
expanding on the positions selected for change to include other
relevant positions in either or both of the framework and CDR
regions. There are numerous other combinations ranging from few
changes to many changes in either or both of the framework regions
and CDRs that can additionally be employed, all of which will
result in a population of altered variable regions that can be
screened for the identification of at least one CDR grafted altered
variable region of the invention. Those skilled in the art will
know, or can determine, which selected residue positions in the
framework or donor CDRs, or subsets thereof, can be varied to
produce a population for screening and identification of a altered
antibody of the invention given the teachings and guidance provided
herein.
[0104] Simultaneous incorporation of all of the CDR encoding
nucleic acids and all of the selected amino acid position changes
can be accomplished by a variety of methods known to those skilled
in the art, including for example, recombinant and chemical
synthesis. For example, simultaneous incorporation can be
accomplished by, for example, chemically synthesizing the
nucleotide sequence for the acceptor variable region, fused
together with the donor CDR encoding nucleic acids, and
incorporating at the positions selected for harboring variable
amino acid residues a plurality of corresponding amino acid
codons.
[0105] One such method well known in the art for rapidly and
efficiently producing a large number of alterations in a known
amino acid sequence or for generating a diverse population of
variable or random sequences is known as codon-based synthesis or
mutagenesis. This method is the subject matter of U.S. Pat. Nos.
5,264,563 and 5,523,388 and is also described in Glaser et al. J.
Immunology 149:3903 (1992). Briefly, coupling reactions for the
randomization of, for example, all twenty codons which specify the
amino acids of the genetic code are performed in separate reaction
vessels and randomization for a particular codon position occurs by
mixing the products of each of the reaction vessels. Following
mixing, the randomized reaction products corresponding to codons
encoding an equal mixture of all twenty amino acids are then
divided into separate reaction vessels for the synthesis of each
randomized codon at the next position. For the synthesis of equal
frequencies of all twenty amino acids, up to two codons can be
synthesized in each reaction vessel.
[0106] Variations to these synthesis methods also exist and include
for example, the synthesis of predetermined codons at desired
positions and the biased synthesis of a predetermined sequence at
one or more codon positions. Biased synthesis involves the use of
two reaction vessels where the predetermined or parent codon is
synthesized in one vessel and the random codon sequence is
synthesized in the second vessel. The second vessel can be divided
into multiple reaction vessels such as that described above for the
synthesis of codons specifying totally random amino acids at a
particular position. Alternatively, a population of degenerate
codons can be synthesized in the second reaction vessel such as
through the coupling of NNG/T nucleotides where N is a mixture of
all four nucleotides. Following synthesis of the predetermined and
random codons, the reaction products in each of the two reaction
vessels are mixed and then redivided into an additional two vessels
for synthesis at the next codon position.
[0107] A modification to the above-described codon-based synthesis
for producing a diverse number of variant sequences can similarly
be employed for the production of the variant populations described
herein. This modification is based on the two vessel method
described above which biases synthesis toward the parent sequence
and allows the user to separate the variants into populations
containing a specified number of codon positions that have random
codon changes.
[0108] Briefly, this synthesis is performed by continuing to divide
the reaction vessels after the synthesis of each codon position
into two new vessels. After the division, the reaction products
from each consecutive pair of reaction vessels, starting with the
second vessel, is mixed. This mixing brings together the reaction
products having the same number of codon positions with random
changes. Synthesis proceeds by then dividing the products of the
first and last vessel and the newly mixed products from each
consecutive pair of reaction vessels and redividing into two new
vessels. In one of the new vessels, the parent codon is synthesized
and in the second vessel, the random codon is synthesized. For
example, synthesis at the first codon position entails synthesis of
the parent codon in one reaction vessel and synthesis of a random
codon in the second reaction vessel. For synthesis at the second
codon position, each of the first two reaction vessels is divided
into two vessels yielding two pairs of vessels. For each pair, a
parent codon is synthesized in one of the vessels and a random
codon is synthesized in the second vessel. When arranged linearly,
the reaction products in the second and third vessels are mixed to
bring together those products having random codon sequences at
single codon positions. This mixing also reduces the product
populations to three, which are the starting populations for the
next round of synthesis. Similarly, for the third, fourth and each
remaining position, each reaction product population for the
preceding position are divided and a parent and random codon
synthesized.
[0109] Following the above modification of codon-based synthesis,
populations containing random codon changes at one, two, three and
four positions as well as others can be conveniently separated out
and used based on the need of the individual. Moreover, this
synthesis scheme also allows enrichment of the populations for the
randomized sequences over the parent sequence since the vessel
containing only the parent sequence synthesis is similarly
separated out from the random codon synthesis.
[0110] Other methods well known in the art for producing a large
number of alterations in a known amino acid sequence or for
generating a diverse population of variable or random sequences
include, for example, degenerate or partially degenerate
oligonucleotide synthesis. Codons specifying equal mixtures of all
four nucleotide monomers, represented as NNN, results in degenerate
synthesis. Whereas partially degenerate synthesis can be
accomplished using, for example, the NNG/T codon described
previously. Other method well know in the art can alternatively be
used such as the use of statistically predetermined, or varigated,
codon synthesis which is the subject matter of U.S. Pat. Nos.
5,223,409 and 5,403,484.
[0111] Once the populations of altered variable region encoding
nucleic acids have been constructed as described above, they can be
expressed to generate a population of altered variable region
polypeptides that can be screened for binding affinity. For
example, the altered variable region encoding nucleic acids can be
cloned into an appropriate vector for propagation, manipulation and
expression. Such vectors are known or can be constructed by those
skilled in the art and should contain all expression elements
sufficient for the transcription, translation, regulation, and if
desired, sorting and secretion of the altered variable region
polypeptides. The vectors also can be for use in either procaryotic
or eukaryotic host systems so long as the expression and regulatory
elements are of compatible origin. The expression vectors can
additionally included regulatory elements for inducible or cell
type-specific expression. One skilled in the art will know which
host systems are compatible with a particular vector and which
regulatory or functional elements are sufficient to achieve
expression of the polypeptides in soluble, secreted or cell surface
forms.
[0112] Appropriate host cells, include for example, bacteria and
corresponding bacteriophage expression systems, yeast, avian,
insect and mammalian cells. Methods for recombinant expression,
screening and purification of populations of altered variable
regions or altered variable region polypeptides within such
populations in various host systems are well known in the art and
are described, for example, in Sambrook et al., Molecular Cloning:
A Laboratory Manual, Cold Spring Harbor Laboratory, New York (1992)
and in Ansubel et al., Current Protocols in Molecular Biology, John
Wiley and Sons, Baltimore, Md. (1998). The choice of a particular
vector and host system for expression and screening of altered
variable regions will be known by those skilled in the art and will
depend on the preference of the user. A specific example of the
expression of recombinant altered variable region polypeptides is
additionally described below in the Examples. Moreover, expression
of diverse populations of hetereomeric receptors in either soluble
or cell surface form using filamentous bacteriophage vector/host
systems is well known in the art and is the subject matter of U.S.
Pat. No. 5,871,974.
[0113] The expressed population of altered variable region
polypeptides can be screened for the identification of one or more
altered variable region species exhibiting binding affinity
substantially the same or greater than the donor CDR variable
region. Screening can be accomplished using various methods well
known in the art for determining the binding affinity of a
polypeptide or compound. Additionaly, methods based on determining
the relative affinity of binding molecules to their partner by
comparing the amount of binding between the altered variable region
polypeptides and the donor CDR variable region can similarly be
used for the identification of species exhibiting binding affinity
substantially the same or greater than the donor CDR variable
region. All of such methods can be performed, for example, in
solution or in solid phase. Moreover, various formats of binding
assays are well known in the art and include, for example,
immobilization to filters such as nylon or nitrocellulose;
two-dimensional arrays, enzyme linked immunosorbant assay (ELISA),
radioimmune assay (RIA), panning and plasmon resonance. Such
methods can be found described in, for example, Sambrook et al.,
supra, and Ansubel et al.
[0114] For the screening of populations of polypeptides such as the
altered variable region populations produced by the methods of the
invention, immobilization of the populations of altered variable
regions to filters or other solid substrate is particularly
advantageous because large numbers of different species can be
efficiently screened for antigen binding. Such filter lifts will
allow for the identification of altered variable regions that
exhibit substantially the same or greater binding affinity compared
to the donor CDR variable region. Alternatively, if the populations
of altered variable regions are expressed on the surface of a cell
or bacteriophage, for example, panning on immobilized antigen can
be used to efficiently screen for the relative binding affinity of
species within the population and for those which exhibit
substantially the same or greater binding affinity than the donor
CDR variable region.
[0115] Another affinity method for screening populations of altered
variable regions polypeptides is a capture lift assay that is
useful for identifying a binding molecule having selective affinity
for a ligand (Watkins et. al., (1997)). This method employs the
selective immobilization of altered variable regions to a solid
support and then screening of the selectively immobilized altered
variable regions for selective binding interactions against the
cognate antigen or binding partner. Selective immobilization
functions to increase the sensitivity of the binding interaction
being measured since initial immobilization of a population of
altered variable regions onto a solid support reduces non-specific
binding interactions with irrelevant molecules or contaminants
which can be present in the reaction.
[0116] Another method for screening populations or for measuring
the affinity of individual altered variable region polypeptides is
through surface plasmon resonance (SPR). This method is based on
the phenomenon which occurs when surface plasmon waves are excited
at a metal/liquid interface. Light is directed at, and reflected
from, the side of the surface not in contact with sample, and SPR
causes a reduction in the reflected light intensity at a specific
combination of angle and wavelength. Biomolecular binding events
cause changes in the refractive index at the surface layer, which
are detected as changes in the SPR signal. The binding event can be
either binding association or disassociation between a
receptor-ligand pair. The changes in refractive index can be
measured essentially instantaneously and therefore allows for
determination of the individual components of an affinity constant.
More specifically, the method enables accurate measurements of
association rates (kon) and disassociation rates (koff).
[0117] Measurements of kon and koff values can be advantageous
because they can identify altered variable regions or optimized
variable regions that are therapeutically more efficacious. For
example, an altered variable region, or heteromeric binding
fragment thereof, can be more efficacious because it has, for
example, a higher kon valued compared to variable regions and
heteromeric binding fragments that exhibit similar binding
affinity. Increased efficacy is conferred because molecules with
higher kon values can specifically bind and inhibit their target at
a faster rate. Similarly, a molecule of the invention can be more
efficacious because it exhibits a lower koff value compared to
molecules having similar binding affinity. Increased efficacy
observed with molecules having lower koff rates can be observed
because, once bound, the molecules are slower to dissociate from
their target. Although described with reference to the altered
variable regions and optimized variable regions of the invention
including, heteromeric variable region binding fragments thereof,
the methods described above for measuring associating and
disassociation rates are applicable to essentially any antibody or
fragment thereof for identifying more effective binders for
therapeutic or diagnostic purposes.
[0118] Methods for measuring the affinity, including association
and disassociation rates using surface plasmon resonance are well
known in the arts and can be found described in, for example,
Jonsson and Malmquist, Advances in Biosnsors, 2:291-336 (1992) and
Wu et al. Proc. Natl. Acad. Sci. USA, 95:6037-6042 (1998).
Moreover, one apparatus well known in the art for measuring binding
interactions is a BIAcore 2000 instrument which is commercially
available through Pharmacia Biosensor, (Uppsala, Sweden).
[0119] Using any of the above described screening methods, as well
as others well known in the art, an altered variable region having
binding affinity substantially the same or greater than the donor
CDR variable region is identified by detecting the binding of at
least one altered variable region within the population to its
antigen or cognate ligand. Additionally, the above methods can
alternatively be modified by, for example, the addition of
substrate and reactants, to identify using the methods of the
invention, altered variable regions having catalytic activity
substantially the same or greater that the donor CDR variable
region within the populations. Comparision, either independently or
simultaneously in the same screen, with the donor variable region
will identify, those binders that have substantially the same or
greater binding affinity as the donor. Those skilled in the art
will know, or can determine using the donor variable region,
binding conditions which are sufficient to identify selective
interactions over non-specific binding.
[0120] Detection methods for identification of binding species
within the population of altered variable regions can be direct or
indirect and can include, for example, the measurement of light
emission, radioisotopes, calorimetric dyes and fluorochromes.
Direct detection includes methods that operate without
intermediates or secondary measuring procedures to assess the
amount of bound antigen or ligand. Such methods generally employ
ligands that are themselves labeled by, for example, radioactive,
light emitting or fluorescent moieties. In contrast, indirect
detection includes methods that operate through an intermediate or
secondary measuring procedure. These methods generally employ
molecules that specifically react with the antigen or ligand and
can themselves be directly labeled or detected by a secondary
reagent. For example, a antibody specific for a ligand can be
detected using a secondary antibody capable of interacting with the
first antibody specific for the ligand, again using the detection
methods described above for direct detection. Indirect methods can
additionally employ detection by enzymatic labels. Moreover, for
the specific example of screening for catalytic antibodies, the
disappearance of a substrate or the appearance of a product can be
used as an indirect measure of binding affinity or catalytic
activity.
[0121] Isolated variable regions exhibit binding affinity as single
chains, in the absence of assembly into a heteromeric structure
with their respective VH or VL subunits. As such, populations of VH
and VL altered variable regions polypeptides can be expressed alone
and screened for binding affinity having substantially the same or
greater binding affinity compared to the CDR donor VH or VL
variable region. Alternatively, populations of VH and VL altered
variable regions polypeptides can be coexpressed so that they
self-assemble into heteromeric altered variable region binding
fragments. The heteromeric binding fragment population can then be
screened for species exhibiting binding affinity substantially the
same or greater than the CDR donor variable region binding
fragment. A specific example of the coexpression and self-assembly
of populations VH and VL altered variable regions into hetermeric
populations is described further below in the Examples.
[0122] Therefore, the invention provides a method of simultaneously
grafting and optimizing the binding affinity of a variable region
binding fragment. The method consists of: (a) constructing a
population of altered heavy chain variable region encoding nucleic
acids consisting of an acceptor variable region framework,
containing donor CDRs and a plurality of different amino acids at
one or more framework region and CDR amino acid positions; (b)
coexpressing the populations of heavy and light chain variable
region encoding nucleic acids to produce diverse combinations of
heteromeric variable region binding fragments, and (c) identifying
one or more heteromeric variable region binding fragments having
affinity substantially the same or greater than the donor CDR
heteromeric variable region binding fragment.
[0123] The invention additionally provides a method of optimizing
the binding affinity of an antibody variable region. The consists
of: (a) constructing a population of antibody variable region
encoding nucleic acids, said population comprising two or more CDRs
containing a plurality of different amino acids at one or more CDR
amino acid positions; (b) expressing said population of variable
region encoding nucleic acids, and (c) identifying one or more
variable regions having binding affinity substantially the same or
greater than the donor CDR variable region.
[0124] The methods described above, for conferring donor CDR
binding affinity onto an antibody acceptor variable region
framework and for simultaneously grafting and optimizing the
binding affinity of a heteromeric variable region binding fragment,
can additionally be employed to modify or optimize the binding
affinity of a variable region or a heteromeric variable region
binding fragment. Similar to the previously described methods, the
method for modifying or optimizing binding affinity involves the
selection of relevant amino acid positions and the construction,
expression and screening of variable region populations containing
variable amino acid residues at all or a fraction of the selected
positions. However, for optimization of binding affinity it is not
necessary to vary amino acid positions in the framework regions.
Instead, all that is required is to alter one or more amino acid
positions in two or more CDR regions. Changing the CDR amino acid
residues directly effects the binding affinity. Once a population
containing variable amino acid residues incorporated in two or more
CDRs is produced, all that is necessary is to screen the population
for species that contain the desired binding affinity modification.
All of the criteria for selecting relevant amino acid positions
described previously are applicable for use in this mode of the
method. Therefore, the methods for modifying or optimizing the
binding affinity of a variable region or a heteromeric variable
region binding fragment by altering one or more amino acid
positions in two or more CDR regions are applicable to essentially
any variable region, grafted variable region as well as applicable
to the altered and optimized variable regions of the invention.
[0125] Moreover, by incorporating variable amino acid residues in
two or more CDRs when employing the methods conferring donor CDR
binding affinity onto an acceptor framework, this method of
modifying binding affinity is therefore useful for simultaneously
optimizing the binding affinity of a grafted antibody. Employing
the methods for simultaneously grafting and optimizing, or for
optimizing, it is possible to generate heteromeric variable region
binding fragments having increases in affinities of greater than
5-, 8- and 10-fold. In particular, heteromeric variable region
binding fragments can be generated having increases in affinities
of greater than 12-, 15-20- and 25-fold as well as affinities
greater than 50-, 100- and 1000-fold compared to the donor or
parent molecule.
[0126] As mentioned above, for optimization of binding affinity, it
is not necessary to vary amino acid positions in the framework.
Prior to the present work, it was believed that at least some of
acceptor framework amino acids had to be changed to donor (e.g.
murine) amino acids to maintain the binding affinity of the donor
CDRs. As disclosed herein, the present invention teaches that the
acceptor framework (e.g. human framework) does not need to be
modified to maintain donor CDR binding affinity. Instead, the
framework may remain unvaried compared to the parental frameworks,
while the CDRs are modified to retain, and preferably optimize
(e.g. increase) the donor CDR activity (e.g. antigen binding
affinity, on-rate, off-rate, etc.). In this regard, optimized
heteromeric variable region binding fragments exhibiting optimized
activity compared to a donor (e.g. non-human) heteromeric variable
region binding fragment may be generated, where the optimized
heteromeric variable region binding fragment has altered light and
heavy chain variable regions. Preferably, the altered light chain
variable region comprises four unvaried light chain framework
regions (e.g. human germline), and three light chain altered
variable region CDRs, with a least one of the light chain altered
variable reigon CDRs being a light chain donor CDR variant (i.e.
the light chain donor CDR variant comprises a different amino acid
at one or more positions when compared to the corresponding light
chain donor CDR). It is also preferred that the altered heavy chain
variable region comprises four unvaried heavy chain framework
regions (e.g. human germline), and three heavy chain altered
variable region CDRs, with a least one of the heavy chain altered
variable region CDRs being a heavy chain donor CDR variant (i.e.
the heavy chain donor CDR variant comprises a different amino acid
at one or more positions when compared to the corresponding heavy
chain donor CDR). In certain preferred embodiments, the donor
heteromeric variable region is non-human (e.g. murine) and the
unvaried light and heavy chain framework regions are human (e.g.
human gernline framework regions).
[0127] In selecting an unvaried framework (e.g. human germline), in
some embodiments, a number of criteria may be employed (although
employing selection criteria is not necessary to understand or
practice the present invention). For example, one may selected
frameworks that are known to be less immunogenic for a particular
host (e.g. human). Also for example, one may compare key amino
acids in the donor framework with the proposed unvaried frameworks,
and select the unvaried framework that is most similar to the donor
framework at the key amino acid positions (e.g. amino acid
positions that are known to be associated with characteristic loop
conformations or based on structural modeling). Another criteria
that can be employed is to use an unvaried framework that has CDRs
that are approximately the same size (length) as the donor
framework CDRs. An additional criteria that may be used (e.g., for
humans) in order to minimize the risk of immunogenicity, is to
eliminate human genes that are not-functional or that are
infrequently used in the human population (i.e. select human
frameworks that are frequently used in the human population).
[0128] One advantage of the present invention is the fact that
unvaried framework regions may be employed. Preferably, the
unvaried frameworks are human frameworks. In particularly preferred
embodiments, the frameworks are human germline sequences. For
example, the NCBI web site contains the sequences for the currently
known human framework regions. Examples of human VH sequences
include, but are not limited to, VH1-18, VH1-2, VH1-24, VH1-3,
VH1-45, VH1-46, VH1-58, VH1-69, VH1-8, VH2-26, VH2-5, VH2-70,
VH3-11, VH3-13, VH3-15, VH3-16, VH3-20, VH3-21, VH3-23, VH3-30,
VH3-33, VH3-35, VH3-38, VH3-43, VH3-48, VH3-49, VH3-53, VH3-64,
VH3-66, VH3-7, VH3-72, VH3-73, VH3-74, VH3-9, VH4-28, VH4-31,
VH4-34, VH4-39, VH4-4, VH4-59, VH4-61, VH5-51, VH6-1, and VH7-81,
which are provided in Matsuda et al., (1998) J. Exp. Med.
188:1973-1975, that includes the complete nucleotide sequence of
the human immunoglobulin chain variable region locus, herein
incorporated by reference. Examples of human VK sequences include,
but are not limited to, A1, A10, A11, A14, A17, A18, A19, A2, A20,
A23, A26, A27, A3, A30, A5, A7, B2, B3, L1, L10, L11, L12, L14,
L15, L16, L18, L19, L2, L20, L22, L23, L24, L25, L4/18a, L5, L6,
L8, L9, O1, O11, O12, O14, O18, O2, O4, and O8, which are provided
in Kawasaki et al., (2001) Eur. J. Immunol. 31:1017-1028; Schable
and Zachau, (1993) Biol. Chem. Hoppe Seyler 374:1001-1022; and
Brensing-Kuppers et al., (1997) Gene 191:173-181, all of which are
herein incorporated by reference. Examples of human VL sequences
include, but are not limited to, V1-V11, V1-13, V1-16, V1-17,
V1-18, V1-19, V1-2, V1-20, V1-22, V1-3, V1-4, V1-5, V1-7, V1-9,
V2-1, V2-11, V2-13, V2-14, V2-15, V2-17, V2-19, V2-6, V2-7, V2-8,
V3-2, V3-3, V3-4, V4-1, V4-2, V4-3, V4-4, V4-6, V5-1, V5-2, V5-4,
and V5-6, which are provided in Kawasaki et al., (1997) Genome Res.
7:250-261, herein incorporated by reference. Unvaried human
frameworks can be selected from any of these functional germline
genes.
[0129] While not necessary to practice or understand the invention,
it is believed that the use of germline frameworks is expected to
help eliminate or reduce adverse immune responses (e.g., when
administered therapeutically) in most individuals. Somatic
mutations frequently occur in the variable region of
immunoglobulins as a result of the affinity maturation step that
takes place during a normal immune response. Although these
mutations are predominantly clustered around the hypervariable
CDRs, they also impact residues in the framework regions. These
framework mutations are not present in the germline genes and
therefore such framework mutations may be immunogenic when
administered to patients. In contrast, the general population has
been exposed to the vast majority of framework sequences expressed
from germline genes and, as a result of immunologic tolerance,
these germline frameworks should be less, or non-immunogenic in
patients. In order to maximize the likelihood of tolerance, genes
encoding the variable regions can be selected from a collection of
commonly occurring, functional germline genes, and genes encoding
VH and VL regions can be further selected to match known
associations between specific heavy and light chains of
immunoglobulin molecules. Also, germlines variable regions genes
that are frequently utilized in the human population are preferred
(again, to limit the likelihood of adverse immunogenic reactions).
For example, the human kappa light chain germline gene that is the
source of the light chain framework may be selected from the
following; A11, A17, A18, A19, A20, A27, A30, L1, L11, L12, L2, L5,
L6, L8, O12, O2, and O8. Likewise, the human heavy chain germline
gene that is the source of the heavy chain framework may be
selected from the following VH2-5, VH2-26, VH2-70, VH3-20, VH3-72,
VH1-46, VH3-9, VH3-66, VH3-74, VH4-31, VH1-18, VH1-69, VH3-7,
VH3-11, VH3-15, VH3-21, VH3-23, VH3-30, VH3-48, VH4-39, VH4-59, and
VH5-51.
[0130] Additionally, the methods described herein for optimizing
are also are applicable for producing catalytic heteromeric
variable region fragments or for optimizing their catalytic
activity. Catalytic activity can be optimized by changing, for
example, the on or off rate, the substrate binding affinity, the
transition state binding affinity, the turnover rate (kcat) or the
Km. Methods for measuring these characteristics are well known in
the art. Such methods can be employed in the screening steps of the
methods described above when used for optimizing the catalytic
activity of a heteromeric variable region binding fragment.
[0131] The methods for conferring donor CDR binding affinity onto
an antibody acceptor variable region framework described previously
are applicable for use with essentially any distinguishable donor
and acceptor pair. Many applications of the methods will be for the
production and optimization of variable region binding fragments
having human acceptor frameworks due to the therapeutic importance
of such molecules in the treatment of human diseases. However, the
method are applicable for conferring donor CDR binding affinity
onto an acceptor originating from the same or a divergent species
as the CDR donor variable region so long as the framework regions
between the donor and acceptor variable regions are distinct.
Therefore, the invention included altered variable regions having
acceptor frameworks derived from human, mouse, rat, rabbit, goat
and chicken, for example.
[0132] Additionally, the methods for conferring donor CDR binding
affinity onto an antibody acceptor variable region framework are
applicable for grafting CDRs as described by Kabat et al., supra,
Chothia et al., supra or MacCallum et al., supra. The methods
similarly can be used for grafting into an acceptor framework
overlapping regions or combinations of CDR as described by these
authors. Generally, the methods will graft variable region CDRs by
identifying the boundries described by one of the CDR definitions
known in the art and set forth herein. However, because the methods
are directed to constructing and screening populations of CDR
grafted altered variable regions which incorporate relevant amino
acid position changes in both the framework and CDR regions, and
such variations can, for example, compensate or augment amino acid
changes elsewhere in the variable region, the exact boundry of a
particular CDR or set of variable region CDRs can be varied.
Therefore, the exact CDR region to graft, whether it is the region
described by Kabat et al., Chothia et al. or MacCallum et al., or
any combination thereof, will essentially depend on the preference
of the user.
[0133] Similarly, the methods described previously for optimizing
the binding affinity of an antibody also are applicable for use
with essentially any variable region for which an encoding nucleic
acid is, or can be made available. As with the methods for
conferring donor CDR binding affinity, many applications of the
methods for optimizing binding affinity will be for modifying the
binding affinity of CDR grafted variable regions having human
frameworks. Again, such molecules are significantly less antigenic
in human patients and therefore therapeutically valuable in the
treatment of human diseases. However, the methods of the invention
for optimizing the binding affinity of a variable region are
applicable to all species of variable regions. Therefore, the
invention includes binding affiity optimization of variable regions
derived from human, mouse, rat, rabbit, goat and chicken, for
example.
[0134] The methods of the invention have been described with
reference to variable regions and heteromic variable region binding
fragments. Given these descriptions and teaching herein, those
skilled in the art will understand that all of such methods are
applicable to whole antibodies and functional fragments thereof as
well as to regions and functional: domains other than the antigen
binding variable region of antibodies. Moreover, the methods
described herein are further applicable to molecules other than
antibodies, variable regions and other antibody functional domains.
Given the teachings of the invention, those skilled in the art will
know how to apply the methods of simultaneously constructing hybrid
molecules and maintaining or optimizing the binding affinity or
catalytic activity of a target molecule, as well as how to apply
the methods of optimizing the binding affinity or catalytic
activity to a variety of different types and classes of
polypeptides and proteins.
[0135] The methods for optimizing the binding affinity of an
antibody variable region can include the selection of relevant
acceptor framework and donor CDR amino acid positions to be
altered. Amino acid residues selected for alteration during binding
affinity optimization are typically amino positions predicted to be
relatively important for structure or function. Criteria that can
be used for identifying amino positions to be altered include, for
example, conservation of amino acids among polypeptide subfamily
members and knowledge that particular amino acids are predicted to
be important in polypeptide conformation or structure, as described
above. Alternatively, potentially important framework residues that
differ between acceptor framework and donor CDR can be
characterized without structural information by synthesizing and
expressing a combinatorial antibody library that contains all
possible combinations of amino acids in framework positions to be
optimized.
[0136] The invention provides a method for identifying one or more
functional amino acid positions of a polypeptide. The method
consists of (a) constructing a population of nucleic acids encoding
a population of altered polypeptides containing substitutions of
one or more amino acid positions within a polypeptide; (b)
expressing the population of nucleic acids; (c) identifying nucleic
acids encoding altered polypeptides having a functional activity of
the polypeptide; (d) sequencing a subset of nucleic acids encoding
altered polypeptides having a functional activity, and (e)
comparing an amino acid position in a polypeptide corresponding to
an amino acid position in the subset of altered polypeptides
wherein an amino acid position exhibiting a biased representation
of amino acid residues indicates a functional amino acid position
in the polypeptide.
[0137] The method of the invention directed to identifying a
functional amino acid position in a polypeptide involves
substituting one or more amino acid positions in a polypeptide with
a plurality of amino acid residues, as described previously for
optimizing the binding affinity of an antibody, and identifying
altered polypeptides having an activity that is substantially the
same or greater than the parent polypeptide. Functional amino acid
positions identified using the methods of the invention are amino
acid positions important for a conformation, functional activity or
structure of a polypeptide. Functional activities of a polypeptide
can include, for example, binding affinity to a substrate, ligand,
or other interacting molecule, and catalytic activity.
[0138] The identification of functional amino acid positions in a
polypeptide involves constructing a population of nucleic acids
encoding a population of altered polypeptides containing amino acid
substitutions at specific amino acid positions. Substituted amino
acids include all twenty naturally occurring amino acid residues or
a subset of amino acid residues, as described previously in detail.
Nucleic acid populations can be constructed by any method known in
the art and as described previously. A population of nucleic acids
encoding altered polypeptides is expressed in an appropriate host
cell, and a functional activity of altered polypeptides is detected
and compared with that of the polypeptide. Any method known in the
art that is appropriate for determining a polypeptide functional
activity can be used to compare polypeptide and altered polypeptide
functional activities.
[0139] A subset of nucleic acids encoding altered polypeptides
having a functional activity that is substantially the same or
greater than that of the polypeptide is sequenced. A subset can
include a few molecules to many members constituting the population
of nucleic acids encoding altered polypeptides. For example, a
subset can consist of about 2-5, 6-10, 10-20, and 21 or greater
members of the population. The actual number sequenced will vary
with the total size of the nucleic acid population. Generally,
however, a subset of about 15-25 and typically about 20 members is
sufficient in order to identify functional amino acids.
[0140] Amino acid residues at substituted positions in the
polypeptide are compared to the corresponding position in altered
polypeptides. An amino acid position that contains the same amino
acid or a conservative substitution among the population of altered
polypeptides exhibits biased representation of that amino acid
residue. Biased representation indicates that a particular amino
acid is required for polypeptide function. Amino acid positions
that are biased are therefore considered important for functional
activity of a polypeptide. Amino acid positions that contain a
variety of substituted amino acids are unbiased and considered not
important or less important for a polypeptide function.
[0141] The method of identifying an amino acid position important
for polypeptide function is useful for a variety of applications,
such as, for example, the determination of a consensus sequence of
amino acids important for a polypeptide functional activity. A
consensus sequence is useful for the optimization of a polypeptide
function because amino acid positions determined to be important
for functional activity can be unaltered while amino acid positions
not important for activity can be varied. Polypeptide functions
that can be optimized using the method of the invention include,
for example, catalytic activity, polypeptide conformation and
binding affinity.
[0142] The identification of a functional amino acid position in a
polypeptide can be applied to determining a consensus sequence of
amino acids that impart a particular activity to a polypeptide. For
example, a consensus sequence that provides a catalytic activity to
an enzyme can be determined using the methods of the invention. To
identify amino acid positions that are important or critical to
catalytic activity of an enzyme, one or more of amino acid
positions are substituted with a plurality of amino acid
substitutions, as described previously. A nucleic acid population
encoding altered enzyme polypeptides is constructed and expressed
in host cells. The catalytic activity of altered enzymes is
measured and compared with a parent enzyme or other catalytically
active form of the enzyme.
[0143] Nucleic acids encoding a subset of altered enzyme
polypeptides identified by functional activity are sequenced, and
the amino acid sequences of altered polypeptides are compared.
Amino acid positions that contain a particular amino acid or a
conservative substitution are determined to be important for a
catalytic activity of the enzyme. A sequence of amino acids
determined to be biased in a polypeptide can thus provide a
consensus sequence that defines amino acid positions required for
catalytic activity. A consensus sequence of residues important for
various aspects of catalytic activity such as, for example,
substrate binding, proper active site conformation, and co-factor
binding can be identified using the methods of the invention by
measuring enzyme catalytic activity, as described above.
[0144] Similarly, a consensus sequence associated with a particular
conformation of a polypeptide can be determined using the method of
the invention in essentially the same manner as described above for
polypeptide catalytic activity. The amino acid positions that have
functional roles in a polypeptide conformation can be determined so
long as a particular conformation state can be detected and
compared between a polypeptide and an altered polypeptide. For
example, a consensus sequence of a polypeptide conformation that
confers a particular functional activity to a polypeptide or a
particular structural feature to a polypeptide can be determined
using the methods of the invention. A structural feature can
include, for example, the exposure of a certain amino acid on the
surface of a polypeptide.
[0145] A consensus sequence of amino acid positions in a
polypeptide important for binding affinity can also be determined
using the methods of the invention. The binding affinities of
polypeptides include, for example, the binding affinity between two
or more polypeptides in a protein-protein interaction and the
binding affinity between a polypeptide and a substrate. For
example, a consensus sequence for the binding affinity of an
antibody for an antigen can be determined, and can be applied to
the process of antibody humanization.
[0146] The identification of a functional amino acid position in a
polypeptide can be applied to determining the consensus sequence
for a humanized version of an antibody that preserves the binding
activity of the parent antibody. For example, a library containing
all possible combinations of human template and murine parent
antibody residues in a selected number of amino positions can be
synthesized by method known in the art, for example, using
codon-based mutagenesis as described previously. Framework
polypeptides containing amino acid substitutions can then be
screened by functional binding to identify altered framework
polypeptides that have a binding affinity substantially the same as
the parent antibody. Of the amino acid positions altered, only a
small percentage of framework positions are typically critical for
antibody binding activity. Therefore, a low throughput screening
method of identifying active humanized framework variants can be
used. Sequencing of nucleic acids encoding humanized frameworks
displaying a functional activity of the parent antibody is then
used to identify altered polypeptides having significant bias
toward murine human residues. Thus, a consensus humanization
sequence for maintaining full binding activity of an antibody can
be prepared by using murine CDRs grafted onto a human template on
which amino acid positions are changed to the corresponding residue
determined to be important for binding activity.
[0147] In certain embodiments, the present invention provides
binding molecules (e.g. heteromeric variable region binding
fragments and antibodies) that are able to bind von Willebrand
factor (vWF) (preferably human vWF). In some embodiments, these vWF
binding molecules comprises an unvaried human framework. In
particular embodiments, the unvaried human framework is a human
germline framework. Exemplary CDRs useful for generating such vWF
binding molecules are shown in tables 4 and 5.
[0148] As described below in tables 4 and 5, the present invention
provides numerous CDRs useful for generating vWF binding molecules.
For example, one or more of the CDRs shown in tables 4 and 5 (and
Example 2) can be combined with a framework sub-region (e.g., a
fully human FR1, FR2, FR3, or FR4) in order to generate a vWF
binding molecule, or a nucleic acid sequence encoding a vWF binding
molecule. Also, the CDRs shown in the tables below may be combined,
for example, such that three CDRs are present in a light chain
variable region, and/or three CDRs are present in a heavy chain
variable region. The CDRs shown below may be inserted into a human
framework (e.g., by recombinant techniques) in order to generate
vWF binding molecules or nucleic acid sequences encoding vWF
binding molecules.
2TABLE 4 Light Chain CDRs CDR SEQ ID NO Name* Sequence SEQ ID NO:9
CDRL1 SASQDINDYLN SEQ ID NO:10 CDRL1 AGTGCAAGTCAGGACATTAACGACTATTTA
AAC SEQ ID NO:11 CDRL2 GTSSLHS SEQ ID NO:12 CDRL2
GGCACATCAAGTTTACACTCA SEQ ID NO:13 CDRL2 NTSSLHS SEQ ID NO:14 CDRL2
AACACATCAAGTTTACACTCA SEQ ID NO:15 CDRL2 YTSVLHS SEQ ID NO:16 CDRL2
TACACATCAGTTTTACACTCA SEQ ID NO:17 CDRL2 NTSVLHS SEQ ID NO:18 CDRL2
AACACATCAGTTTTACACTCA SEQ ID NO:19 CDRL2 YTSSLHV SEQ ID NO:20 CDRL2
TACACATCAAGTTTACACGTG SEQ ID NO:21 CDRL2 NTSSLHV SEQ ID NO:22 CDRL2
AACACATCAAGTTTACACGTA SEQ ID NO:23 CDRL3 QQYEDLPWT SEQ ID NO:24
CDRL3 CAGCAGTATGAAGATCTTCCGTGGACG *The work of Kabat was used to
number residues. CDRs include Kabat and Chothia residues.
[0149]
3TABLE 5 Heavy Chain CDRs CDR SEQ ID NO Name* Sequence SEQ ID NO:25
CDRH1 GFSLGDYGVD SEQ ID NO:26 CDRH1 GGATTCTCATTAGGCGACTATGGTGTAGAC
SEQ ID NO:27 CDRH2a MIWPDGST SEQ ID NO:28 CDRH2a
ATGATATGGCCGGATGGAAGCACA SEQ ID NO:29 CDRH2a MIWQDGST SEQ ID NO:30
CDRH2a ATGATATGGCAGGATGGAAGCACA SEQ ID NO:31 CDRH2a MIWGDGSV SEQ ID
NO:32 CDRH2a ATGATATGGGGTGATGGAAGCGTA SEQ ID NO:33 CDRH2b DINSALKS
SEQ ID NO:34 CDRH2b GACATTAATTCAGCTCTCAAGTCC SEQ ID NO:35 CDRH2b
DYNSALAS SEQ ID NO:36 CDRH2b GACTATAATTCAGCTCTCGCATCC SEQ ID NO:37
CDRH2b DYNSALQS SEQ ID NO:38 CDRH2b GACTATAATTCAGCTCTCCAATCC SEQ ID
NO:39 CDRH2b DVNSALQS SEQ ID NO:40 CDRH2b GACGTTAATTCAGCTCTCCAGTCC
SEQ ID NO:41 CDRH2b DVNSALKS SEQ ID NO:42 CDRH2b
GACGTTAATTCAGCTCTCAAGTCC SEQ ID NO:43 CDRH3 DPADYGNYNYALDY SEQ ID
NO:44 CDRH3 GACCCAGCCGACTATGGTAACTACAATTATGCTTTGGACTAC SEQ ID NO:45
CDRH3 DWADYGNYNYALDY SEQ ID NO:46 CDRH3
GACTGGGCCGACTATGGTAACTACAATTATGCTTTGGACTAC SEQ ID NO:47 CDRH3
DPADYGNYDYKLDY SEQ ID NO:48 CDRH3
GACCCAGCCGACTATGGTAACTACGATTATAAATTGGACTAC SEQ ID NO:49 CDRH3
DWADYGNYDYALDY SEQ ID NO:50 CDRH3
GACTGGGCCGACTATGGTAACTACGACTATGCTTTGGACTAC
[0150] The present invention also provides sequences that are
substantially the same as the CDR sequences (both amino acid and
nucleic acid) shown in the above Tables. For example, one or two
amino acid may be changed in the sequences shown in the Tables.
Also for example, a number of nucleotide bases may be changed in
the sequences shown in the Tables (e.g. based on the degeneracy of
the genetic code, such that the same peptide is still encoded by
the nucleic acid sequence). Changes to the amino acid sequence may
be generated by changing the nucleic acid sequence encoding the
amino acid sequence. A nucleic acid sequence encoding a variant of
a given CDR may be prepared by methods known in the art. These
methods include, but are not limited to, preparation by
site-directed (or oligonucleotide-mediated) mutagenesis, PCR
mutagenesis, and cassette mutagenesis of an earlier prepared
nucleic acid encoding the CDR. Site-directed mutagenesis is a
preferred method for preparing substitution variants. This
technique is well known in the art (see, e.g., Carter et al.,
(1985) Nucleic Acids Res. 13: 4431-4443 and Kunkel et. al., (1987)
Proc. Natl. Acad. Sci. USA 82: 488-492, both of which are hereby
incorporated by reference).
[0151] It is understood that modifications which do not
substantially affect the activity of the various embodiments of
this invention are also included within the definition of the
invention provided herein. Accordingly, the following examples are
intended to illustrate but not limit the present invention.
EXAMPLE I
Simultaneous Humanization and Affinity Maturation of an Anti-CD40
Antibody
[0152] This example shows the simultaneous humanization and
affinity maturation of the murine mAb 40.2.220, directed against
the CD40 receptor.
[0153] The CD40 receptor is a potential therapeutic target for
several diseases. For example, the interaction of the CD40 receptor
and its ligand, gp39, serves a critical role in both humoral and
cell-mediated immune responses (Foy et al., Annu. Rev. Immunol.,
14:591-616, 1996). Immunological rejection of organs from
genetically non-identical individuals, termed
graft-versus-host-disease (GVHD), is mediated through T
cell-dependent mechanisms. In vivo administration of an anti-gp39
mAb blocks GVHD in mice and inhibits many of the GVHD-associated
phenomena (Durie et al., J. Clin. Invest., 94:1333-38, 1994),
providing evidence that the CD40/gp39 interaction plays a critical
role in the development of GVHD. More recently, inhibition of the
CD40/gp39 interaction in vivo in hyperlipidemic mice fed a high
cholesterol diet limited atherosclerosis, suggesting that CD40
signalling may also play a role in atherogenesis (Mach et. al.,
Nature 394:200-203, 1998). In addition, the CD40 receptor is
overexpressed on hematologic malignancies (Uckun et al., Blood,
76:2449-56, 1990) and certain carcinomas (Stamenkovic et al., EMBO
J., 8:1403-10, 1989) and thus, may serve as a target for cytotoxic
agents. An anti-CD40 single chain antibody-toxin fusion was
cytotoxic against CD40-expressing malignant cells in vitro
(Francisco et al., Cancer Res., 55:3099-3104, 1995) and was
efficacious in treating human non-Hodgkin's lymphoma xenografted
SCID mice (Francisco et. al., Blood, 89:4493-4500, 1997).
[0154] Codon-based mutagenesis (Glaser et. al., J. Immunol.,
149:3903-3913, 1992) was used to create libraries of LCDR3, HCDR3
and framework region variants of mAb 40.2.220 sequences. Libraries
composed of framework region variants alone and in combination with
HCDR3 variants and with HCDR3 and LCDR3 variants together were
screened for high affinity variants. It was demonstrated that in
combination higher affinity variants were obtained than those
obtained when codon-based mutagenesis was applied independently
thus showing (1) higher affinity variants that could only be
obtained by the use of codon-based mutagenesis simultaneously on
disparate regions of the mAb and (2) the use of codon-based
mutagenesis to uncover potential direct interactions between
disparate regions of a mAb.
[0155] A vector for the production of a chimeric anti-CD40 murine
mAb 40.2.220 was constructed. Based on the sequence of anti-CD40
murine mAb 40.2.220 (provided by Dr. D. Hollenbaugh, Bristol-Myers
Squibb, Princeton, N.J.) overlapping oligonucleotides encoding VH
and VL (69-75 bases in length) were synthesized and purified. The
variable H and L domains were synthesized separately by combining
25 pmol of each of the overlapping oligonucleotides with Pfu DNA
polymerase (Stratagene) in a 50 .mu.l PCR reaction consisting of 5
cycles of denaturing at 94.degree. C. for 20 sec, annealing at
50.degree. C. for 30 sec, ramping to 72.degree. C. over 1 min, and
maintaining at 72.degree. C. for 30 sec. Subsequently, the
annealing temperature was increased to 55.degree. C. for 25 cycles.
A reverse primer and a biotinylated forward primer were used to
further amplify 1 .mu.l of the fusion product in a 100 .mu.l PCR
reaction using the same program. The products were purified by
agarose gel electrophoresis, electroeluted, and phosphorylated by
T4 polynucleotide kinase (Boehringer Mannheim) and were then
incubated with streptavidin magnetic beads (Boehringer Mannheim) in
5 mM Tris-Cl, pH 7.5, 0.5 mM EDTA, 1 M NaCl, and 0.05% Tween 20 for
15 min at 25.degree. C. The beads were washed and the
non-biotinylated, minus strand DNA was eluted by incubating with
0.15 M NaOH at 25.degree. C. for 10 min. Chimeric anti-CD40 Fab was
synthesized in a modified M13IX104 phage vector (Kristensson et.
al., 1995, Vaccines 95, pages 39-43, Cold Spring Harbor Labs, Cold
Spring Harbor, N.Y.), termed M13IX104CS, by hybridization
mutagenesis (Rosok et. al., JBC, 271:22611-18, 1996); Kunkel, PNAS,
82:488-92,1985) using the VH and VL oligonucleotides in 3-fold
molar excess of the uridinylated vector template. The M13IX104
vector was modified by replacing cysteine residues at the end of
the kappa and 1 constant regions with serine. The reaction was
electroporated into DH10B cells and titered onto a lawn of XL-1
Blue.
[0156] The murine anti-CD40 mAb variable region framework sequences
were used to identify the most homologous human germline sequences.
The H chain framework residues were 74% identical to human germline
VH7 (7-4.1) and JH4 sequences while the L chain was 75% identical
to the corresponding human germline VKIII (L6) and JK4 sequences.
Alignment of the H and L chain variable sequences is shown in FIG.
1. CDR residues, as defined by Kabat et. al. (1977, 1991), are
underlined and were excluded from the homology analysis.
Differences in sequence are indicated by vertical lines and
framework positions characterized in the combinatorial expression
library are marked with an asterisk. Framework residues that
differed between the murine mAb and the human templates were
assessed individually.
[0157] Based on structural and sequence analysis, antibody CDRs
with the exception of HCDR3 display a limited number of main chain
conformations termed canonical structures (Chothia & Lesk,
(1987); Chothia et. al., (1989)). Moreover, certain residues
critical for determining the main chain conformation of the CDR
loops have been identified (Chothia & Lesk, (1987); Chothia et.
al., (1989)). Canonical framework residues of murine anti-CD40 were
identified therefore, and it was determined that amino acids at all
critical canonical positions within the H and L chain frameworks of
the human templates were identical to the corresponding murine
residues.
[0158] Surface-exposed murine amino acids not normally found in
human antibodies are likely to contribute to the immunogenicity of
the humanized mAb (Padlan, Mol. Immunol., 28:489-498, 1991).
Therefore, framework residues differing between murine anti-CD40
and the human templates were analyzed and based on solvent exposure
were predicted to be buried or located on the surface of the
antibody (Padlan, (1991)). Solvent-exposed framework residues
distal to the CDRs were not expected to contribute to antigen
binding significantly and thus, with the exception of two H chain
residues all were changed to the corresponding human amino acid to
decrease potential immunogenicity. H chain residues 28 and 46 were
predicted to be solvent exposed. However, H28 is located within the
HCDR1 region as defined by Chothia & Lesk (1987) and
potentially interacts with the antigen. In addition, the lysine at
H46 in the murine mAb is somewhat unusual and significantly
different from the glutamic acid of the human template. Therefore,
the murine and human residues at H28 and H46 were expressed in the
combinatorial library (FIG. 1, asterisks).
[0159] The remaining differing framework residues, all predicted to
be mostly buried within the antibody, were evaluated for: (1)
proximity to CDRs, (2) potential to contact the opposite domain in
the VK-VH interface, (3) relatedness of the differing amino acids,
and (4) predicted importance in modulating CDR activity as defined
by Studnicka et. al., Protein Eng., 7:805-814, 1994). The majority
of L chain framework differences in buried residues were related
amino acids at positions considered not likely to be directly
involved in the conformation of the CDR. However, L49 is located
adjacent to LCDR2, potentially contacts the VH domain, is unrelated
to the human residue, and may be involved in determining the
conformation of LCDR2. For these reasons, the murine and human
amino acids at L49 were both expressed in the combinatorial
framework library (FIG. 1, asterisk).
[0160] Analysis of the murine H chain sequence and the human
template was performed. Residue H9 is a proline in the murine mAb
while the human template contains an unrelated serine residue.
Position H9 can also play a role in modulating the conformation of
the CDR and thus, was selected as a combinatorial library site
(FIG. 1, asterisks). The remaining buried framework residues that
differed between murine anti-CD40 and the H chain template were at
framework positions 38, 39, 48, and 91. Murine anti-CD40 mAb
contained glutamine and glutamic acid at H38 and H39, respectively,
while the human template contained arginine and glutamine. Residue
H38 is in proximity to the HCDR1, the glutamine-arginine change is
non-conserved, and expression of glutamine at this site in murine
Abs is somewhat unusual. Similarly, glutamic acid-glutamine is a
non-conservative difference for buried amino acids, H39 is a
potential VK contact residue, and glutamic acid is somewhat unusual
in murine mAbs. Residue H48 is in close proximity to HCDR2 and H91
is predicted to be a high risk site (Studnicka et. al., (1994);
Harris & Bajorath, Prot. Sci., 4:306-310, 1995) that
potentially contacts the VK domain. Thus, both murine and human
residues were expressed at H38, 39, 48, and 91 (FIG. 1,
asterisks).
[0161] The combinatorial framework library (Hu I) was synthesized
by the same method used to construct the chimeric anti-CD40, with
modifications. Overlapping oligonucleotides encoding the framework
regions of the H and L variable domains of the human template and
the murine anti-CD40 CDRs as defined by Kabat et. al. (1977, 1991)
were synthesized. Among these, degenerate oligonucleotides encoding
both the murine and the human amino acids at seven VH and one VK
framework position as selected above were synthesized (FIG. 1
residues marked with asterisk). All of these sites were
characterized by synthesizing a combinatorial library that
expressed all possible combinations of the murine and human amino
acids found at these residues. The total diversity of this library,
termed Hu I, was 28 or 256 variants (Table I).
[0162] The Hu I combinatorial library was first screened by an
ELISA that permits the rapid assessment of the relative affinities
of the variants (Watkins et. al., Anal. Biochem. 253:37-45, 1997).
Briefly, microtiter plates were coated with 5 .mu.g/ml goat
anti-human kappa (Southern Biotechnology) and blocked with 3% BSA
in PBS. Certain Fabs were cloned into an expression vector under
the control of the arabinose-regulated BAD promoter. In addition, a
six-histidine tag was fused to the carboxyl-terminus of the H chain
to permit purification with nickel-chelating resins. Purified Fab
was quantitated as described (Watkins et. al., 1997). Next, 50
.mu.l Fab from the Escherichia coli culture supernatant or from the
cell lysate, was incubated with the plate 1 h at 25.degree. C., the
plate was washed three times with PBS containing 0.1% Tween 20, and
incubated with 0.1 .mu.g/ml CD40-Ig in PBS containing 1% BSA for 2
h at 25.degree. C. The plate was washed three times with PBS
containing 0.1% Tween 20 and goat anti-mouse IgG2b-alkaline
phosphatase conjugate diluted 3000-fold in PBS containing 1% BSA
was added for 1 h at 25.degree. C. The plate was washed three times
with PBS containing 0.1% Tween 20 and was developed as described
(Watkins et. al., (1997)).
[0163] Although variants that bind the target antigen with
affinities comparable to, or better than the chimeric Fab were
identified, the majority of Hu I clones screened were less active
than the chimeric anti-CD40 Fab. Approximately 6% of randomly
selected Hu I variants displayed binding activities comparable to
the chimeric Fab (data not shown). The identification of multiple
Hu I variants with activity comparable to the chimeric CD40 is
consistent with the interpretation that the most critical framework
residues were included in the combinatorial library.
[0164] The kinetic constants for the interaction between CD40 and
the anti-CD40 variants were determined by surface plasmon resonance
(BIAcore). CD40-Ig fusion protein was immobilized to a
(1-ethyl-3-[3-dimethylaminopropyl]-carbodiimide hydrochloride) and
N-hydroxysuccinimide-activated sensor chip CM5 by injecting 8 .mu.l
of 10 .mu.g/ml CD40-Ig in 10 mM sodium acetate, pH 4. CD40-Ig was
immobilized at a low density (.about.150 RU) to prevent rebinding
of Fabs during the dissociation phase. To obtain association rate
constants (kon), the binding rate at six different Fab
concentrations ranging from 25-600 nM in PBS was determined at a
flow rate of 20 .mu./min. Dissociation rate constants (koff) were
the average of six measurements obtained by analyzing the
dissociation phase. Sensorgrams were analyzed with the
BlAevaluation 3.0 program. Kd was calculated from Kd=koff/kon.
Residual Fab was removed after each measurement by prolonged
dissociation.
[0165] FIG. 2A shows bacterially-expressed chimeric anti-CD40 Fab
and certain variants from each of the libraries were titrated on
immobilized antigen. Chimeric (filled circles), Hu I-19C11 (open
circles), Hu II-CW43 (open squares), Hu III-2B8 (filled triangles),
and an irrelevant (filled squares) Fab were released from the
periplasmic space of 15 ml bacterial cultures and serial dilutions
were incubated with CD40-Ig antigen immobilized on microtiter
plates. See below for description of HuII and HuIII libraries.
Antibody binding was quantitated as described above. These
measurements confirm the identification of multiple variants with
enhanced affinity. For example, clone 19C11 binds the CD40 receptor
with higher affinity than the chimeric Fab, as demonstrated by the
shift in the titration profile (compare open circles with filled
circles). DNA sequencing of 34 of the most active clones led to the
identification of 24 unique framework combinations, each containing
2-6 murine framework residues (data not shown).
[0166] LCDR3 and HCDR3 contact antigen directly, interact with the
other CDRs, and often affect the affinity and specificity of
antibodies significantly (Wilson & Stanfield, Curr. Opin.
Struct. Biol., 3:113-18, 1993); Padlan, (1994)). In addition, the
conformation of LCDR3 and HCDR3 are determined in part by certain
framework residues. Therefore, to identify the most active antibody
it could be beneficial to construct combinatorial libraries that
optimize the third CDR of the H and L chains in conjunction with
selecting the most active framework.
[0167] Codon-based mutagenesis (Glaser et. al., J. Immunol.,
149:3903-13, 1992) was used to synthesize oligonucleotides that
introduce mutations at every position in HCDR3, one at a time,
resulting in the expression of all 20 amino acids at each CDR
residue from Ser95-Tyr102 (FIG. 1, underlined). Briefly, for
library construction, the overlapping oligonucleotides encoding the
framework library and non-library murine CDR were combined with 25
pmol of the oligonucleotides encoding mutated HCDR3. The pool of
oligonucleotides encoding the HCDR3 library was mixed with the
overlapping oligonucleotides encoding the combinatorial framework
and other CDRs to generate a framework/HCDR3 library. The diversity
of this library, termed Hu II, was 1.1.times.10.sup.5 (Table
I).
[0168] The CDR residues selected for mutagenesis of LCDR3 were
Gln89-Thr97 (FIG. 1, underlined). Oligonucleotides encoding LCDR3
were designed to mutate a single CDR residue in each clone as
described above for HCDR3. Oligonucleotides encoding the LCDR3,
HCDR3, and the combinatorial framework were used to create a
framework/HCDR3/LCDR3 library, termed Hu III. The large number of
framework/CDR3 combinations resulted in a library with a complexity
of 3.1.times.10.sup.7 (Table I).
4TABLE II Summary of phage-expressed anti-CD40 antibody libraries.
Library Library Positions Size* Screened.dagger. Hu I framework 256
2.4 .times. 10.sup.3 Hu II framework, HCDR3 1.1 .times. 10.sup.5
2.0 .times. 10.sup.6 Hu III framework, HCDR3, LCDR3 3.1 .times.
10.sup.7 5.5 .times. 10.sup.5 *Number of unique clones based on DNA
sequence. Thirty-two codons are used to encode all 20 amino acids
at each CDR position.
[0169] An additional library (Hu IV) was synthesized to further
optimize the best variant (clone F4) identified from the Hu III
library. Oligonucleotides encoding LCDR3, designed to mutate a
single CDR residue in each clone, were synthesized by introducing
NN(G/T) at each position (Glaser et. al., (1992)) and were annealed
to uridinylated F4 template (Kunkel, (1985)) which already
contained a 96R.fwdarw.W mutation in LCDR3.
[0170] Combining mutations in LCDR3 and/or HCDR3 with the framework
library increased the potential diversity of humanized anti-CD40
variants from 256 to greater than 10.sup.7. In order to screen
these larger libraries more efficiently a modified plaque lift
assay, termed capture lift, was used (Watkins et. al., (1997)).
Briefly, nitrocellulose filters (82-mm) were coated with goat
anti-human kappa, blocked with 1% BSA, and were applied to an agar
plate containing the phage-infected bacterial lawn. In the initial
screen, phage were plated at 10.sup.5 phage/100-mm plate. After the
capture of phage-expressed anti-CD40 variant Fabs, the filters were
incubated 3 h at 25.degree. C. with 5 ng/ml CD40-Ig in PBS
containing 1% BSA. The filters were rinsed four times with PBS
containing 0.1% Tween 20 and were incubated with goat anti-mouse
IgG2b-alkaline phosphatase conjugate (Southern Biotechnology)
diluted 3000-fold in PBS containing 1% BSA for 1 h at 25.degree. C.
The filters were washed four times with PBS containing 0.1% Tween
20 and were developed as described (Watkins et. al., Anal.
Biochem., 256:169-177, 1998). To isolate individual clones,
positive plaques from the initial screen were picked, replated at
lower density (<10.sup.3 phage/100-mm plate), and were screened
by the same approach. Because the filters were probed with antigen
at a concentration substantially below the Kd of the Fab only
variants displaying enhanced affinity were detectable. Multiple
clones displaying higher affinities were identified following the
screening of >10.sup.6 variants from Hu II and >105 variants
from the Hu III library using 82-mm filters containing 10.sup.5
variants per filter (Table I). Titration of the variants on
immobilized CD40-Ig verified that multiple clones displayed
affinities greater than the chimeric and humanized Fab (FIG. 2A,
compare open squares, filled triangles with circles).
[0171] The framework/CDR mutations that conferred enhanced affinity
were identified by DNA sequencing. Single-stranded DNA was isolated
and the H and L chain variable region genes were sequenced by the
fluorescent dideoxynucleotide termination method (Perkin-Elmer,
Foster City, Calif.). Unique variable region sequences were
identified in 10/13 Hu II variants and 4/5 Hu III variants. Both
the Hu II and Hu III variants contained 1-5 murine framework
residues and 0-2 CDR3 mutations. Representative examples are
summarized in Table II. The affinities of bacterially-expressed
chimeric Fab and certain variants from each of the libraries were
characterized more thoroughly using surface plasmon resonance
measurements to determine the association and dissociation rates of
purified Fab with immobilized CD40-Ig as described above.
[0172] Chimeric anti-CD40 had a dissociation constant Kd=48.3 nM
and, consistent with the screening results, the variants all
displayed higher affinities with Kd ranging from 0.24 nM to 10.5 nM
(Table II). Further optimization of LCDR3 of Hu III clone F4
resulted in the identification of a higher affinity (Kd=0.1 nM)
clone, L3.17, which contained a 94F.fwdarw.Y mutation. The improved
affinities of the anti-CD40 variants were predominantly the result
of slower dissociation rates. However, the association rates of
most variants were also enhanced, increasing by as much as 3-fold
(1.2 vs. 3.2.times.10.sup.6 M.sup.-1s.sup.-1 for chimeric anti-CD40
and clone L3.17, respectively).
5TABLE III Simultaneous optimization of framework and CDR residues.
Kd Library Clone (nM) Murine Fr Residues* CDR Mutations chimeric
48.3 (43) 0 Hu I 19C11 42.4 (2) H28, 48 0 1H11 53.4 (4) H9, 28, 91,
L49 0 9A3 43.9 (3) H9, 28, 91 0 Hu II CW43 10.53 (3) H9, 28, 91
HCDR3, 101A.fwdarw.R Y49K.dagger. 53.4 (4) H9, 28, 91, L49 HCDR3,
101A.fwdarw.R 2B12 4.67 (5) H9, 28, 38, 46, 48 HCDR3, 101A.fwdarw.K
Hu III 2B12 4.67 (5) H9, 28, 38, 46, 48 HCDR3, 101A.fwdarw.K 2B8
2.81 (1) H28 HCDR3, 101A.fwdarw.K LCDR2, 96R.fwdarw.Y F4 0.24 (1)
H28 HCDR3, 101A.fwdarw.K LCDR3, 96R.fwdarw.W Hu IV L3.17 0.10 (1)
H28 HCDR3, 101A.fwdarw.K LCDR3, 94F.fwdarw.Y LCDR3, 96R.fwdarw.W
*The number of murine framework residues that differ from the most
homologous human germline sequence based on definition of CDRs of
Kabat et. al. (1977, 1991) are indicated in parentheses. Differing
murine framework residues retained in the humanized versions are
located predominantly on the H chain (H) at the indicated
positions. Hu I clone 1H11 and the CW43 derivative, clone Y49K,
contain a single differing L chain (L) framework residue at
position 49. .dagger.Clone Y49K was created by site-directed
mutagenesis of clone CW43. The four clones within the shaded boxed
region, 1H11, 9A3, CW43, and Y49K, were characterized to
demonstrate the co-operative interaction between L chain framework
residue tyr49 (human) and HCDR3 residue arg101.
[0173] The variants displaying enhanced affinity were tested for
their ability to block the binding of gp39 ligand to the CD40
receptor. Immulon II microtiter plates were coated with 2 .mu.g/ml
anti-murine CD8 to capture sgp39 fusion protein which expresses the
CD8 domain. The plates were rinsed once with PBS containing 0.05%
Tween 20, and were blocked with 3% BSA in PBS. The plate was washed
once with PBS containing 0.05% Tween 20 and was incubated with cell
culture media containing saturating levels of sgp39 for 2 h at
25.degree. C. Unbound sgp39 was aspirated and the plate was washed
two times with PBS containing 0.05% Tween 20. Next, 25 .mu.l of
purified variant Fabs diluted serially 3-fold in PBS was added
followed by 25 .mu.l of 4 .mu.g/ml CD40-human Ig in PBS. The plates
were incubated 2 h at 25.degree. C. and were washed three times
with PBS containing 0.05% Tween 20. Bound CD40-human Ig was
detected following a 1 h incubation at 25.degree. C. with goat
F(ab')2 anti-human IgG Fc-specific horseradish peroxidase conjugate
(Jackson) diluted 10,000-fold in PBS. The plate was washed four
times with PBS containing 0.05% Tween 20 and binding was
quantitated colorimetrically by incubating with 1 mg/ml
o-phenylenediamine dihydrochloride and 0.003% hydrogen peroxide in
50 mM citric acid, 100 mM Na2HPO4, pH 5. The reaction was
terminated by the addition of H2SO4 to a final concentration of
0.36 M and the absorbance at 490 nm was determined. FIG. 2B shows
purified variants were tested for their ability to inhibit sgp39
binding to CD40-Ig. The ligand for the CD40 receptor, gp39, was
captured in a microtiter plate and subsequently, varying amounts of
purified chimeric (filled circles), Hu II-CW43 (open squares), Hu
III-2B8 (filled triangles), Hu II/III-2B12 (open triangles), and
irrelevant (filled squares) Fab were co-incubated with 2 .mu.g/ml
CD40-human Ig on the microtiter plate. The variants all inhibited
the binding of soluble CD40-Ig fusion protein to immobilized gp39
antigen in a dose-dependent manner that correlated with the
affinity of the Fabs. For example, one of the most potent
inhibitors of ligand binding to CD40-Ig fusion protein was variant
2B8, which was also one of the variants with the highest affinity
for CD40. Variant 2B8 displayed .apprxeq.17-fold higher affinity
for CD40 than did the chimeric Fab and inhibited ligand binding
.apprxeq.7-fold more effectively.
[0174] Screening of the Hu I library identified two variants that
were similar or identical in framework sequence to the Hu II clone
CW43 but displayed 5-fold lower affinities (Table II, clones 1H11
and 9A3). Clone 9A3 has an identical framework structure while 1H11
contained the murine lysine framework residue at L chain position
49. Sequence comparisons and site-directed mutagenesis studies
(data not shown) suggest that the beneficial arginine residue at
HCDR3 position 101 might interact with L chain residue tyr.sup.49.
To test this, L chain residue tyr.sup.49 of clone CW43 was mutated
to the lysine murine framework residue, resulting in a variant with
a framework identical to clone 1H11 that also contained the
beneficial arg.sup.101 residue in HCDR3. The resulting mAb, termed
Y49K, displayed 5-fold lower affinity than CW43. Thus, expression
of tyrosine at L chain framework residue 49 or expression of
arginine at HCDR3 residue 101 alone had no beneficial effect on the
mAb affinity, while the concomitant expression of tyrosine and
arginine at these sites improved the mAb affinity 5-fold. The
non-additive, or dependent nature of the mutations demonstrates
that L chain residue tyr.sup.49 and HCDR3 residue arg.sup.101
interact co-operatively to enhance the affinity of the mAb
(Schreiber & Fersht, J. Mol. Biol., 248:478-486, 1995). In
addition, the co-operative interaction that was observed between
tyr.sup.49 and arg.sup.101 was also observed for variants that
expressed lysine at HCDR3 position 101 (Table II).
[0175] Generally, interacting residues are spatially separated by
no more than 7 .ANG. (Schreiber & Fersht, 1995)). FIG. 3 shows
molecular modeling of anti-CD40 variant CW43. A top view of the
anti-CD40 variant CW43 variable region structure was created by
homology modeling to examine the spatial relationship of L chain
framework residue Y49 and H chain CDR3 residue R101. The L chain is
on the left and the H chain right with the H chain CDR3 loop
depicted in red. The L chain framework residue 49 is in close
proximity to the H chain CDR3 loop and is 7 .ANG. of the predicted
interacting H chain CDR3 R101 residue. Although the interacting
amino acids are located on distinct chains of the mAb, the residues
are predicted to be within a range (7 .ANG.) to permit co-operative
interaction.
EXAMPLE 2
Anti-vWF Binding Molecules
[0176] This example describes the construction and screen of
libraries of anti-human von Willebrand Factor (vWF) Fabs. This
example also describes the identification of clones with optimized
properties compared to the parental/donor NMC-4 antibody (known to
bind human vWF).
[0177] Overlapping oligonucleotides were utilized to generate DNA
libraries encoding antibody variants composed of the heavy chain
VH3-72 (SEQ ID NO:7) and light chain DPK9/012 (SEQ ID NO:8) human
germline framework regions (see FIG. 5) and
complementarity-determining regions closely related to those of the
NMC-4 antibody (parental/donor antibody). As shown in FIG. 5, the
NMC-4 parental/donor antibody is composed of SEQ ID NO:5 (Genbank
accession # U90237) and SEQ ID NO:6 (Genbank accession # U90238).
The human germline light and heavy chain framework regions utilized
were unvaried in this example (i.e. no amino acid residues were
changed from these human germline framework sequences). Also in
this example, each amino acid position in a number of CDRs were
individually randomized to include all amino acids except
wild-type. The process generated libraries with a total diversity
of 45,486 possible sequences.
[0178] The DNA fragments were annealed to uridinylated single
stranded phage DNA such that the VL region was inserted between an
appropriate signal sequence and the human CL region sequences.
Similarly, the heavy chain fragment was designed to insert, in
frame, between a signal sequence and the human CHI region. The
phage DNA and the DNA fragments were mixed, heated to 75.degree. C.
and cooled to 20.degree. C. over the course of 45 minutes. Double
stranded DNA was generated by the addition of T4 DNA polymerase and
T4 DNA ligase with an incubation of 5 minutes at 4.degree. C.
followed by 90 minutes at 37.degree. C. The reaction was phenol
extracted and the double stranded DNA was precipitated by the
addition of ethanol. The DNA was resuspended, electroporated into
E. coli DH10B cells, XL1 Blue cells were added and the mixture was
plated onto agar plates. After 6 hours at 37.degree. C. the phage
plaques were counted and eluted into growth media. Phage stocks
were generated when the elutions were clarified by centrifugation
and sodium azide was added to 0.2%.
[0179] Initial screening of the anti-vWF library was performed by
plaque lift essentially as described in Watkins, J. D. et al.,
(1998) Anal. Biochem., 256:169-177, herein incorporated by
reference. Briefly, nitrocellulose filters were coated with goat
anti-human kappa antibodies and then blocked with 1% BSA. The
filters were then placed on agar plates containing plaques from the
phage stock described above and incubated for 18 hours at
22.degree. C. Filters were removed from the plates, rinsed with PBS
and incubated with various concentrations of biotinylated human
vWF. Fab-bound vWF was detected with NeutrAvidin alkaline
phosphatase conjugate using a colorimetric substrate. Regions of
the agar plate corresponding to the most intense signals were
excised, the phages were eluted and amplified and reprobed until
discreet positive plaques were isolated. Multiple clones were
identified and further characterized by ELISA.
[0180] Phage stocks of positive clones from the initial screen were
used to infect log phase XL1 Blue which were induced with 1 mM
IPTG. After 1 hour at 37.degree. C., 15 ml of infected culture were
grown for a further 16 hours at 22.degree. C. Cells were pelleted,
washed and the periplasmic contents released by the addition of 640
.mu.l of 30 mM Tris pH 8.2, 2 mM EDTA, and 20% sucrose. After 15
minutes at 4.degree. C. the cells were pelleted and the
supernatant, containing Fab fragments, was assayed by ELISA. COSTAR
#3366 microtiter plates were coated with goat anti-human vWF at 2
.mu.g/ml in carbonate buffer for 16 hours at 4.degree. C. The wells
were blocked with 1% BSA, washed and 0.5 .mu.g/ml human vWF was
added to each well for 1 hour at 22.degree. C. After washing, Fab
dilutions were added to the wells for 1 hour at 22.degree. C. Goat
anti-human kappa alkaline phosphatase was then added for 1 hour at
22.degree. C. Addition of a calorimetric substrate identified
clones with the best binding characteristics.
[0181] The best clone was the starting point for the generation of
individual CDR libraries. Briefly, each CDR was separately deleted
by standard mutagenesis methods. Because of its length CDR-H2 was
mutagenized as two separate libraries. Uridinylated single stranded
DNA templates from each CDR-deleted clone were annealed separately
with a pool of oligonucleotides which contained all possible amino
acids at each position of the CDR, except wild-type. Double
stranded DNA was made and libraries generated as described.
Screening was done initially by filter lift, positive clones were
assayed by ELISA and the DNA sequence determined. Table 6
summarizes the beneficial mutations identified in the anti-vWF
light chain CDRs while the heavy chain summary is shown in Table
7.
6TABLE 6 CDR Library Positives - Light Chain CDR L1 Library Clone
(11 amino acids) 24 25 26 27 28 29 30 31 32 33 34 WT S A S Q D I N
K Y L N L1-6 D CDR L2 Clone (7 amino acids) 50 51 52 53 54 55 56 WT
Y T S S L H S L2-8 G L2-1 N L2-6 V L2-4 V CDR L3 - all clones have
a K93D mutation.
[0182]
7TABLE 7 CDR Library Positives - Heavy Chain CDR H1 Library Clone
(10 amino acids) 26 27 28 29 30 31 32 33 34 35 WT G F S L T D Y G V
D H1-5 G CDR H2A Library Clone (8 amino acids) 50 51 52 53 54 55 56
57 WT M I W G D G S T H2a-10 P H2a-6 Q H2a-1 V CDR H2B Library
Clone (8 amino acids) 58 59 60 61 62 63 64 65 WT D Y N S A L K S
H2b-3 I H2b-4 A H2b-7 Q H2b-1 V CDR H3 Library Clone (14 amino
acids) 95 96 97 98 99 100 a b c d e f 101 102 WT D P A D Y G N Y D
Y A L D Y all clones N H3-6 K H3-9 W
[0183] The mutations shown in Tables 6 and 7 were combined into a
new library. This combinatorial library was constructed, screened
and characterized as described above. Table 8 shows the sequences
of clones that had increased binding activity.
8TABLE 8 Positive Combinatorial Library Clones LIGHT HEAVY CDR L1
L2 L3 H1 H2a H2b H3 WT K Y S S K T G T Y K P D A Clone 31 50 53 56
93 30 53 57 59 64 96 100c 100e C1 D N D G P Q N C4 D G D G V V Q N
C7 D N D G P I W N C8 D N V D G P V Q N C9 D N V D G P V D C4-4 D G
D G V V Q D K
[0184] FIG. 6 shows an example of an ELISA in which combinatorial
clones were assayed. These results show that the optimized binding
activity of many of the clones was 2-3 times greater than the
parental/donor NMC-4 antibody.
[0185] Throughout this application various publications have been
referenced within parentheses. The disclosures of these
publications in their entireties are hereby incorporated by
reference in this application in order to more fully describe the
state of the art to which this invention pertains.
[0186] Although the invention has been described with reference to
the disclosed embodiments, those skilled in the art will readily
appreciate that the specific experiments detailed are only
illustrative of the invention. It should be understood that various
modifications can be made without departing from the spirit of the
invention.
Sequence CWU 1
1
50 1 107 PRT Mus musculus 1 Asp Ile Val Leu Thr Gln Ser Pro Ala Thr
Leu Ser Val Thr Pro Gly 1 5 10 15 Asp Arg Val Ser Leu Ser Cys Arg
Ala Ser Gln Ser Ile Ser Asp Tyr 20 25 30 Leu His Trp Tyr Gln Gln
Lys Ser His Glu Ser Pro Arg Leu Leu Ile 35 40 45 Lys Tyr Ala Ser
His Ser Ile Ser Gly Ile Pro Ser Arg Phe Ser Gly 50 55 60 Ser Gly
Ser Gly Ser Asp Phe Thr Leu Ser Ile Asn Ser Val Glu Pro 65 70 75 80
Glu Asp Val Gly Ile Tyr Tyr Cys Gln His Gly His Ser Phe Pro Arg 85
90 95 Thr Phe Gly Gly Gly Thr Lys Leu Glu Ile Lys 100 105 2 107 PRT
Homo sapiens 2 Glu Ile Val Leu Thr Gln Ser Pro Ala Thr Leu Ser Leu
Ser Pro Gly 1 5 10 15 Glu Arg Ala Thr Leu Ser Cys Arg Ala Ser Gln
Ser Val Ser Ser Tyr 20 25 30 Leu Ala Trp Tyr Gln Gln Lys Pro Gly
Gln Ala Pro Arg Leu Leu Ile 35 40 45 Tyr Asp Ala Ser Asn Arg Ala
Thr Gly Ile Pro Ala Arg Phe Ser Gly 50 55 60 Ser Gly Ser Gly Thr
Asp Phe Thr Leu Thr Ile Ser Ser Leu Glu Pro 65 70 75 80 Glu Asp Phe
Ala Val Tyr Tyr Cys Gln Gln Arg Ser Asn Trp Pro Leu 85 90 95 Thr
Phe Gly Gly Gly Thr Lys Val Glu Ile Lys 100 105 3 122 PRT Mus
musculus 3 Gln Ile Gln Leu Val Gln Ser Gly Pro Glu Leu Lys Lys Pro
Gly Glu 1 5 10 15 Thr Val Arg Ile Ser Cys Lys Ala Ser Gly Tyr Ala
Phe Thr Thr Thr 20 25 30 Gly Met Gln Trp Val Gln Glu Met Pro Gly
Lys Gly Leu Lys Trp Ile 35 40 45 Gly Trp Ile Asn Thr His Ser Gly
Val Pro Lys Tyr Val Glu Asp Phe 50 55 60 Lys Gly Arg Phe Ala Phe
Ser Leu Glu Thr Ser Ala Asn Thr Ala Tyr 65 70 75 80 Leu Gln Ile Ser
Asn Leu Lys Asn Glu Asp Thr Ala Thr Tyr Phe Cys 85 90 95 Val Arg
Ser Gly Asn Gly Asn Tyr Asp Leu Ala Tyr Phe Ala Tyr Trp 100 105 110
Gly Gln Gly Thr Leu Val Thr Val Ser Ala 115 120 4 113 PRT Homo
sapiens 4 Gln Val Gln Leu Val Gln Ser Gly Ser Glu Leu Lys Lys Pro
Gly Ala 1 5 10 15 Ser Val Lys Val Ser Cys Lys Ala Ser Gly Tyr Thr
Phe Thr Ser Tyr 20 25 30 Ala Met Asn Trp Val Arg Gln Ala Pro Gly
Gln Gly Leu Glu Trp Met 35 40 45 Gly Trp Ile Asn Thr Asn Thr Gly
Asn Pro Thr Tyr Ala Gln Gly Phe 50 55 60 Thr Gly Arg Phe Val Phe
Ser Leu Asp Thr Ser Val Ser Thr Ala Tyr 65 70 75 80 Leu Gln Ile Ser
Ser Leu Lys Ala Glu Asp Thr Ala Val Tyr Tyr Cys 85 90 95 Ala Arg
Tyr Phe Asp Tyr Trp Gly Gln Gly Thr Leu Val Thr Val Ser 100 105 110
Ser 5 120 PRT Mus musculus 5 Val Gln Leu Leu Glu Ser Gly Pro Gly
Leu Val Ala Pro Ser Gln Ser 1 5 10 15 Leu Ser Ile Thr Cys Thr Val
Ser Gly Phe Ser Leu Thr Asp Tyr Gly 20 25 30 Val Asp Trp Val Arg
Gln Pro Pro Gly Lys Gly Leu Glu Trp Leu Gly 35 40 45 Met Ile Trp
Gly Asp Gly Ser Thr Asp Tyr Asn Ser Ala Leu Lys Ser 50 55 60 Arg
Leu Ser Ile Thr Lys Asp Asn Ser Lys Ser Gln Val Phe Leu Lys 65 70
75 80 Met Asn Ser Leu Gln Thr Asp Asp Thr Ala Arg Tyr Tyr Cys Val
Arg 85 90 95 Asp Pro Ala Asp Tyr Gly Asn Tyr Asp Tyr Ala Leu Asp
Tyr Trp Gly 100 105 110 Gln Gly Thr Ser Val Thr Val Ser 115 120 6
99 PRT Mus musculus 6 Ser Ser Leu Ser Ala Ser Leu Gly Asp Arg Val
Thr Ile Ser Cys Ser 1 5 10 15 Ala Ser Gln Asp Ile Asn Lys Tyr Leu
Asn Trp Tyr Gln Gln Lys Pro 20 25 30 Asp Gly Ala Val Lys Leu Leu
Ile Phe Tyr Thr Ser Ser Leu His Ser 35 40 45 Gly Val Pro Ser Arg
Phe Ser Gly Ser Gly Ser Gly Thr Asp Tyr Ser 50 55 60 Leu Thr Ile
Ser Asn Leu Glu Pro Glu Asp Ile Ala Thr Tyr Tyr Cys 65 70 75 80 Gln
Gln Tyr Glu Lys Leu Pro Trp Thr Phe Gly Gly Gly Thr Lys Leu 85 90
95 Glu Val Lys 7 81 PRT Homo sapiens 7 Glu Val Gln Leu Val Glu Ser
Gly Gly Gly Leu Val Gln Pro Gly Gly 1 5 10 15 Ser Leu Arg Leu Ser
Cys Ala Ala Ser Trp Val Arg Gln Ala Pro Gly 20 25 30 Lys Gly Leu
Glu Trp Val Gly Arg Phe Thr Ile Ser Arg Asp Asp Ser 35 40 45 Lys
Asn Ser Leu Tyr Leu Gln Met Asn Ser Leu Lys Thr Glu Asp Thr 50 55
60 Ala Val Tyr Tyr Cys Ala Arg Trp Gly Gln Gly Thr Thr Val Thr Val
65 70 75 80 Ser 8 80 PRT Homo sapiens 8 Asp Ile Gln Met Thr Gln Ser
Pro Ser Ser Leu Ser Ala Ser Val Gly 1 5 10 15 Asp Arg Val Thr Ile
Thr Cys Trp Tyr Gln Gln Lys Pro Gly Lys Ala 20 25 30 Pro Lys Leu
Leu Ile Tyr Gly Val Pro Ser Arg Phe Ser Gly Ser Gly 35 40 45 Ser
Gly Thr Asp Phe Thr Leu Thr Ile Ser Ser Leu Gln Pro Glu Asp 50 55
60 Phe Ala Thr Tyr Tyr Cys Phe Gly Gly Gly Thr Lys Val Glu Ile Lys
65 70 75 80 9 11 PRT Artificial Sequence Synthetic 9 Ser Ala Ser
Gln Asp Ile Asn Asp Tyr Leu Asn 1 5 10 10 33 PRT Artificial
Sequence Synthetic 10 Ala Gly Thr Gly Cys Ala Ala Gly Thr Cys Ala
Gly Gly Ala Cys Ala 1 5 10 15 Thr Thr Ala Ala Cys Gly Ala Cys Thr
Ala Thr Thr Thr Ala Ala Ala 20 25 30 Cys 11 7 PRT Artificial
Sequence Synthetic 11 Gly Thr Ser Ser Leu His Ser 1 5 12 21 PRT
Artificial Sequence Synthetic 12 Gly Gly Cys Ala Cys Ala Thr Cys
Ala Ala Gly Thr Thr Thr Ala Cys 1 5 10 15 Ala Cys Thr Cys Ala 20 13
7 PRT Artificial Sequence Synthetic 13 Asn Thr Ser Ser Leu His Ser
1 5 14 21 PRT Artificial Sequence Synthetic 14 Ala Ala Cys Ala Cys
Ala Thr Cys Ala Ala Gly Thr Thr Thr Ala Cys 1 5 10 15 Ala Cys Thr
Cys Ala 20 15 7 PRT Artificial Sequence Synthetic 15 Tyr Thr Ser
Val Leu His Ser 1 5 16 21 PRT Artificial Sequence Synthetic 16 Thr
Ala Cys Ala Cys Ala Thr Cys Ala Gly Thr Thr Thr Thr Ala Cys 1 5 10
15 Ala Cys Thr Cys Ala 20 17 7 PRT Artificial Sequence Synthetic 17
Asn Thr Ser Val Leu His Ser 1 5 18 21 PRT Artificial Sequence
Synthetic 18 Ala Ala Cys Ala Cys Ala Thr Cys Ala Gly Thr Thr Thr
Thr Ala Cys 1 5 10 15 Ala Cys Thr Cys Ala 20 19 7 PRT Artificial
Sequence Synthetic 19 Tyr Thr Ser Ser Leu His Val 1 5 20 21 PRT
Artificial Sequence Synthetic 20 Thr Ala Cys Ala Cys Ala Thr Cys
Ala Ala Gly Thr Thr Thr Ala Cys 1 5 10 15 Ala Cys Gly Thr Gly 20 21
7 PRT Artificial Sequence Synthetic 21 Asn Thr Ser Ser Leu His Val
1 5 22 21 PRT Artificial Sequence Synthetic 22 Ala Ala Cys Ala Cys
Ala Thr Cys Ala Ala Gly Thr Thr Thr Ala Cys 1 5 10 15 Ala Cys Gly
Thr Ala 20 23 9 PRT Artificial Sequence Synthetic 23 Gln Gln Tyr
Glu Asp Leu Pro Trp Thr 1 5 24 27 PRT Artificial Sequence Synthetic
24 Cys Ala Gly Cys Ala Gly Thr Ala Thr Gly Ala Ala Gly Ala Thr Cys
1 5 10 15 Thr Thr Cys Cys Gly Thr Gly Gly Ala Cys Gly 20 25 25 10
PRT Artificial Sequence Synthetic 25 Gly Phe Ser Leu Gly Asp Tyr
Gly Val Asp 1 5 10 26 30 PRT Artificial Sequence Synthetic 26 Gly
Gly Ala Thr Thr Cys Thr Cys Ala Thr Thr Ala Gly Gly Cys Gly 1 5 10
15 Ala Cys Thr Ala Thr Gly Gly Thr Gly Thr Ala Gly Ala Cys 20 25 30
27 8 PRT Artificial Sequence Synthetic 27 Met Ile Trp Pro Asp Gly
Ser Thr 1 5 28 24 PRT Artificial Sequence Synthetic 28 Ala Thr Gly
Ala Thr Ala Thr Gly Gly Cys Cys Gly Gly Ala Thr Gly 1 5 10 15 Gly
Ala Ala Gly Cys Ala Cys Ala 20 29 8 PRT Artificial Sequence
Synthetic 29 Met Ile Trp Gln Asp Gly Ser Thr 1 5 30 24 PRT
Artificial Sequence Synthetic 30 Ala Thr Gly Ala Thr Ala Thr Gly
Gly Cys Ala Gly Gly Ala Thr Gly 1 5 10 15 Gly Ala Ala Gly Cys Ala
Cys Ala 20 31 8 PRT Artificial Sequence Synthetic 31 Met Ile Trp
Gly Asp Gly Ser Val 1 5 32 24 PRT Artificial Sequence Synthetic 32
Ala Thr Gly Ala Thr Ala Thr Gly Gly Gly Gly Thr Gly Ala Thr Gly 1 5
10 15 Gly Ala Ala Gly Cys Gly Thr Ala 20 33 8 PRT Artificial
Sequence Synthetic 33 Asp Ile Asn Ser Ala Leu Lys Ser 1 5 34 24 PRT
Artificial Sequence Synthetic 34 Gly Ala Cys Ala Thr Thr Ala Ala
Thr Thr Cys Ala Gly Cys Thr Cys 1 5 10 15 Thr Cys Ala Ala Gly Thr
Cys Cys 20 35 8 PRT Artificial Sequence Synthetic 35 Asp Tyr Asn
Ser Ala Leu Ala Ser 1 5 36 24 PRT Artificial Sequence Synthetic 36
Gly Ala Cys Thr Ala Thr Ala Ala Thr Thr Cys Ala Gly Cys Thr Cys 1 5
10 15 Thr Cys Gly Cys Ala Thr Cys Cys 20 37 8 PRT Artificial
Sequence Synthetic 37 Asp Tyr Asn Ser Ala Leu Gln Ser 1 5 38 24 PRT
Artificial Sequence Synthetic 38 Gly Ala Cys Thr Ala Thr Ala Ala
Thr Thr Cys Ala Gly Cys Thr Cys 1 5 10 15 Thr Cys Cys Ala Ala Thr
Cys Cys 20 39 8 PRT Artificial Sequence Synthetic 39 Asp Val Asn
Ser Ala Leu Gln Ser 1 5 40 24 PRT Artificial Sequence Synthetic 40
Gly Ala Cys Gly Thr Thr Ala Ala Thr Thr Cys Ala Gly Cys Thr Cys 1 5
10 15 Thr Cys Cys Ala Gly Thr Cys Cys 20 41 8 PRT Artificial
Sequence Synthetic 41 Asp Val Asn Ser Ala Leu Lys Ser 1 5 42 24 PRT
Artificial Sequence Synthetic 42 Gly Ala Cys Gly Thr Thr Ala Ala
Thr Thr Cys Ala Gly Cys Thr Cys 1 5 10 15 Thr Cys Ala Ala Gly Thr
Cys Cys 20 43 14 PRT Artificial Sequence Synthetic 43 Asp Pro Ala
Asp Tyr Gly Asn Tyr Asn Tyr Ala Leu Asp Tyr 1 5 10 44 42 PRT
Artificial Sequence Synthetic 44 Gly Ala Cys Cys Cys Ala Gly Cys
Cys Gly Ala Cys Thr Ala Thr Gly 1 5 10 15 Gly Thr Ala Ala Cys Thr
Ala Cys Ala Ala Thr Thr Ala Thr Gly Cys 20 25 30 Thr Thr Thr Gly
Gly Ala Cys Thr Ala Cys 35 40 45 14 PRT Artificial Sequence
Synthetic 45 Asp Trp Ala Asp Tyr Gly Asn Tyr Asn Tyr Ala Leu Asp
Tyr 1 5 10 46 42 PRT Artificial Sequence Synthetic 46 Gly Ala Cys
Thr Gly Gly Gly Cys Cys Gly Ala Cys Thr Ala Thr Gly 1 5 10 15 Gly
Thr Ala Ala Cys Thr Ala Cys Ala Ala Thr Thr Ala Thr Gly Cys 20 25
30 Thr Thr Thr Gly Gly Ala Cys Thr Ala Cys 35 40 47 14 PRT
Artificial Sequence Synthetic 47 Asp Pro Ala Asp Tyr Gly Asn Tyr
Asp Tyr Lys Leu Asp Tyr 1 5 10 48 42 PRT Artificial Sequence
Synthetic 48 Gly Ala Cys Cys Cys Ala Gly Cys Cys Gly Ala Cys Thr
Ala Thr Gly 1 5 10 15 Gly Thr Ala Ala Cys Thr Ala Cys Gly Ala Thr
Thr Ala Thr Ala Ala 20 25 30 Ala Thr Thr Gly Gly Ala Cys Thr Ala
Cys 35 40 49 14 PRT Artificial Sequence Synthetic 49 Asp Trp Ala
Asp Tyr Gly Asn Tyr Asp Tyr Ala Leu Asp Tyr 1 5 10 50 42 PRT
Artificial Sequence Synthetic 50 Gly Ala Cys Thr Gly Gly Gly Cys
Cys Gly Ala Cys Thr Ala Thr Gly 1 5 10 15 Gly Thr Ala Ala Cys Thr
Ala Cys Gly Ala Cys Thr Ala Thr Gly Cys 20 25 30 Thr Thr Thr Gly
Gly Ala Cys Thr Ala Cys 35 40
* * * * *