U.S. patent application number 11/199232 was filed with the patent office on 2008-11-13 for antibody glycosylation variants having increased antibody-dependent cellular cytotoxicity.
This patent application is currently assigned to GlycArt Biotechnology AG. Invention is credited to James E. Bailey, Joel Jean-Mairet, Pablo Umana.
Application Number | 20080280322 11/199232 |
Document ID | / |
Family ID | 23198536 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080280322 |
Kind Code |
A9 |
Umana; Pablo ; et
al. |
November 13, 2008 |
Antibody glycosylation variants having increased antibody-dependent
cellular cytotoxicity
Abstract
The present invention relates to the field of glycosylation
engineering of proteins. More particularly, the present invention
relates to glycosylation engineering to generate proteins with
improved therapeutic properties, including antibodies with
increased antibody-dependent cellular cytotoxicity.
Inventors: |
Umana; Pablo; (Zurich,
CH) ; Jean-Mairet; Joel; (Zurich, CH) ;
Bailey; James E.; (Zurich, CH) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX P.L.L.C.
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
GlycArt Biotechnology AG
Zurich
CH
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20050272128 A1 |
December 8, 2005 |
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|
Family ID: |
23198536 |
Appl. No.: |
11/199232 |
Filed: |
August 9, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10211554 |
Aug 5, 2002 |
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11199232 |
Aug 9, 2005 |
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10633697 |
Aug 5, 2003 |
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11199232 |
Aug 9, 2005 |
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09294584 |
Apr 20, 1999 |
6602684 |
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10633697 |
Aug 5, 2003 |
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60309516 |
Aug 3, 2001 |
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60082581 |
Apr 20, 1998 |
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Current U.S.
Class: |
435/69.1 ;
435/320.1; 435/334; 530/388.22; 536/23.53 |
Current CPC
Class: |
Y02P 20/52 20151101;
C07K 2317/24 20130101; C07K 2317/732 20130101; C07K 2317/14
20130101; C07K 16/2887 20130101; C07K 16/30 20130101; A61P 35/00
20180101; C07K 16/00 20130101; C12P 21/005 20130101; C07K 16/3038
20130101; C07K 16/2896 20130101; C12N 9/1051 20130101; C07K 2317/41
20130101; A61K 2039/505 20130101 |
Class at
Publication: |
435/069.1 ;
435/334; 435/320.1; 530/388.22; 536/023.53 |
International
Class: |
C07K 16/28 20060101
C07K016/28; C07H 21/04 20060101 C07H021/04; C12P 21/06 20060101
C12P021/06; C12N 5/06 20060101 C12N005/06 |
Claims
1. A host cell engineered to produce a polypeptide having increased
Fc-mediated cellular cytotoxicity by expression of at least one
nucleic acid encoding .beta.(1,4)-N-acetylglucosaminyltransferase
III (GnT III), wherein said polypeptide produced by said host cell
is selected from the group consisting of a whole antibody molecule,
an antibody fragment, and a fusion protein which includes a region
equivalent to the Fc region of an immunoglobulin, and wherein said
GnT III is expressed in an amount sufficient to increase the
proportion of said polypeptides carrying bisected hybrid
oligosaccharides or galactosylated complex oligosaccharides or
mixtures thereof in the Fc region relative to polypeptides carrying
bisected complex oligosaccharides in the Fc region.
2. The host cell of claim 1, wherein said polypeptide is IgG or a
fragment thereof.
3. The host cell of claim 1, wherein said polypeptide is IgG1 or a
fragment thereof.
4. The host cell of claim 1, wherein said polypeptide is a fusion
protein that includes a region equivalent to the Fc region of a
human IgG.
5. The host cell of claim 1, wherein a nucleic acid molecule
comprising at least one gene encoding GnTIII has been introduced
into said host cell.
6. The host cell of claim 1, wherein said host cell has been
engineered such that an endogenous GnT III gene is activated.
7. The host cell of claim 6, wherein said endogenous GnTIII has
been activated by insertion of a DNA element which increases gene
expression into the host chromosome.
8. The host cell of claim 6, wherein said host cell has been
selected to carry a mutation triggering expression of an endogenous
GnTIII.
9. The host cell of claim 8, wherein said host cell is the CHO cell
mutant lec 10.
10. The host cell of claim 1, wherein said host cell is a CHO cell,
a BHK cell, a NS0 cell, a SP2/0 cell, a Y0 myeloma cell, a P3X63
mouse myeloma cell, a PER cell, a PER.C6 cell or a hybridoma
cell.
11. The host cell of claim 10, wherein said polypeptide is an
anti-CD20 antibody.
12. The host cell of claim 11, wherein said anti-CD20 antibody is
IDEC-C2B8.
13. The host cell of claim 10, wherein said host cell is a SP2/0
cell.
14. The host cell of claim 13, wherein said antibody is the
chimeric anti-human renal cell carcinoma monoclonal antibody
chG250.
15. The host cell of claim 5, wherein said at least one gene
encoding GnTIII been introduced into said host cell chromosome.
16. The host cell of claim 6, wherein said endogenous GnTIII has
been activated by insertion of a promoter element, a transposon, or
a retroviral element into the host cell chromosome.
17. The host cell of claim 1, further comprising at least one
transfected nucleic acid encoding an antibody molecule, an antibody
fragment, or a fusion protein that includes a region equivalent to
the Fc region of an immunoglobulin.
18. The host cell of claim 1, wherein said at least one nucleic
acid encoding a GnTIII is operably linked to a constitutive
promoter element.
19. The host cell of claim 17, wherein said host cell comprises at
least one transfected nucleic acid encoding an anti-CD20 antibody,
the chimeric anti-human neuroblastoma monoclonal antibody chCE7,
the chimeric anti-human renal cell carcinoma monoclonal antibody
chG250, the chimeric anti-human colon, lung, and breast carcinoma
monoclonal antibody ING-1, the humanized anti-human 17-1A antigen
monoclonal antibody 3622W94, the humanized anti-human colorectal
tumor antibody A33, the anti-human melanoma antibody directed
against GD3 ganglioside R24, the chimeric anti-human squamous-cell
carcinoma monoclonal antibody SF-25, an anti-human EGFR antibody,
an anti-human EGFRvIII antibody, an anti-human PSMA antibody, an
anti-human PSCA antibody, an anti-human CD22 antibody, an
anti-human CD30 antibody, an anti-human CD33 antibody, an
anti-human CD38 antibody, an anti-human CD40 antibody, an
anti-human CD45 antibody, an anti-human CD52 antibody, an
anti-human CD138 antibody, an anti-human HLA-DR variant antibody,
an anti-human EpCAM antibody, an anti-human CEA antibody, an
anti-human MUC1 antibody, an anti-human MUC1 core protein antibody,
an anti-human aberrantly glycosylated MUC1 antibody, an antibody
against human fibronectin variants containing the ED-B domain, or
an anti-human HER2/neu antibody.
20. A method for producing a polypeptide in a host cell comprising
culturing the host cell of claim 1 under conditions which permit
the production of said polypeptide having increased Fc-mediated
cellular cytotoxicity.
21. The method of claim 20, further comprising isolating said
polypeptide having increased Fc-mediated cellular cytotoxicity.
22. The method of claim 20, wherein said host cell comprises at
least one nucleic acid encoding a fusion protein comprising a
region equivalent to a Fc region of an immunoglobulin.
23. The method of claim 20, wherein greater than 50% of the
oligosaccharides in the Fc region of said polypeptides are
bisected.
24. The method of claim 20, wherein greater than 70% of the
oligosaccharides in the Fc region of said polypeptides are
bisected.
25. The method of claim 20, wherein the proportion of bisected
hybrid oligosaccharides or galactosylated complex oligosaccharides
or mixtures thereof in the Fc region is greater than the proportion
of bisected complex oligosaccharides in the Fc region of said
polypeptides.
26. The method of claim 20, wherein said polypeptide is the
anti-CD20 antibody IDEC-C2B8 and the IDEC-C2B8 antibodies produced
by said host cell have a glycosylaton profile, as analyzed by
MALDI/TOF-MS, that is substantially equivalent to that shown in
FIG. 2E.
27. The method of claim 20, wherein said polypeptide is the chG250
monoclonal antibody and the chG250 antibodies produced by said host
cell have a glycosylaton profile, as analyzed by MALDI/TOF-MS, that
is substantially equivalent to that shown in FIG. 7D.
28. An antibody having increased antibody dependent cellular
cytotoxicity (ADCC) produced by the method of claim 21.
29. The antibody of claim 28, wherein said antibody is selected
from the group consisting of IDEC-C2B8, chCE7, ch-G250, a humanized
anti-HER2 monoclonal antibody, ING-1, 3622W94, SF-25, A33, and
R24.
30. An antibody fragment that includes a region equivalent to the
Fc region of an immunoglobulin, having increased Fc-mediated
cellular cytotoxicity produced by the method of claim 21.
31. A fusion protein that includes a region equivalent to the Fc
region of an immunoglobulin and having increased Fc-mediated
cellular cytotoxicity produced by the method of claim 21.
32. A pharmaceutical composition comprising the antibody of claim
28 and a pharmaceutically acceptable carrier.
33. A pharmaceutical composition comprising the antibody fragment
of claim 30 and a pharmaceutically acceptable carrier.
34. A pharmaceutical composition comprising the fusion protein of
claim 31 and a pharmaceutically acceptable carrier.
35-38. (canceled)
39. A eukaryotic cell line that expresses GnTIII and a recombinant
antibody.
40. An antibody produced by a cell line according to claim 39.
41. A method of treating a disorder in a mammal in need thereof
comprising administering a therapeutically effective amount of an
antibody produced by a cell line according to claim 39 to a mammal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the field of glycosylation
engineering of proteins. More particularly, the present invention
relates to glycosylation engineering to generate proteins with
improved therapeutic properties, including antibodies with
increased antibody-dependent cellular cytotoxicity.
[0003] 2. Background Art
[0004] Glycoproteins mediate many essential functions in human
beings, other eukaryotic organisms, and some prokaryotes, including
catalysis, signaling, cell-cell communication, and molecular
recognition and association. They make up the majority of
non-cytosolic proteins in eukaryotic organisms. (Lis et al., Eur.
J. Biochem. 218:1-27 (1993)). Many glycoproteins have been
exploited for therapeutic purposes, and during the last two
decades, recombinant versions of naturally-occurring, secreted
glycoproteins have been a major product of the biotechnology
industry. Examples include erythropoietin (EPO), therapeutic
monoclonal antibodies (therapeutic mAbs), tissue plasminogen
activator (tPA), interferon-.beta., (IFN-.beta.),
granulocyte-macrophage colony stimulating factor (GM-CSF), and
human chorionic gonadotrophin (hCG). (Cumming et al., Glycobiology
1:115-130 (1991)).
[0005] The oligosaccharide component can significantly affect
properties relevant to the efficacy of a therapeutic glycoprotein,
including physical stability, resistance to protease attack,
interactions with the immune system, pharmacokinetics, and specific
biological activity. Such properties may depend not only on the
presence or absence, but also on the specific structures, of
oligosaccharides. Some generalizations between oligosaccharide
structure and glycoprotein function can be made. For example,
certain oligosaccharide structures mediate rapid clearance of the
glycoprotein from the bloodstream through interactions with
specific carbohydrate binding proteins, while others can be bound
by antibodies and trigger undesired immune reactions. (Jenkins et
al., Nature Biotechnol. 14:975-81 (1996)).
[0006] Mammalian cells are the preferred hosts for production of
therapeutic glycoproteins, due to their capability to glycosylate
proteins in the most compatible form for human application.
(Cumming et al., Glycobiology 1: 115-30 (1991); Jenkins et al.,
Nature Biotechnol. 14:975-81 (1996)). Bacteria very rarely
glycosylate proteins, and like other types of common hosts, such as
yeasts, filamentous fungi, insect and plant cells, yield
glycosylation patterns associated with rapid clearance from the
bloodstream, undesirable immune interactions, and in some specific
cases, reduced biological activity. Among mammalian cells, Chinese
hamster ovary (CHO) cells have been most commonly used during the
last two decades. In addition to giving suitable glycosylation
patterns, these cells allow consistent generation of genetically
stable, highly productive clonal cell lines. They can be cultured
to high densities in simple bioreactors using serum-free media, and
permit the development of safe and reproducible bioprocesses. Other
commonly used animal cells include baby hamster kidney (BHK) cells,
NS0- and SP2/0-mouse myeloma cells. More recently, production from
transgenic animals has also been tested (Jenkins et al., Nature
Biotechnol. 14:975-81 (1996)).
[0007] All antibodies contain carbohydrate structures at conserved
positions in the heavy chain constant regions, with each isotype
possessing a distinct array of N-linked carbohydrate structures,
which variably affect protein assembly, secretion or functional
activity. (Wright, A., and Morrison, S. L., Trends Biotech.
15:26-32 (1997)). The structure of the attached N-linked
carbohydrate varies considerably, depending on the degree of
processing, and can include high-mannose, multiply-branched as well
as biantennary complex oligosaccharides. (Wright, A., and Morrison,
S. L., Trends Biotech. 15:26-32 (1997)). Typically, there is
heterogeneous processing of the core oligosaccharide structures
attached at a particular glycosylation site such that even
monoclonal antibodies exist as multiple glycoforms. Likewise, it
has been shown that major differences in antibody glycosylation
occur between cell lines, and even minor differences are seen for a
given cell line grown under different culture conditions. (Lifely,
M. R. et al., Glycobiology 5(8):813-22 (1995)).
[0008] Unconjugated monoclonal antibodies (mAbs) can be useful
medicines for the treatment of cancer, as demonstrated by the U.S.
Food and Drug Administration's approval of Rituximab (Rituxan.TM.;
IDEC Pharmaceuticals, San Diego, Calif., and Genentech Inc., San
Francisco, Calif.), for the treatment of CD20 positive B-cell,
low-grade or follicular Non-Hodgkin's lymphoma, and Trastuzumab
(Herceptin.TM.; Genentech Inc,) for the treatment of advanced
breast cancer (Grillo-Lopez, A.-J., et al., Semin. Oncol. 26:66-73
(1999); Goldenberg, M. M., Clin. Ther. 21:309-18 (1999)). The
success of these products relies not only on their efficacy but
also on their outstanding safety profiles (Grillo-Lopez, A.-J., et
al., Semin. Oncol. 26:66-73 (1999); Goldenberg, M. M., Clin. Ther.
21:309-18 (1999)). In spite of the achievements of these two drugs,
there is currently a large interest in obtaining higher specific
antibody activity than what is typically afforded by unconjugated
mAb therapy.
[0009] One way to obtain large increases in potency, while
maintaining a simple production process and potentially avoiding
significant, undesirable side effects, is to enhance the natural,
cell-mediated effector functions of mAbs by engineering their
oligosaccharide component (Umana, P. et al., Nature Biotechnol.
17:176-180 (1999)). IgG1 type antibodies, the most commonly used
antibodies in cancer immunotherapy, are glycoproteins that have a
conserved N-linked glycosylation site at Asn297 in each CH2 domain.
The two complex bi-antennary oligosaccharides attached to Asn297
are buried between the CH2 domains, forming extensive contacts with
the polypeptide backbone, and their presence is essential for the
antibody to mediate effector functions such as antibody dependent
cellular cytotoxicity (ADCC) (Lifely, M. R., et al., Glycobiology
5:813-822 (1995); Jefferis, R., et al., Immunol Rev. 163:59-76
(1998); Wright, A. and Morrison, S. L., Trends Biotechnol. 15:26-32
(1997)).
[0010] The present inventors showed previously that overexpression
in Chinese hamster ovary (CHO) cells of
.beta.(1,4)-N-acetylglucosaminyltransferase III (GnTIII), a
glycosyltransferase catalyzing the formation of bisected
oligosaccharides, significantly increases the in vitro ADCC
activity of an anti-neuroblastoma chimeric monoclonal antibody
(chCE7) produced by the engineered CHO cells. (See Umana, P. et
al., Nature Biotechnol. 17:176-180 (1999), International
Publication No. WO 99/54342, the entire contents of each of which
are hereby incorporated by reference in their entirety). The
antibody chCE7 belongs to a large class of unconjugated mAbs which
have high tumor affinity and specificity, but have too little
potency to be clinically useful when produced in standard
industrial cell lines lacking the GnTIII enzyme (Umana, P., et al.,
Nature Biotechnol. 17:176-180 (1999)). That study was the first to
show that large increases of maximal in vitro ADCC activity could
be obtained by increasing the proportion of constant region
(Fc)-associated, bisected oligosaccharides above the levels found
in naturally occurring antibodies. To determine if this finding
could be extrapolated to an unconjugated mAb, which already has
significant ADCC activity in the absence of bisected
oligosaccharides, the present inventors have applied this
technology to Rituximab, the anti-CD20, IDEC-C2B8 chimeric
antibody. The present inventors have likewise applied the
technology to the unconjugated anti-cancer mAb chG250
BRIEF SUMMARY OF THE INVENTION
[0011] The present inventors have now generated new glycosylation
variants of the anti-CD20 monoclonal antibody (mAb) IDEC-C2B8
(Rituximab) and the anti-cancer mAb chG250 using genetically
engineered mAb-producing cell lines that overexpress
N-acetylglucosaminyltransferase III (GnTIII; EC 2.1.4.144) in a
tetracycline regulated fashion. GnTIII is required for the
synthesis of bisected oligosaccharides, which are found at low to
intermediate levels in naturally-occurring human antibodies but are
missing in mAbs produced in standard industrial cell lines. The new
glycosylated versions outperformed Mabthera.TM. (the version of
Rixtuximab marketed in Europe) and mouse-myeloma derived chG250 in
biological (ADCC) activity. For example, a ten-fold lower amount of
the variant carrying the highest levels of bisected
oligosaccharides was required to reach the maximal ADCC activity as
Mabthera.TM.. For chG250, the variant carrying the highest levels
of bisected oligosaccharides mediated significant ADCC activity at
a 125-fold lower concentration than that required to detect even
low ADCC activity by the unmodified control chG250. A clear
correlation was found between the level of GnTIII expression and
ADCC activity.
[0012] Accordingly, in one aspect the claimed invention is directed
to a host cell engineered to produce a polypeptide having increased
Fc-mediated cellular cytotoxicity by expression of at least one
nucleic acid encoding .beta.(1,4)-N-acetylglucosaminyltransferase
III (GnT III), wherein the polypeptide produced by the host cell is
selected from the group consisting of a whole antibody molecule, an
antibody fragment, and a fusion protein which includes a region
equivalent to the Fc region of an immunoglobulin, and wherein the
GnT III is expressed in an amount sufficient to increase the
proportion of said polypeptide carrying bisected hybrid
oligosaccharides or galactosylated complex oligosaccharides or
mixtures thereof in the Fc region relative to polypeptides carrying
bisected complex oligosaccharides in the Fc region.
[0013] In a preferred embodiment, the polypeptide is IgG or a
fragment thereof, most preferably, IgG1 or a fragment thereof. In a
further preferred embodiment, the polypeptide is a fusion protein
that includes a region equivalent to the Fc region of a human
IgG.
[0014] In another aspect of the claimed invention, a nucleic acid
molecule comprising at least one gene encoding GnTIII has been
introduced into the host cell. In a preferred embodiment, at least
one gene encoding GnTIII has been introduced into the host cell
chromosome.
[0015] Alternatively, the host cell has been engineered such that
an endogenous GnT III gene is activated, for example, by insertion
of a DNA element which increases gene expression into the host
chromosome. In a preferred embodiment, the endogenous GnTIII has
been activated by insertion of a promoter, an enhancer, a
transcription factor binding site, a transposon, or a retroviral
element or combinations thereof into the host cell chromosome. In
another aspect, the host cell has been selected to carry a mutation
triggering expression of an endogenous GnTIII. Preferably, the host
cell is the CHO cell mutant lec 10.
[0016] In a further preferred embodiment of the claimed invention,
the at least one nucleic acid encoding a GnTIII is operably linked
to a constitutive promoter element.
[0017] In a further preferred embodiment, the host cell is a CHO
cell, a BHK cell, a NS0 cell, a SP2/0 cell, or a hybridoma cell, a
Y0 myeloma cell, a P3X63 mouse myeloma cell, a PER cell or a PER.C6
cell and said polypeptide is an anti-CD20 antibody. In another
preferred embodiment, the host cell is a SP2/0 cell and the
polypeptide is the monoclonal antibody chG250.
[0018] In another aspect, the claimed invention is directed to a
host cell that further comprises at least one transfected nucleic
acid encoding an antibody molecule, an antibody fragment, or a
fusion protein that includes a region equivalent to the Fc region
of an immunoglobulin. In a preferred embodiment, the host cell
comprises at least one transfected nucleic acid encoding an
anti-CD20 antibody, the chimeric anti-human neuroblastoma
monoclonal antibody chCE7, the chimeric anti-human renal cell
carcinoma monoclonal antibody chG250, the chimeric anti-human
colon, lung, and breast carcinoma monoclonal antibody ING-1, the
humanized anti-human 17-1A antigen monoclonal antibody 3622W94, the
humanized anti-human colorectal tumor antibody A33, the anti-human
melanoma antibody directed against GD3 ganglioside R24, or the
chimeric anti-human squamous-cell carcinoma monoclonal antibody
SF-25, an anti-human EGFR antibody, an anti-human EGFRvIII
antibody, an anti-human PSMA antibody, and anti-human PSCA
antibody, an anti-human CD22 antibody, an anti-human CD30 antibody,
an anti-human CD33 antibody, an anti-human CD38 antibody, an
anti-human CD40 antibody, an anti-human CD45 antibody, an
anti-human CD52 antibody, an anti-human CD138 antibody, an
anti-human HLA-DR variant antibody, an anti-human EpCAM antibody,
an anti-human CEA antibody, an anti-human MUC1 antibody, an
anti-human MUC1 core protein antibody, an anti-human aberrantly
glycosylated MUC1 antibody, an antibody against human fibronectin
variants containing the ED-B domain, and an anti-human HER2/neu
antibody.
[0019] In another aspect, the claimed invention is directed to a
method for producing a polypeptide in a host cell comprising
culturing any of the above-described the host cells under
conditions which permit the production of said polypeptide having
increased Fc-mediated cellular cytotoxicity. In a preferred
embodiment, the method further comprises isolating said polypeptide
having increased Fc-mediated cellular cytotoxicity.
[0020] In a further preferred embodiment, the host cell comprises
at least one nucleic acid encoding a fusion protein comprising a
region equivalent to a glycosylated Fc region of an
immunoglobulin.
[0021] In a preferred embodiment, the proportion of bisected
oligosaccharides in the Fc region of said polypeptides is greater
than 50%, more preferably, greater than 70%. In another embodiment,
the proportion of bisected hybrid oligosaccharides or
galactosylated complex oligosaccharides or mixtures thereof in the
Fc region is greater than the proportion of bisected complex
oligosaccharides in the Fc region of said polypeptide.
[0022] In a preferred aspect of the claimed method, the polypeptide
is an anti-CD20 antibody and the anti-CD20 antibodies produced by
said host cell have a glycosylation profile, as analyzed by
MALDI/TOF-MS, that is substantially equivalent to that shown in
FIG. 2E.
[0023] In another preferred aspect of the claimed method, the
polypeptide is the chG250 monoclonal antibody and the chG250
antibodies produced by said host cell have a glycosylaton profile,
as analyzed by MALDI/TOF-MS, that is substantially equivalent to
that shown in FIG. 7D.
[0024] In a further aspect, the claimed invention is directed to an
antibody having increased antibody dependent cellular cytotoxicity
(ADCC) produced by any of the methods described above. In preferred
embodiments, the antibody is selected from the group consisting of
an anti-CD20 antibody, chCE7, ch-G250, a humanized anti-HER2
monoclonal antibody, ING-1, 3622W94, SP-25, A33, and R24.
Alternatively, the polypeptide can be an antibody fragment that
includes a region equivalent to the Fc region of an immunoglobulin,
having increased Fc-mediated cellular cytotoxicity produced by any
of the methods described above.
[0025] In a further aspect, the claimed invention is directed to a
fusion protein that includes a region equivalent to the Fc region
of an immunoglobulin and having increased Fc-mediated cellular
cytotoxicity produced by any of the methods described above.
[0026] In a further aspect, the claimed invention is directed to a
pharmaceutical composition comprising the antibody, antibody
fragment, or fusion protein of the invention and a pharmaceutically
acceptable carrier.
[0027] In a further aspect, the claimed invention is directed to a
method for the treatment of cancer comprising administering a
therapeutically effective amount of said pharmaceutical composition
to a patient in need thereof.
[0028] In a further aspect, the invention is directed to an
improved method for treating an autoimmune disease produced in
whole or in part by pathogenic autoantibodies based on B-cell
depletion comprising administering a therapeutically effective
amount of immunologically active antibody to a human subject in
need thereof, the improvement comprising administering a
therapeutically effective amount of an antibody having increased
ADCC prepared as described above. In a preferred embodiment, the
antibody is an anti-CD20 antibody. Examples of autoimmune diseases
or disorders include, but are not limited to, immune-mediated
thrombocytopenias, such as acute idiopathic thrombocytopenic
purpurea and chronic idiopathic thrombocytopenic purpurea,
dermatomyositis, Sydenham's chorea, lupus nephritis, rheumatic
fever, polyglandular syndromes, Henoch-Schonlein purpura,
post-streptococcal nephritis, erythema nodosum, Takayasu's
arteritis, Addison's disease, erythema multiforme, polyarteritis
nodosa, ankylosing spondylitis, Goodpasture's syndrome,
thromboangitis ubiterans, primary biliary cirrhosis, Hashimoto's
thyroiditis, thyrotoxicosis, chronic active hepatitis,
polymyositis/dermatomyositis, polychondritis, pamphigus vulgaris,
Wegener's granulomatosis, membranous-nephropathy, amyotrophic
lateral sclerosis, tabes dorsalis, polymyaglia, pernicious anemia,
rapidly progressive glomerulonephritis and fibrosing alveolitis,
inflammatory responses such as inflammatory skin diseases including
psoriasis and dermatitis (e.g. atopic dermatitis); systemic
scleroderma and sclerosis; responses associated with inflammatory
bowel disease (such as Crohn's disease and ulcerative colitis);
respiratory distress syndrome (including adult respiratory distress
syndrome; ARDS); dermatitis; meningitis; encephalitis; uveitis;
colitis; glomerulonephritis; allergic conditions such as eczema and
asthma and other conditions involving infiltration of T cells and
chronic inflammatory responses; atherosclerosis; leukocyte adhesion
deficiency; rheumatoid arthritis; systemic lupus erythematosus
(SLE); diabetes mellitus (e.g. Type 1 diabetes mellitus or insulin
dependent diabetes mellitus); multiple sclerosis; Reynaud's
syndrome; autoimmune thyroiditis; allergic encephalomyelitis;
Sjorgen's syndrome; juvenile onset diabetes; and immune responses
associated with acute and delayed hypersensitivity mediated by
cytokines and T-lymphocytes typically found in tuberculosis,
sarcoidosis, polymyositis, granulomatosis and vasculitis;
pernicious amenia (Addison's disease); diseases involving leukocyte
diapedesis; central nervous system (CNS) inflammatory disorder,
multiple organ injury syndrome; hemolytic anemia (including, but
not limited to cryoglobinemia or Coombs positive anemia);
myastheniagravis; antigen-antibody complex mediated diseases;
anti-glomerular basement membrane disease; antiphospholipid
syndrome; allergic neuritis; Graves' disease; Lambert-Eaton
myasthenic syndrome; pemphigoid bullous; pemphigus; autoimmune
polyendocrinopathies; Reiter's disease; stiff-man syndrome; Behcet
disease; giant cell arteritis; immune complex nephritis; IgA
nephropathy; IgM polyneuropathies; immune thrombocytopenic purpura
(ITP) or autoimmune thrombocytopenia etc. In this aspect of the
invention, the antibodies of the invention are used to deplete the
blood of normal B-cells for an extended period.
BRIEF DESCRIPTION OF THE FIGURES
[0029] FIG. 1. Indirect immunofluorescence assay showing the
reactivity of the antibody preparation C2B8-25t to CD20 positive SB
cells. Negative controls, including the HSB CD20 negative cell line
and cells treated only with the secondary FITC-conjugated
anti-human Fc polyclonal antibody are not shown.
[0030] FIG. 2A-2E. MALDI/TOF-MS spectra of the oligosaccharides
derived from Mabthera.TM. (FIG. 2A), C2B8-nt (FIG. 2B), C2B8-2000t
(FIG. 2C), C2B8-50t (FIG. 2D), and C2B8-25t (FIG. 2E) antibody
samples. Oligosaccharides appear as [M+Na.sup.+] and [M+K.sup.+]
ions. Oligosaccharide appearing in the first two spectra were
derived from cell cultures that do not express GnTIII, whereas
oligosaccharides in C, D, and E were derived from a single cell
line expressing GnTIII at different levels (i.e. tetracycline
concentrations).
[0031] FIGS. 3A and 3B. Illustration of a typical human IgG
Fc-associated oligosaccharide structure (A) and partial N-linked
glycosylation pathway (B). (FIG. 3A) The core of the
oligosaccharide is composed of three mannose (M) and two
N-acetylglucosamine (Gn) monosaccharide residues attached to
Asn.sub.297. Galactose (G), fucose (F), and bisecting
N-acetylglucosamine (Gn, boxed) can be present or absent. Terminal
N-acetylneuraminic acid maybe also present but it is not included
in the figure. (FIG. 3B) Partial N-linked glycosylation pathway
leading to the formation of the major oligosaccharide classes
(dotted frames). Bisecting N-acetylglucosamine is denoted as
Gn.sup.b. Subscript numbers indicate how many monosaccharide
residues are present in each oligosaccharide. Each structure
appears together with its sodium-associated [M+Na.sup.+] mass. The
mass of those structures that contain fucose (f) are also
included.
[0032] FIGS. 4A and 4B. ADCC activities of Rituximab glycosylation
variants. The percentage of cytotoxicity was measured via lysis of
.sup.51Cr labeled CD20-positive SB cells by human lymphocytes (E:T
ratio of 100:1) mediated by different mAb concentrations. (FIG. 4A)
Activity of C2B8 samples derived from a single cell line but
produced at increasing GnTIII expression levels (i.e., decreasing
tetracycline concentrations). The samples are C2B8-2000t, C2B8-50t,
C2B8-25t, and C2B8-nt (control mAb derived from a clone that does
not express GnTIII (FIG. 4B) ADCC activity of C2B8-50t and C2B8-25t
compared to Mabthera.TM..
[0033] FIG. 5. Western blot analysis of the seven GnTIII expressing
clones and the wild type. 30 .mu.g of each sample were loaded on a
8.75% SDS gel, transferred to a PVDF membrane and probed with the
anti-c-myc monoclonal antibody (9E10). WT refers to wt-chG250-SP2/0
cells.
[0034] FIG. 6. SDS polyacrylamide gel electrophoresis of resolved
purified antibody samples.
[0035] FIG. 7A-7D. MALDI/TOF-MS spectra of neutral oligosaccharide
mixtures from chG250 mAb samples produced by clones expressing
different GnTIII levels and wt-chG250-SP2/0 cells: WT (FIG. 7A),
2F1 (FIG. 7B), 3D3 (FIG. 7C), 4E6 (FIG. 7D).
[0036] FIG. 8A-8D. MALDI/TOF-MS spectra of neutral oligosaccharide
mixtures from chG250 mAb samples produced by clones expressing
different GnTIII levels: 4E8, (FIG. 8A); 5G2, (FIG. 8B); 4G3, (FIG.
8C); 5H12, (FIG. 8D).
[0037] FIG. 9. In vitro ADCC assay of antibody samples derived from
control wt-chG250-SP2/-cells and GnTIII transected clones 3D3 and
5H12.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Terms are used herein as generally used in the art, unless
otherwise defined as follows:
[0039] As used herein, the term antibody is intended to include
whole antibody molecules, antibody fragments, or fusionproteins
that include a region equivalent to the Fc region of an
immunoglobulin.
[0040] As used herein, the term region equivalent to the Fc region
of an immunoglobulin is intended to include naturally occurring
allelic variants of the Fc region of an immunoglobulin as well as
variants having alterations which produce substitutions, additions,
or deletions but which do not decrease substantially the ability of
the immunoglobulin to mediate antibody dependent cellular
cytotoxicity. For example, one or more amino acids can be deleted
from the N-terminus or C-terminus of the Fc region of an
immunoglobulin without substantial loss of biological function.
Such variants can be selected according to general rules known in
the art so as to have minimal effect on activity. (See, e.g.,
Bowie, J. U. et al., Science 247:1306-10 (1990).
[0041] As used herein, the term glycoprotein-modifying glycosyl
transferase refers to .beta.(1,4)-N-acetylglucosaminyltransferase
III (GnTIII).
[0042] As used herein, the terms engineer, engineered, engineering
and glycosylation engineering are considered to include any
manipulation of the glycosylation pattern of a naturally occurring
polypeptide or fragment thereof. Glycosylation engineering includes
metabolic engineering of the glycosylation machinery of a cell,
including genetic manipulations of the oligosaccharide synthesis
pathways to achieve altered glycosylation of glycoproteins
expressed in cells. Furthermore, glycosylation engineering includes
the effects of mutations and cell environment on glycosylation.
[0043] As used herein, the term host cell covers any kind of
cellular system which can be engineered to generate modified
glycoforms of proteins, protein fragments, or peptides of interest,
including antibodies and antibody fragments. Typically, the host
cells have been manipulated to express optimized levels of GnT III.
Host cells include cultured cells, e.g., mammalian cultured cells,
such as CHO cells, BHK cells, NS0 cells, SP2/0 cells, YO myeloma
cells, P3X63 mouse myeloma cells, PER cells, PER.C6 cells or
hybridoma cells, yeast cells, and insect cells, to name only a few,
but also cells comprised within a transgenic animal or cultured
tissue.
[0044] As used herein, the term Fc-mediated cellular cytotoxicity
includes antibody-dependent cellular cytotoxicity and cellular
cytotoxicity mediated by a soluble Fc-fusion protein containing a
human Fc-region. It is an immune mechanism leading to the lysis of
"antibody-targeted cells" by "human immune effector cells",
wherein: [0045] The "human immune effector cells" are a population
of leukocytes that display Fc receptors on their surface through
which they bind to the Fc-region of antibodies or of Fc-fusion
proteins and perform effector functions. Such a population may
include, but is not limited to, peripheral blood mononuclear cells
(PBMC) and/or natural killer (NK) cells. [0046] The
"antibody-targeted cells" are cells bound by the antibodies or
Fc-fusion proteins. The antibodies or Fc fusion-proteins bind to
target cells via the protein part N-terminal to the Fc region.
[0047] As used herein, the term increased Fc-mediated cellular
cytotoxicity is defined as either an increase in the number of
"antibody-targeted cells" that are lysed in a given time, at a
given concentration of antibody, or of Fc-fusion protein, in the
medium surrounding the target cells, by the mechanism of
Fc-mediated cellular cytotoxicity defined above, and/or a reduction
in the concentration of antibody, or of Fc-fusion protein, in the
medium surrounding the target cells, required to achieve the lysis
of a given number of "antibody-targeted cells", in a given time, by
the mechanism of Fc-mediated cellular cytotoxicity. The increase in
Fc-mediated cellular cytotoxicity is relative to the cellular
cytotoxicity mediated by the same antibody, or Fc-fusion protein,
produced by the same type of host cells, using the same standard
production, purification, formulation and storage methods, which
are known to those skilled in the art, but that has not been
produced by host cells engineered to express the
glycosyltransferase GnTIII by the methods described herein.
[0048] By antibody having increased antibody dependent cellular
cytotoxicity (ADCC) is meant an antibody having increased ADCC as
determined by any suitable method known to those of ordinary skill
in the art. One accepted in vitro ADCC assay is as follows: [0049]
1) the assay uses target cells that are known to express the target
antigen recognized by the antigen-binding region of the antibody;
[0050] 2) the assay uses human peripheral blood mononuclear cells
(PBMCs), isolated from blood of a randomly chosen healthy donor, as
effector cells; [0051] 3) the assay is carried out according to
following protocol: [0052] i) the PBMCs are isolated using standard
density centrifugation procedures and are suspended at
5.times.10.sup.6 cells/ml in RPMI cell culture medium; [0053] ii)
the target cells are grown by standard tissue culture methods,
harvested from the exponential growth phase with a viability higher
than 90%, washed in RPMI cell culture medium, labelled with 100
micro-Curies of .sup.51Cr, washed twice with cell culture medium,
and resuspended in cell culture medium at a density of 10.sup.5
cells/ml; [0054] iii) 100 microliters of the final target cell
suspension above are transferred to each well of a 96-well
microtiter plate; [0055] iv) the antibody is serially-diluted from
4000 ng/ml to 0.04 ng/ml in cell culture medium and 50 microliters
of the resulting antibody solutions are added to the target cells
in the 96-well microtiter plate, testing in triplicate various
antibody concentrations covering the whole concentration range
above; [0056] v) for the maximum release (MR) controls, 3
additional wells in the plate containing the labelled target cells,
receive 50 microliters of a 2% (V/V) aqueous solution of non-ionic
detergent (Nonidet, Sigma, St. Louis), instead of the antibody
solution (point iv above); [0057] vi) for the spontaneous release
(SR) controls, 3 additional wells in the plate containing the
labelled target cells, receive 50 microliters of RPMI cell culture
medium instead of the antibody solution (point iv above); [0058]
vii) the 96-well microtiter plate is then centrifuged at 50.times.g
for 1 minute and incubated for 1 hour at 4.degree. C.; [0059] viii)
50 microliters of the PBMC suspension (point i above) are added to
each well to yield an effector:target cell ratio of 25:1 and the
plates are placed in an incubator under 5% CO.sub.2 atmosphere at
37.degree. C. for 4 hours; [0060] ix) the cell-free supernatant
from each well is harvested and the experimentally released
radioactivity (ER) is quantified using a gamma counter; [0061] x)
the percentage of specific lysis is calculated for each antibody
concentration according to the formula (ER-MR)/(MR-SR).times.100,
where ER is the average radioactivity quantified (see point ix
above) for that antibody concentration, MR is the average
radioactivity quantified (see point ix above) for the MR controls
(see point v above), and SR is the average radioactivity quantified
(see point ix above) for the SR controls (see point vi above);
[0062] 4) "increased ADCC" is defined as either an increase in the
maximum percentage of specific lysis observed within the antibody
concentration range tested above, and/or a reduction in the
concentration of antibody required to achieve one half of the
maximum percentage of specific lysis observed within the antibody
concentration range tested above. The increase in ADCC is relative
to the ADCC, measured with the above assay, mediated by the same
antibody, produced by the same type of host cells, using the same
standard production, purification, formulation and storage methods,
which are known to those skilled in the art, but that has not been
produced by host cells engineered to overexpress the
glycosyltransferase GnTIII.
[0063] As used herein, the term anti-CD20 antibody is intended to
mean an antibody which specifically recognizes a cell surface
non-glycosylated phosphoprotein of 35,000 Daltons, typically
designated as the human B lymphocyte restricted differentiation
antigen Bp35, commonly referred to as CD20.
Identification and Generation of Nucleic Acids Encoding a Protein
for which Modification of the Glycosylation Pattern is Desired
[0064] The present invention provides methods for the generation
and use of host cell systems for the production of glycoforms of
antibodies or antibody fragments or fusion proteins which include
antibody fragments with increased antibody-dependent cellular
cytotoxicity. Identification of target epitopes and generation of
antibodies having potential therapeutic value, for which
modification of the glycosylation pattern is desired, and isolation
of their respective coding nucleic acid sequence is within the
scope of the invention.
[0065] Various procedures known in the art may be used for the
production of antibodies to target epitopes of interest. Such
antibodies include but are not limited to polyclonal, monoclonal,
chimeric, single chain, Fab fragments and fragments produced by an
Fab expression library. Such antibodies may be useful, e.g., as
diagnostic or therapeutic agents. As therapeutic agents,
neutralizing antibodies, i.e., those which compete for binding with
a ligand, substrate or adapter molecule, are of especially
preferred interest.
[0066] For the production of antibodies, various host animals are
immunized by injection with the target protein of interest
including, but not limited to, rabbits, mice, rats, etc. Various
adjuvants may be used to increase the immunological response,
depending on the host species, including but not limited to
Freund's (complete and incomplete), mineral gels such as aluminum
hydroxide, surface active substances such as lysolecithin, pluronic
polyols, polyanions, peptides, saponin, oil emulsions, keyhole
limpet hemocyanin, dinitrophenol, and potentially useful human
adjuvants such as BCG (bacille Calmette-Guerin) and Corynebacterium
parvum.
[0067] Monoclonal antibodies to the target of interest may be
prepared using any technique which provides for the production of
antibody molecules by continuous cell lines in culture. These
include, but are not limited to, the hybridoma technique originally
described by Kohler and Milstein, Nature 256:495-97 (1975), the
human B-cell hybridoma technique (Kosbor et al., Immunology Today
4:72 (1983); Cote et al., Proc. Natl. Acad. Sci. U.S.A. 80:2026-30
(1983) and the EBV-hybridoma technique (Cole et al., Monoclonal
Antibodies and Cancer Therapy 77-96 (Alan R. Liss, Inc., 1985)). In
addition, techniques developed for the production of "chimeric
antibodies" (Morrison et al., Proc. Natl. Acad. Sci. U.S.A.
81:6851-55 (1984); Neuberger et al., Nature 312:604-08 (1984);
Takeda et al., Nature 314:452-54 (1985) by splicing the genes from
a mouse antibody molecule of appropriate antigen specificity
together with genes from a human antibody molecule of appropriate
biological activity can be used. Alternatively, techniques
described for the production of single chain antibodies (U.S. Pat.
No. 4,946,778) can be adapted to produce single chain antibodies
having a desired specificity.
[0068] Antibody fragments which contain specific binding sites of
the target protein of interest may be generated by known
techniques. For example, such fragments include, but are not
limited to, F(ab').sub.2 fragments which can be produced by pepsin
digestion of the antibody molecule and the Fab fragments which can
be generated by reducing the disulfide bridges of the F(ab').sub.2
fragments. Alternatively, Fab expression libraries may be
constructed (Huse et al., Science 246:1275-81 (1989) to allow rapid
and easy identification of monoclonal Fab fragments with the
desired specificity to the target protein of interest.
[0069] Once an antibody or antibody fragment has been identified
for which modification in the glycosylation pattern are desired,
the coding nucleic acid sequence is identified and isolated using
techniques well known in the art.
[0070] a. Generation of Cell Lines for the Production of Proteins
with Altered Glycosylation Pattern
[0071] The present invention provides host cell expression systems
for the generation of proteins having modified glycosylation
patterns. In particular, the present invention provides host cell
systems for the generation of glycoforms of proteins having an
improved therapeutic value. Therefore, the invention provides host
cell expression systems selected or engineered to increase the
expression of a glycoprotein-modifying glycosyltransferase, namely
.beta.(1,4)-N-acetylglucosaminyltransferase III (GnTIII).
Specifically, such host cell expression systems may be engineered
to comprise a recombinant nucleic acid molecule encoding GnTIII,
operatively linked to a constitutive or regulated promoter system.
Alternatively, host cell expression systems may be employed that
naturally produce, are induced to produce, and/or are selected to
produce GnTIII.
[0072] In one specific embodiment, the present invention provides a
host cell that has been engineered to express at least one nucleic
acid encoding GnTIII. In one aspect, the host cell is transformed
or transfected with a nucleic acid molecule comprising at least one
gene encoding GnTIII. In an alternate aspect, the host cell has
been engineered and/or selected in such way that endogenous GnTIII
is activated. For example, the host cell may be selected to carry a
mutation triggering expression of endogenous GnTIII. In one
specific embodiment, the host cell is a CHO lec10 mutant.
Alternatively, the host cell may be engineered such that endogenous
GnTIII is activated. In again another alternative, the host cell is
engineered such that endogenous GnTIII has been activated by
insertion of a constitutive promoter element, a transposon, or a
retroviral element into the host cell chromosome.
[0073] Generally, any type of cultured cell line can be used as a
background to engineer the host cell lines of the present
invention. In a preferred embodiment, CHO cells, BHK cells, NS0
cells, SP2/0 cells, YO myeloma cells, P3X63 mouse myeloma cells,
PER cells, PER.C6 cells or hybridoma cells, yeast cells, or insect
cells are used as the background cell line to generate the
engineered host cells of the invention.
[0074] The invention is contemplated to encompass any engineered
host cells expressing GnTIII as defined herein.
[0075] One or several nucleic acids encoding GnTIII may be
expressed under the control of a constitutive promoter or,
alternately, a regulated expression system. Suitable regulated
expression systems include, but are not limited to, a
tetracycline-regulated expression system, an ecdysone-inducible
expression system, a lac-switch expression system, a
glucocorticoid-inducible expression system, a temperature-inducible
promoter system, and a metallothionein metal-inducible expression
system. If several different nucleic acids encoding GnTIII are
comprised within the host cell system, some of them may be
expressed under the control of a constitutive promoter, while
others are expressed under the control of a regulated promoter. The
maximal expression level is considered to be the highest possible
level of stable GnTIII expression that does not have a significant
adverse effect on cell growth rate, and will be determined using
routine experimentation. Expression levels are determined by
methods generally known in the art, including Western blot analysis
using a GnTIII specific antibody, Northern blot analysis using a
GnTIII specific nucleic acid probe, or measurement of enzymatic
activity. Alternatively, a lectin may be employed which binds to
biosynthetic products of the GnTIII, for example, E.sub.4-PHA
lectin. In a further alternative, the nucleic acid may be
operatively linked to a reporter gene; the expression levels of the
GnTIII are determined by measuring a signal correlated with the
expression level of the reporter gene. The reporter gene may
transcribed together with the nucleic acid(s) encoding said GnTIII
as a single mRNA molecule; their respective coding sequences may be
linked either by an internal ribosome entry site (IRES) or by a
cap-independent translation enhancer (CITE). The reporter gene may
be translated together with at least one nucleic acid encoding said
GnTIII such that a single polypeptide chain is formed. The nucleic
acid encoding the GnTIII may be operatively linked to the reporter
gene under the control of a single promoter, such that the nucleic
acid encoding the GnTIII and the reporter gene are transcribed into
an RNA molecule which is alternatively spliced into two separate
messenger RNA (mRNA) molecules; one of the resulting mRNAs is
translated into said reporter protein, and the other is translated
into said GnTIII.
[0076] If several different nucleic acids encoding GnTIII are
expressed, they may be arranged in such way that they are
transcribed as one or as several mRNA molecules. If they are
transcribed as a single mRNA molecule, their respective coding
sequences may be linked either by an internal ribosome entry site
(IRES) or by a cap-independent translation enhancer (CITE). They
may be transcribed from a single promoter into an RNA molecule
which is alternatively spliced into several separate messenger RNA
(mRNA) molecules, which then are each translated into their
respective encoded GnTIII.
[0077] In other embodiments, the present invention provides host
cell expression systems for the generation of therapeutic
antibodies, having an increased antibody-dependent cellular
cytotoxicity, and cells which display the IgG Fc region on the
surface to promote Fc-mediated cytotoxicity. Generally, the host
cell expression systems have been engineered and/or selected to
express nucleic acids encoding the antibody for which the
production of altered glycoforms is desired, along with at least
one nucleic acid encoding GnTIII. In one embodiment, the host cell
system is transfected with at least one gene encoding GnTIII.
Typically, the transfected cells are selected to identify and
isolate clones that stably express the GnTIII. In another
embodiment, the host cell has been selected for expression of
endogenous GnTIII. For example, cells may be selected carrying
mutations which trigger expression of otherwise silent GnTIII. For
example, CHO cells are known to carry a silent GnT III gene that is
active in certain mutants, e.g., in the mutant Lec10. Furthermore,
methods known in the art may be used to activate silent GnTIII,
including the insertion of a regulated or constitutive promoter,
the use of transposons, retroviral elements, etc. Also the use of
gene knockout technologies or the use of ribozyme methods may be
used to tailor the host cell's GnTIII expression level, and is
therefore within the scope of the invention.
[0078] Any type of cultured cell line can be used as background to
engineer the host cell lines of the present invention. In a
preferred embodiment, CHO cells, BHK cells, NS0 cells, SP2/0 cells,
YO myeloma cells, P3X63 mouse myeloma cells, PER cells, PER.C6
cells or hybridoma cells, yeast cell, or insect cells may be used.
Typically, such cell lines are engineered to further comprise at
least one transfected nucleic acid encoding a whole antibody
molecule, an antibody fragment, or a fusion protein that includes a
region equivalent to the Fc region of an immunoglobulin. In an
alternative embodiment, a hybridoma cell line expressing a
particular antibody of interest is used as background cell line to
generate the engineered host cells of the invention.
[0079] Typically, at least one nucleic acid in the host cell system
encodes GnT III.
[0080] One or several nucleic acids encoding GnTIII may be
expressed under the control of a constitutive promoter, or
alternately, a regulated expression system. Suitable regulated
expression systems include, but are not limited to, a
tetracycline-regulated expression system, an ecdysone-inducible
expression system, a lac-switch expression system, a
glucocorticoid-inducible expression system, a temperature-inducible
promoter system, and a metallothionein metal-inducible expression
system. If several different nucleic acids encoding GnTIII are
comprised within the host cell system, some of them may be
expressed under the control of a constitutive promoter, while
others are expressed under the control of a regulated promoter. The
maximal expression level is considered to be the highest possible
level of stable GnTIII expression that does not have a significant
adverse effect on cell growth rate, and will be determined using
routine experimentation. Expression levels are determined by
methods generally known in the art, including Western blot analysis
using a GnTIII specific antibody, Northern blot analysis using a
GnTIII specific nucleic acid probe, or measurement of GnTIII
enzymatic activity. Alternatively, a lectin may be employed which
binds to biosynthetic products of GnTIII, for example, E.sub.4-PHA
lectin. In a further alternative, the nucleic acid may be
operatively linked to a reporter gene; the expression levels of the
glycoprotein-modifying glycosyl transferase are determined by
measuring a signal correlated with the expression level of the
reporter gene. The reporter gene may transcribed together with the
nucleic acid(s) encoding said glycoprotein-modifying glycosyl
transferase as a single mRNA molecule; their respective coding
sequences may be linked either by an internal ribosome entry site
(IRES) or by a cap-independent translation enhancer (CITE). The
reporter gene may be translated together with at least one nucleic
acid encoding GnTIII such that a single polypeptide chain is
formed. The nucleic acid encoding the GnTIII may be operatively
linked to the reporter gene under the control of a single promoter,
such that the nucleic acid encoding the GnTIII and the reporter
gene are transcribed into an RNA molecule which is alternatively
spliced into two separate messenger RNA (mRNA) molecules; one of
the resulting mRNAs is translated into said reporter protein, and
the other is translated into said GnTIII.
[0081] If several different nucleic acids encoding a GnTIII are
expressed, they may be arranged in such way that they are
transcribed as one or as several mRNA molecules. If they are
transcribed as single mRNA molecule, their respective coding
sequences may be linked either by an internal ribosome entry site
(IRES) or by a cap-independent translation enhancer (CITE). They
may be transcribed from a single promoter into an RNA molecule
which is alternatively spliced into several separate messenger RNA
(mRNA) molecules, which then are each translated into their
respective encoded GnTIII.
[0082] i. Expression Systems Methods which are well known to those
skilled in the art can be used to construct expression vectors
containing the coding sequence of the protein of interest and the
coding sequence of the GnTIII and appropriate
transcriptional/translational control signals. These methods
include in vitro recombinant DNA techniques, synthetic techniques
and in vivo recombination/genetic recombination. See, for example,
the techniques described in Maniatis et al., Molecular Cloning A
Laboratory Manual, Cold Spring Harbor Laboratory, N.Y. (1989) and
Ausubel et al., Current Protocols in Molecular Biology, Greene
Publishing Associates and Wiley Interscience, N.Y (1989).
[0083] A variety of host-expression vector systems may be utilized
to express the coding sequence of the protein of interest and the
coding sequence of the GnTIII. Preferably, mammalian cells are used
as host cell systems transfected with recombinant plasmid DNA or
cosmid DNA expression vectors containing the coding sequence of the
protein of interest and the coding sequence of the GnTIII. Most
preferably, CHO cells, BHK cells, NS0 cells, SP2/0 cells, YO
myeloma cells, P3X63 mouse myeloma cells, PER cells, PER. C6 cells
or hybridoma cells, yeast cells, or insect cells are used as host
cell system. In alternate embodiments, other eukaryotic host cell
systems may be contemplated, including, yeast cells transformed
with recombinant yeast expression vectors containing the coding
sequence of the protein of interest and the coding sequence of the
GnTIII; insect cell systems infected with recombinant virus
expression vectors (e.g., baculovirus) containing the coding
sequence of the protein of interest and the coding sequence of the
GnTIII; plant cell systems infected with recombinant virus
expression vectors (e.g., cauliflower mosaic virus, CaMV; tobacco
mosaic virus, TMV) or transformed with recombinant plasmid
expression vectors (e.g., Ti plasmid) containing the coding
sequence of the protein of interest and the coding sequence of the
GnTIII; or animal cell systems infected with recombinant virus
expression vectors (e.g., adenovirus, vaccinia virus) including
cell lines engineered to contain multiple copies of the DNA
encoding the protein of interest and the coding sequence of the
GnTIII either stably amplified (CHO/dhfr) or unstably amplified in
double-minute chromosomes (e.g., murine cell lines).
[0084] For the methods of this invention, stable expression is
generally preferred to transient expression because it typically
achieves more reproducible results and also is more amenable to
large scale production. Rather than using expression vectors which
contain viral origins of replication, host cells can be transformed
with the respective coding nucleic acids controlled by appropriate
expression control elements (e.g., promoter, enhancer, sequences,
transcription terminators, polyadenylation sites, etc.), and a
selectable marker. Following the introduction of foreign DNA,
engineered cells may be allowed to grow for 1-2 days in an enriched
media, and then are switched to a selective media. The selectable
marker in the recombinant plasmid confers resistance to the
selection and allows selection of cells which have stably
integrated the plasmid into their chromosomes and grow to form foci
which in turn can be cloned and expanded into cell lines.
[0085] A number of selection systems may be used, including, but
not limited to, the herpes simplex virus thymidine kinase (Wigler
et al., Cell 11:223 (1977)), hypoxanthine-guanine
phosphoribosyltransferase (Szybalska & Szybalski, Proc. Natl.
Acad. Sci. USA 48:2026 (1962)), and adenine
phosphoribosyltransferase (Lowy et al., Cell 22:817 (1980)) genes,
which can be employed in tk.sup.-, hgprt.sup.- or aprt.sup.- cells,
respectively. Also, antimetabolite resistance can be used as the
basis of selection for dhfr, which confers resistance to
methotrexate (Wigler et al., Natl. Acad. Sci. USA 77:3567 (1989);
O'Hare et al., Proc. Natl. Acad. Sci. USA 78:1527 (1981)); gpt,
which confers resistance to mycophenolic acid (Mulligan & Berg,
Proc. Natl. Acad. Sci. USA 78:2072 (1981)); neo, which confers
resistance to the aminoglycoside G-418 (Colberre-Garapin et al., J.
Mol. Biol. 150:1 (1981)); and hygro, which confers resistance to
hygromycin (Santerre et al., Gene 30:147 (1984) genes. Recently,
additional selectable genes have been described, namely trpB, which
allows cells to utilize indole in place of tryptophan; hisD, which
allows cells to utilize histinol in place of histidine (Hartman
& Mulligan, Proc. Natl. Acad. Sci. USA 85:8047 (1988)); the
glutamine synthase system; and ODC (ornithine decarboxylase) which
confers resistance to the ornithine decarboxylase inhibitor,
2-(difluoromethyl)-DL-ornithine, DFMO (McConlogue, in: Current
Communications in Molecular Biology, Cold Spring Harbor Laboratory
ed. (1987)).
[0086] ii. Identification Of Transfectants or Transformants that
Express the Protein Having a Modified Glycosylation Pattern
[0087] The host cells which contain the coding sequence and which
express the biologically active gene products may be identified by
at least four general approaches; (a) DNA-DNA or DNA-RNA
hybridization; (b) the presence or absence of "marker" gene
functions; (c) assessing the level of transcription as measured by
the expression of the respective mRNA transcripts in the host cell;
and (d) detection of the gene product as measured by immunoassay or
by its biological activity.
[0088] In the first approach, the presence of the coding sequence
of the protein of interest and the coding sequence of the GnTIII
inserted in the expression vector can be detected by DNA-DNA or
DNA-RNA hybridization using probes comprising nucleotide sequences
that are homologous to the respective coding sequences,
respectively, or portions or derivatives thereof.
[0089] In the second approach, the recombinant expression
vector/host system can be identified and selected based upon the
presence or absence of certain "marker" gene functions (e.g.,
thymidine kinase activity, resistance to antibiotics, resistance to
methotrexate, transformation phenotype, occlusion body formation in
baculovirus, etc.). For example, if the coding sequence of the
protein of interest and the coding sequence of the GnTIII are
inserted within a marker gene sequence of the vector, recombinants
containing the respective coding sequences can be identified by the
absence of the marker gene function. Alternatively, a marker gene
can be placed in tandem with the coding sequences under the control
of the same or different promoter used to control the expression of
the coding sequences. Expression of the marker in response to
induction or selection indicates expression of the coding sequence
of the protein of interest and the coding sequence of the
GnTIII.
[0090] In the third approach, transcriptional activity for the
coding region of the protein of interest and the coding sequence of
the GnTIII can be assessed by hybridization assays. For example,
RNA can be isolated and analyzed by Northern blot using a probe
homologous to the coding sequences of the protein of interest and
the coding sequence of the GnTIII or particular portions thereof.
Alternatively, total nucleic acids of the host cell may be
extracted and assayed for hybridization to such probes.
[0091] In the fourth approach, the expression of the protein
products of the protein of interest and the coding sequence of the
GnTIII can be assessed immunologically, for example by Western
blots, immunoassays such as radioimmuno-precipitation,
enzyme-linked immunoassays and the like. The ultimate test of the
success of the expression system, however, involves the detection
of the biologically active gene products.
[0092] b. Generation and Use of Proteins and Protein Fragments
Having Altered Glycosylation Patterns
[0093] i. Generation and Use of Antibodies Having Increased
Antibody-Dependent Cellular Cytotoxicity
[0094] In preferred embodiments, the present invention provides
glycoforms of antibodies and antibody fragments having increased
antibody-dependent cellular cytotoxicity.
[0095] Clinical trials of unconjugated monoclonal antibodies (mAbs)
for the treatment of some types of cancer have recently yielded
encouraging results. Dillman, Cancer Biother. & Radiopharm.
12:223-25 (1997); Deo et al., Immunology Today 18:127 (1997). A
chimeric, unconjugated IgG1 has been approved for low-grade or
follicular B-cell non-Hodgkin's lymphoma Dillman, Cancer Biother.
& Radiopharm. 12:223-25 (1997), while another unconjugated mAb,
a humanized IgG1 targeting solid breast tumors, has also been
showing promising results in phase III clinical trials. Deo et al.,
Immunology Today 18:127 (1997). The antigens of these two mAbs are
highly expressed in their respective tumor cells and the antibodies
mediate potent tumor destruction by effector cells in vitro and in
vivo. In contrast, many other unconjugated mAbs with fine tumor
specificities cannot trigger effector functions of sufficient
potency to be clinically useful. Frost et al., Cancer 80:317-33
(1997); Surfus et al., J. Immunother. 19:184-91 (1996). For some of
these weaker mAbs, adjunct cytokine therapy is currently being
tested. Addition of cytokines can stimulate antibody-dependent
cellular cytotoxicity (ADCC) by increasing the activity and number
of circulating lymphocytes. Frost et al., Cancer 80:317-33 (1997);
Surfus et al., J. Immunother. 19:1.84-91 (1996). ADCC, a lytic
attack on antibody-targeted cells, is triggered upon binding of
leukocyte receptors to the constant region (Fc) of antibodies. Deo
et al., Immunology Today 18:127 (1997).
[0096] A different, but complementary, approach to increase ADCC
activity of unconjugated IgG1s is to engineer the Fc region of the
antibody to increase its affinity for the lymphocyte receptors
(Fc.gamma.Rs). Protein engineering studies have shown that
Fc.gamma.Rs interact with the lower hinge region of the IgG CH2
domain. Lund et al., J. Immunol. 157:4963-69 (1996). However,
Fc.gamma.R binding also requires the presence of oligosaccharides
covalently attached at the conserved Asn 297 in the CH2 region.
Lund et al., J. Immunol. 157:4963-69 (1996); Wright and Morrison,
Trends Biotech. 15:26-31 (1997), suggesting that either
oligosaccharide and polypeptide both directly contribute to the
interaction site or that the oligosaccharide is required to
maintain an active CH2 polypeptide conformation. Modification of
the oligosaccharide structure can therefore be explored as a means
to increase the affinity of the interaction.
[0097] An IgG molecule carries two N-linked oligosaccharides in its
Fc region, one on each heavy chain. As any glycoprotein, an
antibody is produced as a population of glycoforms which share the
same polypeptide backbone but have different oligosaccharides
attached to the glycosylation sites. The oligosaccharides normally
found in the Fc region of serum IgG are of complex bi-antennary
type (Wormald et al., Biochemistry 36:130-38 (1997), with low level
of terminal sialic acid and bisecting N-acetylglucosamine (GlcNAc),
and a variable degree of terminal galactosylation and core
fucosylation. Some studies suggest that the minimal carbohydrate
structure required for Fc.gamma.R binding lies within the
oligosaccharide core. Lund et al., J. Immunol. 157:4963-69 (1996)
The removal of terminal galactoses results in approximately a
two-fold reduction in ADCC activity, indicating a role for these
residues in Fc.gamma.R receptor binding. Lund et al, J. Immunol.
157:4963-69 (1996)
[0098] The mouse or hamster-derived cell lines used in industry and
academia for production of unconjugated therapeutic mAbs normally
attach the required oligosaccharide determinants to Fc sites. IgGs
expressed in these cell lines lack, however, the bisecting GlcNAc
found in low amounts in serum IgGs. Lifely et al., Glycobiology
318:813-22 (1995). In contrast, it was recently observed that a rat
myeloma-produced, humanized IgG1 (CAMPATH-1H) carried a bisecting
GlcNAc in some of its glycoforms. Lifely et al., Glycobiology
318:813-22 (1995). The rat cell-derived antibody reached a similar
in vitro ADCC activity as CAMPATH-1H antibodies produced in
standard cell lines, but at significantly lower antibody
concentrations.
[0099] The CAMPATH antigen is normally present at high levels on
lymphoma cells, and this chimeric mAb has high ADCC activity in the
absence of a bisecting GlcNAc. Lifely et al., Glycobiology
318:813-22 (1995). In the N-linked glycosylation pathway, a
bisecting GlcNAc is added by the enzyme
.beta.(1,4)-N-acetylglucosaminyltransferase III (GnT III).
Schachter, Biochem. Cell Biol. 64:163-81 (1986).
[0100] The present inventors used a single antibody-producing CHO
cell line, that was previously engineered to express, in an
externally-regulated fashion, different levels of a cloned GnT III
gene. This approach established for the first time a rigorous
correlation between expression of GnTIII and the ADCC activity of
the modified antibody.
[0101] The present inventors previously showed that C2B8 antibody
modified according to the disclosed method had an about
sixteen-fold higher ADCC activity than the standard, unmodified
C2B8 antibody produced under identical cell culture and
purification conditions. Briefly, a C2B8 antibody sample expressed
in CHO-tTA-C2B8 cells that do not have GnT III expression showed a
cytotoxic activity of about 31% (at 1 .mu.g/ml antibody
concentration), measured as in vitro lysis of SB cells (CD20+) by
human lymphocytes. In contrast, C2B8 antibody derived from a CHO
cell culture expressing GnT III at a basal, largely repressed level
showed at 1 .mu.g/ml antibody concentration a 33% increase in ADCC
activity against the control at the same antibody concentration.
Moreover, increasing the expression of GnT III produced a large
increase of almost 80% in the maximal ADCC activity (at 1 .mu.g/ml
antibody concentration) compared to the control at the same
antibody concentration. (See International Publication No. WO
99/54342, the entire contents of which are hereby incorporated by
reference.)
[0102] Further antibodies of the invention having increased
antibody-dependent cellular cytotoxicity include, but are not
limited to, anti-human neuroblastoma monoclonal antibody (chCE7)
produced by the methods of the invention, a chimeric anti-human
renal cell carcinoma monoclonal antibody (ch-G250) produced by the
methods of the invention, a humanized anti-HER2 monoclonal antibody
(e.g., Trastuzumab (HERCEPTIN)) produced by the methods of the
invention, a chimeric anti-human colon, lung, and breast carcinoma
monoclonal antibody (ING-1) produced by the methods of the
invention, a humanized anti-human 17-1A antigen monoclonal antibody
(3622W94) produced by the methods of the invention, a humanized
anti-human colorectal tumor antibody (A33) produced by the methods
of the invention, an anti-human melanoma antibody (R24) directed
against GD3 ganglioside produced by the methods of the invention,
and a chimeric anti-human squamous-cell carcinoma monoclonal
antibody (SF-25) produced by the methods of the invention, an
anti-human small cell lung carcinoma monoclonal antibody (BEC2,
ImClone Systems, Merck KgaA) produced by the methods of the
invention, an anti-human non-Hodgkin's lymphoma monoclonal antibody
(Bexxar (tositumomab, Coulter Pharmaceuticals), Oncolym
(Techniclone, Alpha Therapeutic)) produced by the methods of the
invention, an anti-human squamous cell head and neck carcinoma
monoclonal antibody (C225, ImClone Systems) prepared by the methods
of the invention, an anti-human rectal and colon carcinoma
monoclonal antibody (Panorex (edrecolomab), Centocor, Glaxo
Wellcome) prepared by the methods of the invention, an anti-human
ovarian carcinoma monoclonal antibody (Theragyn, Antisoma) produced
by the methods of the invention, an anti-human acute myelogenous
leukemia carcinoma monoclonal antibody (SmartM195, Protein Design
Labs, Kanebo) produced by the methods of the invention, an
anti-human malignant glioma monoclonal antibody (Cotara,
Techniclone, Cambridge Antibody Technology) produced by the methods
of the invention, an anti-human B cell non-Hodgkins lymphoma
monoclonal antibody (IDEC-Y2B8, IDEC Pharmaceuticals) produced by
the methods of the invention, an anti-human solid tumors monoclonal
antibody (CEA-Cide, Immunomedics) produced by the methods of the
invention, an anti-human colorectal carcinoma monoclonal antibody
(Iodine 131-MN-14, Immunomedics) produced by the methods of the
invention, an anti-human ovary, kidney, breast, and prostate
carcinoma monoclonal antibody (MDX-210, Medarex, Novartis) produced
by the methods of the invention, an anti-human colorectal and
pancreas carcinoma monoclonal antibody (TTMA, Pharmacie &
Upjohn) produced by the methods of the invention, an anti-human
TAG-72 expressing carcinoma monoclonal antibody (MDX-220, Medarex)
produced by the methods of the invention, an anti-human
EGFr-expressing carcinoma monoclonal antibody (MDX-447) produced by
the methods of the invention, Anti-VEGF monoclonal antibody
(Genentech) produced by the methods of the invention, an anti-human
breast, lung, prostate and pancreas carcinoma and malignant
melanoma monoclonal antibody (BrevaRex, AltaRex) produced by the
methods of the invention, and an anti-human acute myelogenous
leukemia monoclonal antibody (Monoclonal Antibody Conjugate,
Immunex) produced by the methods of the invention. In addition, the
invention is directed to antibody fragment and fusion proteins
comprising a region that is equivalent to the Fc region of
immunoglobulins.
[0103] ii. Generation and Use of Fusion Proteins Comprising a
Region Equivalent to an Fc Region of an Immunoglobulin that Promote
Fc-Mediated Cytotoxicity
[0104] As discussed above, the present invention relates to a
method for increasing the ADCC activity of therapeutic antibodies.
This is achieved by engineering the glycosylation pattern of the Fc
region of such antibodies, in particular by maximizing the
proportion of antibody molecules carrying bisected complex
oligosaccharides and bisected hybrid oligosaccharides N-linked to
the conserved glycosylation sites in their Fc regions. This
strategy can be applied to increase Fc-mediated cellular
cytotoxicity against undesirable cells mediated by any molecule
carrying a region that is an equivalent to the Fc region of an
immunoglobulin, not only by therapeutic antibodies, since the
changes introduced by the engineering of glycosylation affect only
the Fc region and therefore its interactions with the Fc receptors
on the surface of effector cells involved in the ADCC mechanism.
Fc-containing molecules to which the presently disclosed methods
can be applied include, but are not limited to, (a) soluble fusion
proteins made of a targeting protein domain fused to the N-terminus
of an Fc-region (Chamov and Ashkenazi, Trends Biotech. 14: 52(1996)
and (b) plasma membrane-anchored fusion proteins made of a type II
transmembrane domain that localizes to the plasma membrane fused to
the N-terminus of an Fc region (Stabila, P. F., Nature Biotech. 16:
1357 (1998)).
[0105] In the case of soluble fusion proteins (a) the targeting
domain directs binding of the fusion protein to undesirable cells
such as cancer cells, i.e., in an analogous fashion to therapeutic
antibodies. The application of presently disclosed method to
enhance the Fc-mediated cellular cytotoxic activity mediated by
these molecules would therefore be identical to the method applied
to therapeutic antibodies.
[0106] In the case of membrane-anchored fusion proteins (b) the
undesirable cells in the body have to express the gene encoding the
fusion protein. This can be achieved either by gene therapy
approaches, i.e., by transfecting the cells in vivo with a plasmid
or viral vector that directs expression of the fusion
protein-encoding gene to undesirable cells, or by implantation in
the body of cells genetically engineered to express the fusion
protein on their surface. The later cells would normally be
implanted in the body inside a polymer capsule (encapsulated cell
therapy) where they cannot be destroyed by an Fc-mediated cellular
cytotoxicity mechanism. However should the capsule device fail and
the escaping cells become undesirable, then they can be eliminated
by Fc-mediated cellular cytotoxicity. Stabila et al., Nature
Biotech. 16: 1357 (1998). In this case, the presently disclosed
method would be applied either by incorporating into the gene
therapy vector an additional gene expression cassette directing
adequate or maximal expression levels of GnT III or by engineering
the cells to be implanted to express adequate or maximal levels of
GnT III. In both cases, the aim of the disclosed method is to
increase or maximize the proportion of surface-displayed Fc regions
carrying bisected complex oligosaccharides and/or bisected hybrid
oligosaccharides.
[0107] The examples below explain the invention in more detail. The
following preparations and examples are given to enable those
skilled in the art to more clearly understand and to practice the
present invention. The present invention, however, is not limited
in scope by the exemplified embodiments, which are intended as
illustrations of single aspects of the invention only, and methods
which are functionally equivalent are within the scope of the
invention. Indeed, various modifications of the invention in
addition to those described herein will become apparent to those
skilled in the art from the foregoing description and accompanying
drawings. Such modifications are intended to fall within the scope
of the appended claims.
EXAMPLE 1
New Versions of the Chimeric Anti-CD20 Antibody IDEC-C2B8 Having
Enhanced Antibody-Dependent Cellular Cytotoxicity Obtained by
Glycosylation Engineering of an IDEC-CEB8 Producing Cell Line
[0108] Synthesis of VH and VL coding regions of IDEC-C2B8 and
construction of mammalian expression vectors. cDNAs encoding the VH
and VL regions of IDEC-C2B8 antibody were assembled from a set of
overlapping single-stranded oligonucleotides in a one-step process
using PCR (Kobayashi, N., et al., Biotechniques 23:500-503(1997)).
The original sequence data coding for IDEC-C2B8 VL and VH were
obtained from a published international patent application
(International Publication Number: WO 94/11026). Assembled VL and
VH cDNA fragments were subcloned into pBluescriptIIKS(+), sequenced
and directly joined by ligation to the human constant light (Ig
.kappa.) and heavy (IgG1) chain cDNAs, respectively, using unique
restriction sites introduced at the variable and constant region
junctions without altering the original amino acid residue sequence
(Umana, P., et al., Nat Biotechnol. 17:176-180 (1999); Reff, M. E.,
et al., Blood 83:435-445 (1994)). Each full-length cDNA was
separately subcloned into pcDNA3.1(+) (Invitrogen, Leek, The
Netherlands) yielding mammalian expression vectors for chimeric
C2B8 light (pC2B8L) and heavy (pC2B8H) chains.
[0109] Production of IDEC-C2B8 in CHO cells expressing different
levels of GnTIII. Establishment of two CHO cell lines,
CHO-tet-GnTIII expressing different levels of GnTIII depending on
the tetracycline concentration in the culture medium; and CHO-tTA,
the parental cell line that does not express GnTIII has been
described previously (Umana, P., et al., Nat Biotechnol. 17:176-180
(1999); Umana, P., et al., Biotechnol Bioeng. 65:542-549 (1999)).
Each cell line was cotranfected with vectors pC2B8L, pC2B8H, and
pZeoSV2(+) (for Zeocin resistance; Invitrogen, Leek, The
Netherlands) using a calcium phosphate method. Zeocin resistant
clones were transferred to a 96-well plate and assayed for
IDEC-C2B8 production using an ELISA assay specific for the human
constant region (4). Three IDEC-C2B8 samples were obtained from
parallel cultures of a selected clone (CHO-tet-GnTIII-C2B8),
differing only in the tetracycline concentration added to the
medium (25, 50 and 2000 ng/mL respectively). Culture supernatants
were harvested in the late exponential phase. An additional
antibody sample was obtained from a CHO-tTA-derived clone,
CHO-tTA-C2B8, cultured under identical conditions but without
adding tetracycline to the medium. Antibody samples were purified
from culture medium by protein A affinity chromatography and buffer
exchanged to PBS on a cation exchange column as previously
described (Umana, P., et al., Nat Biotechnol. 17:176-180 (1999)).
Antibody concentration was measured using a fluorescence-based kit
from Molecular Probes (Leiden, The Netherlands) with Rituximab used
as standard.
[0110] Indirect immunofluorescence. CD20-positive cells (SB cells;
ATCC deposit no. ATCC CCL120) and CD20-negative cells (HSB cells;
ATCC deposit no. ATCC CCL120.1) were each incubated for 1 h with
2.5 .mu.g/ml of CHO-tet-GnTIII-derived IDEC-C2B8 antibody in Hank's
balanced salt solution (GibcoBRL, Basel, Switzerland) and 2% bovine
serum albumin fraction V (Roche Diagnostics, Rotkreuz, Switzerland)
(HBSSB). As a negative control HBSSB was used instead of C2B8
antibody. A FITC-conjugated, anti-human Fc polyclonal antibody was
used as a secondary antibody (SIGMA, St. Louis) for all samples.
Cells were examined using a Leica fluorescence microscope (Wetzlar,
Germany).
[0111] Oligosaccharide profiling by MALDI/TOF-MS. Neutral, N-linked
oligosaccharides were derived from C2B8 antibody samples,
MabThera.TM. (European counterpart of Rituximab; kind gift from R.
Stahel, Universit{dot over (a)}tspital, Switzerland), C2B8-25t,
C2B8-50t, C2B8-2000t, and C2B8-nt, (100 .mu.g each) as previously
described (Umana, P., et al., Nat Biotechnol. 17:176-180 (1999)).
Briefly, the antibody samples were first treated with Arthrobacter
ureafaciens sialidase (Oxford Glycosciences, Abingson, UK) to
remove any sialic acid monosaccharide residues. Neutral N-linked
oligosaccharides were then released from the desialylated antibody
samples using peptide-N-glycosidase F (Oxford Glycosciences),
purified using micro-columns, and analyzed by MALDI/TOF-MS in an
Elite Voyager 400 spectrometer (Perseptive Biosystems, Farmingham,
Mass.).
[0112] ADCC Activity Assay. Peripheral blood mononuclear cells
(PBMC) were separated from heparinated fresh human blood (in all
experiments obtained from the same healthy donor) by centrifugation
over a Ficoll-Paque (Pharmacia Biotech, Dubendorf, Switzerland)
gradient. PBMC (effector) were depleted of monocytes by plastic
adherence. CD20-positive SB (target) cells, were labeled for 90 min
with 100 .mu.Ci .sup.51Cr (Amersham, Dubendorf, Switzerland) at
37.degree. C., washed twice in RPMI (GibcoBRL, Basel, Switzerland)
and resuspended at a concentration of 10.sup.5 cells/ml. Fifty
microliters of C2B8 mAb diluted in RPMI medium was added to 100
.mu.l SB cells (10,000 cells/well) in a 96-well round bottom
microtiter plate (Greiner, Langenthal, Switzerland), centrifuged at
50.times.g for 1 min, and incubated for 1 h at 4.degree. C.
Subsequently, 50 .mu.l of effector cell (suspended at
2.times.10.sup.7 cells/ml in RPMI medium) were added to each
96-well yielding a final E:T ratio of 100. Plates were incubated
for 4 h at 37.degree. C. and 5% CO.sub.2, supernatant was harvested
with a Skatron harvesting system (Skatron Instruments, Sterling,
Va.) and counted (ER, experimental release) in a Cobra 05005
.gamma. counter (Canberra Packard, Meriden, Conn.). Maximum (MR)
and spontaneous (SR) releases were obtained by adding, instead of
C2B8 mAb, 100 .mu.l of 1% Nonidet (Sigma, St. Louis) or 100 .mu.l
of RPMI medium, respectively, to 100 .mu.l labeled target cells.
All data points were performed in triplicate. Specific lysis (%)
was calculated with the following formula:
(ER-SR)/(MR-SR).times.100.
Results and Discussion
[0113] Production of IDEC-C2B8 and verification of specific antigen
binding. CHO-tet-GnTIII cells, with stable, tetracycline-regulated
expression of GnTIII and stable, constitutive expression of
IDEC-C2B8, were established and scaled-up for production of a set
of antibody samples. During scale-up, parallel cultures from the
same clone were grown under three different tetracycline
concentrations, 25, 50 and 2000 ng/ml. These levels of tetracycline
had previously been shown to result in different levels of GnTIII
and bisected oligosaccharides (Umana, P., et al., Nat Biotechnol.
17:176-180(1999); Umana, P., et al., Biotechnol Bioeng. 65:542-549
(1999)). A C2B8-producing, control cell line that does not express
GnTIII was also established and cultured under the same conditions
as for the three parallel cultures of CHO-tet-GnTIII. After Protein
A-affinity chromatography, mAb purity was estimated to be higher
than 95% by SDS-PAGE and Coomassie-blue staining. The samples were
named according to the tetracycline concentration added to the
culture medium for their production: C2B8-25t, C2B 8-50t,
C2B8-2000t and C2B8-nt (i.e., no tetracycline for the non-bisected
control). Sample C2B 8-25t showed specific antigen binding by
indirect immunofluorescence using CD20-positive and CD20-negative
cells (FIG. 1), indicating that the synthesized VL and VH gene
fragments were functionally correct.
[0114] Oligosaccharide profiling with MALDI/TOF-MS. The
glycosylation profile of each antibody sample was analyzed by
MALDI/TOF-MS of the released, neutral oligosaccharide mix. In this
technique, oligosaccharides of different mass appear as separate
peaks in the spectrum and their proportions are quantitatively
reflected by the relative peak heights (Harvey, D. J., Rapid Common
Mass Spectrom. 7:614-619 (1993); Harvey, D. J., et al., Glycoconj
J. 15:333-338 (1998)). Oligosaccharide structures were assigned to
different peaks based on their expected molecular masses, previous
structural data for oligosaccharides derived from IgG1 mAbs
produced in the same host, and information on the N-linked
oligosaccharide biosynthetic pathway.
[0115] A clear correlation was found between GnTIII expression
levels (i.e., tetracycline concentration) and the amount of
bisected oligosaccharides derived from the different antibody
samples. As expected, MabThera.TM. and C2B8-nt, which are derived
from hosts that do not express GnTIII, did not carry bisected
oligosaccharides (FIGS. 2A and 2B). In contrast, bisected
structures amounted up to approximately 35% of the oligosaccharides
pool in sample C2B8-2000t, i.e, at a basal level of GnTIII
expression. In this case, the main bisected oligosaccharide peaks
were of complex type, unequivocally assigned to peaks at m/z 1689
and m/z 1851 (FIG. 2C). The next higher GnTIII expression level,
sample C2B8-50t, led to an increase in these peaks (including their
associated potassium aducts at m/z 1705 and 1861) of around 20%.
This increase was accompanied by a concomitant reduction of their
non-bisected counterparts at m/z 1486 and 1648, respectively (FIG.
2D). At the highest GnTIII expression level, sample C2B8-25t, the
main substrate for GnTIII, m/z 1486, decreased to almost base-line
level, while complex bisected structures (m/z 1689 and 1851)
decreased in favor of increases in peaks at m/z 1664, 1810 and 1826
(FIG. 2E). These peaks can be assigned either to bisected hybrid
compounds, to galactosylated complex oligosaccharides, or to a
mixture of both. Their relative increase, however, is consistent
with the accumulation of bisected hybrid compounds, as GnTIII
overexpression can divert the biosynthetic flux at early stages of
the pathway (see FIGS. 3A and 3B). The amount of bisected
oligosaccharide structures (complex and hybrid type) reached
approximately 80% for this sample.
[0116] ADCC activity of IDEC-C2B8 glycosylated variants. Different
C2B8 mAb glycosylation variants were compared for ADCC activity,
measured as in vitro lysis of CD20-positive SB cells. An additional
mAb sample, C2B8-nt, derived from the parental cell line lacking
GnTIII, was also studied. Sample C2B8-2000t produced at the basal
GnTIII expression level and carrying low levels of bisected
oligosaccharides was slightly more active than C2B8-nt (FIG. 4A).
At the next higher level of GnTIII-expression, sample C2B8-50t
carried approximately equal levels of bisected and non-bisected
oligosaccharides, but did not mediate significantly higher
target-cell lysis. However, at the lowest tetracycline
concentration, sample C2B8-25t, which contained up to 80% of
bisected oligosaccharide structures, was significantly more active
than the rest of the samples in the whole antibody concentration
range. It reached the maximal level of ADCC activity of sample
C2B8-nt at a 10-fold lower antibody concentration (FIG. 4A). Sample
C2B8-25t also showed a significant increase in the maximal ADCC
activity with respect to the control (50% vs. 30% lysis).
[0117] Samples C2B8-50t and C2B8-25t, bearing the highest
proportions of bisected oligosaccharides, were further compared in
ADCC activity to Mabthera.TM., the version of Rituxan.TM. currently
marketed in Europe (FIG. 4B). Sample C2B8-50t showed a slight
increase in activity whereas sample C2B8-25t clearly outperformed
Mabthera.TM. at all antibody concentrations. Approximately a five
to ten-fold lower concentration of C2B8-25t was required to reach
the maximal ADCC activity of Mabthera.TM., and the maximal activity
of C2B8-25t was about 25% higher than that of Mabthera.TM..
[0118] These results show that, in general, the in vitro ADCC
activity of the C2B8 antibody correlates with the proportion of
molecules carrying bisected oligosaccharides in the Fc region. We
had previously reported that in the case of chCE7, an antibody with
a low baseline level of ADCC activity, significant increases of
activity could be obtained by increasing the fraction of bisected
oligosaccharides above the levels found in naturally-occurring
antibodies (Umana, P., et al., Nat Biotechnol. 17:176-180 (1999)).
The same is true for the C2B8 mAb, which already has high ADCC
activity in the absence of bisected oligosaccharides. In the case
of chCE7, however, very large increases of ADCC activity were
observed at a level of GnTIII expression where bisected
oligosaccharides were predominantly of complex type (Umana, P., et
al., Nat Biotechnol. 17:176-180 (1999)). For the potent C2B8 mAb,
such a large boost in activity was only observed at the highest
levels of GnTIII expression studied, where bisected
oligosaccharides had shifted mainly to the hybrid type (FIG. 2).
For both mAbs, the samples with the highest activities had
considerably higher levels of bisected than non-bisected
oligosaccharides. Together, these observations indicate that
probably both complex and hybrid bisected oligosaccharides are
important for ADCC activity.
[0119] In both complex and hybrid oligosaccharides, a bisecting
GlcNAc leads to a large change in oligosaccharide conformations
(Balaji, P. V., et al., Int. J. Biol. Macromol. 18:101-114 (1996)).
The change occurs in a part of the oligosaccharide that interacts
extensively with the polypeptide in the CH2 domain (Jefferis, R.,
et al., Immunol Rev. 163:59-76 (1998)). Since the polypetide is
relatively flexible at this location (Jefferis, R., et al., Immunol
Rev. 163:59-76 (1998)), it is possible that the bisecting
N-acetylglucosamine is mediating its biological effects through a
conformational change in the Fc region. The potentially altered
conformations would already exist in nature, as all serum IgGs
carry bisected oligosaccharides. The main difference between the
engineered and natural antibodies would be the proportion of
molecules displaying the more active conformations.
[0120] Various approaches for increasing the activity of
unconjugated mAbs are currently under clinical evaluation,
including radio-immunotherapy, antibody-dependent
enzyme/prodrugtherapy, immunotoxins and adjuvant therapy with
cytokines (Hjelm Skog, A., et al., Cancer Immunol Immunother.
48:463-470 (1999); Blakey, D. C., et al., Cell Biophys. 25: 175-183
(1994); Wiseman, G. A., et al., Clin Cancer Res. 5:3281s-3296s
(1999); Hank, J. A., et al., Cancer Res. 50:5234-5239 (1990)).
These technologies can give large increases in activity, but they
can also lead to significantly higher side effects, elevated
production costs and complex logistics from production to
administration to patients when compared to unconjugated mAbs. The
technology presented here offers an alternative way to obtain
increases in potency while maintaining a simple production process,
and should be applicable to many unconjugated mAbs.
EXAMPLE 2
New Versions of the Anti-Renal Cell Carcinoma Antibody chG250
Having Enhanced Antibody-Dependent Cellular Cytotoxicity Obtained
by Glycosylation Engineering of a chG250 Producing Cell Line
[0121] 1. Cell Culture
[0122] SP2/0 mouse myeloma cells producing chG250 chimeric mAb
(wt-chG250-SP2/0 cells) were grown in standard cell culture medium
supplemented with 1:100 (v/v) penicillin/streptomycin/antimycotic
solution (SIGMA, Buchs, Switzerland). Cells were cultured at
37.degree. C. in a 5% CO.sub.2 humidified atmosphere in Tissue
Culture Flasks. Medium was changed each 3-4 days. Cells were frozen
in culture medium containing 10% DMSO.
[0123] 2. Generation of SP2/0 Cells with pGnTIII-puro
Expression
[0124] wt-chG250-SP2/O myeloma cells were transfected by
electroporation with a vector for constitutive expression of GnTIII
operatively linked via an IRES to a puromycin resistance gene. 24
hours before electroporation culture medium was changed and cells
were seeded at 5.times.10.sup.5 cells/ml. Seven million cells were
centrifuged for 4 min at 1300 rpm at 4.degree. C. Cells were washed
with 3 mL new medium and centrifuged again. Cells were resuspended
in a volume of 0.3-0.5 ml of reaction mix, containing 1.25% (v/v)
DMSO and 20-30 .mu.g DNA in culture medium. The electroporation mix
was then transferred to a 0.4 cm cuvette and pulsed at low voltage
(250-300 V) and high capacitance (960 .mu.F) using Gene Pulser from
Bio Rad. After electroporation cells were quickly transferred to 6
mL 1.25% (v/v) DMSO culture medium in a T25 culture flask and
incubated at 37.degree. C. Stable integrants were selected by
applying 2 .mu.g/mL puromycin to the medium two days after
electroporation. After 2-3 weeks a stable, puromycin-resitant mixed
population was obtained. Single-cell derived clones were obtained
via FACS and were subsequently expanded and maintained under
puromycin selection.
[0125] 3. Western Blot
[0126] Puromycin-resistant clones were screened for GnTIII
expression by Western blotting. The Western blots clearly showed
that clones 5H12, 4E6 and 4E8 were expressing the highest levels of
GnTIII. 5G2 also showed a GnTIII band of middle intensity, whereas
2F1, 3D3 and 4G3 had the lowest band intensities, therefore
expressing lower amounts of GnTIII (FIG. 5).
[0127] 4. Production and Purification of chG250 Monoclonal Antibody
from Seven GnTIII-Expressing Clones Including Wild Type
[0128] Clones 2F1, 3D3, 4E6, 4E8, 4G3, 5G2, 5H12 and the wild type
(wt-chG250-SP2/0 cells) were seeded at 3.times.10.sup.5 cells/mL in
a total volume of 130 ml culture medium, and cultivated in single
Triple-flasks. Cells used for seeding were all in full exponential
growth phase, therefore cells were considered to be at the same
growth state when the production batches started. Cells were
cultivated for 4 days. Supernatants containing the antibody were
collected in the late exponential growth phase to ensure
reproducibility. The chG250 monoclonal antibody was purified in two
chromatographic steps. Culture supernatants containing the chG250
monoclonal antibody derived from each batch were first purified
using a HiTrap Protein A affinity chromatography. Protein A is
highly specific for the human IgG F, region. Pooled samples from
the protein A eluate were buffer exchanged to PBS by
cation-exchange chromatography on a Resource S 1 ml column
(Amersham Pharmacia Biotech). Final purity was judged to be higher
than 95% from SDS-staining and Coomassie blue staining (FIG. 6).
The concentration of each sample was determined with a standard
calibration curve using wild type antibody with known
concentration.
[0129] 5. Oligosaccharide Profiling of mAb Preparations Derived
from the Seven Clones Expressing Different GnTIII Levels
[0130] Oligosaccharide profiles were obtained by matrix-assisted
laser desorption/ionization time of flight mass spectrometry
(MALDI/TOF-MS), which accurately provides the molecular masses of
the different oligosaccharide structures. This technique allows a
quantitative analysis of proportions between different
oligosaccharide structures within a mixture. Neutral
oligosaccharides appeared predominantly as [M+Na.sup.+] ions,
however sometimes they were accompanied by-smaller [M+K.sup.+]
ions, leading to an increase in mass of m/z of 16. The percentage
of the structure appearing as potassium ion adducts depends on the
content of the matrix and may thus vary between samples. A mixture
of neutral N-linked oligosaccharides derived from each antibody
preparation was analyzed using a 2,5-dehydrobenzoic acid (2,5-DHB)
as matrix. Some of the peaks in the spectra were unequivocally
assigned to specific oligosaccharide structures, because of known
monosaccharide composition and unique mass. However, sometimes
multiple structures could be assigned to a particular mass. MALDI
enables the determination of the mass and cannot distinguish
between isomers. Knowledge of the biosynthetic pathway and previous
structural data enable, in most cases, the assignment of an
oligosaccharide structure to a peak in the spectrum.
[0131] Oligosaccharides derived from the mAb sample produced in
wt-chG250-SP2/0 cell line, that does not express GnTIII, contained
nonbisected biantennary complex (m/z 1486) and mono- or
di-galactosylated nonbisected biantennary complex structures (FIG.
7A), both .alpha.(1,6)-fucosylated in the core region (peaks m/z
1648 and 1810 respectively).
[0132] Expression of GnTIII generated bisected F.sub.c-associated
oligosaccharide structures of two types: complex or hybrid. Complex
bisected oligosaccharides were unequivocally assigned to peaks at
m/z 1543, 1689, 1705, 1851 and 1867 ([M+K.sup.+] adduct). As
expected, the increase in bisected oligosaccharides was accompanied
by a concomitant reduction of peaks m/z 1486 and 1648, that
correspond to nonbisected complex oligosaccharides. For all samples
derived from the GnTIII expressing clones, the main substrate of
GnTIII (m/z 1486) decreased dramatically. As expected, the
percentage of the nonbisected complex oligosaccharide type,
assigned to peak at m/z 1648, had the lowest values for the clones
expressing the highest GnTIII levels (clones 4E6, 4E8, 5G2 and
5H12). These two peaks decreased in favor of the accumulation of
bisected complex and bisected hybrid type oligosaccharides (FIGS.
7A-7D and 8A-8D). The percentage of bisected complex
oligosaccharides was higher for the samples derived from the clones
expressing lower amounts of GnTIII. This is consistent with the
fact that a higher GnTIII expression level probably shifts the
biosynthetic flux to bisected hybrid structures, thereby decreasing
the relative proportions of complex and complex bisected compound.
For bisected hybrid structures, two possible structures could
sometimes be assigned to a single peak. Therefore, some assumptions
were made in order to approximate the percentage of these
structures over the total oligosaccharide pool. Peaks m/z 1664,
1680, 1810 and 1826 can be assigned to either bisected hybrid type,
to galactosylated complex oligosaccharides, or a mixture of them.
Due to the fact that the wt-antibody preparation had a relatively
low percentage of peak 1664, it was assumed that this peak,
appearing in significant amounts in the antibody samples derived
from the different clones, corresponded entirely to bisected hybrid
structures (FIGS. 7A-7D and 8A-8D). However to assign a specific
structure to peaks m/z 1810 and 1826 further characterization has
to be performed. In summary, by overexpression of GnTIII, bisected
oligosaccharides structures were generated and their relative
proportions correlated with GnTIII expression levels.
[0133] 6. Measurement of Antibody Mediated Cytotoxic Activity by
Calcein-AM Retention
[0134] The Calcein-AM retention method of measuring cytotoxicity
measures the dye fluorescence remaining in the cells after
incubation with the antibody. Four million G250 antigen-positive
cells (target) were labelled with 10 .mu.M Calcein-AM (Molecular
Probes, Eugene, Oreg.) in 1.8 mL RPMI-1640 cell culture medium
(GIBCO BRL, Basel, Switzerland) supplemented with 10% fetal calf
serum for 30 min at 37.degree. C. in a 5% CO.sub.2 humidified
atmosphere. The cells were washed twice in culture medium and
resuspended in 12 mL AIMV serum free medium (GIBCO BRL, Basel,
Switzerland). Labelled cells were then transferred to U-bottom
96-wells (30,000 cells/well) and incubated in triplicate with
different concentrations of antibody for 1 hour at 4.degree. C.
Peripheral blood mononuclear cells (PBMC) were separated from
heparinated fresh human blood (in all experiments obtained from the
same healthy donor) by centrifugation over a Ficoll-Paque
(Pharmacia Biotech, Dubendorf, Switzerland) gradient. PBMCs were
added in triplicate wells in a 50 .mu.L volume, yielding an
effector to target ratio (E:T ratio) of 25:1 and a final volume of
200 .mu.L. The 96-well plate was then incubated for 4 hours at
37.degree. C. in a 5% CO.sub.2 atmosphere. Thereafter the 96-well
plate was centrifuged at 700.times.g for 5 min and the supernatants
were discarded. The cell pellets were washed twice with Hank's
balanced salt solution (HBSS) and lysed in 200 .mu.L 0.05M sodium
borate, pH 9, 0.1% Triton X-100. Retention of the fluorescent dye
in the target cells was measured with a FLUOstar microplate reader
(BMG LabTechnologies, Offenburg, Germany). The specific lysis was
calculated relative to a total lysis control, resulting from
exposure of the target cells to saponin (200 mg/mL in AIMV; SIGMA,
Buchs, Switzerland) instead of exposure to antibody. Specific lysis
(%) was calculated with the following formula: % .times. .times.
Cytotoxicity = F med - F exp F med - F det ##EQU1## where F.sub.med
represents the fluorescence of target cells treated with medium
alone and considers unspecific lysis by PMBCs, F.sub.exp represents
the fluorescence of cells treated with antibody and F.sub.det
represents the fluorescence of cells treated with saponin instead
of antibody.
[0135] To determine the effect of modified glycosylation variants
of chG250 on the in vitro ADCC activity, G250 antigen-positive
target cells were cultured with PBMCs with and without chG250
antibody samples at different concentrations. The cytotoxicity of
unmodified chG250 antibody derived from the wild type cell line was
compared with two antibody preparations derived from two cell lines
(3D3, 5H12) expressing intermediate and high GnTIII levels,
respectively (see FIG. 5).
[0136] Unmodified chG250 antibody did not mediate significant ADCC
activity over the entire concentration range used in the assay (the
activity was not significantly different from background).
Augmented ADCC activity (close to 20%, see FIG. 9) at 2 .mu.g/mL
was observed with the antibody sample derived from clone 3D3, which
expressed intermediate GnTIII levels. The cytotoxic activity of
this antibody samples did not grow at higher antibody
concentrations. As expected the antibody preparation derived from
clone 5H12 showed a striking increase over samples 3D3 and
unmodified antibody in its ability to mediate ADCC against target
cells. The maximal ADCC activity of this antibody preparation was
around 50% and was remarkable in mediating significant ADCC
activity at 125-fold less concentrated when comparing with the
unmodified control sample.
EXAMPLE 3
Treatment of Immune-Mediated Thrombocytopenia in a Patient with
Chronic Graft-Versus-Host Disease
[0137] Autoimmune thrombocytopenia in chronic graft-versus-host
disease represents an instance of B-cell dysregulation leading to
clinical disease. To treat immune-mediated thrombocytopenia in a
subject with chronic graft-versus-host disease, an anti-CD20
chimeric monoclonal antibody prepared by the methods of the present
invention and having increased ADCC is administered to the subject
as described in Ratanatharathorn, V. et al., Ann. Intern. Med.
133(4):275-79 (2000) (the entire contents of which is hereby
incorporated by reference). Specifically, a weekly infusion of the
antibody, 375 mg/m.sup.2 is administered to the subject for 4
weeks. The antibody therapy produces a marked depletion of B cells
in the peripheral blood and decreased levels of platelet-associated
antibody.
EXAMPLE 4
Treatment of Severe, Immune-Mediated, Pure Red Cell Aplasia and
Hemolytic Anemia
[0138] Immune-mediated, acquired pure red cell aplasia (PRCA) is a
rare disorder frequently associated with other autoimmune phenomena
To treat immune-mediated, acquired pure red cell aplasia in a
subject, an anti-CD20 chimeric monoclonal antibody prepared by the
methods of the present invention and having increased ADCC is
administered to the subject as described in Zecca, M. et al., Blood
12:3995-97 (1997) (the entire contents of which are hereby
incorporated by reference). Specifically, a subject with PRCA and
autoimmune hemolytic anemia is given two doses of antibody, 375
mg/m.sup.2, per week. After antibody therapy, substitutive
treatment with intravenous immunoglobulin is initiated. This
treatment produces a marked depletion of B cells and a significant
rise in reticulocyte count accompanied by increased hemoglobin
levels.
[0139] It will be clear that the invention may be practiced
otherwise than as particularly described in the foregoing
description and examples. Numerous modifications and variations of
the present invention are possible in light of the above teachings
and, therefore, are within the scope of the appended claims.
[0140] The entire disclosure of all publications (including
patents, patent applications, journal articles, laboratory manuals,
books, or other documents) cited herein are hereby incorporated by
reference.
* * * * *