U.S. patent application number 10/155839 was filed with the patent office on 2003-01-30 for production of a multimeric protein by cell fusion method.
Invention is credited to Davis, Claude Geoffrey, Hori, Nobuaki, Jakobovits, Aya, Zsebo, Krisztina M..
Application Number | 20030022291 10/155839 |
Document ID | / |
Family ID | 27407513 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030022291 |
Kind Code |
A1 |
Hori, Nobuaki ; et
al. |
January 30, 2003 |
Production of a multimeric protein by cell fusion method
Abstract
The present invention features a method of producing a
multimeric protein from a hybrid cell formed from the fusion of two
or more cells, each of which cell is engineered to express one
component of the multimeric protein, as well as a method for
screening for successful fusion of the cells to produce a desired
hybrid cell. The methods of the invention are widely applicable to
the production of proteins having two or more components.
Inventors: |
Hori, Nobuaki; (Hanagawa,
JP) ; Davis, Claude Geoffrey; (Burlingame, CA)
; Zsebo, Krisztina M.; (Boulder, CO) ; Jakobovits,
Aya; (Menlo Park, CA) |
Correspondence
Address: |
BOZICEVIC, FIELD & FRANCIS LLP
200 MIDDLEFIELD RD
SUITE 200
MENLO PARK
CA
94025
US
|
Family ID: |
27407513 |
Appl. No.: |
10/155839 |
Filed: |
May 24, 2002 |
Related U.S. Patent Documents
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Application
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Filing Date |
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10155839 |
May 24, 2002 |
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09945387 |
Aug 30, 2001 |
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09945387 |
Aug 30, 2001 |
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09769070 |
Jan 24, 2001 |
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6420140 |
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09769070 |
Jan 24, 2001 |
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09342301 |
Jun 29, 1999 |
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6207418 |
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09342301 |
Jun 29, 1999 |
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08730639 |
Oct 11, 1996 |
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5916771 |
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Current U.S.
Class: |
435/69.1 ;
435/326; 435/451; 435/452; 435/70.21 |
Current CPC
Class: |
C07K 2317/21 20130101;
C07K 16/244 20130101; C07K 16/00 20130101; C12N 5/166 20130101;
C12N 15/62 20130101; C12N 2510/02 20130101; C12N 5/16 20130101;
C07K 14/00 20130101 |
Class at
Publication: |
435/69.1 ;
435/70.21; 435/451; 435/452; 435/326 |
International
Class: |
C12P 021/04; C12N
005/06 |
Claims
What is claimed is:
1. A method for producing a multi-component protein, said method
comprising: (a) introducing a first nucleotide sequence into a
first cell, wherein the first nucleotide sequence encodes a first
component of the multi-component protein; (b) introducing a second
nucleotide sequence into a second cell, wherein the second
nucleotide sequence encodes a second component of the
multi-component protein; (c) optionally, repeating step (b) for
each remaining component of the multi-component protein; and (d)
fusing cells produced from steps (a)-(c) to form a hybrid cell,
wherein the hybrid cell expresses the multi-component protein.
2. The method of claim 1, further comprising: (e) culturing the
hybrid cells so as to express the multi-component protein; and (f)
recovering the multi-component protein from the hybrid cell
culture.
3. The method of claim 1, wherein said first cells and said second
cells are selected from the group consisting of a mammalian cell, a
myeloma cell, and a non-lymphoid cell.
4. The multi-component protein of claim 1, wherein said protein is
an antibody.
5. A method for producing an antibody, said method comprising: (a)
introducing a nucleotide sequence encoding a desired heavy chain
into a first cell; (b) introducing a nucleotide sequence encoding a
desired light chain into a second cell; and (c) fusing the first
and second cells to form a hybrid cell, wherein the hybrid cell
expresses the antibody.
6. The method of claim 5, further comprising: (e) culturing the
hybrid cells so as to express the multi-component protein; and (f)
recovering the multi-component protein from the hybrid cell
culture.
7. The method of claim 5, wherein said nucleotide sequence is
obtained from a B-cell or a hybridoma cell, wherein said B-cell or
hybridoma cell produce an antibody.
8. The method of claim 5, wherein the first cell expresses an
irrelevant light chain and expresses the desired heavy chain prior
to fusion with the second cell.
9. The method of claim 5, wherein expression of the desired heavy
chain by the first cell is determined by ELISA analysis of lysate
from the first cell.
10. The method of claim 5, wherein the antibody is expressed only
after fusion of said first and second cells.
11. The method of claim 5, wherein the first cell expressing the
desired heavy chain is further selected for one or more desirable
characteristics.
12. The method of claim 5, wherein both the second cell expressing
the desired light chain and the first cell expressing the desired
heavy chain are each further selected for one or more desirable
characteristics.
13. The method of claim 12, wherein said desirable characteristic
is selected from the group consisting of high production rate of
the heavy chain and high production rate of light chain.
14. A method for producing an antibody, said method comprising: (a)
introducing a nucleotide sequence encoding a desired heavy chain
into a first cell, wherein the first cell expresses an irrelevant
light chain; (b) introducing a nucleotide sequence encoding a
desired light chain into a second cell; and (c) fusing the first
and second cells to form a hybrid cell, wherein the hybrid cell
expresses the antibody.
15. The method of claim 14, further comprising: (e) culturing the
hybrid cells so as to express the multi-component protein; and (f)
recovering the multi-component protein from the hybrid cell
culture.
16. The method of claim 14, wherein said irrelevant light chain is
present in an episomal vector.
17. A multi-component protein produced by the method of claim
1.
18. An antibody produced by the method of claim 5.
19. A antibody produced by the method of claim 14.
20. A method for screening for successful fusion of a first cell
containing a first nucleotide sequence encoding a desired antibody
heavy chain and a second cell containing a second nucleotide
sequence encoding a desired antibody light chain, comprising:
including a nucleotide sequence encoding a first marker gene in the
first cell; including a nucleotide sequence encoding a second
marker gene in the second cell; fusing the first cell and the
second cell under fuseogenic conditions to produce a fused cell;
and assaying for the presence of the first and second marker genes
in the fused cell, wherein detection of the presence of the first
and second marker genes in the fused cell indicates a successful
fusion.
21. The method of claim 20, wherein the first marker gene is
independently selected from the group consisting of the hygromycin
resistance gene, the neomycin resistance gene, the hypoxanthine
phosphoribosyl transferase gene, the dihydrofolate reductase gene,
and the LacZ reporter gene and the second marker gene is
independently selected from the group consisting of the hygromycin
resistance gene, the neomycin resistance gene, the hypoxanthine
phosphoribosyl transferase gene, the dihydrofolate reductase gene,
and the LacZ reporter gene.
22. The method of claim 20, wherein the first marker gene is the
hypoxanthine phosphoribosyl transferase and the second marker gene
is the LacZ reporter gene.
23. The method of claim 20, wherein the first marker gene is the
LacZ reporter gene and the second marker gene is the hypoxanthine
phosphoribosyl transferase gene.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to methods for use in gene
expression and cell fusion techniques, particularly in the
production of multi-component proteins.
BACKGROUND OF THE INVENTION
[0002] Recombinant DNA techniques have been used for production of
heterologous proteins in transformed host cells. Generally, the
produced proteins are composed of a single amino acid chain or two
chains cleaved from a single polypeptide chain. More recently,
multichain proteins such as antibodies have been produced by
transforming a single host cell with DNA sequences encoding each of
the polypeptide chains and expressing the polypeptide chains in the
transformed host cell (U.S. Pat. No. 4,816,397).
[0003] The basic immunoglobulin (Ig) structural unit in vertebrate
systems is composed of two identical "light" polypeptide chains
(approximately 23 kDa), and two identical "heavy" chains
(approximately 53 to 70 kDa). The four chains are joined by
disulfide bonds in a "Y" configuration, and the "tail" portions of
the two heavy chains are bound by covalent disulfide linkages when
the immunoglobulins are generated either by hybridomas or by B
cells.
[0004] A schematic of the general antibody structure is shown in
FIG. 1. The light and heavy chains are each composed of a variable
region at the N-terminal end, and a constant region at the
C-terminal end. In the light chain, the variable region (termed
"V.sub.LJ.sub.L") is the product of the recombination of a V.sub.L
gene to a J.sub.L gene. In the heavy chain, the variable region
(V.sub.HD.sub.HJ.sub.H) is the product of recombination of first a
D.sub.H and a J.sub.H gene, followed by a D.sub.HJ.sub.H to V.sub.H
recombination. The V.sub.LJ.sub.L and V.sub.HD.sub.HJ.sub.H regions
of the light and heavy chains, respectively, are associated at the
tips of the Y to form the antibody's antigen binding domain and
together determine antigen binding specificity.
[0005] The (C.sub.H) region defines the antibody's isotype, i.e.,
its class or subclass. Antibodies of different isotypes differ
significantly in their effector functions, such as the ability to
activate complement, bind to specific receptors (Fc receptors)
present on a wide variety of cell types, cross mucosal and
placental barriers, and form polymers of the basic four-chain IgG
molecule.
[0006] Antibodies are categorized into "classes" according to the
C.sub.H type utilized in the immunoglobulin molecule (IgM, IgG,
IgD, IgE, or IgA) There are at least five types of C.sub.H genes
(C.mu., C.gamma., C.delta., C.epsilon., and C.alpha.), and some
species (including humans) have multiple C.sub.H subtypes (e.g.,
C.gamma..sub.1, C.gamma..sub.2, C.gamma..sub.3, and C.gamma..sub.4
in humans). There are a total of nine C.sub.H genes in the haploid
genome of humans, eight in mouse and rat, and several fewer in many
other species. In contrast, there are normally only two types of
light chain constant regions (C.sub.L), kappa (.kappa.) and lambda
(.lambda.), and only one of these constant regions is present in a
single light chain protein (i.e., there is only one possible light
chain constant region for every V.sub.LJ.sub.L produced). Each
heavy chain class can be associated with either of the light chain
classes (e.g., a C.sub.H.gamma. region can be present in the same
antibody as either a .kappa. or .lambda. light chain).
[0007] A process for the immortalization of B cell clones producing
antibodies of a single specificity has been developed involving
fusing B cells from the spleen of an immunized mouse with immortal
myeloma cells. Single clones of fused cells secreting the desired
antibody could then be isolated by drug selection followed by
immunoassay. These cells were given the name "hybridoma" and their
antibody products termed "monoclonal antibodies."
[0008] The use of monoclonal antibodies as therapeutic agents for
human disease requires the ability to produce large quantities of
the desired antibody. One approach to increased production was
simply to scale up the culture of hybridoma cells. Although this
approach is useful, it is limited to production of that antibody
originally isolated from the mouse. In the case where a hybridoma
cell produces a high affinity monoclonal antibody with the desired
biological activity, but has a low production rate, the gene
encoding the antibody can be isolated and transferred to a
different cell with a high production rate.
[0009] In some cases it is desirable to retain the specificity of
the original monoclonal antibody while altering some of its other
properties. For example, a problem with using murine antibodies
directly for human therapy is that antibodies produced in murine
systems may be recognized as "foreign" proteins by the human immune
system, eliciting a response against the antibodies. A human
anti-murine antibody (HAMA) response results in antibody
neutralization and clearance and/or potentially serious
side-effects associated with the anti-antibody immune response.
Such murine-derived antibodies thus have limited therapeutic
value.
[0010] One approach to reducing the immunogenicity of murine
antibodies is to replace the constant domains of the heavy and
light chains with the corresponding human constant domains, thus
generating human-murine chimeric antibodies. Chimeric antibodies
are generally produced by cloning the antibody variable regions
and/or constant regions, combining the cloned sequences into a
single construct encoding all or a portion of a functional chimeric
antibody having the desired variable and constant regions,
introducing the construct into a cell capable of expressing
antibodies, and selecting cells that stably express the chimeric
antibody. Examples of methods using recombinant DNA techniques to
produce chimeric antibodies are described in PCT Publication No. WO
86/01533 (Neuberger et al.), and in U.S. Pat. Nos. 4,816,567
(Cabilly et al.) and 5,202,238 (Fell et al.).
[0011] In another approach, complementarity determining region
(CDR)-grafted humanized antibodies have been constructed by
transplanting the antigen binding site, rather than the entire
variable domain, from a rodent antibody into a human antibody.
Transplantation of the hypervariable regions of an antigen-specific
mouse antibody into a human heavy chain gene has been shown to
result in an antibody retaining antigen-specificity with greatly
reduced immunogenicity in humans (Riechmann et al. (1988) Nature
332:323-327; Caron et al. (1992) J. Exp. Med 176:1191-1195).
[0012] Another approach in the production of human antibodies has
been the generation of human B cell hybridomas. Applications of
human B cell hybridoma-produced monoclonal antibodies have
promising potential in the treatment of cancer, microbial
infections, B cell immunodeficiencies associated with abnormally
low antibody production, and other diseases and disorders of the
immune system. Obstacles remain in the development of such human
monoclonal antibodies. For example, many human tumor antigens may
not be immunogenic in humans and thus it may be difficult to
isolate anti-tumor antigen antibody-producing human B cells for
hybridoma fusion.
[0013] For a given disease indication, one antibody isotype is
likely to be greatly preferred over another. The preferred isotype
may vary from one indication to the next. For example, to treat
cancer it may be desirable that the binding of an antibody to a
tumor cell result in killing of a tumor cell. In this case, an IgG1
antibody, which mediates both antibody-dependent cellular
cytotoxicity and complement fixation, would be the antibody of
choice. Alternatively, for treating an autoimmune disease, it may
be important that the antibody only block binding of a ligand to a
receptor and not cause cell killing. In this case, an IgG4 or IgG2
antibody would be preferred. Thus, even in a situation where a high
affinity, antigen-specific, fully human antibody has been isolated,
it may be desirable to reengineer that antibody and express the new
product in a different cell.
[0014] The growing use of phage display technology also points to a
need for antibody engineering and expression methodologies. Phage
display technology is used for producing libraries of antibody
variable domains cloned into bacteria. This allows variable domains
of desired specificity to be selected and manipulated in vitro.
While bacteria offer a great advantage for selecting and producing
antibody fragments, they are not capable of producing full-size
intact antibodies in native configuration, and it is necessary to
reconstitute fragments selected in bacteria into intact antibodies
and express them in eucaryotic cells.
SUMMARY OF THE INVENTION
[0015] The present invention features a method of producing a
multimeric protein from a hybrid cell formed from the fusion of two
or more cells, each of which cell is engineered to express one
component of the multimeric protein, as well as a method for
screening for successful fusion of the cells to produce a desired
hybrid cell. The methods of the invention are widely applicable to
the production of proteins having two or more components.
[0016] In one specific application of the method of the invention,
the multimeric protein is an antibody composed of antigen-specific
heavy and light chains. DNA encoding the desired heavy chain (or a
fragment of the heavy chain) is introduced into a first mammalian
host cell, while DNA encoding the desired light chain (or a
fragment of the light chain) is introduced into a second mammalian
host cell. The first transformed host cell and the second
transformed host cell are then combined by cell fusion to form a
third cell. Prior to fusion of the first and second cells, the
transformed cells may be selected for specifically desired
characteristics, e.g., high levels of expression. After fusion, the
resulting hybrid cell contains and expresses both the DNA encoding
the desired heavy chain and the DNA encoding the desired light
chain, resulting in production of the multimeric antibody.
[0017] In one aspect the invention features the multimeric protein
produced by the method of the invention. In one embodiment, the
invention includes an antibody produced by the method of the
invention.
[0018] In another aspect the invention features a method for
screening for successful fusion of a first cell containing a first
nucleotide sequence encoding a desired antibody heavy chain and a
second cell containing a second nucleotide sequence encoding a
desired antibody light chain, the method comprising including a
nucleotide sequence encoding a first marker gene in the first cell,
including a nucleotide sequence encoding a second marker gene in
the second cell, fusing the first and second cells to produce a
fused cell and assaying for the presence of the first and second
marker genes in the fused cell.
[0019] One advantage of the method of the invention is that cells
expressing a single component of the final multi-component protein
can be individually selected for one or more desired
characteristics, such as a high rate of production.
[0020] Another advantage is that the method generates a cell which
produces an antibody at a multiplication high rate through the
fusion of two kinds of cells which are each selected prior to
fusion for high production of the desired heavy or light
chains.
[0021] Another advantage is that the final multi-component protein
is not expressed until all the cells expressing the individual
components of the multi-component protein are fused into a single
hybrid cell.
[0022] Other aspects, features, and advantages of the invention
will become apparent from the following detailed description, and
the claims.
BRIEF DESCRIPTION OF THE FIGURES
[0023] FIG. 1 is a schematic showing the basic immunoglobulin
structure.
[0024] FIG. 2 is a flow chart showing one embodiment of the method
of invention when mammalian cells are separately transformed with
the desired light and heavy chain DNA, then fused to form the
hybrid cell expressing both chains.
[0025] FIG. 3 illustrates a specific embodiment of the invention in
which a mammalian cell expressing an irrelevant light chain is
transformed with the desired heavy chain DNA, a second mammalian
cell is transformed with the desired light chain DNA, and the
desired hybrid cell formed from fusion of the transformed host
cells is selected which expresses the desired antibody product.
[0026] FIG. 4 is a schematic illustrating a specific embodiment of
the invention in which DHFR CHO cells are independently transfected
with (i) pManuGamma#6, a human heavy chain Ig construct and (ii)
pManuKappa#14, a human light chain Ig construct. The independent
cell lines are selected, amplified, fused, and selected to yield a
hybrid cell containing the human heavy chain Ig construct and the
human light chain Ig construct.
[0027] FIG. 5 is a schematic diagram of a fusion method in
accordance with the present invention demonstrating the use of HPRT
and LacZ marker genes for the initial determination of the success
of a fusion process.
DETAILED DESCRIPTION
[0028] Before the methods and compositions of the present invention
are described and disclosed it is to be understood that this
invention is not limited to the particular methods and compositions
described as such may, of course, vary. It is also to be understood
that the terminology used herein is for the purpose of describing
particular embodiments only, and is not intended to be limiting
since the scope of the present invention will be limited only by
the appended claims.
[0029] It must be noted that as used in this specification and the
appended claims, the singular forms "a", "an" and "the" include
plural references unless the context clearly dictates otherwise.
Thus, for example, reference to "a DNA sequence" includes a
plurality of DNA sequences and different types of DNA
sequences.
[0030] Unless defined otherwise all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
any materials or methods similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, the preferred methods and materials are now described.
All publications mentioned herein are incorporated herein by
reference for the purpose of describing and disclosing the
particular information for which the publication was cited. The
publications discussed above are provided solely for their
disclosure prior to the filing date of the present application.
Nothing herein is to be construed as an admission that the inventor
is not entitled to antedate such disclosure by virtue of prior
invention.
[0031] Definitions
[0032] By the term "nucleotide sequence" is meant any DNA fragment
of interest which may be introduced into a cell, including an
intact gene or fragment of a gene. When the method of the invention
is used to generate an antibody, the nucleotide sequence of
interest will be all or part of either the constant region and/or
variable region of the light or heavy chains, and may include all,
part, or none of the regulatory nucleotide sequences that control
expression of the light or heavy chain. The nucleotide sequence of
interest for heavy chains includes but is not limited to all or a
portion of the V, D, J, and switch regions (including intervening
sequences) and flanking sequences. For light chains, the nucleotide
sequence of interest includes but is not limited to the V and J
regions, and flanking and intervening sequences. The nucleotide
sequence may be a naturally occurring sequence, synthetic, or
partially natural and partially synthetic. The sequence may also be
a non-naturally occurring or modified naturally-occurring sequence.
The DNA sequence includes sequences taken from different sources,
e.g., different species. For example, when the method is used to
produce an antibody, the DNA chain may encode a chimeric (for
example, human-mouse) immunoglobulin chain, or it may be a
CDR-grafted DNA sequence having a human immunoglobulin sequence
with antigen-specific murine CDR sequences. The DNA of the
nucleotide sequence may encode a fully human antibody. B-cells
obtained from non-human animals immunized with an antigen and also
hybridoma, trioma, and quadromas derived from such B-cells can also
provide the nucleotide sequence introduced into the host cells.
B-cells and hybridomas producing any kind of monoclonal antibody
may be used as a source of the nucleotide sequence, including cells
producing, for example, fully mouse monoclonal antibodies, fully
human monoclonal antibodies, CDR-grafted monoclonal antibodies,
chimeric monoclonal antibodies, and F(ab).sub.2.
[0033] By the terms "multi-component", "multichain", or
"multimeric" protein is meant a protein composed of two or more
proteins or polypeptides. The method of the invention is useful for
producing a multimeric protein by the fusion of two or more cells
each expressing a single component of the multimeric protein. For
example, in one embodiment the multi-component protein is an
antibody generated from two heavy chains encoded by DNA transfected
into a first cell and two light chains encoded by DNA transfected
into a second cell, where the final multimeric antibody is produced
by a hybrid cell formed from the fusion of the first and second
cells. "Multi-component," "multichain," and "multimeric" protein is
meant to include any heterodimeric or hetero-oligomeric protein
(e.g., BMP2/BMP7 heterodimeric osteogenic protein, ICE
(interleukin-1 converting protein), receptors of the nucleus (e.g.,
retinoid receptors), heterodimeric cell surface receptors (e.g., T
cell receptors), integrins (e.g, cell adhesion molecules,
.beta..sub.1-integrins, (see, e.g., Hynes, 1987 Cell 48:549-554;
Hynes 1992 Cell 60:11-25), tumor necrosis factor (TNF) receptor,
and soluble and membrane-bound forms of class I and class II MHC
(major histocompatibility complex proteins). Where the multimeric
protein is a receptor, "multimeric protein" is meant to encompass
soluble and membrane forms of the receptor.
[0034] By the term "introducing" a nucleotide sequence into a cell
means inserting an exogenous piece of DNA into a cell, including
but not limited to transfection or transduction with a vector, such
that all or part of the exogenous nucleotide sequence is stably
maintained in the cell, and the resulting transformed cell
expresses the introduced nucleotide sequence.
[0035] By the term "fusing" or "fusion" of two or more cells is
meant a method in which two or more cells are combined to form a
single hybrid cell which contains all or part of at least the
nucleic acid content of each individual cell. Fusion may be
accomplished by any method of combining cells under fuseogenic
conditions well known in the art (See, for example, Harlow &
Lane (1988) in Antibodies, Cold Spring Harbor Press, New York).
Known methods for fusing cells includes by use with polyethylene
glycol (PEG) or Sendai virus.
[0036] By the term "hybrid cell" is meant a cell formed by
combining two or more cells, e.g., by fusion. In the method of the
invention, hybrid cells are formed from the fusion of one or more
transformed cells each expressing a single component of a
multimeric protein.
[0037] The term "irrelevant" as in, e.g., "an irrelevant light
chain" means a light chain which does not contribute to the binding
of the antigen of interest and is not a component of the multimeric
protein produced by the hybrid cell of the invention.
[0038] By the term "desired" component, e.g., desired heavy chain,
or desired light chain, is meant an immunoglobulin chain which
recognizes the antigen of interest.
[0039] Generation of a Hybrid Cell Producing a Heterologous
Multimeric Protein
[0040] The present invention provides a method for generating a
hybrid cell producing a multi-component protein from two or more
transformed cells each of which cells produces a single component
of the multimeric protein. This method features several important
advantages relative to conventional methods for protein production.
For example, the method of the present invention allows separately
transformed cells to be individually selected for optimal
expression of each component of the multi-component protein. This
selection occurs prior to fusion of cells forming the hybrid cell
and prior to production of the final multimeric protein. The method
of the invention results in a final multi-component protein product
which is not expressed until a single hybrid cell is produced from
the fusion of each cell expressing a component of the final protein
product.
[0041] Generally, when the multi-component protein to be produced
is an antibody, the method of the invention involves generation of
a cell expressing a desired heavy chain, generation of a cell
expressing a desired light chain, and fusion of the two cells to
form a hybrid cell expressing the final antibody protein (FIG. 2).
Generation of a cell expressing the desired heavy chain involves
the following steps: (1) identifying and cloning and/or
synthesizing the gene, gene fragment, or nucleotide sequence
encoding the variable segment or antigen-binding sequences of the
heavy chain. The nucleotide sequence may be obtained from either a
cDNA or genomic source, or synthesized de novo; (2) cloning the
nucleotide sequence encoding the desired constant regions of the
heavy chain; (3) ligating the variable region with the constant
region so that the complete nucleotide sequence can be transcribed
and translated to express the desired heavy chain polypeptide; (4)
ligating the construct into a vector containing a selectable marker
and appropriate gene control regions; (5) amplifying the construct
in bacteria; (6) introducing the vector into eukaryotic cells; (7)
selecting the cells expressing the selectable marker; and (8)
screening the cell supernatants or lysates for the expressed heavy
chain. Similarly, a cell expressing a desired light chain construct
is generated as outlined above.
[0042] Alternatively, the process of generating a cell expressing a
desired heavy or light chain may involve (1) construction of a Ig
chain DNA sequence containing (a) a signal sequence, (b) the gene,
gene fragment, or nucleotide sequence encoding the variable region
or antigen-binding sequences, and (c) the nucleotide sequence
encoding the desired constant region of the Ig chain, followed by
(2) PCR amplification of the Ig construction, (3) insertion of the
construct into eukaryotic cells, (4) selecting the cells expressing
the selectable marker, and (5) screening the cells for the
expressed Ig chain. Optionally, the cells expressing the desired
heavy chain or the desired light chain can be further selected for
desirable characteristics, such as heavy or light chain production
rate or level, ability of the expressed heavy or light chain to
combine with another light or heavy chain, respectively, to provide
an antibody having a desired antigen binding affinity, and/or other
characteristics desirable for heavy or light chain production or
function in an antibody.
[0043] Transformed cells expressing or capable of expressing the
desired component of the multimeric protein are fused by methods
known in the art to form a hybrid cell expressing the multimeric
protein. When the multimeric protein is an antibody, the DNA
sequences encoding the desired immunoglobulin may be composed
entirely of sequences originating from a single species, e.g.,
fully human or fully murine, or may be contain sequences
originating from more than one species, e.g., a human-mouse chimera
or CDR-grafted humanized antibody. The hybrid cell produced
antibody product may also contain a desired antigen binding site
(variable region) linked to a desired constant region. Thus, a
specifically designed antibody may be generated with a desired
antigenicity combined with the desired isotype.
[0044] Prior art methods for independently expressing the light and
heavy chains in a single host cells are known, see, for example,
U.S. Pat. No. 4,816,397, European patent application publication
No. 88,994, PCT published patent application WO 93/19172, U.S. Pat.
No. 4,816,567, U.S. Pat. No. 4,975,369, U.S. Pat. No. 5,202,238,
PCT published patent application WO 86/01533, PCT published patent
application WO 94/02602, and European published patent application
No. 273,889.
[0045] Vector Constructs
[0046] The vectors of the invention are recombinant DNA vectors
including, but not limited to, plasmids, phages, phagemids,
cosmids, viruses, retroviruses, and the like, which insert a
nucleotide sequence into a cell.
[0047] Methods for introducing an exogenous nucleotide sequence of
interest into a cell, including into antibody-producing cells, are
known in the art. These methods typically include use of a DNA
vector to introduce the nucleotide sequence into the genome or a
cell or cells, and then growing the cells to generate a suitable
population. Nucleotide sequences may also be introduced directly
into a cell by methods known in the art.
[0048] In a preferred embodiment, nucleotide sequences are
introduced into mammalian cells according to the CaPO.sub.4
transfer procedure described by Graham and van der Eb (1973)
Virology 52:456-467, herein specifically incorporated by reference.
Transfection of mammalian cell lines may be accomplished by any of
a number of methods known to those skilled in the art, including
but not limited to, CaPO.sub.4 precipitation, electroporation,
microinjection, liposome fusion, RBC ghost fusion, protoplast
fusion, and the like.
[0049] DNA Sequences
[0050] The nucleotide sequence encoding a component of the desired
multi-component protein may be obtained as a cDNA or as a genomic
DNA sequence by methods known in the art. For example, messenger
RNA coding for a desired component may be isolated from a suitable
source employing standard techniques of RNA isolation, and the use
of oligo-dT cellulose chromatography to segregate the poly-A mRNA.
When the product multi-component protein is an antibody, suitable
sources of desired nucleotide sequences may be isolated from mature
B cells or a hybridoma culture.
[0051] In addition to the nucleotide sequence encoding the desired
component of the product multi-component protein, vector constructs
can include additional components to facilitate replication in
prokaryotic and/or eukaryotic cells, integration of the construct
into a eukaryotic chromosome, and markers to aid in selection of
and/or screening for cells containing the construct (e.g., the
detectable markers and drug resistance genes discussed above for
the targeting construct). For eukaryotic expression, the construct
should preferably additionally contain a polyadenylation sequence
positioned 3' of the gene to be expressed. The polyadenylation
signal sequence may be selected from any of a variety of
polyadenylation signal sequences known in the art. Preferably, the
polyadenylation signal sequence is the SV40 early polyadenylation
signal sequence.
[0052] Transformation of Host Cells
[0053] Antibodies have been expressed in a variety of host cells,
including bacterial, yeast, and insect cells. For the production of
large, multimeric proteins, mammalian cell expression systems
generally provide the highest level of secreted product (Bebbington
(1991) Methods: A Companion to Methods Enzymol. 2:136-145). Myeloma
cells have been used as-fusion partners for splenic cells to
generate hybridomas cells expressing antibodies. Transformed
myeloma cells may be used as fusable host cells in the method of
the invention.
[0054] Host Cells
[0055] Nonlymphoid cells lines have been investigated for use in
producing antibodies (Cattaneo & Neuberger (1987) EMBO J.
6:2753-2758; Deans et al. (1984) Proc. Natl. Acad. Sci.
81:1292-1296; Weidle et al. (1987) Gene 51:21-29). The ability of
nonlymphoid cell lines to assemble and secrete fully functional
antibodies may be exploited for antibody production. For example,
Chinese hamster ovary (CHO) cells and COS cells have
well-characterized efficient expression systems and have been used
for both long-term and transient expression of a variety of
proteins (Bebbington (1991) supra). A method for achieving a high
level of expression of DNA sequences encoding a chimeric antibody
in transformed NSO myeloma cells has been described (Bebbington et
al. (1992) Bio/Technology 10:169-175).
[0056] Any mammalian cell line capable of expressing the desired
multimeric protein and amenable to fusion is suitable for use in
the present invention. For example, where the desired protein is an
antibody, the cell line is any mammalian cell capable of expressing
a functional antibody. A preferred host cell is a mammalian myeloma
cell; most preferably, an non-secreting (NS) myeloma cell (e.g., a
non-secreting (NSO) myeloma). Other myeloma cells include mouse
derived P3/X63-Ag8.653, P3/NS1/1-Ag4-l(NS-1), P3/X63Ag8.U1 (P3U1),
SP2/O-Ag14 (Sp2/O, Sp2), PAI, F0, and BW5147; rat derived
210RCY3-Ag.2.3; and human derived U266AR1, GM1500-6TG-A1-2, UC729,
CEM-AGR, DIR11, and CEM-T15.
[0057] Selection of Transformed Cells
[0058] Detection of transfectants with properly integrated vector
sequences can be accomplished in a number of ways, depending on the
nature of the integrated sequences. If the transferred nucleotide
sequence includes a selectable marker, the initial screening of the
transfected cells is to select those which express the marker. Any
of a variety of selectable markers known in the art may be included
in the construct, including dihydrofolate reductase (DHFR),
guanosine phosphoryl transferase gene (gpt), neomycin resistance
gene (Neo), hygromycin resistance gene (Hyg) and hypoxanthine
phosphoribosyl transferase (HPRT). For example, when using a drug
resistance gene, those transfectants that grow in the selection
media containing the drug (which is lethal to cells that do not
contain the drug resistance gene) can be identified in the initial
screening. It will be appreciated that a variety of other positive,
as well as negative (i.e., HSV-TK, cytosine deaminase, and the
like), selectable markers that are well known in the art can be
utilized in accordance with the present invention for selection of
specific cells and transfection or other events. As well, a variety
of other marker genes (i.e, the LacZ reporter gene and the like)
can be utilized in similar manners.
[0059] After a period of time sufficient to allow selection to
occur (in most cases, about 2 weeks) the surviving cells are then
subjected to a second screening to identify those transfectants
which express the desired peptide component of interest. This may
be accomplished by, for instance, an immunoassay using antibodies
specific for the particular immunoglobulin class.
[0060] The protocol for the second screening depends upon the
nature of the inserted sequences. For example, where the cell is
transformed with a sequence which does not result in a secreted
product, selection for the presence of the foreign DNA can be
detected by Southern blot using a portion of the exogenous sequence
as a probe, or by polymerase chain reaction (PCR) using sequences
derived from the exogenous sequence as amplifiers. The cells having
an appropriately integrated sequence can also be identified by
detecting expression of a functional product, e.g.,
immuno-detection of the product. Alternatively, the expression
product can be detected using a bioassay to test for a particular
effector function conferred by the exogenous sequence.
[0061] Where the first host cell is transfected-with DNA encoding
heavy chain, the expression of the heavy chain can be tested using
any conventional immunological screening method known in the art,
for example, ELISA conducted with cell lysate samples (see, for
example, Colcher et al. Protein Engineering 1987 1:499-505). The
cell can be further selected for additional desirable
characteristics such as heavy chain production rate or level,
ability of the expressed heavy chain to combine with light chain to
provide S an antibody of a desired antigen binding affinity, and
other characteristics desirable for heavy chain production and
heavy chain function in an antibody.
[0062] Nonlymphoid cells expressing a desired protein may be
transfected in a number of ways known to the art. One example of
the method of the invention is described in Example 1 below. A
first CHO cell may be transfected with a vector comprising a DNA
sequence encoding a desired light chain and a second CHO cell
transfected with a vector comprising a DNA sequence encoding a
desired heavy chain. Transfected cells are selected and fused.
Fused cells are selected for expression of an antibody having the
desired light chain Ig and heavy chain Ig.
[0063] In one embodiment, a cell expressing an Ig heavy chain gene
also expresses an irrelevant Ig light chain gene. In some
instances, co-expression of a light chain may be required for
secretion and expression of the Ig heavy chain. Failure of a cell
to secrete the heavy chain peptide may make detection of
transfectants more difficult since it necessitates assaying the
cells themselves (e.g., by Northern blot analysis or
immuno-detection), as opposed to conveniently screening the cell
supernatant by ELISA.
[0064] In a specific embodiment of the invention, this problem is
avoided by transfecting a first host cell expressing an irrelevant
light chain with a plasmid bearing the desired heavy chain (FIG.
3). The gene encoding the irrelevant light chain may either be
integrated into a chromosome or be present in an episomal vector,
such as bovine papilloma virus (BPV) or other episomal vector known
in the art. After selection for transformants, expression of the
heavy chain is easily confirmed by an ELISA assay of the cell
lysates for secreted antibody.
[0065] Cells expressing the desired heavy chain are then fused with
a second cell that has been transfected with the desired light
chain under appropriate fuseogenic conditions according to methods
well known in the art (see, e.g., Harlow & Lane, supra). Any
combination of cells capable of expressing a desired heavy chain or
desired light chain and that can be fused to produce a hybrid cell
expressing both heavy and light chains can be used. Thus, the first
cell (e.g., expressing the desired heavy chain) can be of the same
or different type as the second cell (e.g, expressing the desired
light chain), e.g., the first cell can be a myeloma cell and the
second cell can be a non-lymphoid cell. The fusion product cells
which are candidates for manufacturing lines will express the
desired heavy chain and light chain, but will have lost the
irrelevant light chain. During the fusion process, random
chromosomes are normally lost. Thus, it is expected that cells
lacking the irrelevant Ig light chain will be generated during the
fusion process. These hybrid cells can easily be identified by
ELISA assay of the supernatants for the presence of the desired
chains and absence of the irrelevant chain.
[0066] Thus, in one embodiment, the desired light chain of the
final antibody product is the .kappa. light chain. In such cases, a
Ig.lambda. expressing myeloma cell is transfected with the desired
IgH gene. After transfection with a plasmid carrying the desired
heavy chain and selection, cells expressing the heavy chain are
examined directly for expression of the desired heavy chain, e.g.,
ELISA assay of the supernatants with antibody specific to the heavy
chain. The second cell, e.g., a non-secreting myeloma cell, is
transfected with the K light chain, and transfectants detected
through e.g., Northern blot analysis or immuno-detection with an
antibody specific to the K light chain. The cells expressing the
light chain can be further selected for desirable characteristics
associated with production of a functional light chain, such as
light chain production rate or level, ability of the expressed
light chain to combine with heavy chain to provide an antibody of a
desired antigen binding affinity, and other characteristics
desirable for light chain production and heavy chain function in an
antibody. The cells are then fused, and the hybrid cell expressing
the desired IgH/IgK antibody is selected for the presence of the
.kappa. light chain and desired heavy chain (e.g., C.sub..gamma.)
and the absence of .lambda. light chain, e.g., by ELISA assay of
the culture medium.
[0067] When the desired product antibody contains a .lambda. light
chain, the first cell transfected with DNA encoding the desired
heavy chain will express a .kappa. light chain, and final selection
of hybrid cells expressing the desired antibody will select for the
presence of the .lambda. light chain and the absence of the .kappa.
light chain.
[0068] In an alternative embodiment of the invention, selection of
fused or hybrid cells can be initially determined through the
utilization of distinct marker genes in each of the "parental"
cells or cell lines. Such technique is shown in FIG. 4. There, a
parental CHO cell line, that is DHFR, is transfected with a vector
(pManu Kappa) that contains the DHFR resistance gene and the
hygromycin resistance gene (HYGRO). Another parental CHO cell line,
that is DHFR, is transfected with a vector (pManu Gamma) that
contains the DHFR resistance gene and the neomycin resistance gene.
Each cell line, following transfection, contains distinct
selectable markers (i.e., hygromycin resistance in the first and
neomycin/G418 resistance in the second). Thus, upon fusion,
resulting "daughter" cells in which fusion has been successful will
be resistant to both hygromycin and G418. The screening technique
of the invention is advantageous in that it mitigates the need to
determine expression of immunoglobulin molecules in order to
determine if a fusion has been successfully performed.
[0069] Under certain fusion conditions, cells and cell lines can
become spontaneously resistant to G418, and, possibly, other
selectable markers. Thus, in certain embodiments of the invention,
it is preferable to utilize selectable markers to which cells and
cell lines are less likely to spontaneously generate resistance. An
example of one such marker is the hypoxanthine phosphoribosyl
transferase gene (HPRT) which confers resistance to hypoxanthine
aminopterin. Another marker that can be used in tandem with HPRT
resistance is the LacZ gene. The LacZ gene is not a selectable
marker; but, rather, acts as a marker gene which, when expressed by
a cell, stains blue in the presence of .beta.-galactosidase.
[0070] Thus, through following a similar scheme as described in
connection with FIG. 4, a first parental cell line, which is HPRT
deficient (such as the P3X, NSO, and NSO-bc12 myeloma cell lines),
is transfected with an antibody gene cassette. The cassette
includes, for example, appropriate antibody genes, a gene
amplification system, and an HPRT selectable marker. Transfected
cells can be selected through HPRT selection and cells producing
high levels of antibodies can be picked. A second parental cell
line, which is also preferably HPRT deficient, is transfected with
an antibody gene cassette. The cassette includes, for example,
appropriate antibody genes, a gene amplification system, and the
LacZ gene. Transfected cells can be selected through staining with
.beta.-gal. As will be appreciated, either the first or second
parental cell line can include the light chain genes or the heavy
chain genes and the other of the first or second parental cell line
will contain the other of the light or heavy chain genes. As will
also be appreciated, other selectable markers can be included in
the cassettes utilized to transfect the cells. Upon fusion of the
first and second parental cell lines, successful fusion can be
determined through HPRT selection and .beta.-gal staining of
daughter cells. Daughter cells can be further selected based upon
expression levels of immunoglobulin molecules.
[0071] Specific embodiments of this technique is illustrated in
FIG. 5 in several exemplary schemes. In the Figure, a first
parental cell line, exemplified by the myeloma cell line, NSO,
which is HPRT deficient, is transfected with a light chain cassette
containing a gene amplification system (AM), an antibody light
chain gene system (V.sub.KJ.sub.KC.sub.K), and an HPRT selectable
marker (HPRT) (Step 1). A second parental cell line, exemplified by
any one of J558L, Ag.1, or NSO, are transfected with a heavy chain
cassette containing a gene amplification system (AM), an antibody
heavy chain gene system (V.sub.HD.sub.HJ.sub.Hh.gamma.), and the
LacZ gene (Step 2). The transfection of J558L cell line is
indicated as Step 2a, the transfection of the Ag.1 cell line is
indicated as Step 2b, and the transfection of the NSO cell line is
indicated as Step 2c. With respect of each Step 1 and Steps 2a-2c,
the success of the transfection can be determined through the use
of the selectable marker HPRT in Step 1 and through .beta.-gal
staining in connection with each of Steps 2a-2c. Additionally cells
can be picked for expression of light chain (Step 1) or heavy chain
(Step 2a-2c).
[0072] Following isolation and generation of parental cell lines
incorporating the antibody gene cassettes, fusion between a
parental cell line including heavy chain genes and a parental cell
line including light chain genes is conducted. Utilizing techniques
described herein, the parental cell line resulting from Step 1 is
fused with a parental cell line resulting from Steps 2a-2c. This is
indicated in the Figure as fusion 1-2a, fusion 1-2b, and fusion
1-2c, which results in fused cells 1-2a, 1-2b, and 1-2c,
respectively. Such fused cells can be readily identified through
dual marker selection, that is, HPRT selection and .beta.-gal
staining. Cells which have been successfully fused, will be HPRT
resistant and will stain positive with .beta.-gal.
[0073] As will be appreciated, the parental cell lines utilized in
fusions 1-2a and 1-2b additionally contain mouse m.lambda. and rat
.gamma.K genes. Thus, daughter cells from fusions 1-2a and 1-2b are
preferably selected to ensure that they are m.lambda. and .gamma.K.
Loss of mouse m.lambda. genes and rat .gamma.K genes will generally
occur naturally through recombination events during the fusion
process.
EXAMPLES
[0074] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how to make and use various constructs and perform
the various methods of the present invention and are not intended
to limit the scope of what the inventors regard as their invention.
Unless indicated otherwise, parts are parts by weight, temperature
is in degrees centigrade, and pressure is at or near atmospheric
pressure. Efforts have been made to ensure accuracy with respect to
numbers used, (e.g., length of DNA sequences, molecular weights,
amounts, particular components, etc.) but some deviations should be
accounted for.
Example 1
Generation of Hybrid Cells Containing Light and Heavy Ig
Chains.
[0075] The human heavy chain Ig construct (IgH gamma) was ligated
into the pManugamma#6 vector (FIG. 4; Cell Genesys, Inc., Foster
City, Calif.) containing DHFR and neo marker genes. The human kappa
light chain Ig construct was ligated into the pManukappa#14 (FIG.
4; Cell Genesys, Inc.) which contains DHFR and hygromycin
resistance marker genes.
[0076] Overview of the Cell Fusion Method
[0077] In general, the experiment proceeds as follows: A first cell
is transfected with the pManukappa vector comprising the human
kappa light chain transgene, and MTX and hygromycin selection
marker genes. A second cell is transfected with the pManugamma
vector comprising a human .gamma..sub.4 heavy chain transgene and
Neo and MTX selectable marker genes. After the appropriate
selection and amplification, the selected first and second cells
are fused to form the hybrid cell of the invention expressing a
human antibody.
[0078] Cell Transfection
[0079] Chinese hamster ovary (CHO) cells are transfected by
electroporation as follows: DHFR-deficient CHO cells in exponential
growth are fed with growth medium 4 hours prior to electroporation
[growth medium: DMEM/Ham's F12 (50:50 mixture; JRH BioSciences,
Woodland, Calif.), 10% FBS, 2 mM glutamine, non-essential amino
acids (NEAA) plus glycine, hypoxanthine and thymidine (GHT)]. Cells
are collected, washed in PBS, and resuspended in PBS to a
concentration of 5.times.10.sup.6 cells per 0.8 ml. The cell
suspension is aliquoted into 0.4 cm electroporation cuvettes (0.8
ml per cuvette) and 5-20 ug linearized DNA added. The suspension is
mixed and left on ice for 10 min. Each cuvette is electroporated at
260 V and 960 uF. Each cuvette is place on ice for 10 min, the
cells resuspended in 20 ml growth medium, then plated onto 2 10 cm
cell culture plates. After 48 hrs, cells from each culture plate
are replated in 10 culture plates in the presence of selective
media [DMEM, 4.5 g/l glucose (JRH Biosciences), 10% dialyzed FBS
(Life Technologies, Bethesda, Md.), 5 mM glutamine, NEAA, 0.6 mg/ml
G418].
[0080] Selection of Transfectants
[0081] Cells transfected with the kappa light chain transgene were
selected in the presence of methotrexate (MTX) and hygromycin.
Cells were plated 48 hr post-electroporation into 10 plates in DHFR
selective media [DMEM, 4.5 g/l glucose (JRH Biosciences), 10%
dialyzed FBS (Life Technologies, Bethesda, Md.), 5 mM glutamine,
NEAA, supplemented with hygromycin (Calbiochem, San Diego, Calif.)
at concentrations ranging from 250-750 ug/ml]. Recombinant protein
expression can be increased by DHFR-mediated amplification of the
transfected gene. Methods for selecting cell lines bearing gene
amplifications are known in the art, e.g., for example, as
described in Ausubel et al. (1989) Current Protocols in Molecular
Biology John Wiley & Sons, New York; such methods generally
involve extended culture in medium containing gradually increasing
levels of methotrexate.
[0082] Heavy chain transfectant CHO cells are selected in the
presence of MTX and neomycin following the above described
procedures.
[0083] Generation of a Hybrid Cell Expressing an Antibody
[0084] Prior to fusion, PEG/DMSO fusion solution (50% PEG, 10% DMSO
in PBS) (Sigma) is placed in a 37.degree. C. incubator overnight,
and 500-1000 ml incomplete Ham's F12 solution (without FCS) is
filtered. At fusion, warm fusion medium and incomplete
DMEM/Hams.degree. F12 are placed in a 37.degree. C. water bath. A
water-filled beaker and a 15 ml conical tube filled with incomplete
DMEM/Ham's F12 are also placed in the water bath. Harvested
transfected CHO cells are washed once with incomplete DMEM/Ham's
F12, pelleted at 1200 rpm, resuspended in incomplete DMEM/Ham's
F12, and counted. The kappa light chain and the .gamma..sub.4
transfected cells are mixed in a 1:1 ratio, and centrifuged at
800.times. g (2060 rpm). The following fusion steps are followed:
(1) add 1 ml PEG/DMSO fusion solution to cells over 1 min period;
(2) stir cells gently for 1 min; (3) add 2 ml incomplete DMEM/Ham's
F12 over a 2 min period with slow stirring; and (4) add 8 ml of
incomplete DMEM/Ham's F12 over a 3 min period with slow stirring.
The cells are then centrifuged at room temperature at 400.times. g
for 5 min (1460 rpm). Selection medium [complete DMEM/Ham's F12+10%
FCS+250-750 ug/ml hygromycin+0.6 mg/ml G418] is added to the cell
pellet. 10 ml of selection medium are added to the cell pellet;
cells are gently stirred to resuspend.
[0085] The cells are plated onto 10 cm dishes as dilutions of 1:10,
1:20, and 1:40 in selection medium. The plates are refed with fresh
medium every 3 days until clones appear. Clones are picked and
transferred to a 96-well plate in selection medium. As will be
appreciated, growth of cells to reach confluence, which
demonstrates survival of cells through selection with hygromycin
and G418, is indicative that the cells contain both the heavy and
light chain Ig genes, since hygromycin resistance was contributed
by the light chain gene containing parental cells and neomycin
resistance was contributed by the heavy chain gene containing
parental cells. As such, dual marker selection provides an
expedient method to initially determine whether a fusion has been
successfully accomplished. Following such an initial screen,
supernatant can be assayed for expression of the desired antibody
as described below. When the wells are confluent, the supernatant
is assayed for expression of the desired antibody as described
below.
[0086] Selection for Desired Hybrid Cell
[0087] Expression of the desired antibody may be assayed by
immunological procedures, such as Western blot or
immunoprecipitation analysis of hybrid cell extracts, or by
immunofluorescence of intact cells (using, e.g., the methods
described in Ausubel et al. (1989) supra). The desired antibody is
detected using antibody specific for each component of the desired
antibody, e.g., antibodies specific to the kappa light chain and
.gamma..sub.4 heavy chain.
[0088] Confirmation of Desired Characteristics of Antibody Produced
by Hybrid Cell
[0089] After the hybrid cell is produced and antibody production in
the cell is confirmed, the hybrid cell is grown under conditions to
allow expression of the antibody and secretion of the antibody into
the cell culture supernatant. For example, the cells can be grown
in roller bottles in selective growth medium (DMEM/Ham's F12 (50:50
mixture), 10% FBS, 2 mM glutamine, non-essential amino acids plus
glycine, hypoxanthine and thymidine, plus hygromycin and G418 to
provide continued selection for the heavy and light chain
constructs in the hybrid cell) for several hours prior to assay.
Cell culture supernatant is collected and the antibodies are tested
for various desired characteristics, e.g., antigen binding affinity
(e.g., preferably antigen binding affinity that is similar to that
of the original antibody from which the recombinant antibody is
derived) using immunological assays well known in the art (e.g.,
ELISA, or competition binding assays).
[0090] The instant invention is shown and described herein in what
is considered to be the most practical and the preferred
embodiments. It is recognized, however, that departures may be made
therefrom which are within the scope of the invention, and that
obvious modifications will occur to one skilled in the art upon
reading this disclosure.
* * * * *