Methods for inducing a population of T cells to proliferate by activating the population of T cells and stimulating an accessory molecule on the surface of the T cells with a ligand which binds the accessory molecule are described. T cell proliferation occurs in the absence of exogenous growth factors or accessory cells. T cell activation is accomplished by stimulating the T cell receptor (TCR)/CD3 complex or the CD2 surface protein. To induce proliferation of an activated population T cells, an accessory molecule on the surface of the T cells, such as CD28, is stimulated with a ligand which binds the accessory molecule. The T cell population expanded by the method of the invention can be genetically transduced and used for immunotherapy or can be used in methods of diagnosis.

SUMMARY OF THE INVENTION

This invention pertains to methods for selectively inducing ex vivo expansion of a population of T cells in the absence of exogenous growth factors, such as lymphokines, and accessory cells. In addition, T cell proliferation can be induced without the need for antigen, thus providing an expanded T cell population which is polyclonal with respect to antigen reactivity. The method provides for sustained proliferation of a selected population of CD4.sup.+ or CD8.sup.+ T cells over an extended period of time to yield a multi-fold increase in the number of these cells relative to the original T cell population.

According to the method of the invention, a population of T cells is induced to proliferate by activating the T cells and stimulating an accessory molecule on the surface of the T cells with a ligand which binds the accessory molecule. Activation of a population of T cells is accomplished by contacting the T cells with a first agent which stimulates a TCR/CD3 complex-associated signal in the T cells. Stimulation of the TCR/CD3 complex-associated signal in a T cell is accomplished either by ligation of the T cell receptor (TCR)/CD3 complex or the CD2 surface protein, or by directly stimulating receptor-coupled signaling pathways. Thus, an anti-CD3 antibody, an anti-CD2 antibody, or a protein kinase C activator in conjunction with a calcium ionophore is used to activate a population of T cells.

To induce proliferation, an activated population of T cells is contacted with a second agent which stimulates an accessory molecule on the surface of the T cells. For example, a population of CD4.sup.+ T cells can be stimulated to proliferate with an anti-CD28 antibody directed to the CD28 molecule on the surface of the T cells. Alternatively, CD4.sup.+ T cells can be stimulated with a natural ligand for CD28, such as B7-1 and B7-2. The natural ligand can be soluble, on a cell membrane, or coupled to a solid phase surface. Proliferation of a population of CD8.sup.+ T cells is accomplished by use of a monoclonal antibody ES5.2D8 which binds to CD9, an accessory molecule having a molecular weight of about 27 kD present on activated T cells. Alternatively, proliferation of an activated population of T cells can be induced by stimulation of one or more intracellular signals which result from ligation of an accessory molecule, such as CD28.

The agent providing the primary activation signal and the agent providing the costimulatory agent can be added either in soluble form or coupled to a solid phase surface. In a preferred embodiment, the two agents are coupled to the same solid phase surface.

Following activation and stimulation of an accessory molecule on the surface of the T cells, the progress of proliferation of the T cells in response to continuing exposure to the ligand or other agent which acts intracellularly to simulate a pathway mediated by the accessory molecule is monitored. When the rate of T cell proliferation decreases, the T cells are reactivated and restimulated, such as with additional anti-CD3 antibody and a co-stimulatory ligand, to induce further proliferation. In one embodiment, the rate of T cell proliferation is monitored by examining cell size. Alternatively, T cell proliferation is monitored by assaying for expression of cell surface molecules in response to exposure to the ligand or other agent, such as B7-1 or B7-2. The monitoring and restimulation of the T cells can be repeated for sustained proliferation to produce a population of T cells increased in number from about 100- to about 100,000-fold over the original T cell population.

In a specific embodiment, a population of CD4.sup.+ T cells is stimulated to proliferate to produce a population of T cells increased in number from about 10 log.sub.10 to 12 log.sub.10. In this embodiment the population of CD4.sup.+ T cells is contacted with a solid phase surface comprising anti-CD3 and anti-CD28 antibodies, or a solid phase surface comprising anti-CD3 and a stimulatory form of B7-2. In another embodiment of the invention, stimulation of a population of CD28.sup.+ T cells to proliferate is accompanied by selective enrichment of the population in CD4.sup.+ T cells.

The method of the invention can be used to expand selected T cell populations for use in treating an infectious disease or cancer. The resulting T cell population can be genetically transduced and used for immunotherapy or can be used for in vitro analysis of infectious agents such as HIV. Proliferation of a population of CD4.sup.+ cells obtained from an individual infected with HIV can be achieved and the cells rendered resistant to HIV infection. The cells can be rendered resistant to the viral infection by the addition of antiretroviral agents to the cell culture. Alternatively, the cells can be rendered resistant to the viral infection by culture in the presence of an agent, such as immobilized anti-CD28 antibody, which inhibits viral production. Following expansion of the T cell population to sufficient numbers, the expanded T cells are restored to the individual. The method of the invention also provides a renewable source of T cells. Thus, T cells from an individual can be expanded ex vivo, a portion of the expanded population can be readministered to the individual and another portion can be frozen in aliquots for long term preservation, and subsequent expansion and administration to the individual. Similarly, a population of tumor-infiltrating lymphocytes can be obtained from an individual afflicted with cancer and the T cells stimulated to proliferate to sufficient numbers and restored to the individual.

Alternatively, the population of CD4.sup.+ T cells of an individual, such as an HIV infected individual, can be expanded in vivo, by administering to the individual a biodegradable solid phase surface comprising a first agent that provides a primary activation signal, such as an agent which stimulates the TCR/CD3 complex, and a second agent that stimulates an accessory molecule on the T cell. A preferred method of treatment of an individual having an infectious disease, such as an HIV-1 infection, consists of administering an anti-CD28 antibody immobilized onto a solid phase surface. The solid phase surface may further comprise an agent which provides a primary activation signal. In another embodiment of the invention, supernatants from cultures of T cells expanded in accordance with the method of the invention are a rich source of cytokines and can be used to sustain T cells in vivo or ex vivo.

The invention also pertains to compositions comprising an agent that provides a costimulatory signal to a T cell for T cell expansion (e.g., an anti-CD28 antibody, B7-1 or B7-2 ligand), coupled to a solid phase surface which may additionally include an agent that provides a primary activation signal to the T cell (e.g., an anti-CD3 antibody) coupled to the same solid phase surface. These agents are preferably attached to beads. Compositions comprising each agent coupled to different solid phase surfaces (i.e., an agent that provides a primary T cell activation signal coupled to a first solid phase surface and an agent that provides a costimulatory signal coupled to a second solid phase surface) are also within the scope of this invention. Furthermore, the invention provides kits comprising the compositions, including instructions for use.

DETAILED DESCRIPTION OF THE INVENTION

The methods of this invention enable the selective stimulation of a T cell population to proliferate and expand to significant numbers in vitro in the absence of exogenous growth factors or accessory cells. Interaction between the T cell receptor (TCR)/CD3 complex and antigen presented in conjunction with either major histocompatibility complex (MHC) class I or class II molecules on an antigen-presenting cell initiates a series of biochemical events termed antigen-specific T cell activation. The term "T cell activation" is used herein to define a state in which a T cell response has been initiated or activated by a primary signal, such as through the TCR/CD3 complex, but not necessarily due to interaction with a protein antigen. A T cell is activated if it has received a primary signaling event which initiates an immune response by the T cell.

T cell activation can be accomplished by stimulating the T cell TCR/CD3 complex or via stimulation of the CD2 surface protein. An anti-CD3 monoclonal antibody can be used to activate a population of T cells via the TCR/CD3 complex. Although a number of anti-human CD3 monoclonal antibodies are commercially available, OKT3 prepared from hybridoma cells obtained from the American Type Culture Collection or monoclonal antibody G19-4 is preferred. Similarly, binding of an anti-CD2 antibody will activate T cells. Stimulatory forms of anti-CD2 antibodies are known and available. Stimulation through CD2 with anti-CD2 antibodies is typically accomplished using a combination of at least two different anti-CD2 antibodies. Stimulatory combinations of anti-CD2 antibodies which have been described include the following: the T11.3 antibody in combination with the T11.1 or T11.2 antibody (Meuer, S. C. et al. (1984) Cell 36:897-906) and the 9.6 antibody (which recognizes the same epitope as T11.1) in combination with the 9-1 antibody (Yang, S. Y. et al. (1986) J. Immunol. 137:1097-1100). Other antibodies which bind to the same epitopes as any of the above described antibodies can also be used. Additional antibodies, or combinations of antibodies, can be prepared and identified by standard techniques.

A primary activation signal can also be delivered to a T cell through use of a combination of a protein kinase C (PKC) activator such as a phorbol ester (e.g., phorbol myristate acetate) and a calcium ionophore (e.g., ionomycin which raises cytoplasmic calcium concentrations). The use of these agents bypasses the TCR/CD3 complex but delivers a stimulatory signal to T cells. These agents are also known to exert a synergistic effect on T cells to promote T cell activation and can be used in the absence of antigen to deliver a primary activation signal to T cells.

Although stimulation of the TCR/CD3 complex or CD2 molecule is required for delivery of a primary activation signal in a T cell, a number of molecules on the surface of T cells, termed accessory or costimulatory molecules have been implicated in regulating the transition of a resting T cell to blast transformation, and subsequent proliferation and differentiation. Thus, in addition to the primary activation signal provided through the TCR/CD3 complex, induction of T cell responses requires a second, costimulatory signal. One such costimulatory or accessory molecule, CD28, is believed to initiate or regulate a signal transduction pathway that is distinct from those stimulated by the TCR complex.

Accordingly, to induce an activated population of T cells to proliferate (i.e., a population of T cells that has received a primary activation signal) in the absence of exogenous growth factors or accessory cells, an accessory molecule on the surface of the T cell, such as CD28, is stimulated with a ligand which binds the accessory molecule or with an agent which acts intracellularly to stimulate a signal in the T cell mediated by binding of the accessory molecule. In one embodiment, stimulation of the accessory molecule CD28 is accomplished by contacting an activated population of T cells with a ligand which binds CD28. Activation of the T cells with, for example, an anti-CD3 antibody and stimulation of the CD28 accessory molecule results in selective proliferation of CD4.sup.+ T cells. An anti-CD28 monoclonal antibody or fragment thereof capable of crosslinking the CD28 molecule, or a natural ligand for CD28 (e.g., a member of the B7 family of proteins, such as B7-1(CD80) and B7-2 (CD86) (Freedman, A. S. et al. (1987) J. Immunol. 137:3260-3267; Freeman, G. J. et al. (1989) J. Immunol. 143:2714-2722; Freeman, G. J. et al. (1991) J. Exp. Med 174:625-631; Freeman, G. J. et al. (1993) Science 262:909-911; Azuma, M. et al. (1993) Nature 366:76-79; Freeman, G. J. et al. (1993) J. Exp. Med. 178:2185-2192)) can be used to induce stimulation of the CD28 molecule. In addition, binding homologues of a natural ligand, whether native or synthesized by chemical or recombinant technique, can also be used in accordance with the invention. Ligands useful for stimulating an accessory molecule can be used in soluble form, attached to the surface of a cell, or immobilized on a solid phase surface as described herein. Anti-CD28 antibodies or fragments thereof useful in stimulating proliferation of CD4.sup.+ T cells include monoclonal antibody 9.3, an IgG2a antibody (Dr. Jeffery Ledbetter, Bristol Myers Squibb Corporation, Seattle, Wash.), monoclonal antibody KOLT-2, an IgG1 antibody, 15E8, an IgG1 antibody, 248.23.2, an IgM antibody and EX5.3D10, an IgG2a antibody. In one specific embodiment, the molecule providing the primary activation signal, for example a molecule which provides stimulation through the TCR/CD3 complex or CD2, and the costimulatory molecule are coupled to the same solid phase support. In particular, T cell activation and costimulation can be provided by a solid phase surface containing anti-CD3 and anti-CD28 antibodies.

A preferred anti-CD28 antibody is monoclonal antibody 9.3 or EX5.3D10. The EX5.3DI0 monoclonal antibody was derived from immunizing a Balb/c mouse with CHO (Chinese hamster ovary) cells transfected with the human CD28 gene (designated CHO-hh). Hybridomas from the fusion were selected by whole cell ELISA screening against Jurkat (human T leukemia) CD28 tranfectants designated Jurkat #7. Reactivity of the EX5.3D10 with CD28 was further confirmed by fluorescent activated cell sorter analysis (FACS) analysis in which it was tested side by side with the monoclonal 9.3 (FIG. 6). Neither antibody bound to untransfected CHO-DG44 cells and their binding profiles were nearly identical for the two CD28 transfectant lines, CHO-hh and Jurkat #7, as well as normal human peripheral blood lymphocytes. A hybridoma which produces the monoclonal antibody EX5.3D10 has been deposited with the American Type Culture Collection on Jun. 4, 1993, at ATCC Deposit No. HB11373.

In a specific embodiment of the invention, activated T cells are contacted with a stimulatory form of a natural ligand for CD28 for costimulation. The natural ligands of CD28 include the members of the B7 family of proteins, such as B7-1 (CD80) (SEQ ID NO:1 and 2) and B7-2 (CD86) (SEQ ID NO:3 and 4). B7-1 and B7-2 are collectively referred to herein as "B7 molecules". A "stimulatory form of a natural ligand for CD28" is a form of a natural ligand that is able to bind to CD28 and costimulate the T cell. Costimulation can be evidenced by proliferation and/or cytokine production by T cells that have received a primary activation signal, such as stimulation through the CD3/TCR complex or through CD2.

Expression or Coupling of B7 Molecules on the Surface of Cells

In a preferred embodiment of the invention, a B7 molecule or a portion of a B7 molecule or a modified form of a B7 molecule capable of inducing costimulation is localized on the surface of a cell. This can be accomplished by transfecting a cell with a nucleic acid encoding the B7 molecule (e.g. B7-1, B7-2) in a form suitable for its expression on the cell surface or alternatively by coupling a B7 molecule to the cell surface.

The B7 molecules are preferably expressed on the surface of a cell by transfection of the cell with a nucleic acid encoding the B7 molecule in a form suitable for expression of the molecule on the surface of the cell. The terms "transfection" or "transfected with" refers to the introduction of exogenous nucleic acid into a mammalian cell and encompass a variety of techniques useful for introduction of nucleic acids into mammalian cells including electroporation, calcium-phosphate precipitation, DEAE-dextran treatment, lipofection, microinjection and infection with viral vectors. Suitable methods for transfecting mammalian cells can be found in Sambrook et al. (Molecular Cloning: A Laboratory Manual. 2nd Edition. Cold Spring Harbor Laboratory press (1989)) and other laboratory textbooks. The nucleic acid to be introduced may be, for example, DNA encompassing the gene(s) encoding B7-1 and/or B7-2, sense strand RNA encoding B7-1 and/or B7-2 or a recombinant expression vector containing a cDNA encoding B7-1 and/or B7-2. The nucleotide sequence of a cDNA encoding human B7-1 is shown in SEQ ID NO: 1, and the amino acid sequence of a human B7-1 protein is shown in SEQ ID NO:2. The nucleotide sequence of a cDNA encoding human B7-2 is shown in SEQ ID NO: 3, and the amino acid sequence of a human B7-2 protein is shown in SEQ ID NO:4. The nucleic acids encoding B7-1 and B7-2 are further described in Freedman, A. S. et al. (1987) J. Immunol. 137:3260-3267; Freeman, G. J. et al. (1989) J. Immunol. 143:2714-2722; Freeman, G. J. et al. (1991) J. Exp. Med. 174:625-631; Freeman, G. J. et al. (1993) Science 262:909-911; Azuma, M. et al. (1993) Nature 366:76-79 and; Freeman, G. J. et al. (1993) J. Exp. Med. 178:2185-2192.

The nucleic acid is in a form suitable for expression of the B7 molecule in which the nucleic acid contains all of the coding and regulatory sequences required for transcription and translation of a gene, which may include promoters, enhancers and polyadenylation signals, and sequences necessary for transport of the molecule to the surface of the tumor cell, including N-terminal signal sequences. When the nucleic acid is a cDNA in a recombinant expression vector, the regulatory functions responsible for transcription and/or translation of the cDNA are often provided by viral sequences. Examples of commonly used viral promoters include those derived from polyoma, Adenovirus 2, cytomegalovirus and Simian Virus 40, and retroviral LTRs. Regulatory sequences linked to the cDNA can be selected to provide constitutive or inducible transcription, by, for example, use of an inducible promoter, such as the metallothionin promoter or a glucocorticoid-responsive promoter. Expression of B7-1 or B7-2 on the surface of a cell can be accomplished, for example, by including the native transmembrane coding sequence of the molecule in the nucleic acid sequence, or by including signals which lead to modification of the protein, such as a C-terminal inositol-phosphate linkage, that allows for association of the molecule with the outer surface of the cell membrane.

The B7 molecule can be expressed on a cell using a plasmid expression vector which contains nucleic acid, e.g., a cDNA, encoding the B7 molecule. Suitable plasmid expression vectors include CDM8 (Seed, B., Nature 329, 840 (1987)) and pMT2PC (Kaufman, et al., EMBO J. 6, 187-195 (1987)). Since only a small fraction of cells (about 1 out of 10.sup.5) typically integrate transfected plasmid DNA into their genomes, it is advantageous to transfect a nucleic acid encoding a selectable marker into the tumor cell along with the nucleic acid(s) of interest. Preferred selectable markers include those which confer resistance to drugs such as G418, hygromycin and methotrexate. Selectable markers may be introduced on the same plasmid as the gene(s) of interest or may be introduced on a separate plasmid. Following selection of transfected cells using the appropriate selectable marker(s), expression of the costimulatory molecule on the surface of the cell can be confirmed by immunofluorescent staining of the cells. For example, cells may be stained with a fluorescently labeled monoclonal antibody reactive against the costimulatory molecule or with a fluorescently labeled soluble receptor which binds the costimulatory molecule such as CTLA4Ig. Expression of the B7 costimulatory molecule can be determined using a monoclonal antibody, such as BB1 or 133, which recognizes B7-1 or the monoclonal antibody IT2 which recognizes B7-2. Alternatively, a labeled soluble CD28 or CTLA4 protein or fusion protein (e.g., CTLA4Ig) which binds to the B7 molecules can be used to detect expression of B7 on the cell surface.

The cell to be transfected can be any eukaryotic cell, preferably cells that allow high level expression of the transfected gene, such as chinese hamster ovary (CHO) cells or COS cells. The cell is most preferably a CHO cell and a specific protocol for transfection of these cells is provided in Example 11.

In another embodiment, B7 molecules (e.g., B7-1, B7-2) are coupled to the cell surface by any of a variety of different methods. In this embodiment, the B7 molecule to be coupled to the cell surface can be obtained using standard recombinant DNA technology and expression systems which allow for production and isolation of the costimulatory molecule(s) or obtained from a cell expressing the costimulatory molecule, as described below for the preparation of a soluble form of the B7 molecules. The isolated costimulatory molecule is then coupled to the cell. The terms "coupled" or "coupling" refer to a chemical, enzymatic or other means (e.g., antibody) by which the B7 molecule is linked to a cell such that the costimulatory molecule is present on the surface of the cell and is capable of triggering a costimulatory signal in T cells. For example, the B7 molecule can be chemically crosslinked to the cell surface using commercially available crosslinking reagents (Pierce, Rockford Ill.). Another approach to coupling a B7 molecule to a cell is to use a bispecific antibody which binds both the costimulatory molecule and a cell-surface molecule on the cell. Fragments, mutants or variants of a B7 molecule which retain the ability to trigger a costimulatory signal in T cells when coupled to the surface of a cell can also be used.

The level of B7 molecules expressed on or coupled to the cell surface can be determined by FACS analysis, as described in Example 11.

For T cell costimulation, the B7-expressing cells can be cultured to a high density, mitomycin C treated (e.g., at 25 .mu.g/ml for an hour), extensively washed, and incubated with the T cells to be costimulated. The ratio of T cells to B7-expressing cells can be anywhere between 10:1 to 1:1, preferably 2.5:1 T cells to B7-expressing cells.

Soluble Forms of B7 Molecules as Costimulator

The natural ligands of CD28 can also be presented to T cells in a soluble form. Soluble forms of B7 molecules include natural B7 molecules (e.g., B7-1, B7-2), a fragment thereof, or modified form of the full length or fragment of the B7 molecule that is able to bind to CD28 and costimulate the T cell. Costimulation can be evidenced by proliferation and/or cyotkine production by T cells that have received a primary activation signal. Modifications of B7 molecules include modifications that preferably enhance the affinity of binding of B7 molecules to CD28 molecules, but also modifications that diminish or do not affect the affinity of binding of B7 molecules to CD28 molecules. Modifications of B7 molecules also include those that increase the stability of a soluble form of a B7 molecule. The modifications of B7 molecules are usually produced by amino acid substitutions, but can also be produced by linkage to another molecule.

In one specific embodiment, the soluble form of a B7 molecule is a fusion protein containing a first peptide consisting of a B7 molecule (e.g., B7-1, B7-2), or fragment thereof and a second peptide corresponding to a moiety that alters the solubility, binding, affinity, stability, or valency (i.e., the number of binding sites available per molecule) of the first peptide. Preferably, the first peptide includes an extracellular domain portion of a B7 molecule (e.g., about amino acid residues 24-245 of the B7-2 molecule having an amino acid sequence shown in SEQ ID NO: 4) that interacts with CD28 and is able to provide a costimulatory signal as evidenced by stimulation of proliferation of T cells or secretion of cytokines from the T cells upon exposure to the B7Ig fusion protein and a primary T cell activation signal. Thus, a B7-1Ig fusion protein will comprise at least about amino acids 1-208 (SEQ ID NO:2) of B7-1 and a B7-2Ig fusion protein will comprise at least about amino acids 24-245 (SEQ ID NO:4) of B7-2.

The second peptide is a fragment of an Ig molecule, such as an Fc fragment that comprises the hinge, CH2 and CH3 regions of human IgG1 or IgG4. Several Ig fusion proteins have been previously described (see e.g., Capon, D. J. et al. (1989) Nature 337:525-531 and Capon U.S. Pat. No. 5,116,964 [CD4-IgG1 constructs]; Linsley, P. S. et al. (1991) J. Exp. Med 173:721-730 [a CD28-IgG1 construct and a B7-1-IgG1 construct]; and Linsley, P. S. et al. (1991) J. Exp. Med. 174:561-569 [a CTLA4-IgG1]). A resulting B7Ig fusion protein (e.g., B7-1Ig, B7-2Ig) may have altered B7-2 solubility, binding affinity, stability, or valency and may increase the efficiency of protein purification. In particular fusion of a B7 molecule or portion thereof to the Fc region of an immunoglobulin molecule generally provides an increased stability to the protein, in particular in the plasma.

Fusion proteins within the scope of the invention can be prepared by expression of a nucleic acid encoding the fusion protein in a variety of different systems. Typically, the nucleic acid encoding a B7 fusion protein comprises a first nucleotide sequence encoding a first peptide consisting of a B7 molecule or a fragment thereof and a second nucleotide sequence encoding a second peptide corresponding to a moiety that alters the solubility, binding, stability, or valency of the first peptide, such as an immunoglobulin constant region. Nucleic acid encoding a peptide comprising an immunoglobulin constant region can be obtained from human immunoglobulin mRNA present in B lymphocytes. It is also possible to obtain nucleic acid encoding an immunoglobulin constant region from B cell genomic DNA. For example, DNA encoding C.gamma.1 or C.gamma.4 can be cloned from either a cDNA or a genomic library or by polymerase chain reaction (PCR) amplification in accordance standard protocols. A preferred nucleic acid encoding an immunoglobulin constant region comprises all or a portion of the following: the DNA encoding human C.gamma.1 (Takahashi, N. S. et al. (1982) Cell 29:671-679), the DNA encoding human C.gamma.2; the DNA encoding human C.gamma.3 (Huck, S., et al. (1986) Nucl. Acid Res. 14:1779); and the DNA encoding human C.gamma.4. When an immunoglobulin constant region is used in the B7 fusion protein, the constant region can be modified to reduce at least one constant region mediated biological effector function. For example, DNA encoding a C.gamma.1 or C.gamma.4 constant region can be modified by PCR mutagenesis or site directed mutagenesis. Protocols and reagents for site directed mutagenesis systems can be obtained commercially from Amersham International PLC, Amersham, UK.

In a particularly prefered embodiment of the invention, B7-1Ig and B7-2Ig fusion proteins comprise about amino acids 1-208 of B7-1 (SEQ ID NO: 2) and about amino acids 24-245 of B7-2 (SEQ ID NO: 4), respectively, fused to the heavy chain of IgG1.

In one embodiment the first and second nucleotide sequences are linked (i.e., in a 5' to 3' orientation by phosphodiester bonds) such that the translational frame of the B7 protein or fragment thereof and the IgC (i.e., Fc fragment that comprises the hinge, CH2, and CH3 regions of human IgG) coding segments are maintained (i.e., the nucleotide sequences are joined together in-frame). Thus, expression (i.e., transcription and translation) of the nucleotide sequence produces a functional B7Ig fusion protein. The nucleic acids of the invention can be prepared by standard recombinant DNA techniques. For example, a B7Ig fusion protein can be constructed using separate template DNAs encoding B7 and an immunoglobulin constant region. The appropriate segments of each template DNA can be amplified by polymerase chain reaction (PCR) and ligated in frame using standard techniques. A nucleic acid of the invention can also be chemically synthesized using standard techniques. Various methods of chemically synthesizing polydeoxynucleotides are known, including solid-phase synthesis which has been automated in commercially available DNA synthesizers (See e.g., Itakura et al. U.S. Pat. No. 4,598,049; Caruthers et al. U.S. Pat. No. 4,458,066; and Itakura U.S. Pat. Nos. 4,401,796 and 4,373,071, incorporated by reference herein).

The nucleic acids encoding B7 molecules or B7Ig fusion proteins (e.g., B7-1, B7-2) can be inserted into various expression vectors, which in turn direct the synthesis of the corresponding protein in a variety of hosts, particularly eucaryotic cells, such as mammalian or insect cell culture and procaryotic cells, such as E. coli. Expression vectors within the scope of the invention comprise a nucleic acid as described herein and a promotor operably linked to the nucleic acid. Such expression vectors can be used to transfect host cells to thereby produce fusion proteins encoded by nucleic acids as described herein. An expression vector of the invention, as described herein, typically includes nucleotide sequences encoding a B7 molecule or B7Ig fusion protein operably linked to at least one regulatory sequence. "Operably linked" is intended to mean that the nucleotide sequence is linked to a regulatory sequence in a manner which allows expression of the nucleotide sequence in a host cell (or by a cell extract). Regulatory sequences are art-recognized and can be selected to direct expression of the desired protein in an appropriate host cell. The term regulatory sequence is intended to include promoters, enhancers, polyadenylation signals and other expression control elements. Such regulatory sequences are known to those skilled in the art and are described in Goeddel, Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990). It should be understood that the design of the expression vector may depend on such factors as the choice of the host cell to be transfected and/or the type and/or amount of protein desired to be expressed.

An expression vector of the invention can be used to transfect cells, either procaryotic or eucaryotic (e.g., mammalian, insect or yeast cells) to thereby produce fusion proteins encoded by nucleotide sequences of the vector. Expression in procaryotes is most often carried out in E. coli with vectors containing constitutive or inducible promotors. Certain E. coli expression vectors (so called fusion-vectors) are designed to add a number of amino acid residues to the expressed recombinant protein, usually to the amino terminus of the expressed protein. Such fusion vectors typically serve three purposes: 1) to increase expression of recombinant protein; 2) to increase the solubility of the target recombinant protein; and 3) to aid in the purification of the target recombinant protein by acting as a ligand in affinity purification. Examples of fusion expression vectors include pGEX (Amrad Corp., Melbourne, Australia) and pMAL (New England Biolabs, Beverly, Mass.) which fuse glutathione S-tranferase and maltose E binding protein, respectively, to the target recombinant protein. Accordingly, a B7 molecule or B7Ig fusion gene may be linked to additional coding sequences in a procaryotic fusion vector to aid in the expression, solubility or purification of the fusion protein. Often, in fusion expression vectors, a proteolytic cleavage site is introduced at the junction of the fusion moiety and the target recombinant protein to enable separation of the target recombinant protein from the fusion moiety subsequent to purification of the fusion protein. Such enzymes, and their cognate recognition sequences, include Factor Xa, thrombin and enterokinase.

Inducible non-fusion expression vectors include pTrc (Amann et al., (1988) Gene 69:301-315) and pET 11d (Studier et al., Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990) 60-89). Target gene expression from the pTrc vector4 relies on host RNA polymerase transcription from the hybrid trp-lac fusion promoter. Target gene expression from the pET 11d vector relies on transcription from the T7 gn10-lac 0 fusion promoter mediated by a coexpressed viral RNA polymerase (T7 gn1). This viral polymerase is supplied by host strains BL21(DE3) or HMS 174(DE3) from a resident .lamda. prophage harboring a T7 gn1 under the transcriptional control of the lacUV 5 promoter.

One strategy to maximize expression of at B7 molecule or B7Ig fusion protein in E. coli is to express the protein in a host bacteria with an impaired capacity to proteolytically cleave the recombinant protein (Gottesman, S., Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990) 119-128). Another strategy would be to alter the nucleotide sequence of the B7 molecule or B7Ig fusion protein construct to be inserted into an expression vector so that the individual codons for each amino acid would be those preferentially utilized in highly expressed E. coli proteins (Wada et al. (1992) Nuc. Acids Res. 20:2111-2118). Such alteration of nucleic acid sequences are encompassed by the invention and can be carried out by standard DNA synthesis techniques.

Alternatively, a B7 molecule or B7Ig fusion protein can be expressed in a eucaryotic host cell, such as mammalian cells (e.g., Chinese hamster ovary cells (CHO) or NS0 cells), insect cells (e.g., using a baculovirus vector) or yeast cells. Other suitable host cells may be found in Goeddel, (1990) supra or are known to those skilled in the art. Eucaryotic, rather than procaryotic, expression of a B7 molecule or B7Ig may be preferable since expression of eucaryotic proteins in eucaryotic cells can lead to partial or complete glycosylation and/or formation of relevant inter- or intra-chain disulfide bonds of a recombinant protein. For expression in mammalian cells, the expression vector's control functions are often provided by viral material. For example, commonly used promoters are derived from polyoma, Adenovirus 2, cytomegalovirus and Simian Virus 40. To express a B7 molecule or B7Ig fusion protein in mammalian cells, generally COS cells (Gluzman, Y., (1981) Cell 23:175-182) are used in conjunction with such vectors as pCDM8 (Seed, B., (1987) Nature 329:840) for transient amplification/expression, while CHO (dhfr.sup.- Chinese Hamster Ovary) cells are used with vectors such as pMT2PC (Kaufman et al. (1987), EMBO J. 6:187-195) for stable amplification/expression in mammalian cells. A preferred cell line for production of recombinant protein is the NSO myeloma cell line available from the ECACC (catalog #85110503) and described in Galfre, G. and Milstein, C. ((1981) Methods in Enzymology 73(13):3-46; and Preparation of Monoclonal Antibodies: Strategies and Procedures, Academic Press, N.Y., N.Y.). Examples of vectors suitable for expression of recombinant proteins in yeast (e.g., S. cerivisae) include pYepSec1 (Baldari. et al, (1987) Embo J. 6:229-234), pMFa (Kujan and Herskowitz, (1982) Cell 30:933-943), pJRY88 (Schultz et al., (1987) Gene 54:113-123), and pYES2 (Invitrogen Corporation, San Diego, Calif.). Baculovirus vectors available for expression of proteins in cultured insect cells (SF 9 cells) include the pAc series (Smith et al., (1983) Mol. Cell Biol. 3:2156-2165) and the pVL series (Lucklow, V. A., and Summers, M. D., (1989) Virology 170:31-39).

Vector DNA can be introduced into procaryotic or eucaryotic cells via conventional transformation or transfection techniques such as calcium phosphate or calcium choloride co-precipitation, DEAE-dextran-mediated transfection, lipofection, or electroporation. Suitable methods for transforming host cells can be found in Sambrook et al. (Molecular Cloning: A Laboratory Manual, 2nd Edition, Cold Spring Harbor Laboratory press (1989)), and other laboratory textbooks.

For stable transfection of mammalian cells, it is known that, depending upon the expression vector and transfection technique used, only a small faction of cells may integrate DNA into their genomes. In order to identify and select these integrants, a gene that encodes a selectable marker (e.g., resistance to antibiotics) is generally introduced into the host cells along with the gene of interest. Preferred selectable markers include those which confer resistance to drugs, such as G418, hygromycin and methotrexate. Nucleic acid encoding a selectable marker may be introduced into a host cell on the same plasmid as the gene of interest or may be introduced on a separate plasmid. Cells containing the gene of interest can be identified by drug selection (e.g., cells that have incorporated the selectable marker gene will survive, while the other cells die). The surviving cells can then be screened for production of B7 molecules or B7Ig fusion proteins by, for example, immunoprecipitation from cell supernatant with an anti-B7 monoclonal antibody.

B7 molecules or B7Ig fusion proteins produced by recombinant technique may be secreted and isolated from a mixture of cells and medium containing the protein. Alternatively, the protein may be retained cytoplasmically and the cells harvested, lysed and the protein isolated. A cell culture typically includes host cells, media and other byproducts. Suitable mediums for cell culture are well known in the art. Protein can be isolated from cell culture medium, host cells, or both using techniques known in the art for purifying proteins.

For T cell costimulation, the soluble forms of the natural ligands for CD28 are added to the T cell culture in an amount sufficient to result in costimulation of activated T cells. The appropriate amount of soluble ligand to be added will vary with the specific ligand, but can be determined by assaying different amounts of the soluble ligand in T cell cultures and measuring the extent of costimulation by proliferation assays or production of cytokines, as described in the Examples.

Coupling of the Natural Ligands to a Solid Phase Surface

In another embodiment of the invention, a natural ligand of CD28 (B7-1, B7-2) can be presented to T cells in a form attached to a solid phase surface, such as beads. The B7 molecules, fragments thereof or modified forms thereof capable of binding to CD28 and costimulating the T cells (e.g., B7 fusion proteins) can be prepared as described for the soluble B7 forms. These molecules can then be attached to the solid phase surface via several methods. For example the B7 molecules can be crosslinked to the beads via covalent modification using tosyl linkage. In this method, B7 molecules or B7 fusion proteins are in 0.05M borate buffer, pH 9.5 and added to tosyl activated magnetic immunobeads (Dynal Inc., Great Neck, N.Y.) according to manufacturer's instructions. After a 24 hr incubation at 22.degree. C., the beads are collected and washed extensively. It is not mandatory that immunmagnetic beads be used, as other methods are also satisfactory. For example, the B7 molecules may also be immobilized on polystyrene beads or culture vessel surfaces. Covalent binding of the B7 molecules or B7Ig fusion proteins to the solid phase surface is preferrable to adsorption or capture by a secondary monoclonal antibody. B7Ig fusion proteins can be attached to the solid phase surface through anti-human IgG molecules bound to the solid phase surface. In particular, beads to which anti-human IgG molecules are bound can be obtained from Advanced Magnetics, Inc. These beads can then be incubated with the B7Ig fusion proteins in an appropriate buffer such as PBS for about an hour at 5.degree. C., and the uncoupled B7Ig proteins removed by washing the beads in a buffer, such as PBS.

It is also possible to attach the B7 molecules to the solid phase surface through an avidin- or streptavidin-biotin complex. In this particular embodiment, the soluble B7 molecule is first crosslinked to biotin and then reacted with the solid phase surface to which avidin or streptavidin molecules are bound. It is also possible to crosslink the B7 molecules with avidin or streptavidin and to react these with a solid phase surface that is covered with biotin molecules.

The amount of B7 molecules attached to the solid phase surface can be determined by FACS analysis if the solid phase surface is that of beads or by ELISA if the solid phase surface is that of a tissue culture dish. Antibodies reactive with the B7 molecules, such as mAb BBI, mAb IT2, and mAb 133 can be used in these assays. Alternatively, CTLA4Ig can also be used for that purpose.

In a specific embodiment, the stimulatory form of a B7 molecule is attached to the same solid phase surface as the agent that stimulates the TCR/CD3 complex, such as an anti-CD3 antibody. In addition to anti-CD3, other antibodies that bind to receptors that mimic antigen signals may be used, for example, the beads or other solid phase surface may be coated with combinations of anti-CD2 and a B7 molecule. The two stimulatory molecules can be bound to the solid phase surface in various ratios, but preferably in equimolar amounts.

In a typical experiment, B7-coated beads or beads coated with B7 molecules and an agent that stimulates the TCR/CD3 complex will be added at a ratio of 3 beads per T cell.

Agents which Act Intracellularly to Stimulate a Signal Associated with CD28 Ligation

In another embodiment of the invention, an activated population of CD4.sup.+ T cells is stimulated to proliferate by contacting the T cells with an agent which acts intracellularly to stimulate a signal in the T cell mediated by ligation of an accessory molecule, such as CD28. The term "agent", as used herein, is intended to encompass chemicals and other pharmaceutical compounds which stimulate a costimulatory or other signal in a T cell without the requirement for an interaction between a T cell surface receptor and a costimulatory molecule or other ligand. For example, the agent may act intracellularly to stimulate a signal associated with CD28 ligation. In one embodiment, the agent is a non-proteinaceous compound. As the agent used in the method is intended to bypass the natural receptor:ligand stimulatory mechanism, the term agent is not intended to include a cell expressing a natural ligand. Natural ligands for CD28 include members of the B7 family of proteins, such as B7-1(CD80) and B7-2 (CD86).

It is known that CD28 receptor stimulation leads to the production of D-3 phosphoinositides in T cells and that inhibition of the activity of phosphatidylinositol 3-kinase (PI3K) in a T cell can inhibit T cell responses, such as lymphokine production and cellular proliferation. Protein tyrosine phosphorylation has also been shown to occur in T cells upon CD28 ligation and it has been demonstrated that a protein tyrosine kinase inhibitor, herbimycin A, can inhibit CD28-induced IL-2 production (Vandenberghe, P. et al. (1992) J. Exp. Med. 175:951-960; Lu, Y. et al. (1992) J. Immunol. 149:24-29). Thus, to selectively expand a population of CD4.sup.+ T cells, the CD28 receptor mediated pathway can be stimulated by contacting T cells with an activator of PI3K or an agent which stimulates protein tyrosine phosphorylation in the T cell, or both. An activator of PI3K can be identified based upon its ability to stimulate production of at least one D-3 phosphoinositide in a T cell. The term "D-3 phosphoinositide" is intended to include derivatives of phosphatidylinositol that are phosphorylated at the D-3 position of the inositol ring and encompasses the compounds phosphatidylinositol(3)-monophosphate (PtdIns(3)P), phosphatidylinositol(3,4)-bisphosphate (PtdIns(3,4)P.sub.2), and phosphatidylinositol(3,4,5)-trisphosphate (PtdIns(3,4,5)P.sub.3). Thus, in the presence of a PI3K activator, the amount of a D-3 phosphoinositide in the T cell is increased relative to the amount of the D-3 phosphoinositide in the T cell in the absence of the substance. Production of D-3 phosphoinositides (e.g., PtdIns(3)P, PtdIns(3,4)P.sub.2 and/or PtdIns(3,4,5)P.sub.3) in a T cell can be assessed by standard methods, such as high pressure liquid chromatography or thin layer chromatography, as discussed above. Similarly, protein tyrosine phosphorylation can be stimulated in a T cell, for example, by contacting the T cell with an activator of protein tyrosine kinases, such as pervanadate (see O'Shea, J. J. et al. (1992) Proc. Natl. Acad. Sci. USA 89:10306-103101; and Secrist, J. P. (1993) J. Biol. Chem. 268:5886-5893). Alternatively, the T cell can be contacted with an agent which inhibits the activity of a cellular protein tyrosine phosphatase, such as CD45, to increase the net amount of protein tyrosine phosphorylation in the T cell. Any of these agents can be used to expand an activated population of CD4.sup.+ T cells in accordance with the methods described herein.

Techniques for Expansion of CD8.sup.+ T Cells

In order to induce proliferation and expand a population of CD8.sup.+ T cells, an activated population of T cells is stimulated through a 27 kD accessory molecule found on activated T cells and recognized by the monoclonal antibody ES5.2D8. As described in Example 9, a population of CD8.sup.+ T cells was preferentially expanded by stimulation with an anti-CD3 monoclonal antibody and the ES5.2D8 monoclonal antibody. The monoclonal antibody ES5.2D8 was produced by immunization of mice with activated human blood lymphocytes and boosted with recombinant human CTLA4 protein produced in E. coli. The ES5.2D8 monoclonal antibody is of the IgG2b isotype and specifically binds to cells transfected with human CTLA4. Hybridomas producing CTLA4-specific antibody were identified by screening by ELISA against human CTLA4 protein as well as by differential FACS against wild type CHO-DG44 cells vs. CHO-105A cells, which are transfected with the human CTLA4 gene. As shown in FIG. 7, the ES5.2D8 clone reacts strongly with both activated human T cells and CHO-105A cells but not with CHO-DCA4 cells, indicating that it does indeed bind to CTLA4. Immunoprecipitation of detergent lysates of surface labeled activated human T cells revealed that ES5.2D8 also reacts with a 27 kD cell surface protein (FIG. 8). A hybridoma which produces the monoclonal antibody ES5.2D8 was deposited on Jun. 4, 1993 with the American Type Culture Collection at ATCC Deposit No. HB11374.

Accordingly, to expand a population of CD8.sup.+ T cells, an antibody, such as monoclonal antibody ES5.2D8, or other antibody which recognizes the same 27 kD ligand as ES5.2D8 can be used. As described in Example 10, the epitope recognized by the monoclonal antibody ES5.2D8 was identified by screening a phage display library (PDL). Antibodies which bind to the same epitope as the monoclonal antibody ES5.2D8 are within the scope of the invention. Such antibodies can be produced by immunization with a peptide fragment including the epitope or with the native 27 kD antigen. The term "epitope", as used herein, refers to the actual structural portion of the antigen that is immunologically bound by an antibody combining site. The term is also used interchangeably with "antigenic determinant". A preferred epitope which is bound by an antibody or other ligand which is to be used to stimulate a CD8.sup.+ T cell population includes or encompasses, an amino acid sequence:

(Xaa.sub.1).sub.n-Gly-Xaa.sub.2-Trp-Leu-Xaa.sub.3-Xaa.sub.4-Asp(Glu)-(Xaa.- sub.5).sub.n (SEQ ID NO: 5),

wherein Xaa.sub.4 may or may not be present, Xaa.sub.1, Xaa.sub.2, Xaa.sub.3, Xaa.sub.4 and Xaa.sub.5 are any amino acid residue and n=0-20, more preferably 0-10, even more preferably 0-5, and most preferably 0-3. In a preferred embodiment, Xaa.sub.2 is Cys, Ile or Leu, Xaa.sub.3 is Leu or Arg and Xaa.sub.4, if present, is Arg, Pro or Phe. As described in Example 10, the monoclonal antibody ES5.2D8, which specifically binds a 27 kD antigen on activated T cells was used to screen a cDNA library from activated T cells to isolate a clone encoding the antigen. Amino acid sequence analysis identified the antigen as CD9 (SEQ ID NO: 6). In the native human CD9 molecule, epitope defined by phage display library screening is located at amino acid residues 31-37 (i.e., G L W L R F D (SEQ ID NO: 7)). Accordingly, Xaa.sub.1 and Xaa.sub.4 are typically additional amino acid residues found at either the amino or carboxy side, or both the amino and carboxy sides, of the core epitope in the human CD9 (the full-length amino acid sequence of which is shown in SEQ ID NO: 6). It will be appreciated by those skilled in the art that in the native protein, additional non-contiguous amino acid residues may also contribute to the conformational epitope recognized by the antibody. Synthetic peptides encompassing the epitope can be created which includes other amino acid residues flanking the core six amino acid residues (i.e., Xaa can alternatively be other amino acid residues than those found in the native CD9 protein). These flanking amino acid residues can function to alter the properties of the resulting peptide, for example to increase the solubility, enhance the immunogenicity or promote dimerization of the resultant peptide. When the peptide is to be used as an immunogen, one or more charged amino acids (e.g., lysine, arginine) can be included to increase the solubility of the peptide and/or enhance the immunogenicity of the peptide. Alternatively, cysteine residues can be included to increase the dimerization of the resulting peptide.

Other embodiments of the invention pertain to expansion of a population of CD8.sup.+ T cells by use of an agent which acts intracellularly to stimulate a signal in the T cell mediated by ligation of CD9 or other CD9-associated molecule. It is known that CD9 belongs to the TM4 superfamily of cell surface proteins which span the membrane four times (Boucheix, C. et al. (1990) J. Biol. Chem. 266, 117-122 and Lanza, F. et al. (1990) J. Biol. Chem. 266, 10638-10645). Other members of the TM4 superfamily include CD37, CD53, CD63 and TAPA-1. A role for CD9 in interacting with GTP binding proteins has been suggested (Sechafer, J. G. and Shaw, A. R. E. (1991) Biochem. Biophys. Res. Commun. 179, 401-406). As used herein the term "agent" encompasses chemicals and other pharmaceutical compounds which stimulate a signal in a T cell without the requirement for an interaction between a T cell surface receptor and a ligand. Thus, this agent does not bind to the extracellular portion of CD9, but rather mimics or induces an intracellular signal (e.g., second messenger) associated with ligation of CD9 or a CD9-associated molecule by an appropriate ligand. The ligands described herein (e.g., monoclonal antibody ES5.2D8) can be used to identify an intracellular signal(s) associated with T cell expansion mediated by contact of the CD9 antigen or CD9-associated molecule with an appropriate ligand (as described in the Examples) and examining the resultant intracellular signalling that occurs (e.g., protein tyrosine phosphorylation, calcium influx, activation of serine/threonine and/or tyrosine kinases, phosphatidyl inositol metabolism, etc.). An agent which enhances an intracellular signal associated with CD9 or a CD9-associated molecule can then be used to expand CD8.sup.+ T cells. Alternatively, agents (e.g., small molecules, drugs, etc.) can be screened for their ability to inhibit or enhance T cell expansion using a system such as that described in the Examples.

Techniques for Expansion of Antigen Specific T Cells

In yet another aspect of the invention, methods for expanding a population of antigen specific T cells are provided. To produce a population of antigen specific T cells, T cells are contacted with an antigen in a form suitable to trigger a primary activation signal in the T cell, i.e., the antigen is presented to the T cell such that a signal is triggered in the T cell through the TCR/CD3 complex. For example, the antigen can be presented to the T cell by an antigen presenting cell in conjuction with an MHC molecule. An antigen presenting cell, such as a B cell, macrophage, monocyte, dendritic cell, Langerhans cell, or other cell which can present antigen to a T cell, can be incubated with the T cell in the presence of the antigen (e.g., a soluble antigen) such that the antigen presenting cell presents the antigen to the T cell. Alternatively, a cell expressing an antigen of interest can be incubated with the T cell. For example, a tumor cell expressing tumor-associated antigens can be incubated with a T cell together to induce a tumor-specific response. Similarly, a cell infected with a pathogen, e.g., a virus, which presents antigens of the pathogen can be incubated with a T cell. Following antigen specific activation of a population of T cells, the cells can be expanded in accordance with the methods of the invention. For example, after antigen specificity has been established, T cells can be expanded by culture with an anti-CD3 antibody and an anti-CD28 antibody according to the methods described herein.

Production of Antibodies and Coupling of Antibodies to Solid Phase Surfaces

The term "antibody" as used herein refers to immunoglobulin molecules and immunologically active portions of immunoglobulin molecules, i.e., molecules that contain an antigen binding site which specifically binds (immunoreacts with) an antigen, such as CD3, CD28. Structurally, the simplest naturally occurring antibody (e.g., IgG) comprises four polypeptide chains, two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds. It has been shown that the antigen-binding function of an antibody can be performed by fragments of a naturally-occurring antibody. Thus, these antigen-binding fragments are also intended to be designated by the term "antibody". Examples of binding fragments encompassed within the term antibody include (i) an Fab fragment consisting of the VL, VH, CL and CH1 domains; (ii) an Fd fragment consisting of the VH and CH1 domains; (iii) an Fv fragment consisting of the VL and VH domains of a single arm of an antibody, (iv) a dAb fragment (Ward et al., (1989) Nature 341:544-546) which consists of a VH domain; (v) an isolated complimentarity determining region (CDR); and (vi) an F(ab').sub.2 fragment, a bivalent fragment comprising two Fab fragments linked by a disulfide bridge at the hinge region. Furthermore, although the two domains of the Fv fragment are coded for by separate genes, a synthetic linker can be made that enables them to be made as a single protein chain (known as single chain Fv (scFv); Bird et al. (1988) Science 242:423-426; and Huston et al. (1988) PNAS 85:5879-5883) by recombinant methods. Such single chain antibodies are also encompassed within the term "antibody". Preferred antibody fragments for use in T cell expansion are those which are capable of crosslinking their target antigen, e.g., bivalent fragments such as F(ab').sub.2 fragments. Alternatively, an antibody fragment which does not itself crosslink its target antigen (e.g., a Fab fragment) can be used in conjunction with a secondary antibody which serves to crosslink the antibody fragment, thereby crosslinking the target antigen. Antibodies can be fragmented using conventional techniques as described herein and the fragments screened for utility in the same manner as described for whole antibodies. An antibody of the invention is further intended to include bispecific and chimeric molecules having a desired binding portion (e.g., CD28).

The language "a desired binding specificity for an epitope", as well as the more general language "an antigen binding site which specifically binds (immunoreacts with)", refers to the ability of individual antibodies to specifically immunoreact with a T cell surface molecule, e.g., CD28. That is, it refers to a non-random binding reaction between an antibody molecule and an antigenic determinant of the T cell surface molecule. The desired binding specificity is typically determined from the reference point of the ability of the antibody to differentially bind the T cell surface molecule and an unrelated antigen, and therefore distinguish between two different antigens, particularly where the two antigens have unique epitopes. An antibody which binds specifically to a particular epitope is referred to as a "specific antibody".

"Antibody combining site", as used herein, refers to that structural portion of an antibody molecule comprised of a heavy and light chain variable and hypervariable regions that specifically binds (immunoreacts with) antigen. The term "immunoreact" or "reactive with" in its various forms is used herein to refer to binding between an antigenic determinant-containing molecule and a molecule containing an antibody combining site such as a whole antibody molecule or a portion thereof.

Although soluble forms of antibodies may be used to activate T cells, it is preferred that the anti-CD3 antibody be immobilized on a solid phase surface (e.g., beads). An antibody can be immobilized directly or indirectly by, for example, by a secondary antibody, to a solid surface, such as a tissue culture flask or bead. As an illustrative embodiment, the following is a protocol for immobilizing an anti-CD3 antibody on beads. It should be appreciated that the same protocol can be used to immobilize other antibodies or fragments thereof (e.g., an anti-CD28 antibody), and Ig fusion proteins, such as B7Ig fusion proteins, to beads. The same protocol can also be used to immobilize more than one antibody, or an antibody and another molecule, such as a fusion protein, to the the solid phase surface.

Protocols

I. Pre-absorbing Goat anti-mouse IgG with OKT-3 A) BioMag Goat anti-Mouse IgG (Advanced Magnetics, Inc., catalog number 8-4340D) is incubated with at least 200 .mu.g of OKT-3 per 5.times.10.sup.8 magnetic particles in PBS for 1 hour at 5.degree. C. B) Particles are washed three time in PBS with the aid of a magnetic separation unit. Note: Advanced Magnetics also has an anti-Human CD3 directly conjugated (Catalog number 8-4703N) which will induce T-cell stimulation. II. Pre-labeling Lymphocytes with OKT-3 A) 1.times.10.sup.6 cells (PBMC) are incubated in PBS with 10 .mu.g/ml of OKT-3 for 15 minutes at room temperature. B) Cells are washed twice with PBS. III. Binding Magnetic Particles to PBMC for Stimulation A) PBMC surface labeled with OKT-3 are cultured with Goat anti-Mouse IgG (see above) at one bead per cell following a 30 minute incubation at 20.degree. C. with gentle agitation. B) Goat anti-Mouse IgG beads which were previously absorbed to OKT-3 are incubated with PBMC (1:1) for 30 minutes at 20.degree. C. with gentle agitation and cultured. IV. Binding Magnetic Particles to PBMC for Separation Same as above (Part III) except the bead to cell ratio is increased to 20:1 rather than 1:1.

Alternatively, antibodies can be coupled to a solid phase surface, e.g., beads by crosslinking via covalent modification using tosyl linkage. In one method, an antibody such as OKT3 is in 0.05M borate buffer, pH 9.5 and added to tosyl activated magnetic immunobeads (Dynal Inc., Great Neck, N.Y.) according to the manufacturer's instructions. After a 24 hr incubation at 22.degree. C., the beads are collected and washed extensively. It is not mandatory that immunomagnetic beads be used, as other methods are also satisfactory.

To practice the method of the invention, a source of T cells is obtained from a subject. The term subject is intended to include living organisms in which an immune response can be elicited, e.g., mammals. Examples of subjects include humans, dogs, cats, mice, rats, and transgenic species thereof. T cells can be obtained from a number of sources, including peripheral blood leukocytes, bone marrow, lymph node tissue, spleen tissue, and tumors. Preferably, peripheral blood leukocytes are obtained from an individual by leukopheresis. To isolate T cells from peripheral blood leukocytes, it may be necessary to lyse the red blood cells and separate peripheral blood leukocytes from monocytes by, for example, centrifugation through a PERCOLL.TM. gradient. A specific subpopulation of T cells, such as CD28.sup.+, CD4.sup.+, CD8.sup.+, CD28RA.sup.+, and CD28RO.sup.+ T cells, can be further isolated by positive or negative selection techniques. For example, negative selection of a T cell population can be accomplished with a combination of antibodies directed to surface markers unique to the cells negatively selected. A preferred method is cell sorting via negative magnetic immunoadherence which utilizes a cocktail of monoclonal antibodies directed to cell surface markers present on the cells negatively selected. For example, to isolate CD4.sup.+ cells, a monoclonal antibody cocktail typically includes antibodies to CD14, CD20, CD11b, CD16, HLA-DR, and CD8. Additional monoclonal antibody cocktails are provided in Table 1.

The process of negative selection results in an essentially homogenous population of CD28.sup.+, CD4.sup.+ or CD8.sup.+ T cells. The T cells can be activated as described herein, such as by contact with a anti-CD3 antibody immobilized on a solid phase surface or an anti-CD2 antibody, or by contact with a protein kinase C activator (e.g., bryostatin) in conjunction with a calcium ionophore. To stimulate an accessory molecule on the surface of the T cells, a ligand which binds the accessory molecule is employed. For example, a population of CD4.sup.+ cells can be contacted with an anti-CD3 antibody and an anti-CD28 antibody, under conditions appropriate for stimulating proliferation of the T cells. Similarly, to stimulate proliferation of CD8.sup.+ T cells, an anti-CD3 antibody and the monoclonal antibody ES5.2D8 can be used. Conditions appropriate for T cell culture include an appropriate media (e.g., Minimal Essential Media or RPMI Media 1640) which may contain factors necessary for proliferation and viability, including animal serum (e.g., fetal bovine serum) and antibiotics (e.g., penicillin streptomycin). The T cells are maintained under conditions necessary to support growth, for example an appropriate temperature (e.g., 37.degree. C.) and atmosphere (e.g., air plus 5% CO.sub.2).

The primary activation signal and the costimulatory signal for the T cell can be provided by different protocols. For example, the agents providing each signal can be in solution or coupled to a solid phase surface. When coupled to a solid phase surface, the agents can be coupled to the same solid phase surface (i.e., in "cis" formation) or to separate surfaces (i.e., in "trans" formation). Alternatively, one agent can be coupled to a solid phase surface and the other agent in solution. In one embodiment, the agent providing the costimulatory signal is bound to a cell surface and the agent providing the primary activation signal is in solution or coupled to a solid phase surface. In a preferred embodiment, the two agents are coupled to beads, either to the same bead, i.e., in "cis", or to separate beads, i.e., in "trans". Alternatively, the agent providing the primary activation signal is an anti-CD3 antibody and the agent providing the costimulatory signal is an anti-CD28 antibody; both agents are coupled to the same beads. In this embodiment, it has been determined that the optimal ratio of each antibody bound to the beads for CD4.sup.+ T cell expansion and T cell growth for up to at least 50 days is a 1:1 ratio. However, ratios from 1:9 to 9:1 can also be used to stimulate CD2.sup.+ T cell expansion. The ratio of anti-CD3 and anti-CD28 coated (with a ratio of 1:1 of each antibody) beads to T cells that yield T cell expansion can vary from 1:3 to 3:1, with the optimal ratio being 3:1 beads per T cell. Moreover, it has been determined that when T cells are expanded under these conditions, they remain polyclonal.

To maintain long term stimulation of a population of T cells following the initial activation and stimulation, it is necessary to separate the T cells from the activating stimulus (e.g., the anti-CD3 antibody) after a period of exposure. The T cells are maintained in contact with the co-stimulatory ligand throughout the culture term. The rate of T cell proliferation is monitored periodically (e.g., daily) by, for example, examining the size or measuring the volume of the T cells, such as with a Coulter Counter. A resting T cell has a mean diameter of about 6.8 microns. Following the initial activation and stimulation and in the presence of the stimulating ligand, the T cell mean diameter will increase to over 12 microns by day 4 and begin to decrease by about day 6. When the mean T cell diameter decreases to approximately 8 microns, the T cells are reactivated and restimulated to induce further proliferation of the T cells. Alternatively, the rate of T cell proliferation and time for T cell restimulation can be monitored by assaying for the presence of cell surface molecules, such as B7-1, B7-2, which are induced on activated T cells. As described in Example 5, it was determined that CD4.sup.+ T cells do not initially express the B7-1 receptor, and that with culture, expression is induced. Further, the B7-1 expression was found to be transient, and could be re-induced with repeated anti-CD3 restimulation. Accordingly, cyclic changes in B7-1 expression can be used as a means of monitoring T cell proliferation; where decreases in the level of B7-1 expression, relative to the level of expression following an initial or previous stimulation or the level of expression in an unstimulated cell, indicates the time for restimulation.

For inducing long term stimulation of a population of CD4.sup.+ or CD8.sup.+ T cells, it may be necessary to reactivate and restimulate the T cells with a anti-CD3 antibody and an anti-CD28 antibody or monoclonal antibody ES5.2D8 several times to produce a population of CD4.sup.+ or CD8.sup.+ cells increased in number from about 10- to about 1,000-fold the original T cell population. Using this methodology, it is possible to get increases in a T cell population of from about 100- to about 100,000-fold an original resting T cell population. Moreover, as described in Example 6, T cells expanded by the method of the invention secrete high levels of cytokines (e.g., IL-2, IFN.gamma., IL-4, GM-CSF and TNF.alpha.) into the culture supernatants. For example, as compared to stimulation with IL-2, CD4.sup.+ T cells expanded by use of anti-CD3 and anti-CD28 costimulation secrete high levels of GM-CSF and TNF.alpha. into the culture medium. These cytokines can be purified from the culture supernatants or the supernatants can be used directly for maintaining cells in culture. Similarly, the T cells expanded by the method of the invention together with the culture supernatant and cytokines can be administered to support the growth of cells in vivo. For example, in patients with tumors, T cells can be obtained from the individual, expanded in vitro and the resulting T cell population and supernatant, including cytokines such as TNF.alpha., can be readministered to the patient to augment T cell growth in vivo.

The invention also provides methods for expanding a population of T cells by a factor of about 10 log.sub.10 to about 12 log.sub.10, while maintaining the polyclonality of the population of T cells, as described in Example 18. In this embodiment, the T cells are stimulated with anti-CD3 and anti-CD28 coated beads and IL-2 is added to the culture at about day 49 of the culture. It is important to replenish the culture medium with IL-2, since it has been shown that the amount of IL-2 produced by T cells in long term culture decreases with time. This can for example be seen in FIG. 28, which shows that T cells stimulated with anti-CD3 and anti-CD28 in trans secrete progressively less IL-2 with time in culture as can be seen by comparing the amount of IL-2 secreted on day 1, day 12, and on day 21 of the culture.

The amount of IL-2 that should be added to the T cell culture to obtain expansion of the order of about 10 log.sub.10 to about 12 log.sub.10 can be determined without undue experimentation. In preliminary experiments, the amount of IL-2 secreted and the proliferation of the T cells are measured during long term proliferation assays (see Example 20). Thus, it is possible to determine the concentrations of IL-2 required for optimal T cell proliferation and the amount of IL-2 that should be added to the culture once proliferation of the T cells has slowed down. Moreover, amounts of IL-2 required for T cell growth are well known in the art and can thus easily be determined.

In one embodiment of the invention pertaining to polyclonal expansion of T cells to about 10 log.sub.10 to about 12 log.sub.10, the amount of IL-2 in the culture medium is monitored and IL-2 is added to the culture when the level of IL-2 in the supernatant is lower than the amount of IL-2 sufficient to maintain proliferation, preferably optimal proliferation, of the T cells. The phrase "IL-2 is added in amounts sufficient to maintain proliferation" of the T cells, e.g., CD4.sup.+ T cells, refers to the amount of IL-2 that is added to obtain a final concentration of IL-2 in the supernatant that corresponds to the amount determined to allow for the proliferation of the T cells. The optimal amount of IL-2 that is required can be determined as described in the previous paragraph and in Example 20. In another embodiment, IL-2 is added from the first day of the culture, and added every other day of the culture in amounts sufficient to maintain proliferation of the T cells. Alternatively, IL-2 can be added to the cultures to obtain a final concentration of about 100 U/ml and added every other day to the culture, such as every second or third day, when new medium is added to the cell culture.

It is also possible to obtain expansion of T lymphocytes by a factor from about 10 log.sub.10 to about 12 log.sub.10 by incubating the T cells with beads coated with anti-CD3 antibody, such as OKT3 and a stimulatory form of B7-2, such as B7-2Ig and the addition of IL-2 in amounts sufficient to maintain proliferation of the T cells.

Although the antibodies used in the methods described herein can be readily obtained from public sources, such as the ATCC, antibodies to T cell surface accessory molecules, the CD3 complex, or CD2 can be produced by standard techniques. Methodologies for generating antibodies for use in the methods of the invention are described in further detail below.

Specific Methodology for Antibody Production

A. The Immunogen. The term "immunogen" is used herein to describe a composition containing a peptide or protein as an active ingredient used for the preparation of antibodies against an antigen (e.g., CD3, CD28). When a peptide or protein is used to induce antibodies it is to be understood that the peptide can be used alone, or linked to a carrier as a conjugate, or as a peptide polymer.

To generate suitable antibodies, the immunogen should contain an effective, immunogenic amount of a peptide or protein, optionally as a conjugate linked to a carrier. The effective amount of peptide per unit dose depends, among other things, on the species of animal inoculated, the body weight of the animal and the chosen immunization regimen as is well known in the art. The immunogen preparation will typically contain peptide concentrations of about 10 micrograms to about 500 milligrams per immunization dose, preferably about 50 micrograms to about 50 milligrams per dose. An immunization preparation can also include an adjuvant as part of the diluent. Adjuvants such as complete Freund's adjuvant (CFA), incomplete Freund's adjuvant (IFA) and alum are materials well known in the art, and are available commercially from several sources.

Those skilled in the art will appreciate that, instead of using natural occurring forms of the antigen (e.g., CD3, CD28) for immunization, synthetic peptides can alternatively be employed towards which antibodies can be raised for use in this invention. Both soluble and membrane bound forms of the protein or peptide fragments are suitable for use as an immunogen and can also be isolated by immunoaffinity purification as well. A purified form of protein, such as may be isolated as described above or as known in the art, can itself be directly used as an immunogen, or alternatively, can be linked to a suitable carrier protein by conventional techniques, including by chemical coupling means as well as by genetic engineering using a cloned gene of the protein. The purified protein can also be covalently or noncovalently modified with non-proteinaceous materials such as lipids or carbohydrates to enhance immunogenecity or solubility. Alternatively, a purified protein can be coupled with or incorporated into a viral particle, a replicating virus, or other microorganism in order to enhance immunogenicity. The protein may be, for example, chemically attached to the viral particle or microorganism or an immunogenic portion thereof.

In an illustrative embodiment, a purified CD28 protein, or a peptide fragment thereof (e.g., produced by limited proteolysis or recombinant DNA techniques) is conjugated to a carrier which is immunogenic in animals. Preferred carriers include proteins such as albumins, serum proteins (e.g., globulins and lipoproteins), and polyamino acids. Examples of useful proteins include bovine serum albumin, rabbit serum albumin, thyroglobulin, keyhole limpet hemocyanin, egg ovalbumin and bovine gamma-globulins. Synthetic polyamino acids such as polylysine or polyarginine are also useful carriers. With respect to the covalent attachment of CD28 protein or peptide fragments to a suitable immunogenic carrier, there are a number of chemical cross-linking agents that are known to those skilled in the art. Preferred cross-linking agents are heterobifunctional cross-linkers, which can be used to link proteins in a stepwise manner. A wide variety of heterobifunctional cross-linkers are known in the art, including succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC), m-Maleimidobenzoyl-N-hydroxysuccinimide ester (MBS); N-succinimidyl (4-iodoacetyl) aminobenzoate (SIAB), succinimidyl 4-(p-maleimidophenyl) butyrate (SMPB), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC); 4-succinimidyl-oxycarbonyl-a-methyl-a-(2-pyridyldithio)-tolune (SMPT), N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP), succinimidyl 6-[3-(2-pyridyldithio) propionate] hexanoate (LC-SPDP).

It may also be desirable to simply immunize an animal with whole cells which express a protein of interest (e.g., CD28) on their surface. Various cell lines can be used as immunogens to generate monoclonal antibodies to an antigen, including, but not limited to T cells. For example, peripheral blood T cells can be obtained from a subject which constituitively express CD28, but can be activated in vitro with anti-CD3 antibodies, PHA or PMA. Alternatively, an antigen specific (e.g., alloreactive) T cell clone can be activated to express CD28 by presentation of antigen, together with a costimulatory signal, to the T cell. Whole cells that can be used as immunogens to produce CD28 specific antibodies also include recombinant transfectants. For example, COS and CHO cells can be reconstituted by transfection with a. CD28 cDNA to produce cells expressing CD28 on their surface. These transfectant cells can then be used as immunogens to produce anti-CD28 antibodies. Other examples of transfectant cells are known, particularly eukaryotic cells able to glycosylate the CD28 protein, but any procedure that works to express transfected CD28 genes on the cell surface could be used to produce the whole cell immunogen.

Alternative to a CD28-expressing cell or an isolated CD28 protein, peptide fragments of CD28 or other surface antigen such as CD9 can be used as immunogens to generate antibodies. For example, the CD9 epitope bound by the ES5.2D8 monoclonal antibody comprises an amino acid sequence: (Xaa.sub.1).sub.n-Gly-Xaa.sub.2-Trp-Leu-Xaa.sub.3-Xaa.sub.4-Asp(Glu)-(Xaa- .sub.5).sub.n (SEQ ID NO: 5), wherein Xaa.sub.4 may or may not be present, Xaa.sub.1, Xaa.sub.2, Xaa.sub.3, Xaa.sub.4 and Xaa.sub.5 are any amino acid residue and n=0-20, more preferably 0-10, even more preferably 0-5, and most preferably 0-3. In a preferred embodiment, Xaa.sub.2 is Cys, Ile or Leu, Xaa.sub.3 is Leu or Arg and Xaa.sub.4, if present, is Arg, Pro or Phe. Thus, a peptide having the amino acid sequence of SEQ ID NO: 5 can be used as an immunogen. Accordingly, the invention further encompasses an isolated CD9 peptide comprising an amino acid sequence: (Xaa.sub.1).sub.n-Gly-Xaa.sub.2-Trp-Leu-Xaa.sub.3-Xaa.sub.4-Asp(Glu)-(Xaa- .sub.5).sub.n (SEQ ID NO: 5), wherein Xaa.sub.4 may or may not be present, Xaa.sub.1, Xaa.sub.2, Xaa.sub.3, Xaa.sub.4 and Xaa.sub.5 are any amino acid residue and n=0-20, more preferably 0-10, even more preferably 0-5, and most preferably 0-3. In a preferred embodiment, Xaa.sub.2 is Cys, Ile or Leu, Xaa.sub.3 is Leu or Arg and Xaa.sub.4, if present, is Arg, Pro or Phe. Alternatively, it has been found that the ES5.2D8 monoclonal antibody cross-reacts with a number of other peptide sequences (determined by phage display technology as described in Example 3). Examples of these other peptide sequences are shown below:

TABLE-US-00001 (SEQ ID NO: 8) 2D8#2 H Q F C D H W G C W L L R E T H I F T P (SEQ ID NO: 8) 2D8#4 H Q F C D H W G C W L L R E T H I F T P (SEQ ID NO: 8) 2D8#10 H Q F C D H W G C W L L R E T H I F T P (SEQ ID NO: 9) 2D8#6 L R L V L E D P G I W L R P D Y F F P A G C W L L R E (phage 2D8#2, 4, 10; SEQ ID NO: 10) G I W L R P D (phage 2D8#6; SEQ ID NO: 11) G L W L R F D (CD9 sequence; SEQ ID NO: 7)

Any of these peptides, or other peptides containing a stretch of seven amino acids bracketed in bold type (representing the epitope bound by the antibody) possibly flanked by alternative amino acid residues, can also be used as immunogens to produce an antibody for use in the methods of the invention and are encompassed by the invention. For use as immunogens, peptides can be modified to increase solubility and/or enhance immunogenicity as described above.

B. Polyclonal Antibodies. Polycolonal antibodies to a purified protein or peptide fragment thereof can generally be raised in animals by multiple subcutaneous (sc) or intraperitoneal (ip) injections of an appropriate immunogen, such as the extracellular domain of the protein, and an adjuvant. A polyclonal antisera can be produced, for example, as described in Lindsten, T. et al. (1993) J. Immunol. 151:3489-3499. In an illustrative embodiment, animals are typically immunized against the immunogenic protein, peptide or derivative by combining about 1 .mu.g to 1 mg of protein with Freund's complete adjuvant and injecting the solution intradermally at multiple sites. One month later the animals are boosted with 1/5 to 1/10 the original amount of immunogen in Freund's complete adjuvant (or other suitable adjuvant) by subcutaneous injection at multiple sites. Seven to 14 days later, the animals are bled and the serum is assayed for anti-protein or peptide titer (e.g., by ELISA). Animals are boosted until the titer plateaus. Also, aggregating agents such as alum can be used to enhance the immune response.

Such mammalian-produced populations of antibody molecules are referred to as "polyclonal" because the population comprises antibodies with differing immunospecificities and affinities for the antigen. The antibody molecules are then collected from the mammal (e.g., from the blood) and isolated by well known techniques, such as protein A chromatography, to obtain the IgG fraction. To enhance the specificity of the antibody, the antibodies may be purified by immunoaffinity chromatography using solid phase-affixed immunogen. The antibody is contacted with the solid phase-affixed immunogen for a period of time sufficient for the immunogen to immunoreact with the antibody molecules to form a solid phase-affixed immunocomplex. The bound antibodies are separated from the complex by standard techniques.

C. Monoclonal Antibodies. The term "monoclonal antibody" or "monoclonal antibody composition", as used herein, refers to a population of antibody molecules that contain only one species of an antigen binding site capable of immunoreacting with a particular epitope of an antigen. A monoclonal antibody composition thus typically displays a single binding affinity for a particular protein with which it immunoreacts. Preferably, the monoclonal antibody used in the subject method is further characterized as immunoreacting with a protein derived from humans.

Monoclonal antibodies useful in the methods of the invention are directed to an epitope of an antigen(s) on T cells, such that complex formation between the antibody and the antigen (also referred to herein as ligation) induces stimulation and T cell expansion. A monoclonal antibody to an epitope of an antigen (e.g., CD3, CD28) can be prepared by using a 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 (1975, Nature 256:495-497), and the more recent human B cell hybridoma technique (Kozbor et al. (1983) Immunol Today 4:72), EBV-hybridoma technique (Cole et al. (1985), Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96), and trioma techniques. Other methods which can effectively yield monoclonal antibodies useful in the present invention include phage display techniques (Marks et al. (1992) J Biol Chem 16007-16010).

In one embodiment, the antibody preparation applied in the subject method is a monoclonal antibody produced by a hybridoma cell line. Hybridoma fusion techniques were first introduced by Kohler and Milstein (Kohler et al. Nature (1975) 256:495-97; Brown et al. (1981) J. Immunol 127:539-46; Brown et al. (1980) J Biol Chem 255:4980-83; Yeh et al. (1976) PNAS 76:2927-31; and Yeh et al. (1982) Int. J. Cancer 29:269-75). Thus, the monoclonal antibody compositions of the present invention can be produced by the following method, which comprises the steps of:

(a) Immunizing an animal with a protein (e.g., CD28) or peptide thereof. The immunization is typically accomplished by administering the immunogen to an immunologically competent mammal in an immunologically effective amount, i.e., an amount sufficient to produce an immune response. Preferably, the mammal is a rodent such as a rabbit, rat or mouse. The mammal is then maintained for a time period sufficient for the mammal to produce cells secreting antibody molecules that immunoreact with the immunogen. Such immunoreaction is detected by screening the antibody molecules so produced for immunoreactivity with a preparation of the immunogen protein. Optionally, it may be desired to screen the antibody molecules with a preparation of the protein in the form in which it is to be detected by the antibody molecules in an assay, e.g., a membrane-associated form of the antigen (e.g., CD28). These screening methods are well known to those of skill in the art, e.g., enzyme-linked immunosorbent assay (ELISA) and/or flow cytometry.

(b) A suspension of antibody-producing cells removed from each immunized mammal secreting the desired antibody is then prepared. After a sufficient time, the mouse is sacrificed and somatic antibody-producing lymphocytes are obtained. Antibody-producing cells may be derived from the lymph nodes, spleens and peripheral blood of primed animals. Spleen cells are preferred, and can be mechanically separated into individual cells in a physiologically tolerable medium using methods well known in the art. Mouse lymphocytes give a higher percentage of stable fusions with the mouse myelomas described below. Rat, rabbit and frog somatic cells can also be used. The spleen cell chromosomes encoding desired immunoglobulins are immortalized by fusing the spleen cells with myeloma cells, generally in the presence of a fusing agent such as polyethylene glycol (PEG). Any of a number of myeloma cell lines may be used as a fusion partner according to standard techniques; for example, the P3-NS1/1-Ag4-1, P3-x63--Ag8.653 or Sp2/O-Ag14 myeloma lines. These myeloma lines are available from the American Type Culture Collection (ATCC), Rockville, Md.

The resulting cells, which include the desired hybridomas, are then grown in a selective medium, such as HAT medium, in which unfused parental myeloma or lymphocyte cells eventually die. Only the hybridoma cells survive and can be grown under limiting dilution conditions to obtain isolated clones. The supernatants of the hybridomas are screened for the presence of antibody of the desired specificity, e.g., by immunoassay techniques using the antigen that has been used for immunization. Positive clones can then be subcloned under limiting dilution conditions and the monoclonal antibody produced can be isolated. Various conventional methods exist for isolation and purification of the monoclonal antibodies so as to free them from other proteins and other contaminants. Commonly used methods for purifying monoclonal antibodies include ammonium sulfate precipitation, ion exchange chromatography, and affinity chromatography (see, e.g., Zola et al. in Monoclonal Hybridoma Antibodies: Techniques And Applications, Hurell (ed.) pp. 51-52 (CRC Press 1982)). Hybridomas produced according to these methods can be propagated in vitro or in vivo (in ascites fluid) using techniques known in the art.

Generally, the individual cell line may be propagated in vitro, for example in laboratory culture vessels, and the culture medium containing high concentrations of a single specific monoclonal antibody can be harvested by decantation, filtration or centrifugation. Alternatively, the yield of monoclonal antibody can be enhanced by injecting a sample of the hybridoma into a histocompatible animal of the type used to provide the somatic and myeloma cells for the original fusion. Tumors secreting the specific monoclonal antibody produced by the fused cell hybrid develop in the injected animal. The body fluids of the animal, such as ascites fluid or serum, provide monoclonal antibodies in high concentrations. When human hybridomas or EBV-hybridomas are used, it is necessary to avoid rejection of the xenograft injected into animals such as mice. Immunodeficient or nude mice may be used or the hybridoma may be passaged first into irradiated nude mice as a solid subcutaneous tumor, cultured in vitro and then injected intraperitoneally into pristane primed, irradiated nude mice which develop ascites tumors secreting large amounts of specific human monoclonal antibodies.

Media and animals useful for the preparation of these compositions are both well known in the art and commercially available and include synthetic culture media, inbred mice and the like. An exemplary synthetic medium is Dulbecco's minimal essential medium (DMEM; Dulbecco et al. (1959) Virol. 8:396) supplemented with 4.5 gm/l glucose, 20 mM glutamine, and 20% fetal caf serum. An exemplary inbred mouse strain is the Balb/c.

D. Combinatorial Antibodies. Monoclonal antibody compositions of the invention can also be produced by other methods well known to those skilled in the art of recombinant DNA technology. An alternative method, referred to as the "combinatorial antibody display" method, has been developed to identify and isolate antibody fragments having a particular antigen specificity, and can be utilized to produce monoclonal antibodies (for descriptions of combinatorial antibody display see e.g., Sastry et al. (1989) PNAS 86:5728; Huse et al. (1989) Science 246:1275; and Orlandi et al. (1989) PNAS 86:3833). After immunizing an animal with an appropriate immunogen (e.g., CD3, CD28) as described above, the antibody repertoire of the resulting B-cell pool is cloned. Methods are generally known for directly obtaining the DNA sequence of the variable regions of a diverse population of immunoglobulin molecules by using a mixture of oligomer primers and PCR. For instance, mixed oligonucleotide primers corresponding to the 5' leader (signal peptide) sequences and/or framework 1 (FR1) sequences, as well as primer to a conserved 3' constant region primer can be used for PCR amplification of the heavy and light chain variable regions from a number of murine antibodies (Larrick et al. (1991) Biotechniques 11:152-156). A similar strategy can also been used to amplify human heavy and light chain variable regions from human antibodies (Larrick et al. (1991) Methods: Companion to Methods in Enzymology 2:106-110).

In an illustrative embodiment, RNA is isolated from activated B cells of, for example, peripheral blood cells, bone marrow, or spleen preparations, using standard protocols (e.g., U.S. Pat. No. 4,683,202; Orlandi, et al. PNAS (1989) 86:3833-3837; Sastry et al., PNAS (1989) 86:5728-5732; and Huse et al. (1989) Science 246:1275-1281.) First-strand cDNA is synthesized using primers specific for the constant region of the heavy chain(s) and each of the .kappa. and .lamda. light chains, as well as primers for the signal sequence. Using variable region PCR primers, the variable regions of both heavy and light chains are amplified, each alone or in combinantion, and ligated into appropriate vectors for further manipulation in generating the display packages. Oligonucleotide primers useful in amplification protocols may be unique or degenerate or incorporate inosine at degenerate positions. Restriction endonuclease recognition sequences may also be incorporated into the primers to allow for the cloning of the amplified fragment into a vector in a predetermined reading frame for expression.

The V-gene library cloned from the immunization-derived antibody repertoire can be expressed by a population of display packages, preferably derived from filamentous phage, to form an antibody display library. Ideally, the display package comprises a system that allows the sampling of very large variegated antibody display libraries, rapid sorting after each affinity separation round, and easy isolation of the antibody gene from purified display packages. In addition to commercially available kits for generating phage display libraries (e.g., the Pharmacia Recombinant Phage Antibody System, catalog no. 27-9400-01; and the Stratagene SurfZAP.TM. phage display kit, catalog no. 240612), examples of methods and reagents particularly amenable for use in generating a variegated antibody display library can be found in, for example, Ladner et al. U.S. Pat. No. 5,223,409; Kang et al. International Publication No. WO 92/18619; Dower et al. International Publication No. WO 91/17271; Winter et al. International Publication WO 92/20791; Markland et al. International Publication No. WO 92/15679; Breitling et al. International Publication WO 93/01288; McCafferty et al. International Publication No. WO 92/01047; Garrard et al. International Publication No. WO 92/09690; Ladner et al. International Publication No. WO 90/02809; Fuchs et al. (1991) Bio/Technology 9:1370-1372; Hay et al. (1992) Hum Antibod Hybridomas 3:81-85; Huse et al. (1989) Science 246:1275-1281; Griffths et al. (1993) EMBO J. 12:725-734; Hawkins et al. (1992) J Mol Biol 226:889-896; Clackson et al. (1991) Nature 352:624-628; Gram et al. (1992) PNAS 89:3576-3580; Garrad et al. (1991) Bio/Technology 9:1373-1377; Hoogenboom et al. (1991) Nuc Acid Res 19:4133-4137; and Barbas et al. (1991) PNAS 88:7978-7982.

In certain embodiments, the V region domains of heavy and light chains can be expressed on the same polypeptide, joined by a flexible linker to form a single-chain Fv fragment, and the scFV gene subsequently cloned into the desired expression vector or phage genome. As generally described in McCafferty et. al., Nature (1990) 348:552-554, complete V.sub.H and V.sub.L domains of an antibody, joined by a flexible (Gly.sub.4-Ser).sub.3 linker (SEQ ID NO: 15) can be used to produce a single chain antibody which can render the display package separable based on antigen affinity. Isolated scFV antibodies immunoreactive with the antigen can subsequently be formulated into a pharmaceutical preparation for use in the subject method.

Once displayed on the surface of a display package (e.g., filamentous phage), the antibody library is screened with the protein, or peptide fragment thereof, to identify and isolate packages that express an antibody having specificity for the protein. Nucleic acid encoding the selected antibody can be recovered from the display package (e.g., from the phage genome) and subcloned into other expression vectors by standard recombinant DNA techniques.

E. Hybridomas and Methods of Preparation. Hybridomas useful in the present invention are those characterized as having the capacity to produce a monoclonal antibody which will specifically immunoreact with an antigen of interest (e.g., CD3, CD28). Methods for generating hybridomas that produce, e.g., secrete, antibody molecules having a desired immunospecificity, e.g., having the ability to immunoreact with the CD28 antigen, and/or an identifiable epitope of CD28 are well known in the art. Particularly applicable is the hybridoma technology described by Niman et al. (1983) PNAS 80:4949-4953; and by Galfre et al. (1981) Meth. Enzymol. 73:3-46.

Uses of the Methods of the Invention

The method of this invention can be used to selectively expand a population of CD28.sup.+, CD4.sup.+, CD8.sup.+, CD28RA.sup.+, or CD28RO.sup.+ T cells for use in the treatment of infectious disease, cancer and immunotherapy. As a result of the method described herein, a population of T cells which is polyclonal with respect to antigen reactivity, but essentially homogeneous with respect to either CD4.sup.+ or CD8.sup.+ can be produced. In addition, the method allows for the expansion of a population of T cells in numbers sufficient to reconstitute an individual's total CD4.sup.+ or CD8.sup.+ T cell population (the population of lymphocytes in an individual is approximately 10.sup.11). The resulting T cell population can be genetically transduced and used for immunotherapy or can be used in methods of in vitro analyses of infectious agents. For example, a population of tumor-infiltrating lymphocytes can be obtained from an individual afflicted with cancer and the T cells stimulated to proliferate to sufficient numbers. The resulting T cell population can be genetically transduced to express tumor necrosis factor (TNF) or other factor and restored to the individual.

One particular use for the CD4.sup.+ T cells expanded by the method of the invention is in the treatment of HIV infection in an individual. Prolonged infection with HIV eventually results in a marked decline in the number of CD4.sup.+ T lymphocytes. This decline, in turn, causes a profound state of immunodeficiency, rendering the patient susceptible to an array of life threatening opportunistic infections. Replenishing the number of CD4.sup.+ T cells to normal levels may be expected to restore immune function to a significant degree. Thus, the method described herein provides a means for selectively expanding CD4.sup.+ T cells to sufficient numbers to reconstitute this population in an HIV infected patient. It may also be necessary to avoid infecting the T cells during long-term stimulation or it may desirable to render the T cells permanently resistant to HIV infection. There are a number of techniques by which T cells may be rendered either resistant to HIV infection or incapable of producing virus prior to restoring the T cells to the infected individual. For example, one or more anti-retroviral agents can be cultured with CD4.sup.+ T cells prior to expansion to inhibit HIV replication or viral production (e.g., drugs that target reverse transcriptase and/or other components of the viral machinery, see e.g., Chow et al. (1993) Nature 361, 650-653).

Several methods can be used to genetically transduce T cells to produce molecules which inhibit HIV infection or replication. For example, in one embodiment, T cells can be genetically transduced to produce transdominant inhibitors, which are mutated, nonfunctional forms of normal HIV gene products. Transdominant inhibitors function to oligomerize or compete for binding with the wild type HIV proteins. Several transdominant inhibitors have been derived from HIV proteins including tat, rev, and gag. The function of tat is to enhance the transcription of viral genes by binding to the trans activation response element (tar) found in the promoter region of most HIV genes. Rev, through binding to the rev response element (RRE) found at the 5' end of unspliced HIV transcripts, facilitates the transport of unprocessed mRNA from the nucleus to the cytoplasm for packaging into virions. Gag is first synthesized as a single polypeptide and subsequently cleaved by a virus-encoded protease to yield three structural proteins, p15, p17, and p24. Transdominant inhibitors derived from these gene products have been demonstrated to inhibit infection of cells cultured with lab pet HIV isolates. One example of a transdominant inhibitor which appears to act by forming nonfunctional multimers with wild-type Rev is RevM10. RevM10 construct has blocked infection of CEM cells by HTLV-IIIB for up to 28 days (Malim et al. JEM 176:1197, Bevec et al. PNAS 89:9870). In these studies, RevM10 failed to demonstrate adverse effect on normal T cell function as judged by the criteria of growth rate and IL-2 secretion.

In another approach T cells can be transduced to produce molecules known as "molecular decoys" which are binding elements for viral proteins critical to replication or assembly, such as TAR. High level retrovirus-mediated expression of TAR in CEM SS cells has been found to effectively block the ARV-2 HIV isolate, as measured by RT assay (Sullenger et al. Cell 63;601). Importantly, it also blocked SIV (SIV mac251) infection, suggesting that inhibition of HIV infection with molecular decoys may be generally applicable to various isolates and thereby alleviate the problem of hypervariability. Further, it has been demonstrated that TAR expression has no discernible effects on cell viability (Sullenger et al. J. Virol. 65:6811). Another "molecular decoy" which T cells can be transduced to produce is a soluble CD4 tagged at the carboxy terminus with a KDEL (lysine-aspartic acid-glutamic acid-leucine; SEQ ID NO: 16) sequence, a signal for ER retention (Buonocore and Rose, PNAS 90:2695)(Nature 345:625). The sCD4-KDEL (KDEL disclosed SEQ ID NO: 16) gene expression is driven by the HIV LTR. H9 cells transduced with the sCD4-KDEL (KDEL disclosed as SEQ ID NO: 16) construct show up regulation of expression of intracellular CD4 upon HIV infection. This strategy effectively blocked production of HIV MN for up to 60 days post infection. The proposed advantage of this inhibitor is that the virus should not be able to escape its effect by mutating because CD4 binding is essential for HIV infectivity.

T cells can also be transduced to express antisense molecules and ribozyme which block viral replication or infection. Viral replication can be inhibited with a variety of antisense strategies. One particular ribozyme which cleaves HIV integrase (Sioud and Drlica, PNAS 88:7303), has been developed and may offer an approach to blocking infection as opposed to merely viral production.

Another approach to block HIV infection involves transducing T cells with HIV-regulated toxins. Two examples of this type of approach are the diphtheria toxin A gene (Harrison et al. AIDS Res. Hum. Retro. 8:39) and the herpes simplex virus type 1 thymidine kinase gene (HSV TK) (Caruso and Klatzmann, PNAS 89:182). In both cases, transcription was under the control of HIV regulatory sequences. While the diphtheria toxin is itself toxic, the HSV TK requires the addition of acyclovir to kill infected cells. For example the use of HSV TK followed by the addition of 10 .mu.m acyclovir for 17 days totally blocks HIV infection of HUT 78 cells for up to 55 days of culture.

It has been demonstrated that when CD4.sup.+ T cells from an HIV infected individual are stimulated with a primary activation signal, such as anti-CD3 antibodies, and anti-CD28 antibodies attached to a solid phase support, such as beads, the cell culture proliferates exponentially and the amount of HIV particles produced is significantly reduced as compared to conventional methods for stimulating T cells, such as with PHA and IL-2 (see Examples 16 and 21-27). Thus, when CD4.sup.+ T cells from an HIV infected individual are expanded ex vivo with a primary activation agent, such as an anti-CD3 antibody, and anti-CD28 on a solid phase surface, the presence of anti-retroviral agents may not be required in the culture to limit replication of HIV. Since anti-retroviral drugs have toxic effects on cells, no anti-retroviral agent or reduced amounts of these agents to the T cell culture will result in expansion to higher cell numbers. Thus, in a preferred embodiment of the invention, CD4.sup.+ T cells from an HIV infected individual are isolated, expanded ex vivo with a primary activation agent and anti-CD28 antibody coated beads (preferably, at a ratio of 3 beads per T cell) in the absence of or in the presence of reduced amounts of anti-retroviral agents and readministered to the individual. In an even more preferred embodiment, the primary activation agent is an anti-CD3 antibody, which can be in soluble form or attached to a solid phase support, e.g., the solid phase support on which the anti-CD28 antibody is immobilized. Moreover, it has been demonstrated (Example 18) that stimulation of a population of CD4.sup.+ T cells with anti-CD3 and anti-CD28 antibody coated beads and addition of IL-2 to the culture results in polyclonal expansion of the population of T cells in number of from about 10 log.sub.10 to 12 log.sub.10 fold the original CD4.sup.+ T cell population. Thus, ex vivo expansion of CD4.sup.+ T cells from an HIV infected individual with anti-CD3 and anti-CD28 antibody coated beads and added IL-2 results in expansion of the CD4.sup.+ T cells by about 12 log.sub.10 with significantly reduced amounts of virus being produced. The addition of low doses of anti-retroviral agents to the culture may further limit replication of HIV without exerting toxic effects on the cells.

In a further embodiment of the invention, CD4.sup.+ T cells obtained from an individual and expanded ex vivo according to the method of the invention can be cryo-preserved. Thus, it is possible to obtain CD4.sup.+ T cells from an individual, expand the cells ex vivo, readminister a portion of the expanded population of cells to the individual and cryo-preserve one or several portions of the expanded cell population. This is particularly useful if treatment of the individual requires more than one administration of CD4.sup.+ T cells. The cryo-preserved cells can also be thawed, and expanded according to the method of the invention. Thus, the method of the invention provides a renewable source of polyclonal CD4.sup.+ T cells.

The invention also provides for in vivo expansion of CD4.sup.+ T cells in an individual, particularly in an HIV infected individual. It has been shown that when CD4.sup.+ T cells infected with HIV are cultured in vitro with an agent which provides a primary activation signal, such as an anti-CD3 antibody and anti-CD28 attached to a solid phase surface, expansion of the T cell population is obtained and the amount of HIV produced is significantly reduced compared to the amount of virus produced when the cells are stimulated with PHA and IL-2 (Example 15). Moreover, is has been demonstrated (Example 18) that stimulation of a population of CD4.sup.+ T cells with anti-CD3 and anti-CD28 antibody coated beads and addition of IL-2 to the culture results in polyclonal expansion of the population of T cells in number of from about 10 log.sub.10 to 12 log.sub.10 fold the original CD4.sup.+ T cell population. Thus, in one embodiment of the invention, polyclonal expansion of the population of CD4.sup.+ T cells in an HIV infected individual is achieved by administration to the individual of anti-CD3 and anti-CD28 antibodies attached to a solid phase surface, such as biodegradable beads (Bang Laboratory). Additionally, IL-2 can be administered to the individual to further promote CD4.sup.+ T cell proliferation. This particular embodiment should be useful as a therapeutic method for increasing the number of CD4.sup.+ T cells in an individual, since the expansion of the T cells will occur with limited HIV replication.

The the invention also provides methods for restoring the proportion of Th1 versus Th2 cells in an individual having an infection. It has been shown herein (Example 23) that CD4.sup.+ T cells from HIV-infected individuals secrete preferentially Th1-type cytokines upon stimulation with immobilized anti-CD28 antibody. Accordingly, treatment of an HIV-infected individual with immobilized anti-CD28 antibody will result in a preferential increase of Th1 cells versus Th2 cells. This is particularly relevant since the ratio of Th1 versus Th2 cells declines progressively in HIV-infected patients, which may explain the susceptibility of these patients to infections by intracellular microbes.

It has been shown herein that expansion of CD4.sup.+ T cells with immobilized anti-CD28 antibody results in prevention of infection of the CD4.sup.+ T cells by HIV-1 (Examples 25-27). It is thus likely that infection of CD4.sup.+ T cells by other types of viruses will also be inhibited, or at least reduced. Infections which can be treated according to the methods of the invention include infections by viruses that infect CD4.sup.+ T cells, such as retroviruses. These include oncomaviruses or oncoviruses, such as human T-lymphotropic virus (HTLV) 1, 2, and 5; and lentiviruses, such as human immunodeficiency viruses (HIV) 1 and 2. Other types of viruses, such as DNA viruses, including Herpes viruses, e.g., Human Herpes Viruses (HHV) and Cytomegalovirus (CMV) and RNA viruses are also within the scope of the invention. Accordingly, an individual having a viral infection, such as a retroviral infection, can be treated in vivo or ex vivo by contacting its T cells with an agent which provides a costimulatory signal which inhibits viral production, such as an immobilized anti-CD28 antibody, in the presence of an agent which delivers a primary activation signal. The agent which provides a primary activation signal can be administered to the individual, or it can be an agent which is already in the individual, such as one or more antigens. The methods of the invention include those that provide treatments of individuals infected with a virus that causes a decrease in numbers of T cells and those that provide treatments of individuals infected with a virus that transforms the T cells, such as HTLV.

The invention further provides methods for vaccination of an individual against infection by viruses infecting CD4.sup.+ T cells and/or other types of cells. In fact, Examples 25-27 demonstrate that CD4.sup.+ T cells are protected from infection by HIV when cultured in the presence of immobilized anti-CD28 antibodies. Accordingly, in one embodiment of the invention, a costimulatory agent which blocks or reduces viral production, such as immobilized anti-CD28 antibody, is administered to an individual prior to a viral infection. The method can further comprise administration to the individual of an agent which provides a primary activation signal to the T cells.

Also within the scope of the invention are agents which interact with CD28 and provide to the T cell a protective effect against a viral infection. Preferred agents are those which transduce in the T cell a signal significantly similar to that transduced by immobilized anti-CD28 antibody, such as the monoclonal antibody 9.3. The invention also provides methods for isolating such agents, by, for example, incubating T cells with the agent to be tested, adding a virus to the cell culture, and measuring viral production.

The methods for stimulating and expanding a population of antigen specific T cells are useful in therapeutic situations where it is desirable to upregulate an immune response (e.g., induce a response or enhance an existing response) upon administration of the T cells to a subject. For example, the method can be used to enhance a T cell response against tumor-associated antigens. Tumor cells from a subject typically express tumor-associated antigens but may be unable to stimulate a costimulatory signal in T cells (e.g., because they lacks expression of costimulatory molecules). Thus, tumor cells can be contacted with T cells from the subject in vitro and antigen specific T cells expanded according to the method of the invention and the T cells returned to the subject. Alternatively, T cells can be stimulated and expanded as described herein to induce or enhance responsiveness to pathogenic agents, such as viruses (e.g., human immunodeficiency virus), bacteria, parasites and fungi.

The invention further provides methods to selectively expand a specific subpopulation of T cells from a mixed population of T cells. In particular, the invention provides a method to specifically enrich a population of CD28.sup.+ T cells in CD4.sup.+T cells. Indeed, stimulation of a population of CD28.sup.+ T cells with anti-CD3 and anti-CD28 antibodies or a natural ligand of CD28, such as B7-1 or B7-2 present on the surface of CHO cells results in expansion of the population of CD4.sup.+ T cells at the expense of the CD8.sup.+ T cells, which progressively die by apoptosis (see Example 15). Thus, expansion of CD28.sup.+ T cells under these conditions results in a selective enrichment in CD4.sup.+ T cells in long term cultures. A population of CD28.sup.+ T cells can also be stimulated to proliferate and become enriched in CD4.sup.+ T cells by contacting the CD28.sup.+ T cells with a solid phase surface comprising anti-CD3 and anti-CD28 antibodies or an anti-CD3 antibody and a stimulatory form of B7-2, as described in Example 19.

Another embodiment of the invention, provides a method for selectively expanding a population of either TH1 or TH2 cells or from a population of CD4.sup.+ T cells. A population of CD4.sup.+ T cells can be enriched in either TH1 or TH2 cells by stimulation of the T cells with a first agent which provides a primary activation signal and a second agent which provides a CD28 costimulatory signal i.e., an anti-CD28 antibody or a natural ligand for CD28, such as B7-1 or B7. For example, to selectively expand TH2 cells from a population of CD4.sup.+ cells, CD4.sup.+ T cells are costimulated with a natural ligand of CD28, such as B7-1 or B7-2, present on the surface of cells, such as CHO cells, to induce secretion of TH2 specific cytokines, such as IL-4 and IL-5, resulting in selective enrichment of the T cell population in TH2 cells. On the contrary, to expand TH 1 cells from a population of CD4.sup.+ T cells, CD4.sup.+ T cells are costimulated with an anti-CD28 antibody, such as the monoclonal antibody 9.3, inducing secretion of TH1-specific cytokines, including IFN-.gamma., resulting in enrichment of TH1 cells over TH2 cells (Example 14).

Compositions and Kits

This invention also provides compositions and kits comprising an agent which stimulates an accessory molecule on the surface of T cells (e.g., an anti-CD28 antibody) coupled to a solid phase surface and, optionally, including an agent which stimulates a TCR/CD3 complex-associated signal in T cells (e.g., an anti-CD3 antibody) coupled to the same solid phase surface. For example, the composition can comprise an anti-CD28 antibody and an anti-CD3 antibody coupled to the same solid phase surface (e.g. bead). Alternatively, the composition can include an agent which stimulates an accessory molecule on the surface of T cells coupled to a first solid phase surface and an agent which stimulates a TCR/CD3 complex-associated signal in T cells coupled to a second solid phase surface. For example, the composition can include an anti-CD28 antibody coupled to a first bead and an anti-CD3 antibody coupled to a second bead. Kits comprising such compositions and instructions for use are also within the scope of this invention.
 

Claim 1 of 64 Claims

1. A method for expanding a population of CD4.sup.+T cells from an HIV-infected individual to sufficient numbers for use in therapy, comprising: a) contacting the population of CD4.sup.+T cells from an HIV-infected individual ex vivo with a surface comprising: (1) a first agent which provides a primary activation signal, thereby activating the CD4.sup.+T cells, wherein the first agent is selected from the group consisting of an anti-CD3 antibody or a CD3-binding fragment thereof, an anti-CD2 antibody or a CD2-binding fragment thereof, and an antigen in a form suitable to trigger a primary activation signal in the CD4.sup.+T cell when complexed with the TCR/CD3 complex; and (2) a second agent which stimulates a CD28 antigen, thereby inducing proliferation of the activated CD4.sup.+T cells, wherein the second agent is selected from the group consisting of an anti-CD28 antibody or a CD28-binding fragment thereof, B7-1, a CD28-binding fragment of B7-1, B7-2, a CD28-binding fragment of B7-2, a B7-1Ig fusion protein that interacts with CD28, and a B7-2Ig fusion protein that interacts with CD28, wherein the first agent and second agent are attached on the same surface, thereby expanding the CD4.sup.+T cells to sufficient numbers for use in therapy.

____________________________________________
If you want to learn more about this patent, please go directly to the U.S. Patent and Trademark Office Web site to access the full patent.