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Novel polypeptides involved in immune response

This application is a divisional of Ser. No. 09/728,421, filed Nov. 28, 2000, currently pending, which is a continuation of international application Serial No. PCT/US00/01871 (Ser. No. 09/890,729), filed Jan. 27, 2000, currently pending, which is a continuation-in-part of Ser. No. 09/264,527, filed Mar. 8, 1999, now abandoned, which is a continuation of Ser. No. 09/244,448, filed Feb. 3, 1999, now abandoned, which are hereby incorporated by reference.

The present invention relates to polypeptides that are involved in T-lymphocyte activation. Specifically, the invention relates to T-lymphocyte costimulatory polypeptides, the nucleic acids encoding the polypeptides, expression vectors and host cells for production of the polypeptides, and compositions and methods for the treatment of diseases related to immunosuppression and immune activation.

For the generation of a proper T-lymphocyte (T-cell) immune response, two signals must be provided to the T-cell by antigen presenting cells (APC). First, antigen must be presented to the T-cell receptor (TCR) via a major histocompatibility complex (MHC), in an event that determines specificity. Second, an antigen-independent, costimulatory signal must be delivered by engagement of members of the B7 family on the APC with the CD28 protein on T-cells. A productive immune response leads to proliferation, differentiation, clonal expansion, and effect or function. In the absence of the second, costimulatory signal, T-cells undergo a state of long-lasting antigen-specific unresponsiveness, termed anergy.

T-cells initiate the immune response, mediate antigen-specific effector functions, and regulate the activity of other leukocytes by secreting cytokines. The T-cell receptor (TCR) distinguishes the T-cell from other lymphocytes and can bind antigen only when it is presented by the APC within the context of a MHC. The functional activity of a particular T-cell can be correlated with the expression of membrane antigens, such as CD4 and CD8. For instance, CD4+ T-cells generally function as T helper cells (TH) and are MHC class II restricted, whereas CD8+ cells generally function as cytotoxic T-cells (TC) and are MHC class I restricted.

Potent T-cell costimulatory polypeptides which has been previously identified include polypeptides termed B7.1 (Freeman et al. J. Immunology 143, 2714-2722 (1989), Freeman et al. Jour. Expt. Med. 174, 625-31 (1991)) and B7.2 (Freeman et al. Science 262, 909-911 (1993), and Freeman et al. Jour. Expt. Med. 178, 2185-2192 (1993)), (or CD80 and CD86, respectively). These polypeptides are either inducibly or constitutively expressed on various APCs and are membrane-bound ligands for CD28 and CTLA-4, respectively, on T-cells. CD28 (Aruffo and Seed Proc. Natl. Acad. Sci. 84, 8573-8577 (1987) and Gross et al. J. Immun. 144, 3201-3210 (1990)) is expressed on resting T-cells and mediates a positive costimulatory signal. CTLA-4 (Brunet et al. Nature 328, 267-270 (1987) and Dariavach et al. Eur. Jour. Immun. 18, 1901-1905 (1988)) expression is induced upon T-cell activation and negatively regulates the CD28 signal, due to its higher binding affinity for B7.1 and B7.2. Mice without the CTLA-4 gene exhibit dramatically high levels of T-cells, since the switch off mechanism for the proliferation signal is impaired in the absence of CTLA-4. This phenotype clearly demonstrates the major inhibitory effect that the CTLA-4 costimulatory protein has on T-cell proliferation. Mice lacking CD28 or B7.1 or B7.2 have a less severe phenotype, indicating that alternate pathways for T-cell costimulation may exist.

There has been considerable interest in the CD28/CTLA-4 pathway as means for regulating T-cell activation and proliferation. A chimeric protein containing the extracellular portion of CTLA-4 fused to human Fc has strong immunosuppressive effects and has been studied in a variety of clinical settings. Antibodies to B7.1 and B7.2 proteins have also been evaluated for similar indications in the area of immunosuppression. Anti-CTLA-4 antibodies have shown utility in promoting T-cell activation. In addition, B7.1 and B7.2 gene therapy has shown great promise in the area of cancer immunotherapy.

Thus far, CD28, CTLA-4, B7.1 and B7.2 are involved in a single T-cell costimulatory pathway. Given the capability of modulating an immune response by regulating T-cell costimulation, it would be desirable to identify other members of the same or a separate T-cell costimulatory pathway which may have advantageous properties in regulating host T-cell function and immune response.

Accordingly, it is an object of the invention to provide novel polypeptides for stimulation of T-cell activity and/or proliferation. It is a further object of the invention to use the novel polypeptides for the prevention and treatment of T-cell mediated immune disorders.

Surprisingly, two novel polypeptides of a T-cell costimulatory pathway have been identified. The polypeptides represent a ligand-receptor pair in a unique costimulatory pathway which appears to be distinct from the pathway consisting of previously described proteins CD28, CTLA-4, B7.1, and B7.2. The polypeptides are referred to as CD28 related protein-1, or CRP1, and B7 related protein-1, or B7RP1.

The invention provides for nucleic acid molecules encoding CRP1 and B7RP1 polypeptides and related polypeptides. An isolated nucleic acid molecule of the invention comprises a nucleotide sequence selected from the group consisting of:

a) the nucleotide sequence as set forth in FIG. 1A (SEQ ID NO:1);

b) the nucleotide sequence encoding the polypeptide from residues 1-200 or from residues 21-200 as set forth in FIG. 1A (SEQ ID NO:1);

c) a nucleotide sequence encoding a polypeptide that is at least about 70 percent identical to the polypeptide as set forth in FIG. 1A (SEQ ID NO: 1);

d) a naturally occurring allelic variant or alternate splice variant of any of (a), (b) or (c);

e) a nucleotide sequence complementary to any of (a), (b) or (c);

f) a nucleotide sequence of (b), (c) or (d) encoding a polypeptide fragment of at least about 25, 50, 75, 100, or greater than 100 amino acid residues;

g) a nucleotide sequence of (a), (b) or (c comprising a fragment of at least about 10, 15, 20, 25, 50, 75, 100, or greater than 100 nucleotides; and

h) a nucleotide sequence which hybridizes under stringent conditions to any of (a)-(g).