Enhancing immune responses with B7-1 or B7-2 in the absence of a crosslinking agent

Soluble Costimulatory Molecules Enhance CTL Responses

[0116]Optimal T cell activation requires both signaling through the T cell receptor and co-stimulation. B7-1 and B7-2 are two potent co-stimulatory molecules on the surface of APCs. The effects of a soluble form of B7-2 on in vivo T cell responses have been examined. The soluble molecule is a chimeric protein containing the extra-cellular domain of B7-2 fused to the Fc region of mouse IgG2a. Administration of B7-2Ig fusion protein at the time of immunization with class II restricted peptides significantly enhanced antigen-specific T cell proliferation and cytokine responses. B7-2Ig administration also enhanced the CTL response to immunization with a class I-restricted peptide. Enhancement of the CTL response by B7-2Ig was significantly increased in the presence of a T helper cell response to class II-restricted peptides. These findings demonstrate the immune stimulatory activity of a soluble protein form of costimulatory molecules, e

Materials and Methods Used in Example 2

[0150]The expression plasmids for the murine B7-1-IgGIgG and B7-2-IgG2a fusion proteins were constructed by joining the DNA encoding the signal and extracellular domains of murine B7-1 or B7-2 to the DNA encoding the hinge-CH2—CH3 domains derived from a murine IgG2a antibody. The cysteine residues within the antibody hinge region remained conserved such that the mB7-1-IgGIgG2a or mB7-2-IgG2a produced is dimeric and bivalent. Fusion proteins were generated in which the IgG2a region is mutated in order to prevent binding by high affinity Fc receptors and complement activation (designated B7-IgG2mut). The following amino acid residues in the CH2 domain were replaced by alanine: leucine at position #235, glutamic acid at #318, lysine at #320, and lysine at #322. For production of B7-IgG protein, the plasmids were expressed in CHO cell lines and the proteins were isolated.

[0151]P815 is a mastocytoma derived tumor cell line that grows as a solid tumor a