Immune response enhancement by in vivo administration of B7.2Ig, a soluble costimulatory protein.

The identification of both class I- and class II-restricted tumor-associated peptides recognized by T cells has led to the test of these peptides as immunogens in experimental immunotherapy for cancer patients. However, optimal T cell activation requires signaling both through the T cell receptor for antigen and through costimulatory pathways. B7.1 and B7.2 are powerful costimulatory molecules expressed on the surface of antigen-presenting cells. Using a mouse model, we have sought to optimize costimulatory signals during antipeptide responses by administering a soluble form of B7.2 at the time of peptide immunization. Administration of B7. 2Ig fusion protein significantly enhanced T helper cell and CTL responses. These findings suggest that soluble forms of human B7.2 protein may provide a straightforward and practical method of supplying optimal costimulation during clinical immunotherapy.