Monoclonal antibody to the HLA class I alpha 3 domain inhibits T cell activation and prolongs cardiac allograft survival in HLA-transgenic mice

Antibodies recognizing MHC class I molecules expressed on the surface of T cells have been shown to inhibit T cell responses in vitro. These findings suggested that therapy with such an antibody may prevent rejection and promote graft acceptance, We therefore tested the effect of an anti-HLA class 1 alpha 3 domain antibody (TPZ5.99) in vivo using transgenic C57BL 6 mice expressing HLA-B2705. Flow cytometric analysis confirmed the binding of TP25.99 to normal human peripheral blood lymphocytes and to mouse spleen cells. bone marrow cells and thymocytes isolated from hemizygous (+/-) transgenic littermates but not from homozygous (-/-) littermates. TP25.99 inhibited OKT-3-induced, but not PMA+ionomycin-induced. proliferation of human peripheral blood lymphocyte as well as anti-CD3 or Con A-induced proliferation of HLA+ mouse T cells. Both intact monoclonal antibody TP25.99) and TP25.99 Fab inhibited T cell proliferation. Red used proliferation was associated with suppressed product ion of interleukin 2 as measured by ELISA. The efficacy of TP25.99 Fab in vivo was evaluated in a heart allograft model. Antibody therapy of (H-2(b). B2705(+)) transgenic recipients of allogeneic Balb/c (H-2(d)) heart grafts prolonged graft survival significantly (MST = 19.8 +/- 6.4, p = 0.003) compared to treated (H-2(b), B2705(=)) (MST = 9.17 +/- 2.2) or untreated (H-2(b), B2705(+)) (MST = 10.0 +/- 2.8) transgenic recipients. This demonstrates that immunomodulation through anti-HLA class I antibody therapy can lead to prolongation of graft survival.