Use of the methylxanthine derivative A802715 in transplantation immunology .1. Strong in vitro inhibitory effects on CD28-costimulated T cell activities

Background. Recently, methylxanthines such as pentoxifylline (PTX) were shown to be immunosuppressive in vitro. Unfortunately, when used in transplant patients, PTX was poorly active as an immunosuppressant, Here we report that the new methylxanthine derivative A802715 not only is more active than PTX, it also suppresses the cyclosporine (CsA)-resistant ''signal two''-dependent pathway of T cell proliferation, making it an interesting drug to associate with CsA. Methods. ''Signal one''- and ''signal two''-dependent T cell activation was investigated with purified human T cells stimulated with immobilized anti-CD3 or anti-CD28 monoclonal antibody (mAb) plus phorbol myristate acetate (PMA) or with a 3T6 mouse fibroblast cell line presenting anti-CD3 mAb on transfected human Fc gamma receptors II (Fc gamma RII) in the presence or absence of transfected B7-1 (CD80) molecules. Results. A802715 was more immunosuppressive in the mixed lymphocyte reaction (MLR) than PTX, A802715 dose-dependently suppressed polyclonal signal one-dependent T cell activation induced by anti-CD3 mAb/PMA. In addition, A802715 also suppressed signal two-dependent T cell proliferation induced by anti-CD28 mAb/PMA. The expression of the interleukin-a receptor on T cells stimulated by anti-CD3 mAb presented on 3T6/Fc gamma RII cells was equally well suppressed by A802715 and PTX, In contrast, interleukin-a receptor or CD40L (gp39) expression by T cells after stimulation with the same anti-CDS mAb- 3T6/Fc gamma RII cells, but coexpressing transfected B7-1, was only suppressed by A802715. The anticipated synergism between A802715 and CsA was confirmed in MLR assays, Moreover, generation of cytotoxic T lymphocytes during MLR with Epstein-Barr virus-transformed B cells, which strongly express B7-1 and B7-2, was also inhibited by A802715. Conclusions. These in vitro data indicate that the A802715 (1) is a stronger immunosuppressant for T cells than PTX, (2) suppresses T cell activation pathways that are resistant to PTX or CsA, and (3) acts synergistically with CsA.