Requirements for the promotion of allogeneic engraftment by anti-CD154 (anti-CD40L) monoclonal antibody under nonmyeloablative conditions

The promotion of alloengraftment in the absence of global immune suppressio n and multiorgan toxicity is a major goal of transplantation. It is demonst rated that the infusion of a single modest bone marrow dosage in 200 cGy-ir radiated recipients treated with anti-CD154 (anti-CD40L) monoclonal antibod y (mAb) resulted in chimerism levels of 48%, Reducing irradiation to 100 or 50 cGy permitted 24% and 10% chimerism, respectively. In contrast, pan-T-c ell depletion resulted in only transient engraftment in 200 cGy-irradiated recipients. Host CD4(+) cells were essential for alloengraftment as depleti on of CD4(+) cells abrogated engraftment in anti-CD154-treated recipients. Strikingly, the depletion of CD8(+) cells did not further enhance engraftme nt in anti-CD154 mAb-treated recipients in a model in which rejection is me diated by both CD4(+) and CD8+ T cells. However, anti-CD154 mAb did facilit ate engraftment in a model in which only CD8(+) T cells mediate rejection. Furthermore, CD154 deletional mice irradiated with 200 cGy irradiation were not tolerant of grafts, suggesting that engraftment promotion by anti-CD15 4 mAb may not simply be the result of CD154:CD40 blockade. Together, these data suggest that a CD4+ regulatory T cell may be induced by anti-CD154 mAb , In contrast to anti-CD154 mAb, anti-87 mAb did not promote donor engraftm ent. Additionally, the administration of either anti-CD28 mAb or anti-CD152 (anti-CTLA-4) mAb or the use of CD28 deletional recipients abrogated engra ftment in anti-CD154 mAb-treated mice, suggesting that balanced CD28/CD152: B7 interactions are required for the engraftment-promoting capacity of anti -CD154 mAb, These data have important ramifications for the design of clini cal nonmyeloablative regimens based on anti-CD154 mAb administration. (C) 2 001 by The American Society of Hematology.