LONG-TERM SURVIVAL OF SKIN ALLOGRAFTS INDUCED BY DONOR SPLENOCYTES AND ANTI-CD154 ANTIBODY IN THYMECTOMIZED MICE REQUIRES CD4(-CELLS, INTERFERON-GAMMA, AND CTLA4() T)

Treatment of C57BL/6 mice with one transfusion of BALB/c spleen cells and anti-CD154 (anti-CD40-ligand) antibody permits BALB/c islet grafts to survive indefinitely and BALB/c skin grafts to survive for similar to 50 d without further intervention. The protocol induces long-term allograft survival, but the mechanism is unknown, We now report: (a) a ddition of thymectomy to the protocol permitted skin allografts to sur vive for > 100 d, suggesting that graft rejection in euthymic mice res ults from thymic export of alloreactive T cells, (b) Clonal deletion i s not the mechanism of underlying long-term graft survival, as recipie nt thymectomized mice were immunocompetent and harbor alloreactive T c ells. (c) Induction of skin allograft acceptance initially depended on the presence of IFN-gamma, CTLA4, and CD4(+) T cells. Addition of ant i-CTLA4 or anti-IFN-gamma mAb to the protocol was associated with prom pt graft rejection, whereas anti-IL-d, mAb had no effect. The role of IFN-gamma was confirmed using knockout mice. (d) Graft survival was as sociated with the absence of IFN-gamma in the graft. (e) Long-term gra ft maintenance required the continued presence of CD4(+) T cells, The results suggest that, with modification, our short-term protocol may y ield a procedure for the induction of long-term graft survival without prolonged immunosuppression.