Regulatory cells potentiate the efficacy of IL-4 gene transfer by up-regulating Th2-dependent expression of protective molecules in the infectious tolerance pathway in transplant recipients

We have previously shown that the tolerant state in allograft recipients ca n be maintained and perpetuated by an "infectious" T cell-dependent regulat ory mechanism. Hence, 1) treatment of LEW rats with RIB-5/2, a CD4 nondeple ting mAb, produces indefinite survival of LBNF1 cardiac allografts; 2) dono r-specific tolerance can be then transferred by spleen cells into new cohor ts of test allograft recipients; and 3) putative regulatory CD4(+) Th2-like cells are instrumental in this tolerance model. We now report on studies a imed at exposing mechanisms underlying the infectious tolerance pathway, wi th emphasis on the interactions between intragraft adenovirus-IL-4 gene tra nsfer and systemic infusion of regulatory cells from tolerant hosts. Unlike individual treatment regimens, adjunctive therapy with adenovirus-IL-4 and suboptimal doses of regulatory spleen cells was strongly synergistic and e xtended donor-type test cardiac allograft survival to about 2 mo, RT-PCR-ba sed expression of intragraft mRNA coding for IL-2 and IFN-gamma remained de pressed, whereas that of IL-4 and IL-10 reciprocally increased selectively in the combined treatment group, data supported by ELISA studies. In parall el, only adjunctive treatment triggered intragraft induction of molecules w ith antioxidant (HO-1) and anti-apoptotic (Bcl-x(L)/Bag-1) but not with pro -apoptotic (CPP-32) functions, both in the early and late posttransplant ph ases. Hence, systemic infusion of regulatory cells potentiates the effects of local adenovirus-IL-4 gene transfer in transplant recipients. Th2-driven up-regulation of protective molecule programs at the graft site, such as o f anti-oxidant HO-1 and/or anti-apoptotic Bcl-x(L) and Bag-1, may contribut e, at least in part, to the maintenance of the infectious tolerance pathway in transplant recipients.