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 can be maintained and perpetuated by an 'infectious' T cell-dependent regulatory mechanism. Hence, 1) treatment of LEW rats with RIB-5/2, a CD4 nondepleting mAb, produces indefinite survival of LBNF₁ cardiac allografts; 2) donor-specific tolerance can be then transferred by spleen cells into new cohorts of test allograft recipients; and 3) putative regulatory CD4⁺ Th2- like cells are instrumental in this tolerance model. We now report on studies aimed at exposing mechanisms underlying the infectious tolerance pathway, with emphasis on the interactions between intragraft adenovirus-IL-4 gene transfer 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 extended donor-type test cardiac allograft survival to about 2 mo. RT-PCR- based expression of intragraft mRNA coding for IL-2 and IFN-γ remained depressed, whereas that of IL-4 and IL-10 reciprocally increased selectively in the combined treatment group, data supported by ELISA studies. In parallel, only adjunctive treatment triggered intragraft induction of molecules with 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 phases. 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 of anti-oxidant HO-1 and/or anti-apoptotic Bcl-x(L) and Bag-1, may contribute, at least in part, to the maintenance of the infectious tolerance pathway in transplant recipients.