Allochimeric therapy induces unique regulatory T cells that mitigate chronic rejection

Induction of tolerance to an allogeneic graft without the need for nonspecific immunosuppression is a major goal of transplantation therapy. We have shown that treatment with molecularly engineered, allochimeric [alpha(1h)(1/u)]-RT1.Aa class I MHC antigens bearing donor-type Wistar-Furth (WF, RT1.A(u)) or Lewis (LEW, RT1A(1)) amino acid substitutions for host-type ACI (RTI.A(a)) sequences in the alpha(1)-helical region induces donor-specific tolerance to cardiac allografts in rat recipients. The mechanisms involved in the establishment and maintenance of specific allograft tolerance are still not fully understood. It is now clear that acquisition of transplantation tolerance is an active, highly regulated, multistep process. According to the pool size model of allograft tolerance, the allograft outcome, rejection, or tolerance often depend on the balance between cytopathic and regulatory T cells (T-regs). This study examined mechanisms of chronic rejection (CR) development on a model of cardiac transplant tolerance after adoptive transfer of T-regs followed by allochimeric therapy. Generation of T-regs was demonstrated in vitro by MLR coculture and confirmed by adoptive transfer of T cells from primary recipients to secondary hosts. To confirm the true nature of regulatory cells, we performed a second transfer into tertiary recipients. Unlike T-regs from tolerant hosts, T cells from naive rats did not prolong graft survival. Histological evaluation of T-regs-transfected groups showed absence of visible CR. In contrast, T-regs generated in recipients after high-dose cyclosporine treatment failed to inhibit CR in transferred singeneic recipients. Allochimeric therapy triggers generation of unique regulatory lymphocytes that mitigate development of chronic rejection through regulation of anti-inflammatory mechanisms and down-regulation of alloantibody response.