Defining the requirements for peptide recognition in gene therapy-induced T cell tolerance

Expression of a retrovirally transduced MHC class I Ag, H-2K(b) (K-b), in bone marrow-derived cells leads to specific prolongation of K-b disparate skin grafts, To examine the extent to which peptides derived from K-b contribute to the induction of tolerance, retroviruses carrying mutant Iib genes designed to enter separate pathways of Ag presentation were constructed Thymectomized and CD8 T cell-depleted mice that had been irradiated and reconstituted with bone marrow cells expressing a secreted form of K-b shelved prolongation of K-b disparate skin graft survival. Skin graft prolongation was not observed when similar experiments were performed using mice that were not CD8 T cell depicted. This suggests that hyporesponsiveness can he induced in CD4T cells, but not CD8 T cells by Ags presented via the exogenous pathway of Ag processing Modest prolongation of skin allografts was observed in mice reconstituted with bone marrow cells transduced with retroviruses carrying a gene encoding a mutant Kb molecule expressed only in the cytoplasm. Prolongation was also observed in similar experiments in mice that were thymectomized and CD4 T cell depleted following complete reconstitution, but not in mice that were reconstituted and then thymectomized and CD8 T cell depleted. Thus, hyporesponsiveness can he induced in a subset of CD8 T cells by recognition of peptides derived from K-b through both the direct and indirect pathways of Ag recognition, while CD4 T cell hyporesponsiveness to MHC class I disparate grafts occurs only through the indirect pathway of Ag recognition.