455. Drug Resistance Gene Therapy to Induce Donor-Specific Tolerance after Nonmyeloablative Allogeneic Stem Cell Transplantation in Dogs

We have previously shown successful engraftment of gene-modified, chemoprotected allogeneic stem cells after conditioning with a myeloablative dose of total body irradiation. In this setting we have also been able to demonstrate the modulation of mixed chimerism, i.e. increase of donor-derived cells after administration of chemotherapy. In the present study we asked whether allogeneic chemoprotected stem cells could be used to induce donor-specific tolerance after a nonmyeloablative conditioning regimen or without conditioning at all. In addition we were interested whether tolerance could be induced with a T-cell depleted graft.