The goal of the research program is to develop immune tolerance to combined HLA haplotype matched living related kidney and hematopoietic cell transplants in order to remove the requirement for the lifelong use of maintenance immunosuppressive drugs and to improve long term graft survival. The program builds on the success of inducing tolerance in patients with combined HLA matched living related kidney and hematopoietic cell transplants during the previous grant period using a posttransplant conditioning regimen of total lymphoid irradiation (TLI) and rabbit anti-thymocyte globulin (ATG). The regimen was shown to be safe and effective in achieving persistent mixed chimerism without graft versus host disease (GVHD). This allowed for immunosuppressive drug withdrawal without kidney allograft rejection episodes in chimeric patients. In addition, patients given HLA haplotype matched hematopoietic cell transplants for the treatment of leukemia and lymphoma using the TLI/ATG conditioning regimen developed persistent engraftment without acute GVHD. The results of these clinical studies performed during the previous grant period provide the basis for the proposed new trial for 25 HLA haplotype matched patients. Patients that achieve stable chimerism without GVHD or evidence of rejection will be withdrawn from immunosuppressive drugs at 6 months posttransplant. Patients will be monitored for evidence of the establishment of immune tolerance by testing specific immune unresponsiveness to donor alloantigens in vitro and by performing serial gene microarray testing of peripheral blood mononuclear cells to look for the posttransplant acquisition of a previously described tolerant gene expression pattern. Patients will also be monitored for immune reconstitution by studying the recovery of T cell subsets; T cell excision circles (TRECs), in vitro immune responses to new and recall microbial antigens, incidence of infections, and responses to vaccination. Outcome parameters will be compared at that of an equal number of HLA haplotype matched transplant patients given conventional therapy. The research project will interact with all other Projects and with Cores.