We have achieved successful induction of long-term immunosuppression (IS) free allograft survival in HLA mismatched renal allograft recipients using cyclophosphamide (CP) based conditioning regimen (NKD03, ITN036) and combined donor bone marrow transplantation. Transient mixed chimera for up to 3 weeks was induced in all recipients. IS was successfully discontinued in 7/10 recipients for more than 5 years. Four of them remain off IS and continue doing well with normal kidney function after more than 8 to 14 years. Three recipients resumed IS after 5, 7 and 8 years due to either recurrence of the original kidney disease or development of DSA and chronic rejection (Table 1). However, wider clinical application of this protocol was hampered by acute kidney injury (AKI), which was observed when host hematopoietic cells started to recover (day 10-15). Biopsies taken during AKI showed hemorrhage and endothelial, pericapillary and tubular injury without cellular infiltrates (Fig. 1). Since AKI had not been observed in nonhuman primates which received low dose TBI–based regimen, a pilot study, in which cyclophosphamide was replaced with low-dose TBI, was conducted. Both recipients who received the TBI/anti-CD2 mAb regimen did well without development of AKI (Fig.1). Immunosuppression was discontinued in the first recipient at one year after transplantation. At 4 years after transplantation, the recipient remains well with normal kidney function without ongoing IS. The second subject failed to develop chimerism and IS was not discontinued. Since the anti-CD2 mAb, which all of these previous subjects received, is not currently available, we most recently evaluated another pilot study, the low dose TBI/belatacept/ATG regimen, in which anti-CD2 mAb was replaced with ATG and belatacept. The recipient tolerated the treatment well without AKI and developed transient mixed chimerism. Because of IgA recurrence observed in the protocol biopsy, his IS has been tapered slowly. At 2 years, he is doing well with MMF only to control IgA recurrence. Conclusion: Nonmyeloablative conditioning with low dose TBI in  place of CP induced chimerism and long-term IS free kidney survival without AKI.