385

Induction of donor specific tolerance in recipients of HLA disparate living donor kidney allografts by donor stem cell infusion

Joseph Leventhal¹, Lorenzo Gallon¹, Jayesh Mehta¹, Anaadriana Zakarajia¹, Roger Herzig², Michael Abecassis¹, Suzanne Ildstad²

¹Nortwestern University, Chicago, IL; ²University of Louisville, Louisville, KY, United States

Background: Renal transplantation is the preferred therapeutic approach for end stage renal disease. However, the chronic use of nonspecific immunosuppressive agents (IS) is costly and has significant toxicities including opportunistic infection, an increased rate of malignancy, nephrotoxicity, and other end organ damage. The induction of donor-specific tolerance would address these limitations. Bone marrow chimerism induces tolerance to transplanted organs and tissues. However, the toxicity associated with conventional hematopoietic stem cell transplants (HSCT), primarily graft versus-host disease (GVHD), and the need for aggressive ablative conditioning, has limited the therapeutic application of HSCT to tolerance induction. We have identified a novel tolerogenic bone marrow cell population of CD8+/TCR- facilitating cells (FC) that enhances engraftment of bone marrow in mismatched recipients without causing GVHD. The discovery of FC is an important finding as it opens the door to employing HSCT as a viable cell-based approach for tolerance induction.

Methods: 8 HLA mismatched living donor renal transplant recipients have been entered into a tolerogenic protocol involving low intensity conditioning (fludarabine, cyclophosphamide, 200cGy TBI days -4 to -1). Patients received a living donor kidney transplant on day 0, followed by infusion of cryopreserved FC-enriched donor-derived CD34+ hematopoietic stem cells on Day +1 (0.49 - 4.48 X106 FC/kg recipient body weight). All subjects were discharged by post operative day 3 and managed as outpatients. Maintenance IS consisted of FK506 and MMF without steroids. Weaning of immunosuppression was designed to occur over a one year period.

Results: The first 8 patients are now 6,9,9,9,20,21,22,24 post-Tx. All pts demonstrated peripheral blood macrochimerism post-Tx, ranging from 6% to 100% at 1 month. Chimerism was lost in two evaluable patients at 3 and 6 months post-Tx. 7 evaluable pts demonstrated donor-specific hyporesponsiveness and are being weaned from IS, with one pt now off all IS for 10 months (22 months post-Tx)and three additional patients also weaned off of all immunosuppression. None of these pts have developed GVHD. None of the patients developed anti-donor antibody as assessed by flow crossmatch. Serious adverse events have included herpes zoster reactivation in 2 pts; no clinically significant CMV or polyoma viral infections have occurred. Renal allograft loss has occurred in one patient who developed aplastic anemia and sepsis following an atypical viral infection 2 months post-Tx, successful rescue with banked autologous HSCT. Subsequent re-transplantation with a living donor kidney was performed.

Conclusions: We conclude that low intensity conditioning in conjunction with FC enriched HSCT can safely achieve durable mixed chimerism in mismatched kidney transplant recipients, allowing for IS withdrawal.