Novel Strategy for Tolerance Induction in Living Donor Renal Transplantation

Abstract

Introduction: Transplantation using conventional triple immunosuppression (IS) practiced worldwide has disadvantages of graft/patient loss due to drug toxicity/infections/malignancies apart from financial burden. Tolerance induction and maintenance is the goal of present-day research in transplantation to overcome these problems. We have been using stem cells (SC) to achieve transplantation with minimum IS. In furtherance of our objective, we designed a prospective trial to study the functional integration of clonal deletion, generation of peripheral T-regulatory cells (CD4+/25 High/127+) (p-Tregs) and SC transplantation (SCT) for tolerance induction (transplantation with no conventional immunosuppression) and its maintenance in live-donor renal transplantation (LDRT). Material and methods: First batch of 292 Tolerance Induction Protocol (TIP) patients (252 males, 40 females) with mean post-transplant period, 5.8 years, mean age 31.4 years and mean HLA match, 2.53 were recruited in the trial. At this point IS has been withdrawn in the first 50 patients (44 males, 6 females) with mean age 31.4 years and HLA match, 2.84 and mean follow-up, 5.5 years. All these patients underwent LDRT using pretransplant SCT between September'98 to December,'08 and had stable graft function for ≥ 6 months. Other inclusion criteria were serum creatinine (SCr) ≤ 2.5 mg/dL and absence of chronic rejections. Unwilling patients were excluded from the trial. TIP consisted of stimulation with hematopoietic SC ± adipose tissue derived mesenchymal stem cells ± donor specific transfusions, and deletion with total lymphoid irradiation (TLI)/Bortezomib along with Cyclophosphamide, rabbit-antithymocyte globulin (r-ATG) and Rituximab. Maintenance IS consisted of calcineurin inhibitor (CNI) [Cyclosporin (3 mg/kgBW/day)/Tacrolimus (0.02 mg/kgBW/day)] and/or MMF (360 mg BD)/Azathioprine (50-100 mg/day) and Prednisone (7.5 ± 2.5 mg/day). Functional integrity of TIP was tested by mixed lymphocyte culture (MLR), p-Tregs and antibodies (luminex single antigen assay). IS withdrawal was started with CNI followed by anti-proliferative agents. Rejections were planned to be treated by anti-rejection therapy. Protocol biopsies were planned after 100 days of IS withdrawal with patient consent. TIP and present trial were approved by Institutional Review Board. Results: IS was successfully withdrawn in all 50 patients without any episode of rejection. Mean follow-up since IS withdrawal is 1.86 years. They are on no IS (20%)/Prednisone, 5-10 mg/day (80%) and have negative MLR. Donor-specific antibodies were absent in 30 patients tested so far. Results of others are awaited. Mean p-Tregs was 3.77% and SCr, 1.42 mg/dL at the time of IS withdrawal. After IS withdrawal SCr has decreased to 1.32 mg/dL (p < 0.001) and remained at that level. Protocol biopsies were performed in 10 patients who gave their consent and all were unremarkable. Conclusion: SCT is the principal theme of tolerance induction in LDRT, and clonal deletion and p-Tregs generation is emerging as an effective adjuvant strategy towards realization of this goal.