ALLOGENEIC HEMATOPOIETIC STEM CELL TRANSPLANTATION, MIXED CHIMERISM AND TOLERANCE IN LIVING RELATED DONOR RENAL ALLOGRAFT RECIPIENTS

Abstract

P911 Aims: We designed a prospective, randomized control clinical trial to evaluate the efficacy and safety of achieving mixed chimerism associated tolerance protocol in living related donor (LRD) renal allograft recipients. Methods: Sixty six consecutive patients divided in two equal groups of 33 patients with end stage renal disease, were enrolled for transplantation after negative lymphocytotoxicity cross-matching (LCM). Both groups {treated (Tn) and control (Cn)} were well-balanced in their clinical, lab parameters and donor HLA match profile. Tn underwent thymic transplantation of donor renal tissue, 2 donor specific transfusions, low intensity conditioning and high dose hematopoietic stem cell transplantation (HSCT) before renal transplantation. Conditioning regimen included low dose target specific irradiation (to abdominal and inguinal lymph nodes, bone marrow(BM) of thoracolumbar vertebrae and part of pelvis on alternate days, 100 rads x 4), anti-T cell antibodies (15 mg/kg body weight (BW)), cyclophosphamide (10 mg/kg BW x 2 consecutive days) and cyclosporine (CsA) (3 mg/kg BW/day). Unfractionated HSCT procured from donor marrow was administered in recipient’s BM, portal and peripheral circulation within 24 hours of achieving CD 4+/ CD 8 + T- cell count < 10% of normal. This was supplemented by peripherally mobilized stem cells, with mean total dose of 20 x 10 8 cells/kg BW of recipient administered peripherally. Renal transplantation was performed after negative LCM. Donor specific cytotoxic antibodies were eliminated with intravenous immunoglobulins and plasmapheresis before renal transplantation. Mixed chimerism was evaluated before and after transplantation at monthly intervals in patients with donors of opposite gender by FISH technique. Both groups received CsA and prednisolone for immunosuppression, Cn received mycofenolate mofetil/ Azathioprine in addition. Rejection was treated with standard anti-rejection treatment. Immunosuppression was withdrawn 6 months after renal transplantation in patients with consistent positive chimerism. Clinical tolerance was defined by achieving stable allograft function for more than 100 days without immunosuppression confirmed by allograft biopsy. Results: Over a mean follow-up of 210 days, all Tn patients had stable allograft function with mean serum creatinine (SCr) of 1.20 mg/dl, no rejection/ CMV infections/ graft and patient loss. Low level donor-specific cytotoxic antibodies were observed in all of them. CsA toxicity was noted in 10 (30.3%) patients. Persistent mixed hematopoietic chimerism was noted in all 21 patients irrespective of donor-recipient HLA matching (mean 0.5 % before and 1 ± 0.3 % after transplantation). All 4 patients on drug withdrawal have developed donor-specific tolerance with a mean follow up of 129.8 days. Other Tn patients are in the process of being weaned off immunosuppression. Mean SCr of Cn was 1.45 mg/dl over a mean follow up of 216 days. Acute rejection was observed in 17 (51.5 %) patients, no CMV infection / patient loss was noted and 1(3.03%) graft was lost in Cn. No graft Vs host disease was observed in Tn. Conclusions: We have achieved mixed hematopoietic chimerism associated tolerance with high dose HSCT, intrathmic donor renal tissue transplantation and minimum conditioning without any adverse effects.