*Purpose: Initial experience under kidney allocation system (KAS) implemented in December 2014 showed equivalent outcomes for A2 to B kidney transplantation compared with ABO compatible kidney transplants. Despite the advantages, A2 to B kidney transplantation has been underused and significant knowledge gaps are noted in areas of rejections, infection rate, anti-A titer thresholds post-transplant. The purpose of our study is: 1) To assess AMR rates in A2 to B DDKT and determine association with anti-A IgG titers. 2) To assess graft function, rejection and infection rates (bacterial, viral and fungal).

*Methods: We conducted a retrospective chart review of 55 A2 to B DDKT performed at the University of Michigan from January 2015 to September 2020. All patients received Thymoglobulin for induction and were maintained on triple immunosuppression. All patients underwent monitoring of anti-A2 titers and surveillance biopsy at 3-, 6- and 12- months after transplant. Other outcomes included graft function, rejection and infection rates in our cohort at last follow-up.

*Results: Our cohort consisted of 55 recipients with mean age of 54(±13) years, 67% males and 29% African Americans. The median follow-up time was 2.5 [0.5-5] years. Ten (15%) developed acute rejection at 3 [1-6] months after transplant. One patient developed hyper-acute rejection due to ABO incompatibility, five developed T cell mediated rejection, and four had antibody mediated rejection. Anti-A titers remained undetectable or less < 1:4 in 54 (98 %) in post-transplant period with no increase in titers at 3-6 month follow up. The patient with hyper-acute rejection in one out of four patients with AMR anti-A titers increased to 1:128, in rest three anti-A titers remained same (1:2) and rejection was due to donor specific antibodies against HLA. Overall, 20% (11/55) mortality was noted, unrelated to graft dysfunction at median follow-up of 1.8 [0.08-4] years. Post-transplant infections (bacterial, viral and fungal) accounted for 41% cases (23/55). Bacterial infections were reported in 16 % (9/55), viral in 25% (14/55) and fungal in 3.6 % (2/55) respectively. BK viremia noted in 20% (11/55) with BK nephropathy in six. The mean (SD) glomerular filtration rate (GFR) mL/min, creatinine mg/dL and urine protein creatinine ratio (UPCR) at three months, one year and at last follow up post-transplant was 49 (14.69), 1.4(0.47), 0.32 (0.55); 54 (14.49), 1.3 (0.43), 0.17( 0.20) and 52.8 (14.69), 1.4(0.59), 0.22 (0.27) respectively.

*Conclusions: Our study showed no overall increase in AMR due to ABOi in A2 to B DDKT. The rise in anti-A titer was noted in one AMR and rejections were associated with increase in donor specific anti-HLA antibodies. Our study is the first study to assess AMR along with anti-A titers in A2 to B DDKT. More such studies are needed to assess anti-A trajectory with AMR. We also noted high infection and BK viremia rates, attributed to use of Thymoglobulin induction therapy. While A2B transplants have good graft outcomes, infectious complications are more frequent.

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