*Purpose: The new kidney allocation system implemented in December 2014 allowed for use of A2/A2B donors to B recipients. However there is no mandate by UNOS regarding what anti-A2 titers are acceptable. Most centers accept anti-A2 titers less than 1/8. We aimed to investigate the safety of kidney transplant in patients with anti-A2 titers equal or less than 1/16.

*Methods: Between 5/2015 and 8/2017, we performed 28 A2-incompatible kidney transplants at our institution. A2-incompatible transplantation was performed if pretransplant anti-A2 titers are equal or less than 1/16 and both T and B cell cross-match negative. All patients received anti-thymocyte globulin induction and maintenance immunosuppression with tacrolimus, mycophenolate and prednisone. Patients with donor-specific-anti HLA-antibodies (DSA) received IVIG 0.5 mg/kg X 3 doses.

*Results: Of the 28 recipients, 89% were male, 50% African-American, with a median age of 54 (32, 73) years. There were 27 deceased donor renal transplants and one living related. Median donor age was 43 (23, 65) years, KDPI 48 (24, 86) and cold ischemia time 30.8 (9.3, 44) hours. Sixteen patients had both class I and II PRA 0% and 8 of the remaining patients with PRA > 10% had pre transplant DSA (Four patients had class I, 3 class II and one patient both class I and II). Pretransplant anti-A2 titers were 1/2 in 11, 1/4 in 5, 1/8 in 4, and 1/16 in 4 and too weak to titer in 4 recipients. During a median follow-up of 27 months (12 , 41) patient survival was 100% and graft survival was 96.4%. Seven patients underwent a clinically indicated kidney biopsy. There was only one case of acute T cell mediated rejection type IIA, and one case of chronic antibody-mediated rejection which was due to non-compliance leading to graft loss. Interestingly C4d positivity was seen in 6 biopsies, of which 5 did not have any findings of antibody-mediated rejection and no microvascular inflammation (glomerulitis+peritubular capillaritis score of zero). The median serum creatinine level at last follow up was 1.3 (0.7, 3.1) mg/dl and only 2 patients had spot urine protein/creatinine more than 0.75 g/d at the last follow-up.

*Conclusions: A2-incompatible transplantation appears to be safe in patients with anti-A2 titers equal or less than 1/16 with excellent short-term kidney allograft outcomes. C4d positivity is frequent in allograft biopsies without histologic findings of acute rejection.

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