Clinical Outcomes in A2-Incompatible Kidney Transplantation: A Single-Center Experience

Background: We aimed to study the clinical outcomes and safety of performing A2-incompatible kidney transplants to blood group B recipients at our center using a cutoff of anti-A2 titers < 1/32 Methods: Retrospective review of patients receiving A2-incompatible kidney transplants at our center from May 2015 till March 2024. Patients with anti-A2 IgG and IgM titers of < 1/32 at least 2 measurements were accepted for transplantation. All patients received anti-thymocyte induction (1.5 mg/kg X 3 doses) along with triple immunosuppression with tacrolimus, mycophenolate and prednisone. Patients with pretransplant donor-specific antibodies (DSA) received intravenous immunoglobulin 500 mg/kg X 3 doses Results: Of the 81 recipients, 70% were male, 59% African American, with a median age of 56 (47-66). 77 (95%) were deceased-donor and 4 (5%) were living-donor kidney transplant recipients. Pretransplant anti-A2 IgG titers were 1/2 in 23, 1/4 in 21, 1/8 in 12, 1/ 16 in 10 and too weak to titer in 15 recipients. 17 patients had pretransplant DSA. During a median follow-up of 36.8 months (21–74) patient and graft survival were 89% and 79%, respectively. Median serum creatinine was 1.3 mg/dL (1.05-1.93) and proteinuria was 170 mg (100-575) at the last clinic visit. 24 recipients underwent 28 clinically indicated kidney biopsies. One patient with pretransplant DSA developed active antibody-mediated rejection, and 5 patients (6%) had acute T-cell–mediated rejection. Only one patient developed transplant glomerulopathy. Interestingly, peritubular capillary C4d positivity was seen in 12 biopsies which did not have any findings of acute rejection or microvascular inflammation. C4d positivity was persistent in 5 of those patients who had follow-up biopsies. 15 patients (19%) developed BK viremia and 18 (22%) CMV viremia during the follow-up period Conclusion: A2-incompatible kidney transplantation in patients with anti-A2 titers < 1/32 with anti-thymocyte induction is safe without increasing risk of rejection, despite some had pre-transplant DSA. However, isolated C4d staining is common in clinically indicated biopsies without rejection suggesting accommodation to the allograft