Background: The costimulatory inhibitor belatacept (Bela) has been shown to be an effective alternative in several clinical situations, including calcineurin toxicity, de novo alloantibody formation and thrombotic microscopic angiopathy. To further explore the usefulness of Bela under various clinical scenarios, we performed a retrospective analysis of a prospective database of all recipients who were converted to a belatacept maintenance immunosuppression regimen after kidney transplantation.

Methods: This single-center study reviewed the electronic records of all patients who received a KT between 2016 and 2020. A total of 57 patients were converted to Bela. Of these recipients, 25 (43.8%) converted within the first 6 months, and 32 (56.2%) converted after 6 months. The indications for conversion were: calcineurin inhibitor (CNI) toxicity (26.3%), thrombotic microangiopathy (8.8%), de novo DSA (36.8%), chronic antibody rejection (AMR) with or without significant fibrosis (IFTA) (28.1%).

Results: Early conversion significantly improved GFR at 3, 6- and 12-months post-conversion. However, late conversion does not affect GFR. Thirty-four (59.63%) patients were converted Bela, mycophenolate and steroids, and 23 (40.4%) converted to Bela, low dose CNI and steroids. Only 6 patients (10.5%) developed rejection after conversion, 5 (83.4%) in early conversion group. Five patients (83.4%) had T cell-mediated cellular rejection, and one (16.6%) had acute antibody-mediated rejection. The rejection rate was 14.7% in the group on belatacept without CNI compared to 4.3% on belatacept with low-dose CNI (p<0.001). All patients with chronic AMR±IFTA were in the late conversion group (59.2%), leading to stabilization in their GFR (32 vs 30 mL/min) at 1-year post-conversion. Out of 21 patients who converted to belatacept due to de-novoDSA, 9 (42.9%) patients had complete or partial resolution of DSA. Interestingly, in the early conversion group, 80% responded vs (31.2%) in the late conversion group (P<0.001).

Conclusions: This study showed that conversion to belatacept was effective, especially when performed early after kidney transplantation. Late conversion to belatacept was beneficial for a subgroup of patients with chronic changes.