Factors Associated With Reduced Anti-SARS-CoV-2 Antibody Responses After mRNA Vaccination in Kidney Transplant Recipients on Belatacept

Belatacept is a costimulation blocker used for maintenance immunosuppression in kidney transplant recipients (KTRs) as an alternative to calci-neurin inhibitors.1 Studies evaluating SARS-CoV-2 vaccine responses in KTRs have shown reduced anti-body responses in KTRs on belatacept.2-4 Nevertheless, many of these studies included only a small number of patients on belatacept,5 and had low rates of serocon-version, limiting the ability to evaluate factors associ-ated with the development of antibody responses.3,4 As a result, factors associated with lower odds of devel-oping antibody responses in KTRs on belatacept are not known. To address this gap, we conducted a retrospective multicenter cohort study of all KTRs on belatacept who received 3 homologous mRNA vaccine doses at Massa-chusetts General Hospital and Brigham and Women's Hospital. Per the institutions' policies, all KTRs on belatacept had anti-SARS-CoV-2 receptor-binding domain (RBD) antibodies measured by the Roche Elecsys immunoassay ($0.80 U/ml defined as a positive result). KTRs who were not on belatacept for all 3 vaccinations, who had received different types of SARS-CoV-2 vac-cines, or who had received anti-SARS-CoV-2 monoclonal antibodies for treatment or pre-exposure prophylaxis prior to antibody measurement were excluded. The primary outcome was the development of anti-RBD an-tibodies after the third vaccination. Secondary outcomes included factors associated with lower odds of devel-oping anti-RBD antibody responses and the develop-ment of breakthrough infections. GraphPad Prism v9.1.2 (San Diego, CA) and SPSS v24 (Chicago, IL) were used for statistical analysis. This study was approved by Mass General Brigham's institutional review board (protocol:2019P002526).