*Purpose: This study describes our experience with early conversion to belatacept therapy in a diverse patient population including patients with donor specific antibodies (DSA). The aim was to identify risk factors for sub-optimal outcomes at one year following conversion to belatacept, which was defined as a composite of graft loss, biopsy proven acute rejection, de novo DSA formation, unexplained new proteinuria > 1 g per day, or a decrease in eGFR of 25% or more.

*Methods: This was a single-center, retrospective cohort review of adult kidney transplant recipients converted from a calcineurin inhibitor (CNI) to belatacept between January 2011 and October 2017. Patients were included if they were switched to belatacept within the first year following transplantation due to slow graft function or clinical CNI intolerance in the absence of histological evidence of CNI toxicity. Patients were excluded if enrolled in previously published trials, did not receive at least 3 months of belatacept, or had HIV. Logistic regression was performed to identify clinical variables associated with the primary composite outcome.

*Results: A total of 32 patients with diverse ethnic backgrounds were studied. The cohort was predominantly male (81.3%) with a mean age of 54.4 ± 13.8 years and weight of 77.7 ± 17.8 kg. All patients had negative crossmatches at the time of transplantation; however, 9 (28.1%) patients had DSA levels > 1,000 MFI. Thymoglobulin induction was utilized for all patients with tacrolimus based immunosuppression. After a median of 75.5 days (6-364), patients were converted from tacrolimus to belatacept either by a rapid conversion protocol if < 4 months post-transplant or a gradual taper if ≥ 4 months. At one year post-conversion, patient survival was 96.9% and graft survival was 93.8%. At study conclusion, after a median follow-up of 2.7 years, graft survival remained high at 90.6%. Three (9.4%) episodes of rejection occurred within the first year post-conversion, but only one patient was converted back to a CNI due to concern for ongoing rejection. Among patients with a functioning graft at one year, serum creatinine levels decreased from a baseline of 2.3 ± 1.1 mg/dL to 1.6 ± 0.7 mg/dL. Of the 9 patients with pre-existing DSA, 4 patients cleared their DSA while 3 patients maintained stable DSA and 2 patients developed new DSA. Three additional patients without pre-existing DSA developed de novo DSA post-conversion, all 3 of whom had rejection. After logistic regression, patient weight was the only clinical variable found to be associated with the composite outcome.

*Conclusions: In our diverse patient cohort, conversion from a CNI to belatacept within the first year post-transplant was associated with good one-year patient and allograft outcomes. Neither ethnicity nor pre-transplant DSA were found to be associated with the development of sub-optimal allograft outcomes following conversion to belatacept, but patient weight may warrant further exploration.

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