*Purpose: Describe the impact of conversion from a calcineurin inhibitor (CNI) based immunosuppressive regimen to belatacept in elderly renal transplant recipients.

*Methods: Adult renal transplant patients aged ≥ 60 years who were converted to belatacept from a CNI between 3/2013-6/2020 were included. Belatacept conversion was defined as CNI withdrawal or minimization (cyclosporine trough < 75 ng/mL or tacrolimus < 5 ng/mL) following belatacept initiation. Primary objective was to describe our experience with the safety of conversion defined as 6 month incidence of infection and malignancy. Secondary endpoints included efficacy defined as change in estimated GFR (eGFR), incidence of rejection, death-censored graft loss and death at last follow-up.

*Results: Fifty-one patients met inclusion criteria, 86% with CNI withdrawal and 14% with minimization. Median time to conversion was 6.3 (IQR 2.3-20) months post-transplant with median follow-up of 12 (IQR 7-27) months. Mean age at time of conversion was 67 (SD 0.8) years. Conversion was pursued due to desire to improve renal function in 51%, neurotoxicity in 22% and metabolic/cardiovascular concerns in 16% of patients. Discontinuation of belatacept occurred in 27% of patients during follow-up. Primary reason for discontinuation was rejection (29%) followed by infection (21%). There were no instances of transplant lymphoproliferative disorder. However, 7.8% of patients experienced other malignancies. Thirty-nine percent of patients experienced at least one infection within 6 months of conversion with mean time from conversion to first infection of 1.8 (SD 0.4) months. Bacterial infections occurred in 27%, viral in 24%, and fungal in 2% of patients. eGFR significantly improved following belatacept conversion (31 ml/min/1.73m² pre vs 42 ml/min/1.73m² post; p = 0.002). Rejection occurred in 20% of patients at a median of 2 (IQR 1.9-2.7) months post conversion. There was a cumulative incidence of 5.7 death-censored graft losses per 100 person-years and 10.3 deaths per 100 person-years.

*Conclusions: In our observational study, conversion from a CNI based regimen to belatacept in elderly renal transplant recipients resulted in improved eGFR. However, infection occurred in over a third of the population, which is at higher risk of infection due to age-related immune senescence, and rejection in a fifth of patients. The discontinuation rate was over 25%. Further studies evaluating safety, particularly infectious risk, in elderly patients converted to belatacept are warranted.

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