*Purpose: Due to the lack of data utilizing belatacept as primary immunosuppression for adult recipients of very small pediatric donor kidneys, this study seeks to evaluate 1 year post-transplant outcomes of belatacept versus tacrolimus in this population.

*Methods: This retrospective, descriptive study assessed outcomes of adult transplant recipients utilizing very small pediatric donor kidney (defined as kidney size <6 cm, body weight <15 kg, or <3 years old) from 1/1/2018-1/1/2021. Primary outcomes compared patient survival, graft survival, and serum creatinine at 6 and 12 months post-transplant in patients on belatacept versus tacrolimus maintenance immunosuppression. Secondary outcomes assessed rates of acute rejection, de novo donor specific antibodies (DSA), infection, and graft thrombosis between the groups at 1 year.

*Results: Of the 24 patients identified, 1 patient experienced immediate graft thrombosis leading to graft loss and was excluded as the patient did not start therapy with either belatacept or tacrolimus. Thus, 23 recipients were included with 65% receiving belatacept. Other baseline characteristics seen in Table 1. Overall, 1 year post-transplant patient survival was 100% and graft survival was 91.3%. No difference was seen in patient survival, graft survival, serum creatinine, CMV or BK viremia requiring treatment, or bacterial infections between comparison groups (see Table 2). Besides the excluded patient, two other patients had graft thrombosis within 1 week of transplant which required intervention. One dual transplant on belatacept was salvaged with a single nephrectomy, and 1 en bloc transplant on tacrolimus required a complete nephrectomy. In the tacrolimus group, 1 patient developed acute cellular rejection and 1 developed a de novo DSA compared to no rejection or de novo DSA in the belatacept group.

*Conclusions: Belatacept appears to be an appropriate alternative maintenance agent to tacrolimus for adult recipients of very small pediatric kidneys with comparable rates of patient survival, graft survival, serum creatinine, acute rejection, and infection rates at 1 year post-transplant when compared to tacrolimus. Early graft thrombosis remains a concerning risk in this population and warrants further investigation.

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