*Purpose: Belatacept is a selective co-stimulation blocker used in adult renal transplantation and has shown improvement in glomerular filtration rate (GFR) compared to calcineurin inhibitors (CNI). Use in pediatric and young adult kidney transplant recipients is limited. We report outcomes for 10 pediatric patients converted to belatacept.

*Methods: All patients received basiliximab induction and maintenance immunosuppression consisting of CNI, antimetabolite and steroid. Patients were converted to belatacept between 6/2018-11/2019 based on medical need for long-term CNI avoidance. Positive EBV serostatus and absence of subclinical rejection on biopsy were confirmed prior to conversion to belatacept. Infusions were administered at 5mg/kg/dose every 4 weeks and CNI was weaned. Serum creatinine, donor specific antibody (DSA) and latent viral infections were monitored every 2-4 weeks.

*Results: Conversion to belatacept occurred at a median age of 17.2 years (range 13.5-19.8) and 27.5 months (IQR 10.2-50.4) post-transplant. Seven out of 10 patients were male; 6/10 black and 4/10 white. Two patients were converted early (<30 days) post-transplant to minimize CNI in the setting of delayed graft function. Two patients were converted after treatment for rejection (one to improve adherence and one to minimize CNI due to post-transplant diabetes). Six patients were converted with stable graft function. CNI was discontinued in 70% of patients by a median of 56 days (IQR 32-78) after starting belatacept. One early conversion patient developed BK viremia and one patient developed transient CMV viremia. Three patients had preexisting Class II DSA of which 2 decreased (from MFI of 15k-20k to <5 k) and one remained stable (at low MFI 2k) after conversion. One patient developed new Class II DSA (MFI 12k) at 5 months after belatacept initiation. Six patients have remained DSA negative. No episodes of rejection were observed. GFR was stable or improved over a median follow-up time of 287 days (IQR 175-375) as seen in Figure 1.

*Conclusions: Conversion to belatacept allowed CNI minimization or elimination, stable or improved GFR, and no rejection in pediatric kidney transplant recipients. The potential to favorably impact pre-existing DSA or the rate of de novo DSA formation requires further evaluation.

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