Assessment of Biomarker-Guided CNI Substitution In Kidney Transplantation

800 adult first time kidney transplant recipients will be enrolled in the Observational Study and followed to evaluate their Human Leukocyte Antigen (HLA)-DR/DQ molecular mismatch (mMM) score as a risk-stratifying prognostic biomarker. Six months after transplant the study will identify those who meet the eligibility criteria for the Nested Randomized Control Trial (RCT). 300 eligible subjects will be randomized 2:1 to abatacept or Standard of care (SOC) in the randomization and followed for 18 months monitoring for safety and improvement in renal function, neurocognitive function, and a life participation patient reported outcome measure (PROM). The primary objective of the Observational Study is to test the validity of the HLA-DR/DQ mMM score as a prognostic biomarker for stratification of post-transplant alloimmune risk. Whereas the objective of the Nested RCT is to test whether a superior outcome in kidney function (primary endpoint), as well as secondary endpoints (neurocognitive function, and life participation PROM), will be achieved in patients who are transitioned from Tacrolimus (TAC) to abatacept, while maintaining efficacy (freedom from biopsy proven acute rejection).