Belatacept as a Replacement for CNIs 3 to 12 Months Post-transplantation in Patients With Early Graft Dysfunction

Inclusion Criteria: * adult older than 18 years old. * transplantation of a deceased or living donor kidney (non-human leukocyte antigen(HLA)-identical) with blood type (ABO) compatibility * no contraindication to the protocol graft biopsy (10 weeks post transplant) * treatment by CNI / MPA +/- prednisone * renal function estimated by creatinine clearance according to CKD-EPI \<30 ml / min / 1.73m2. * having no difficulty in understanding and communicating with the investigator and his representatives. * Agreeing to give informed written consent * benefiting from a Social Security policy. * results of the 10-week post-transplant renal biopsy finding no rejection or BK virus (member of the polyomavirus family) nephropathy, no recurrence, no thrombotic microangiopathy, no cortical necrosis. * Seropositivity for Epstein-Barr virus (EBV) * negative pregnancy test and agreement on the use of effective contraception throughout the study Exclusion Criteria: * Presence of Donor Specific Antibody during kidney transplant or appeared at 3 months post-transplantation. * seropositivity for HIV * another history of other solid organ transplants (outside the kidney) * primary non-function (persistence of a need for dialysis at 3 months post-transplantation) * participation in progress to another interventional clinical study * any clinical condition that the investigator considers incompatible with the course of the study. * contraindication to belatacept and Tacrolimus * Pregnant or breastfeeding woman * Inability of the patient to comply with study procedures * Person placed under guardianship or curatorship, under safeguard of justice