| Outcome Measures: |
Primary: Feasibility of a transient replacement of CNIs by belatacept in renal transplant patients with early graft dysfunction. Creatinine clearance did not decrease by more than 25% from the cessation of belatacept 6 months after reintroduction of CNI., Feasibility was defined by preserved renal function and good tolerance 6 months after reintroduction of CNI. Renal function was defined as preserved if creatinine clearance (according to Chronic Kidney Disease - Epidemiology Collaboration (CKD-EPI)) did not decrease by more than 25% from the cessation of belatacept. The good tolerance of CNI was defined by the absence of complications leading to the cessation of treatment., Month 15 | Secondary: Evaluate the effectiveness of belatacept treatment on renal function (creatinine clairance) and to prevent rejection. (Number of rejection épisodes), Longitudinal monitoring of renal function (Day 0, Month 3, Month 6, Month 9) and collection of rejection episodes., Day 0, Month 3, Month 6, Month 9|Evaluate the tolerance of treatments (belatacept during phase 1 and CNI during phase 2). Number of adverse events., Collection of infectious episodes and neoplasias, Month 3, Month 6, Month 9, Month 12, Month 15|Estimate the cost of care (from 3 months to 18 months post-transplant) and compare with the cost of a theoretical arm benefiting from belatacept continuously and a theoretical arm benefiting from CNIs continuously., Number of care resources used for treatment : number of medication, number of hospitalization, number of transportation, number of consultations, number of medical procedures, possible home help and associated costs over 15 months of follow-up, and collection of cost data in the literature for the comparison., Month 3, Month 6, Month 9, Month 12, Month 15|Evaluate the evolution of the quality of life during the 15 months of follow-up and compare it to a theoretical arm benefiting from belatacept continuously, and a theoretical arm benefiting from CNIs continuously: generic EuroQol-5D scale, Measurement of quality of life scores (generic EuroQol-5D scale) every 3 months for 15 months and collection of quality of life data in the literature for comparison., Month 3, Month 6, Month 9, Month 12, Month 15|Evaluate the differential impact of SNFs and belatacept on cell populations of the immune system, Differential analysis of cell populations by standardised flow cytometry combined with unbiased analysis., Month 3, Month 6, Month 9, Month 12, Month 15|Evaluate the differential impact of NICs and belatacept on the level of CMV replication and its clinical consequences., Longitudinal monitoring of CMV PCR, Month 3, Month 6, Month 9, Month 12, Month 15
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