Prospective experimental study using PBMC from a limited number of adult patients (15) treated at Nantes University Hospital for a kidney transplant from a related living donor. The study will be carried out on PBMC from both donors and recipients, collected during visits scheduled as part of the clinical management of the donor/recipient pair. The study will test the hypothesis that DP8α Tregs expressing CD73, whose frequency in blood increases stably after non-rejected kidney transplants, but not when patients have undergone or will subsequently undergo rejection, are enriched in donor-specific cells, which would be a strong argument in favor of a direct role for these Tregs in preventing transplant rejection, through their ability to inhibit immune responses directed against donor alloantigens.