In our study, the investigators want to use gene and protein expression profiling and functional assays of human (ESKD patients on chronic HD or naive uremic patients not yet on HD) CD4+ TCM to identify the mechanisms underlying their maintenance or dysfunction. Our results will provide a molecular basis for the capacity of CD4+ TCM to resist apoptosis and to persist in a stable manner in the host, thereby conferring long-term protective immunity against reinfection. To test this hypothesis, it will be important to determine whether TCM producing cytokines represent a distinct subset of memory cells expressing a specific differentiation phenotype. To the other part the investigators will analyse the role played by Tregs in uremic patients using a new membrane, namely HCO 1100.