To complement this research with a clinical portion that document operational tolerance, a pilot efficacy study of safely achieving kidney graft tolerance after complete withdrawal of maintenance immunosuppressive therapy will follow pending on the fact that the results of biological/mechanistic tests (at 12 months post-transplant) will document that MSC infusion allows the development of an immune microenvironment permissive to graft tolerance, as higher inhibition of donor specific memory T cells and/or higher generation of alloantigen-specific regulatory T cells than the drug immunosuppressive treatment alone.