The study concerns donors and patients receiving allogeneic stem cell haematopoietic transplantation. The aim of the study is to analyse HSC graft content in immune effector T (naive, memory, activated, exhausted) and immunoregulatory cell subtypes (Tregs, iNKT, MDSC) and correlate the results with post-transplant immune reconstitution of those different cell subtypes and clinical events (graft-versus-host-disease, relapse, infections). An ancillary study will focus on the impact of microbiota dysbiosis on post-transplant immune response and regulatory cell subsets.