Outcome Measures: The Primary Outcome Measure is freedom from cGVHD at 12 months from transplantation, defined as withdrawal of all systemic immunosuppressive agents and without resumption up to 12 months (a binary end-point, yes/no). Secondary outcome measures: Quality of Life, overall incidence of cGVHD (including untreated cases and resolved cases), the incidence of "extensive" cGVHD, time to non-relapse mortality, time to all-cause mortality, time to relapse of leukemia, graft rejection or failure (Yes vs. No), serious infection (Yes vs. No), CMV activation (Yes vs. No), organ-specific grading of chronic graft versus host disease, resumption of immunosuppressive agents after 12 months (Yes vs. No), doses of immunosuppressive drugs still required at 12 months, and incidence of acute graft versus host disease.