Although pretransplant alemtuzumab can reduce GVHD following allogeneic transplantation, it may also increase the risk of mixed donor T-cell chimerism and infections. We hypothesized that the early use of DLI without withdrawal of immunosuppressive drugs in patients with mixed T-cell chimerism would lower the risk of relapse without significantly increasing the risk of GVHD post DLI. Thirty-six patients (median age 59 years) were treated in this phase II trial using reduced-intensity conditioning including s.c. alemtuzumab (total dose 43 mg) and a PBSC graft from a matched unrelated donor (UD). DLI without withdrawal of immunosuppressive drugs was administered to all 25 patients with <50% donor T-cell chimerism on day +60. The cumulative risks of acute and chronic GVHD were 42% and 59%, respectively. Estimated probabilities of non-relapse mortality (NRM) at day 100 and 1 year were 3% and 14%, respectively. With a median follow up 2.4 years, estimated survivals at day 100, 1 and 2 years were 97%, 71% and 57%, respectively. In multivariate analysis, the occurrence of acute GVHD was associated with an increased risk of mortality, whereas the occurrence of chronic GVHD had a protective effect, associated with decreased relapse and improved disease-free survival. Low-dose alemtuzumab and preemptive DLI provides favorable transplant outcomes including low NRM in an older patient population with high-risk malignancies undergoing UD transplantation.