Lenalidomide may prevent relapses after allogeneic stem cell transplantation by promoting the immune-mediated graft-versus-tumor effect. We performed a prospective phase I/II study to define the dose-limiting toxicity and the immunologic effects of lenalidomide given early (day 100-180) after allograft for four cycles in patients with multiple myeloma. According to the Fibonacci design, 24 patients with a median age of 53 years were included. Dose-limiting toxicity was organ toxicity owing to graft-versus-host disease, and the maximum tolerable dose was 5 mg. The incidence of graft-versus-host disease after lenalidomide was 38%, occurring after a median of 22 days, and was beside organ toxicity, a leading cause to discontinue the study in 29% of the patients. Immune monitoring revealed a significant increase in peripheral ?-interferon-secreting CD4(+) and CD8(+) T cells within the first week of lenalidomide treatment followed by a delayed increase in T regulatory cells. Furthermore, natural killer (NK) cells isolated from the peripheral blood of patients evidenced a significantly improved antimyeloma activity after lenalidomide treatment. The immune effect might have contributed to the increased CR rate from 24-42% after lenalidomide treatment because nonresponding patients showed significantly less natural killer and T cell activation. (Study registered under: NCT 00778752.).
