Based on a safety immunologic platform (ATG based reduced toxicity conditioning regimens), it is needed to develop post Allo-HSCT strategies to decrease the incidence of relapse. In this context, the modulation of immune cell activity could play a role to prevent relapse. NK cells have a unique capacity to exert potent GVT effects without inducing GVHD. Moreover, NK cells recovery occurs early after Allo-HSCT and NK cells function are not severely impaired by the use of ciclosporin A, that is given for few months after Allo-HSCT as GVHD prophylaxis. Thus, NK cell modulation appears as a viable option for early immune intervention after Allo-HSCT.