Rationale: Delayed and deficient reconstitution of T cells and their functions are a major obstacle to the success of a hematopoietic stem cell transplant (HSCT). CYT-107 may have potential clinical use after allogeneic HSCT to enhance lymphoid reconstitution which could have a number of beneficial effects including decreased morbidity and mortality from post-transplant infections. Our preliminary data with a previous generation IL-7, CYT 99 007, raise the possibility that IL-7 could have, in some cases, an anti-GVHD effect while keeping the anti-tumor effect of the allograft intact.