Abstract
Several factors influence the engraftment of allogeneic hematopoietic stem cells (HSC). Recently, there has been increased utilization of transplant-conditioning regimens that use reduced doses of chemotherapy and radiation that are considered to be non-myeloablative. These non-myeloablative (or reduced-intensity) allogeneic HSC transplants (RIST) decrease early post-transplant complications, but they are associated with higher incidences of mixed chimerism and graft rejection compared with transplantation after myeloablative conditioning. RIST provides a unique opportunity to study allogeneic HSC engraftment. In particular, host immune status and stem cell graft composition have emerged as important factors affecting engraftment after RIST. Based on these observations, it has been hypothesized that conditioning regimens and allograft composition can be tailored to an individual patient's immune and disease status prior to transplant.