Abstract
The success of hematopoietic stem cell transplantation depends on the engraftment of pluripotent hematopoietic stem cells and the regulated proliferation and maturation of committed progenitor cells. It is generally agreed that these processes cannot occur without an appropriate milieu provided by a competent marrow microenvironment (ME). The ME is composed of both non-hematopoietic and hematopoietic stem cell derived cells and consequently is chimeric following allogeneic stem cell transplantation, containing recipient stromal cells and donor macrophages.