Homing, cell cycle kinetics and fate of transplanted hematopoietic stem cells

Homing of transplanted hematopoietic stem cells to recipient bone marrow is a critical step In engraftment and initiation of marrow reconstitution. At present, only partial understanding of the cellular and molecular mechanis ms governing homing exists. Likewise, only an Incomplete list of adhesion m olecules implicated in directing the trafficking of stem cells to the marro w microenvironment Is available. Opposing hypotheses that attribute homing to an orderly and orchestrated cascade of events or to random migration of circulating cells find ample experimental support. Also unsettled Is the fa te of marrow-homed cells shortly after transplantation and the rapidity at which they begin to proliferate in their new marrow microenvironment. The l imited number of studies In this field and disparities In their experimenta l design intensifies the confusion surrounding these critical aspects of st em cell biology. However, this area of research Is moving forward rapidly a nd results capable of clarifying many of these issues are forthcoming.