Stromal cell-derived factor-1 (SDF-1)\CXCR4 couple plays multiple roles on haematopoietic progenitors at the border between the old cytokine and new chemokine worlds: survival, cell cycling and trafficking.

Generation of haematopoietic cells is regulated by cellular and humoral interactions in which stromal cells, adhesion molecules, cytokines and chemokines play a crucial role. Among the chemokines, SDF-1 and its CXCR4 receptor have been reported to be key players in the nesting of haematopoietic progenitors within the bone marrow. Disruption of the SDF-1\CXCR4 axis results in cell mobilization and may participate in leukaemia extramedullary infiltration. In this review we will discuss the manifold roles of the SDF-1 chemokine and of its receptor in haematopoiesis regulation. By recruiting quiescent progenitors, by participating in their survival\cycling and by sensitizing them to further cytokine synergistic action, SDF-1 likely contributes to haematopoiesis homeostasis under physiological conditions and in stress situations. The complexity of the SDF-1\CXCR4 interactions in the regulation of haematopoiesis illustrates a dynamic and sequential cross-talk between chemokine and cytokine\growth factor worlds. Because of their pleiotropic effects on haematopoietic progenitor trafficking, survival and proliferation, the SDF-1\CXCR4 couple could be considered as promising molecules for improvement of cell-based therapy protocols in haematopoietic transplantation.