The hematopoietic system is mediated in part by cell-to-cell interacti
ons and soluble mediators or growth factors (cytokines). A large numbe
r of cytokines directly and potently control hematopoietic stem and pr
ecursor cell proliferation and differentiation. This review focuses on
the recent studies devoted to the role of cytokines in the ex vivo ex
pansion and differentiation of hematopoietic stem and precursor cells.