ABSTRACT
I. INTRODUCTION The flt3 ligand (FL) is a growth and survival factor for hematopoietic stem and progenitor cells. Much of the biology of this molecule shows overlap with a related growth factor, stem cell factor (SCF). There are notable differences, however, including the narrow target cell spectrum of FL versus SCF, the low circulating levels of FL in normal individuals compared to nanogram/milliliter levels of SCF, and the absence of mast cell-associated toxicities with FL. In addition, FL is a potent growth factor for dendritic cells, natural killer cells, and B lymphocytes, but it has no direct erythroid-potentiating activity. Pharmacological administration of FL to experimental animals has demonstrated that it has potent effects on the mobilization of hematopoietic precursors and dendritic cells into the peripheral blood and profound effects on dendritic cell expansion which may allow FL to be used to promote antigen presentation in the tumor and infectious disease settings.
