Hematopoiesis in the fetus and neonate.

Advances in molecular biology and in hematopoietic progenitor cell culture techniques have produced new tools with which to explore previously enigmatic aspects of developmental hematopoiesis. Studies using these tools are contributing mechanistic understanding to what was previously an entirely descriptive discipline and are generating new insight into the pathophysiology of various cytopenias in fetal and neonatal patients. This review of developmental hematopoiesis will address four related topics: 1) ontogeny of blood cells, 2) ontogeny of hematopoietic progenitors, 3) developmental regulation of hematopoietic growth factors, and 4) developmental aspects of interactions between hematopoietic progenitors and hematopoietic growth factors.