Multiple specialized stem cell niches characterize hematopoiesis in the human fetal liver

Before birth, different organs retain hematopoiesis. The liver is involved in the 6 th -8 th week of gestation. The hepatic hematopoietic stem cell (HSC) niche begins when HSCs colonize the liver and make contact with sinusoidal endothelial cells. The aim of this study is to characterize the development of each hematopoietic cell lineage in 9 human liver specimens between 10 and 29 weeks of gestation with immunohistochemistry. Hematopoietic activity was coherent with gestational age. Erythropoiesis was the greatest fraction of fetal liver hematopoiesis: myeloid/erythroid ratio was inverted compared to the adult bone marrow. Myelopoiesis was compartmentalized in the periportal zone. Factor-VIII-positive cells were small, with a megakaryoblast-like morphology. Lymphoid precursors were absent. A small quantity of T and B lymphocytes was found. CD34-reactive hematopoietic stem and progenitor cells were found in a minority of cells. The understanding of the hematopoietic process during gestation could in the future contribute to better understand child and adult hematologic conditions.