Hematopoietic stem cells, under the regulation of certain microenvironment and certain factors, proliferate and differentiate into progenitor cells of various blood cells, called hematopoietic progenitor cells, which are also quite primitive cells with proliferative ability, but have lost the ability of multi-directional differentiation, and can only proliferate and differentiate to one or several blood cell lines, so they are also called directional stem cells.
