FETAL LIVER GENERATES LOW CD4 HEMATOPOIETIC-CELLS IN MURINE STROMAL CULTURES

We have demonstrated that 0.2% to 11% of cells from the fetal liver (F L) reacted specifically with high concentrations of anti-CD4 monoclona l antibody (MoAb). CD4(+) cells from FL were similar in surface phenot ype and fluorescence characteristics to the CD4(+) population found pr eviously in adult bone marrow (BM). FL and BM cells were seeded in cul tures that allow differentiation to primitive precursors. FL cells rel eased many low CD4(+) and low Thy(+) cells in the supernatant, while B M cells seeded under the same conditions did not. We studied the nonad herent cells harvested from 10-day FL cultures (greater than 90% low C D4(+)). In methylcellulose, they were able to produce more colonies th at appear to be characteristic of earlier stages in the hierarchy of h ematopoietic precursors (especially erythroid bursts and colonies comp osed of both myeloid and erythroid elements) in comparison with CD4(-) cells from 10-day BM cultures. CD4(+) cells harvested from FL culture s initiated secondary cultures containing both a stromal layer and lar ge hematopoietic colonies when replated under conditions similar to th ose of primary cultures. Furthermore, a limited number of CD4(+) cells from 10-day FL cultures were able to repopulate lethally irradiated m ice. Although we cannot formally exclude the possibility that the low CD4 cells produced in FL cultures were derived exclusively from the pr oliferation of the few CD4 cells found in fresh FL, the dynamic analys is of the development of these cells in culture favors the generation of this important population from a CD4(-) subset of hematopoietic ste m cells (HSCs). We speculate that FL contains a prevalent population o f very primitive cells not expressing the CD4 antigen, tentatively cal led ''pre-low CD4 precursors.'' These primitive cells can differentiat e into low CD4(+) cells that share many characteristics with pluripote nt HSCs of the adult type. These data indicate the possibility of usin g hematopoietic progenitors obtained by the expansion/differentiation of fetal stem cells in culture for transplantation purposes. (C) 1995 by The American Society of Hematology.