Stroma from different developmental stages of fetal liver has different effects on human mononuclear fraction of umbilical cord blood during ex vivo co-culture

Fetal liver (FL) has transient and intense hematopoietic activity during gestation. It has been shown that hematopoietic activity in FL begins at embryonic day (E)11, is maximal at E16 and rapidly ceases thereafter. This development of FL is simultaneous with transition of several hematopoietic features. Stromal cells (SCs) appear to regulate hematopoiesis in FL. To compare in vitro hematopoietic support ability of FL SCs from different developmental stages, we established three mouse primary FL SCs from different gestation days and compared their capacity in supporting the growth and differentiation of human umbilical cord blood, by flow cytometry and long-term culture-initiating cell (LTC-IC) assays. Results showed that expansion of hematopoietic progenitor in an E15.5 FL SC microenvironment was superior to that in E12.5 and E18.5 FL SC microenvironments. Co-culture on E15.5 FL SCs resulted in a 3.04-fold increase in early CD34⁺/CD38^– progenitors and a 6.4-fold increase in LTC-ICs after 2 weeks. However, the comparison of CD2⁺/CD19^– cell output and CD19⁺ cell output in different conditions did not attain statistical significance. These results show that murine E15.5 FL SCs are most effective in sustaining stem cell function along with greatest expansion of total nuclear cells of human umbilical cord blood (hUCB). We conclude that the change in SC function is responsible for the transition of hematopoietic function in FL.