DIFFERENTIATION OF HUMAN CD34(-)CORD BLOOD STEM-CELLS INTO B-CELL PROGENITORS IN-VITRO()CD38()

Umbilical cord blood CD34(+)CD38(-) cells are a rare, quiescent, primi tive progenitor subpopulation lacking expression of lymphoid and myelo id lineage specific antigens. Although myeloid, erythroid, and megakar yocytic differentiation from these cells has been described, B lineage differentiation has not been demonstrated previously. We report here that highly enriched human B cell progenitors can be consistently gene rated from CD34(+)CD38(-) cord blood cells using long-term culture on the murine stromal line, S17, in the absence of added cytokines., Afte r 6-8 weeks, cell numbers increased up to 160-fold, and cultures conta ined >80-90% CD10(+)CD19(+) B progenitors. Consistent with previous re ports describing delayed myeloid cell differentiation from CD34(+)CD38 (-) cells, production of B cell progenitors from CD34(+)CD38(-) cord b lood cells was delayed 2-1 weeks relative to cultures initiated with e ither CD34(+)CD38(bright) or CD34(+)CD38(dim) progenitors. Addition of Flt3 ligand to long-term cultures resulted in a 2-3-fold greater incr ease in the number of CD19(+) cells generated after 4-8 weeks. The sel ective outgrowth of B cell progenitors using this culture model will b e useful for a range of in vitro studies using primitive hematopoietic progenitors.