LINEAGE COMMITMENT OF CD34(+) HUMAN HEMATOPOIETIC PROGENITOR CELLS

Hematopoietic cells occur in a continuum of many different stages of f unctional differentiation, from totipotential stem cells to terminally differentiated lineage-specific cells. At some point during different iation, progenitor cells become committed to a particular lineage. Lit tle is known about the surface molecules that distinguish lineage-comm itted progenitor cells from multipotential progenitor cells; this stud y was undertaken to address this issue. Exploiting a thymic stromal ce ll co-culture system, we show that CD34(+) bone marrow cells expressin g the T lymphocyte-associated CD2 and CD7 molecules, the B lymphocyte- associated CD10 and CD19, or the myeloid-associated CD33, contain prog enitor cells that can generate T lymphocytes, granulocytes, and monocy tes, indicating that the expression of any of these molecules on proge nitor cells does not imply lineage commitment. CD34(+)CD13(bright), CD 34(+)CD14(+), and CD34(+)CD15(+) cells generated myeloid progeny, and CD34(+)CD20(+) cells failed to differentiate along the T lymphoid and myeloid lineages. Thus expression of CD13, which precedes that of CD14 and CD15 during early hematopoiesis, appears to coincide within commi tment to myeloid development. Our findings also indicate that expressi on of CD20 is restricted to progenitor cells committed to B lymphocyte development.