Lineage commitment of CD34+ human hematopoietic progenitor cells.

Hematopoietic cells occur in a continuum of many different stages of functional differentiation, from totipotential stem cells to terminally differentiated lineage-specific cells. At some point during differentiation, progenitor cells become committed to a particular lineage. Little is known about the surface molecules that distinguish lineage-committed progenitor cells from multipotential progenitor cells; this study was undertaken to address this issue. Exploiting a thymic stromal cell co-culture system, we show that CD34+ bone marrow cells expressing the T lymphocyte-associated CD2 and CD7 molecules, the B lymphocyte-associated CD10 and CD19, or the myeloid-associated CD33, contain progenitor cells that can generate T lymphocytes, granulocytes, and monocytes, indicating that the expression of any of these molecules on progenitor cells does not imply lineage commitment. CD34+CD13bright, CD34+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 with commitment to myeloid development. Our findings also indicate that expression of CD20 is restricted to progenitor cells committed to B lymphocyte development.