Initial human myeloid/dendritic cell progenitors identified by absence of myeloperoxidase protein expression

Myeloperoxidase (MPO) represents an early-appearing and highly reliable intracellular myeloid lineage marker molecule. MPO protein can be detected in a subset of human hematopoietic bone marrow progenitor cells and in granulomonopoietic (GM) cells. However, other myeloid-related cell types such as epidermal Langerhans-type dendritic cells (LC) lack MPO. Therefore, human myeloid progenitors might be subdivided based on MPO protein expression into functional subsets. Here we identified two consecutive myelopoietic cell stages, i.e., early myeloid progenitors that lack MPO, as well as their immediate MPO+ progeny. MPO− myeloid progenitors possess previously described granulomonocyte (GM) progenitor–associated cell-surface characteristics (CD34+CD45RA+CD13+lin−). They are specifically recruited and can be expanded in cultures of CD34+ cord blood cells in response to early-acting hematopoietic cytokines. Furthermore, cell fractions enriched in MPO− myeloid progenitors efficiently developed along Langerhans-type dendritic cell (LC) and granulomonocytic (GM) lineages, whereas progeny enriched in MPO+ cells showed diminished LC potential. In line with this, peripheral blood progenitors, known to possess LC differentiation potential, lacked MPO expression. We conclude that differential expression of MPO therefore further characterizes cells with myeloid or LC potential.