Expression of ALDH and CD34 during early hematopoietic development. Our studies suggested that ALDH^br CD34⁺ cells contained high frequencies of primitive multilineage progenitors, as monitored in NOD/SCID repopulation assays and in LTC. CD34⁺ cells contained short-term progenitors for myeloid and lymphoid compartments; however, the expression of ALDH was maintained most strongly by myeloid progenitors. In contrast, ALDH^neg CD34⁺ cells enriched short-term lymphoid progenitors, suggesting that ALDH may have a diminishing role during early lymphopoiesis. Finally, a population of ALDH^br CD34^neg cells was not efficiently supported within any of the developmental assays used. Based on recent reports,³³  this cell may represent a progenitor for the CD34⁺ compartment.