Lymphoid Priming in Human Bone Marrow Begins Prior to CD10 Expression with Up-Regulation of L-selectin

The expression of CD10 has long been used to define human lymphoid commitment. We report a unique lymphoid-primed population in human bone marrow that was generated from hematopoietic stem cells (HSCs) before the onset of CD10 expression and B cell commitment. This subset was identified by high expression of the homing molecule L-selectin (CD62L). CD10(−)CD62L(hi) progenitors possessed full lymphoid and monocytic potential, but lacked erythroid potential. Gene expression profiling placed the CD10(−)CD62L(hi) population at an intermediate stage of differentiation between HSCs and lineage-negative (Lin(−)) CD34(+)CD10(+) progenitors. L-selectin was expressed on immature thymocytes and its ligands were expressed at the cortico-medullary junction, suggesting a possible role in thymic homing. These studies identify the earliest stage of lymphoid priming in human bone marrow.