Lymphoid lineage fate decision of hematopoietic stem cells.

To understand the mechanism in lymphoid development, it is critical to identify developmental intermediates downstream of hematopoietic stem cells, including cells responsible for seeding the thymus. Although early studies showed that hematopoietic stem cells choose either the myeloid-erythroid or the lymphoid pathway, recent data suggest that myelo-lymphoid precursors lacking erythroid potential exist in early hematopoiesis before cells are fully committed to the lymphoid lineage. We here summarize the phenotype and functional properties of such progenitors and the current developmental map for the lymphoid lineage.