Lymphopoiesis in the adult: identification of early progenitors in both B cell and thymocyte development

The progression of commitment from hematopoietic stem cell to progenitors with specific lineage potentials remains largely undefined, in spite of decades of investigation. This dissertation reports the discovery of a novel hematopoietic progenitor population from adult mouse bone marrow defined as Lin\Neg Sca1\Pos Thy1.1\Neg] This population generates both lymphoid and myeloid cell types, but produces lymphoid forms more frequently in vitro and in transplant assays. It also lacks the ability to rescue lethally irradiated mice that is characteristic of stem cells, but as such, it represents a broad intermediary population in lineage commitment. Immunofluorescent staining and multiparameter flow cytometry supported by functional assays for lineage commitment were employed to separate and enrich the progenitors within this compartment responsible for the differing lineage potentials. cKit, the AA4.1 antigen, and L-selectin were found to distinguish functional subsets within this population, and several progenitors were successfully identified. These included a cKit[\Low AA4.1\ progenitor committed to the B cell lineage, but at a CD45R<super>Neg