Characterization of CD62L as a marker of hematopoietic differentiation in adult mice

The progression of early hematopoietic differentiation remains a topic of controversy. Topics of ongoing debate include the identification of a pure hematopoietic stem cell population and bifurcation of the lymphoid and myeloid lineages following commitment by multipotent progenitors. This dissertation contributes to the current knowledge of early hematopoietic differentiation and enhances the understanding of hematopoietic stem cell and progenitor biology by characterizing CD62L as a novel marker of early hematopoietic differentiation. Transplant studies revealed in vivo evidence for the existence of stem cell-containing CD62L- fraction and multipotent progenitor-containing CD62L+ fraction within the traditionally defined hematopoietic stem cell population. Sca-1 fractionation of the hematopoietic stem cell compartment demonstrated that cells of the Sca-1HIGH subset were almost homogeneous in their lack of CD62L expression. In contrast, the Sca-1LOW subset contained a heterogeneous mixture of CD62L+ and CD62L- cells. Engraftment analysis of the Sca-1LOW and Sca-1HIGH fractions demonstrated that the CD62L- cells of both Sca-1 fractions contained hematopoietic stem cells, with a higher frequency of stem cells within the Sca-1HIGH CD62L- fraction. Within the traditionally defined multipotent progenitor population, CD62L segregated a CD62L+ lymphoid-biased multipotent progenitor and a CD62L- multipotent progenitor with robust multipotency. Flow cytometric analysis of CD62L expression pattern within the multipotent progenitor population demonstrated that CD62L-based separation of progenitors was achieved independently of Flt3 expression. Lastly, the concomitant expression of CD62L and Flt3 revealed a rare population of v multipotent progenitors and a possible B cell/erythroid bipotent precursor within the previously demonstrated myeloid compartment. Simultaneous loss of CD62L and Flt3 was observed in the myeloid lineage-specific population. Together, these data demonstrate the expression of CD62L within the context of early hematopoietic differentiation and establish CD62L as a useful tool in the study of early hematopoiesis.