EPCR Expression Defines the Most Primitive Subset of Human HSPC and Is Required for Their In Vivo Activity

Cell purification technology combined with whole transcriptome sequencing and small molecule agonist of hematopoietic stem cell self-renewal has allowed us to identify the endothelial protein c receptor protein (EPCR) as a surface maker that defines a rare subpopulation of human cells which is highly enriched for stem cell activity in vivo. EPCR-positive cells exhibit a robust multi-lineage differentiation potential and serial reconstitution in immunocompromised mice. In culture, most if not all of the HSC activity is detected in the EPCR+ subset, arguing for the stability of this marker on the surface of cultured cells, a feature not found with more recently described markers such as CD49f. Functionally EPCR is essential for human HSC activity in vivo. Cells engineered to express low EPCR expression proliferate normally in culture but lack the ability to confer long-term reconstitution. EPCR is thus a stable marker for human HSC. Its exploitation should open new possibilities in our effort to understand the molecular bases behind HSC self-renewal. Overall design: Examining 3 cellular subsets: EPCR+, EPCRlow, EPCR- derived form CD34+CD45RA- cord blood cells after 7 day expansion in UM171