Summary Most circulating endothelial cells are apoptotic, but rare circulating endothelial colony forming cells (C-ECFCs) with proliferative and vasculogenic activity can be cultured; the origin and naïve function of these C-ECFCs remains obscure. Herein, detailed lineage tracing reveals murine C-ECFCs emerge in the early postnatal period, display high vasculogenic potential, with enriched frequency of clonal proliferative cells compared to tissue-resident ECFCs, and are not committed to or derived from the bone marrow hematopoietic system but from tissue-resident ECFCs. In human subjects, C-ECFCs are present in the CD34 bright cord blood mononuclear subset, possess proliferative potential and in vivo vasculogenic function in a naïve or cultured state, and display a single cell transcriptome sharing some umbilical venous endothelial cell features like, higher Protein C Receptor and extracellular matrix gene expression. This study provides an advance for the field by identifying the origin, naïve function, and antigens to prospectively isolate C-ECFCs for translational studies.

Origin, Prospective Identification, and Function of Circulating Endothelial Colony Forming Cells in Mouse and Human