CD34 hybrid cells promote endothelial colony-forming cell bioactivity and therapeutic potential for ischemic diseases.

OBJECTIVE Although endothelial progenitor cells (EPCs) have been reported to promote neovessel formation during vascular injury, the function of supporting cells of EPCs and their interaction with EPCs during EPC isolation remain unclear. APPROACH AND RESULTS We investigated the functional properties of 2 types of EPCs, also known as endothelial colony-forming cells (ECFCs), CD34(-)/CD34(+) cell-derived ECFCs (hybrid-dECFCs) and CD34(+) cell-derived ECFCs (stem-dECFCs), isolated using different methods, to elucidate the role of CD34(-) cell populations as cell-supporting niches. Using EPC colony-forming and insert coculture assays, we found that CD34(-) accessory cells dynamically modulate hematopoietic stem cell-derived endothelial cell progenitor commitment via angiogenic cytokines secreted by CD34(-)/CD11b(+) macrophages. On the basis of these findings, we isolated 2 types of ECFCs and investigated their bioactivities. We found that stem-dECFCs showed remarkably retarded cell growth, enhanced senescence, and decreased characteristics of ECFCs, whereas hybrid-dECFCs showed greater proliferative properties but delayed senescence. In a murine hind-limb ischemia model, hybrid-dECFCs showed significantly enhanced blood perfusion, capillary density, transplanted cell survival and proliferation, and angiogenic cytokine secretion compared with stem-dECFCs. In particular, the migratory capacity of hybrid-dECFCs was significantly enhanced, in part mediated via an augmented phosphorylation cascade of focal adhesion kinase and Src, resulting in a highly increased incorporation capacity of hybrid-dECFCs compared with stem-dECFCs. CD34(-) accessory cells of hybrid-dECFCs might be niche-supporting cells that facilitate cell survival, increase the secretion of angiogenic cytokines, and increase incorporation. CONCLUSIONS This study provided important insight into blood vessel formation and repair in ischemic diseases for ECFC-based cell therapy.