Cross Talk with Hematopoietic Cells Regulates the Endothelial Progenitor Cell Differentiation of CD34 Positive Cells

INTRODUCTION: Despite the crucial role of endothelial progenitor cells (EPCs) in vascular regeneration, the specific interactions between EPCs and hematopoietic cells remain unclear. METHODS: In EPC colony forming assays, we first demonstrated that the formation of EPC colonies was drastically increased in the coculture of CD34(+) and CD34(−) cells, and determined the optimal concentrations of CD34(+) cells and CD34(−) cells for spindle-shaped EPC differentiation. RESULTS: Functionally, the coculture of CD34(+) and CD34(−) cells resulted in a significant enhancement of adhesion, tube formation, and migration capacity compared with culture of CD34(+) cells alone. Furthermore, blood flow recovery and capillary formation were remarkably increased by the coculture of CD34(+) and CD34(−) cells in a murine hind-limb ischemia model. To elucidate further the role of hematopoietic cells in EPC differentiation, we isolated different populations of hematopoietic cells. T lymphocytes (CD3(+)) markedly accelerated the early EPC status of CD34(+) cells, while macrophages (CD11b(+)) or megakaryocytes (CD41(+)) specifically promoted large EPC colonies. CONCLUSION: Our results suggest that specific populations of hematopoietic cells play a role in the EPC differentiation of CD34(+) cells, a finding that may aid in the development of a novel cell therapy strategy to overcome the quantitative and qualitative limitations of EPC therapy.