['The regulatory molecule for cell life span, telomerase, was modified by human telomerase reverse transcriptase (hTERT) gene transfer to investigate its effect on regenerative properties of endothelial progenitor cells (EPCs) in neovascularization.', 'Telomerase activity was enhanced in hTERT-transduced EPCs (Td-TERTs) (1.2-fold versus no transduced EPCs [no-Td] and 1.2-fold versus GFP-transduced EPCs [Td/GFPs] at day 8; 5.2-fold versus no-Td and 4.8-fold versus Td/GFP at day 21, respectively) Mitogenic capacity in Td/TERTs exceeded that in Td/GFPs at day 8 (0.62+/-0.02 versus 0.53+/-0.01, respectively; P<0.01). Vascular endothelial growth factor-induced cell migration in EPCs was markedly enhanced by hTERT overexpression (Td/TERTs versus Td/GFPs, 292+/-12 versus 174+/-6 cells, respectively; P<0.01). hTERT overexpression has rescued EPCs from starvation-induced cell apoptosis, an outcome that was further enhanced in response to vascular endothelial growth factor. The colony appearance of totally differentiated endothelial cells (tdECs) was detected before day 30 only in Td/TERT, whereas no tdEC colonies could be detected in both Td/GFPs and no-Tds. Finally, we investigated in vivo transplantation of heterologous EPCs. Td/TERTs dramatically improved postnatal neovascularization in terms of limb salvage by 4-fold in comparison with that of Td/GFPs; limb perfusion was measured by laser Doppler (0.77+/-0.10 versus 0.47+/-0.06; P=0.02), and capillary density (224+/-78 versus 90+/-40 capillaries/mm2; P<0.01).'] Does constitutive human telomerase reverse transcriptase expression enhance regenerative properties of endothelial progenitor cells?