Transplant arteriosclerosis is the leading cause of graft failure and death in patients with heart transplantation. Endothelial progenitor cells (EPCs) contribute to endothelial regeneration in allografts. We investigated whether increased HDL cholesterol induced by adenoviral human apoA-I (AdA-I) transfer increases number and function of EPCs, promotes incorporation of EPCs in Balb/c allografts transplanted paratopically in C57BL/6 ApoE-/- mice, and attenuates transplant arteriosclerosis. EPC number in ApoE-/- mice was increased after AdA-I transfer as evidenced by 1.5-fold (P<0.01) higher Flk-1 Sca-1-positive cells and 1.4-fold (P<0.01) higher DiI-acLDL isolectin-positive spleen cells. In addition, HDL enhanced EPC function in vitro. Incorporation of bone marrow-derived EPCs was 5.8-fold (P<0.01) higher at day 21 after transplantation in AdA-I-treated apoE-/- mice compared with control mice. Enhanced endothelial regeneration in AdA-I-treated apoE-/- mice as evidenced by a 2.6-fold (P<0.01) increase of CD31-positive endothelial cells resulted in a 1.4-fold (P=0.059) reduction of neointima and a 3.9-fold (P<0.01) increase of luminal area. Human apoA-I transfer increases the number of circulating EPCs, enhances their incorporation into allografts, promotes endothelial regeneration, and attenuates neointima formation in a murine model of transplant arteriosclerosis.