Abstract: Objective: To investigate the feasibility of using endothelial progenitor cells (EPCs), induced from humanmesenchymal stem cells (MSCs) in vitro, as targeted vectors to deliver the human γ-interferon (hγIFN) genefor cancer immunotherapy. Methods : MSCs were isolated from healthy bone marrow and cultured in mediumcontaining vascular endothelial growth factor (VEGF165, 20ng/mL) for 2 weeks, followed by detection for cellsurface markers of MSCs with flow cytometry. The transduction efficiency of adenoviral vectors carrying theenhanced green fluorescent protein gene (Ad5-EGFP) to EPCs was evaluated by flow cytometry. After EPCswere transduced by Ad5-hγIFN in vitro, the hγIFN concentration in the medium of EPCs-hγIFN was determined by ELISA. The inhibitory effect of EPCs-hγIFN cells on cancer cells was studied by co-culturing EPCs-hγIFN cells and Lovo colon cancer cells. EPCs-EGFP cells were injected intravenously into nude mice with Lovo xenograft tumors to investigate the distribution of EPCs in vivo. EPCs-h γIFN were injected in the sameway to evaluate the effect of EPCs-h γ IFN on antitumor capacity and survival. Results : Co-cultured withVEGF165 for 2 weeks, MSCs transformed to EPCs with positive expression of CD133, KDR and CD34. Morethan 95% of EPCs were EGFP positive when multiplicity of infection (MOI) of EPCs transduced by Ad5-EGFPwas 150 pfu/EPC. The hγIFN could be detected in EPCs–hγIFN culture medium. The concentration of γIFNwas more than 1400 pg/mL and remained constant for a certain period. Compared with the control, the growthof Lovo cells was inhibited significantly (P<0.05) when co-cultured with EPCs–hγIFN at a ratio of 5:1 (Lovocells:EPCs- hγIFN). EPCs-EGFP administered intravenously could be detected in the margin of xenograft tu-mors, but not in other organs, indicating that EPCs-EGFP were mainly localized in the margin of xenograft tumors. EPCs–h γIFN administered intravenously inhibited the growth of xenograft tumors as seen in differences in the average tumor weight (0.48±0.78g in the treated group and 2.47±2.58g in the control group, P<0.05) and survival time (median overall survival: 35 days in the treated group vs. 32 days in the untreatedgroup, P<0.05). No significant inhibitory effect on tumor growth was observed when hγIFN was injected subcutaneously or when EPCs-EGFP were injected intravenously. Conclusion : EPCs migrate to the tumor area andare excellent potential gene vectors for cancer immunotherapy.