['This study investigated use of mesenchymal stem cells (MSCs) genetically engineered to produce interferon-β (IFN-β) as a gene delivery system to treat prostate cancer in an animal model.', 'To measure the effects on tumour cell growth in vitro, IFN-β-producing  MSCs (IFN-β-MSCs) were co-cultured with the prostate cancer cell line PC-3. The in vivo migration of intravenously injected fluorescently-labelled MSCs to healthy tissues and PC-3 xenograft tumours grown in immuno-deficient mice was determined by fluorescence microscopy. The antitumour  effects of intravenously injected IFN-β-MSCs on PC-3 xenograft growth and animal survival were also investigated.', 'IFN-β-MSCs inhibited the growth of PC-3 cells in vitro. Fluorescently-labelled MSCs migrated to the margins and centre of tumour masses but not into healthy  tissues. Intravenously injected IFN-β-MSCs significantly reduced PC-3 xenograft tumour weight and increased animal survival compared with controls.'] Do mesenchymal stem cells modified to express interferon-β inhibit the growth of prostate cancer in a mouse model?