Immortalized human fetal bone marrow-derived mesenchymal stromalcell expressing suicide gene for anti-tumor therapy in vitro andin vivo

Background aims: Cancer is one of the greatest health challenges facing the world today with >10 million new cases of cancer every year. The self-renewal, tumor-homing ability and low immunogenicity of mesenchymal stromal cells (MSCs) make them potential delivery candidates for suicide genes for anti-tumor therapy. However, unstable supply and short life span of adult MSCs in vitro have limited this therapeutic potential. In this study, we aimed to evaluate if immortalization of human fetal bone marrow-derived mesenchymal stromal cells by simian virus 40 (SV40-hfBMSCs) could be a stable source of MSCs for clinical application of suicide gene therapy. Methods and Results: Transduction of SV40 and herpes simplex virus thymidine kinase-IRES-green fluorescent protein (TK-GFP) did not cause significant change in the stem cell properties of hfBMSCs. The anti-tumor effect of SV40-TK-hfBMSCs in the presence of the prodrug ganciclovir was demonstrated in vitro and in nude mice bearing human prostate cancer cells, DU145 and PC3, which had been transduced with luciferase and GFP for imaging evaluation by an in vivo live imaging system (IVIS200 imaging system; Caliper Life Sciences). Repeated injection of low doses (1× 10⁶ cells/kg) of SV40-TK-hfBMSCs was as effective as previously reported and did not cause observable harmful side effects in multiple organs. Mixed lymphocyte reaction showed that SV40-TK-hfBMSCs did not induce significant proliferation of lymphocytes isolated from healthy adults. Conclusions: Taken together, immortalized hfBMSCs represent a reliable and safe source of MSCs for further clinical translational study.