Lentiviral expression of TRAIL in human mesenchymal stem cells (MSC) induces apoptosis in interacting colon carcinoma cells

4608 RATIONALE: It has been previously shown that MSC are potent vehicles for delivery of antineoplastic mediators. For clinical use an efficient gene transfer as well as transgenes without systemic toxicity are required. Lentiviral transduction allows stable transgene expression at high levels even in resting cells. The use of TRAIL promises low toxicity as most non-malignant cells are resistant to TRAIL-induced apoptosis. Here we show that lentivirally TRAIL-transduced MSC can induce apoptosis in colon carcinoma cells in vitro and delay tumor growth in vivo.
 METHODS: Human bone marrow MSC were transduced with the TRAIL cDNA using a lentiviral system. Transduced cells were analyzed for TRAIL expression (flow cytometry, western blot), proliferation (growth kinetics) and in vitro differentiation capacity (cytochemistry) as well as for soft agar growth. For coculture and in vivo studies the TRAIL-sensitive colon carcinoma cell line DLD-1 was used. In direct coculture of dsRed-DLD-1 with TRAIL-MSC and of dsRed-DLD-1 with WT-MSC over 72h the ratio of DLD-1 cells and MSC was determined (flow cytometry). Apoptosis was verified with annexin-V staining and western blot. Subcutaneous xenografts of DLD-1 mixed with WT- or TRAIL-MSC were generated in nude mice.
 RESULTS: After lentiviral transduction TRAIL-MSC showed stable TRAIL expression over up to 10 passages without signs of apoptosis, growth delay or malignant transformation. TRAIL-MSC retained an identical expression of cell surface antigens as well as proliferation and differentiation capacity when compared to non-transduced MSC. Lentiviral TRAIL expression was functional in vitro as seen in direct cocultures. DLD-1 cells underwent apoptosis after reaching cell-cell contact with TRAIL-MSC while incubation of DLD-1 cells with TRAIL-MSC supernatant did not result in apoptosis. The absolute number of DLD-1 cells decreased significantly during direct coculture with TRAIL-MSC in contrast to continued increase of DLD-1 cells in cocultures with WT-MSC. Thus the observed decrease in the number of tumor cells was due to apoptosis and not growth inhibition. In preliminary animal studies DLD-1 xenografts containing TRAIL-MSC showed an altered tumor stroma and a growth delay when compared to xenografts containing WT-MSC.
 CONCLUSIONS: We show for the first time that lentivirally transduced MSC can express antineoplastic mediators without changes in their characteristic properties. Secondly, we demonstrate that lentiviral TRAIL expression in MSC can induce apoptosis in TRAIL-sensitive tumor cells by direct cellular interaction. We therefore suggest that TRAIL-MSC may serve as a new therapeutic tool with a low risk of systemic toxicity and should be further evaluated for clinical applications under GMP-conditions.