Background Malignant pleural mesothelioma (MPM) is an aggressive fatal cancer with no effective treatments. Mesenchymal stem cells (MSCs) migrate and incorporate into tumour stroma making them good vehicles for the delivery ofanti-cancer therapies. TNF-relatedapoptosis inducing ligand (TRAIL) selectively induces apoptosis in malignant cells without affecting healthy tissues. This study aimed to test whether MSCs modified to express TRAIL (MSCTRAIL) could be a successful cell therapy for MPM.

Methods Human MSCs were transduced with a lentiviral vector containing TRAIL IRES-GFP under the control of a tetracycline dependent promoter. Successful transduction was measured using flow cytometry and TRAIL expression was confirmed by immuno-blotting and ELISA. The biological activity of MSCTRAIL was determined using co-culture experiments. DiI stained MPM cells were plated in a 1:1 ratio with MSCTRAIL cells. TRAIL production was activated and cells were treated for 48 hours. Both cells and supernatant were collected and stained with Annexin V and DAPI to detect apoptosis and death respectively on flow cytometry.

To test the effect of MSCTRAIL in vivo a bioluminescent tumour model was established. Plasmid containing fireflyluciferase and YFP was expanded and the correct sequences confirmed by restriction digest. Lentivirus was produced, viral titres were determined using flow cytometry and MPM cells were transduced (MPMLuc). A pure population was generated using hygromycin selection. 80,000 MPMLuc cells were injected into the pleural cavity of NOD/SCID mice and their growth was assessed using an IVIS Lumina system to detect bioluminescence. 1 million MSCTRAIL cells were delivered via tail vein injections on days 5, 9, 12, 15 and 18 post tumour inoculation and bioluminescence was measured twice weekly.

Results MSCs were successfully transduced with TRAIL with 96% efficiency and TRAIL production was confirmed by ELISA. Seven human MPM cell lines were tested with 6/7 (86%) being sensitive to MSCTRAIL. In vivo delivery of MSCTRAIL resulted in a significant reduction in MPM tumour growth.

Conclusions Delivery of TRAIL via MSCs causes a significant reduction in MPM tumour growth and is a potential novel cellular therapy for this currently incurable disease.