HUMAN BONE MARROW MESENCHYMAL STROMAL CELLS DO NOT INCREASE LOCAL RECURRENCE OF HUMAN SOFT TISSUE SARCOMAS IN MICE XENOGRAFT MODELS AFTER RADIOTHERAPY AND SURGERY

Purpose Mesenchymal stromal cells (MSCs) are an attractive choice for regenerative medicine. We previously showed that MSCs enhance wound healing in animals after radiotherapy. The effect of MSCs on tumor growth is not well understood. The potential use of MSCs to enhance wound healing after radiotherapy (RT) and resection of soft tissue sarcoma (STS) is dependent on a satisfactory safety profile to ensure that tumor proliferation does not occur and recurrence is not increased. Method Primary cell lines (human myxofibrosarcoma and undifferentiated sarcoma) derived from sarcoma bearing patients and a commercialized human fibrosarcoma cell line (HT1080) were used. Cell line proliferation assay after co-culture with MSCs was done using flow cytometry (CFSE) and bioluminescence emission (BLI) (using eGFP/Fluc transduced cell lines). Five xenograft models were developed with NOD/SCID gc-null mice (n=164) harbouring primary tissue lines obtained from patients biopsies (myxofibrosarcoma and three pleomorphic undifferentiated sarcoma [PUS A, B and C]) and a a fibrosarcoma cell line previously transduced with eGFP/Fluc. Tumors were passaged to three mouse generations before a tissue line was established and the model was then used. For the fibrosarcoma model, eGFP/Fluc HT1080 were injected under the dorsal skin. When tumors reached 1cm in diameter, they received localized RT and 48hr later were resected. MSCs (n=82) or medium alone (n=82) was injected subcutaneously adjacent to the wound after tumor resection. Histological and in vivo BLI analysis were performed 3 and 12 weeks after surgery. Results In Vitro Proliferation Assay. For the flow cytometric proliferation assay, there was an increase in the doubling time after five days in the myxofibrosarcoma-MSCs co-culture system (140.4h) compared with controls (55.4 h, p Conclusion We showed that MSCs decrease the proliferation rate of the myxofibrosarcoma cell line in vitro and have no effect, or even decrease, local recurrence of different STS tissue lines in vivo after RT and resection. Clinical investigation of this approach is warranted.