Pooosite Effects Of The Co-Injection And Distant Injection Of Mesenchvmal Stem Cells On Breast Tumor Cell Growth

Mesenchymal stem cells (MSCs) usually promote tumor growth and metastasis. By using a breast tumor 4T1 cell-based animal model, this study determined that co-injection and distant injection of allogeneic bone marrow-derived MSCs with tumor cells could exert different effects on tumor growth. While the co-injection of MSCs with 4T1 cells promoted tumor growth, surprisingly, the injection of MSCs at a site distant from the 4T1 cell inoculation site suppressed tumor growth. We further observed that, in the distant injection model, MSCs decreased the accumulation of myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs) in tumor tissues via enhancing pro-inflammatory factors such as interferon-y (IFN-y),tumor necrosis factor-α (TNF-α), toll-like receptor-3 (TLR-3) and TLR-4, promoting the host anti-tumor immunity, and inhibiting tumor growth. Different from previous reports, this is the first study reporting that MSCs may exert opposite roles on tumor growth in the same animal model by modulating the host immune system, which may shed light on the potential application of MSCs as vehicles for tumor therapy or any other clinical applications.