P-MSCs promote tumor growth in vivo. a Tumor promoting effects of P-MSCs in a xenograft mouse model. PMSC + A549, n = 6. 2 × 106 A549 cells and 2 × 105 exosomes-treated MSCs were injected. MSC + A549, n = 4. 2 × 106 A549 cells and 2 × 105 DF12-treated MSCs were injected. A549, n = 3, only 2 × 106 A549 cells were injected. b the tumors in each group were dissected and tumor diameters were measured at 2 weeks after subcutaneous cell injection. c The macrophage infiltration was examined by F4/80 immunohistochemical staining of the tumor tissues harvested 2 weeks after A549 cell inoculation. Representatives of F4/80 staining from each group are shown (magnification 200×). d F4/80 + macrophages were quantitated and the data represent the mean number of F4/80+ macrophages per 200 × field (three fields per group). e Tumor cell proliferation was examined by Ki67 immunohistochemical staining of the tumor tissues. Representatives of Ki67 staining from each group are shown (magnification 200×). f Ki67 staining-positive cells were quantified and the data represent the mean number per 200 × field (three fields per group)