In vivo tolerance of B16 cells is induced by MSCs through a systemic and dose-independent immunosuppressive effect. (A) Tumor incidence of B16 melanoma cells in allogeneic mice is similar regardless of the route of MSC injection. B16 tumor cells (5 × 105) were injected subcutaneously and 5 × 105 C3 MSCs were injected either subcutaneously (SC) at a distant site (B16/SC + MSC/SC) or systemically in the tail vein of BALB/c mice (B16/SC + MSC/IV). As control, a mix of both cell types was injected subcutaneously (B16 + MSC/SC). (B) Incidence of B16 tumors is independent of the number of coinjected MSCs. C3 MSCs mixed with B16 tumor cells (5 × 105 cells) at various ratios (1:1; 1:10; 1:100, respectively) were implanted in subcutaneous locations and tumor growth was monitored at different time intervals.
