Injection of MSCs induces tolerance of B16 melanoma cells in allogeneic mice. C3 MSCs (5 × 105) and 5 × 105 B16 melanoma cells (alone or as a mix) were injected subcutaneously into C3H mice and tumor development was monitored over time. (A) Tumor incidence was evaluated in the groups of mice either coinjected with B16 and MSCs in allogeneic C3H mice or injected with B16 melanoma cells in syngeneic C57Bl/6 mice. As negative controls, B16 cells or C3 MSCs alone were injected in C3H mice. (B-C) Hematoxylin-eosin staining of B16 melanoma tumor grown in allogeneic (B) or syngeneic (C) recipients. The brown pigment corresponding to the melanin produced by the melanocytes in both tumors is easily observed. (D-E) Distribution of CM-DiI-labeled C3 MSCs is shown by histology, at the periphery of the tumor in the stroma reaction where no melanocytes were observed (D) and by fluorescence microscopy as red fluorescent cells (E). Original magnification, × 200.
