Primary mMSCs trigger tolerance of B16 melanomas. A mix of 5 × 10⁵ B16 tumor cells and 5 × 10⁵ mMSCs was implanted in subcutaneous sites of BALB/c mice and compared with the injection of B16 cells alone. C3 MSCs or 2 different sources of primary MSCs (mMSC1 and mMSC2) were used. The difference in tumor incidence between animals injected with B16 and MSCs and those receiving B16 alone was highly significant (P < .0001) using the Fisher exact test.