MSCs are not rejected by allogeneic immunocompetent mice. (A-C) Radiologic analysis of mice injected with MSCs, on day 11. C9 MSCs (10⁶ cells in PBS) were injected into BALB/c allogeneic mice either intra-articularly (A) or intramuscularly (B). Bone formation is indicated by arrows. A BALB/c mouse is shown as control (C). (D) Histologic analysis of muscle injected with C9 MSCs, on day 60. Hematoxylin-eosin-safranin O staining of injected muscle revealed presence of cartilage (c) and bone (b) inside the muscle (m). A lymphocytic infiltrate could be observed either lining or invading the neotissue (arrows). Original magnification, × 200.