Subcutaneous transplantation of human BMMSCs rescues bone marrow elements. (A) Representative femur sections showed increment of trabecular bone in 3 BMMSC transplant recipient mice at 16 months of age (Transplant) compared with the untreated age-matched littermates (Control; n = 3). Abundant red marrow elements, characteristic of increased hematopoietic cells, were observed in the transplant recipients compared with the fatty, acellular marrow compartment in the control mice. EP indicates epiphyseal cartilage; TB, trabecular bone. *Bone marrow. Original magnification ×200. (B) Immunohistochemical staining showed numerous CD45⁺, B220⁺, and TER119⁺ cells (open arrows) in the femur bone marrow of recipient mice (Transplant, n = 3) compared with the age-matched control mice (Control, n = 3). Bars represent SD. (C) BMMSCs isolated from mice that received subcutaneous BMMSC transplants (n = 3) were transplanted into new immunocompromised recipients mice using HA/TCP (HA) as a carrier. At 8 weeks after transplantation, the transplants showed significantly increased bone (top panel) and bone marrow (bottom panel) formation compared with the BMMSC transplants from control mice (n = 3). Bars represent SD. (D) Immunohistochemical staining showed increased CD45⁺, B220⁺, and TER119⁺ cells (arrows) in the ectopic bone marrow compartment (BM) generated by BMMSCs from the mice received subcutaneous BMMSC transplants (Transplant; n = 3) compared with the ectopic bone marrow compartment (BM) generated by BMMSCs from regular mice (Control, n = 3). B indicates bone; HA, HA/TCP. Bars represent SD.