Characterization of WT and SPI6^−/− MSCs. MSCs were harvested from femurs and tibia bone marrow of WT and SPI6^−/− mice. Stem cell markers were assessed at passage 5 by FACS analysis (n = 4). (A) CD29, CD44, CD73, CD105, and Sca-1 were positive in WT and SPI6^−/− MSCs. (B) MSCs from WT and SPI6^−/− mice showed similar fibroblastic morphology. Both WT and SPI6^−/− MSCs differentiated into chondrocytes, osteocytes, and adipocytes when stimulated with differentiation medium. Nikon E-1000 epifluorescence microscope with 200× magnification was used to capture images. (C) Lymphocyte proliferation was assessed in the presence of an increasing concentration of MSCs from WT (open bars) and SPI6^−/− (shaded bars) mice. MSCs from WT and SPI6^−/− mice significantly and comparably inhibited lymphocyte proliferation (P < .01). This is the average of 3 experiments, with every parameter performed in 6 replicates. NEG CTRL indicates negative control (lymphocytes in medium); POS CTRL, positive control (lymphocytes cocultured with anti-CD3/CD28); and CPM, counts per minute.