Longevity assessment of MSCs from WT and SPI6^−/− mice. (A) Schematic showing the vesicular stomatitis virus glycoprotein (VSV-G) pseudotyped lentiviral vector (HRST-hGH) generated by transient transfection of 5 plasmids (pHDM-Hgpm2, pMD-Tat, pRC/CMV-rev, pHDM-G, and pHRST-hGH) into human 293T cells. CMV indicates cytomegalovirus. (B) Before injection, lentiviral transduction was assessed in vitro, at several time points, for the detection of hGH in MSC culture medium. Neg Ctrl indicates negative control; and Post-Tryp, after trypsinization. (C) Transduced MSCs were injected into allogeneic or syngeneic recipients, and serum was collected at 6 time points to assess hGH secretion (n = 5 mice with serum hGH assessed in duplicates). (C) Syngeneic MSC injections showed a stable hGH concentration in the serum at all time points assessed. Allogeneic MSCs showed a decrease in hGH at day 14, which indicates their rejection by the host immune response. The hGH secretion was significantly lower for SPI6^−/− MSCs than for WT MSCs (P < .02). (D) Transduced WT MSCs were injected into NOD-SCID-IL-2rγ^−/− mice, and serum concentration of hGH was stable for the same time points assessed.