MSC-induced antigen-specific immune responses in vivo. C57BL/6 MSCs or MEF cells were treated in vitro with recombinant IFNγ and soluble ovalbumin for 20 hours, washed with PBS, and injected (0.1 × 106 cells) intraperitoneally into syngeneic C57BL/6 mice. Two weeks later, the mice were injected a second time with the corresponding cells (0.2 × 106) and 1 week after, ovalbumin-specific immune responses were assessed. (A) Serum samples of immunized mice were collected at day 20 after the first immunization, added at different dilutions to ovalbumin-coated 96-well plates and titered for antiovalbumin anti-bodies. (B) Splenocytes were isolated from immunized mice at day 21 after the first immunization and restimulated in vitro with mitomycin C-treated ovalbumin-expressing E.G7 cells. Five days later, CD8+ T cells were purified from the reactivated splenocytes (> 90% purity) and used as effectors in annexin-V-based CTL assays against EL4 or E.G7 target cells (1 of 2 representative experiments is shown). (C) Immunized mice were challenged at day 21 after the first immunization with a subcutaneous injection of 2 × 106 ovalbumin-expressing E.G7 tumor cells.
