911. MHC Class I and II Mismatched Marrow Stromal Cells from C57Bl/6 Mice Are Immune Rejected by Recipient Balb/c Mice
Authors: Nicoletta Eliopoulos, John Stagg, Laurence Lejeune, Jacques Galipeau
Journal: Molecular Therapy (2004)

Bone marrow stromal cells (MSCs) can be easily harvested, culture expanded, and genetically engineered, and thus can be utilized therapeutically in regenerative medicine and in transgenic cell therapy strategies for delivery of therapeutic proteins. Recent studies have suggested that MSCs possess immunosuppressive properties and can be “tolerated” in allogeneic transplant setting without immunosuppression of the host. The objective of our investigation was to determine if the implantation of primary murine MSCs genetically engineered to release a soluble protein, erythropoietin (Epo), would be feasible in MHC-mismatched allogeneic mice without immunosuppression. Firstly, primary MSCs from donor C57Bl/6 (H-2Kb, H-2Db, I-Ab) mice were retrovirally engineered to release murine Epo (Epo+MSCs). These cells were admixed in a collagen-based matrix at 20 million cells/ml. Balb/c (H-2Kd, H-2Dd, I-Ad, I-Ed) mice are class I and II MHC-mismatched relative to C57Bl/6 donors and 5 recipient Balb/c mice were injected subcutaneously with 0.5 ml of Epo+MSCs/matrix. In parallel, 5 recipient syngeneic C57Bl/6 mice were likewise implanted with Epo+MSCs. In these latter syngeneic recipients, the hematocrit (Hct) rapidly rose from a baseline 54 ± 0.6 % (mean ± SEM) to 86 ± 0.3 % within 4 weeks post-implantation and remained >88 % for >200 days. However, in MHC-mismatched recipient Balb/c mice, the Hct rose from a basal 56 ± 0.6 % to a peak 79 ± 2.0 % at 4 weeks post-implantation and then rapidly declined to baseline values by day 52. Moreover, when these allogeneic mice received a 2nd implant of the same Epo+MSCs, the Hct increase was significantly more modest and of shorter duration. A 3rd identical implant in these same Balb/c mice led to no significant effect on Hct. Repeat experiments performed in the absence of collagen matrix led to similar results. To elucidate the host-derived immune response to the MHC-mismatched Epo+MSC implant, allogeneic Balb/c and syngeneic C57Bl/6 mice were identically implanted with C57Bl/6 derived EpoEpo+MSCs, sacrificed at day 15 and implants recovered. Implants were collagenase dissociated and flow cytometric analysis conducted on host-derived lymphoid cells revealed that allogeneic implants compared to syngeneic comprised significantly greater proportions of CD8+, NK T, CD11c, and NK cells. These results are consistent with a robust host cellular immune response to donor allogeneic EpoEpo+MSCs. To determine whether Epo production was causative in the observed immune response, “null” C57Bl/6 MSCs, lacking Epo production, were implanted in Balb/c mice and splenocytes from recipients were isolated 15 days later and tested for their interferon gamma (IFNγ) activation by C57Bl/6 MSCs in vitro. We found that splenocytes from these test Balb/c mice displayed a robust, specific, and significant IFNγ response to C57Bl/6 MSCs when compared to controls. Therefore, our results reveal that class I and II MHC-mismatched MSCs will elicit a cellular immune response by allogeneic hosts with normal immune systems, and that rejection is amplified by repeated challenge. These results strongly suggest that MSCs, at least in the murine system, cannot serve as a “universal donor” in cell therapy applications.