Effects of MS Donor-Derived Mesenchymal Stem Cell-Neural Progenitors (MSC-NP) on Microglial Polarization (P1.405)

Objective: To identify the mechanism by which mesenchymal stem cell-derived neural progenitor (MSC-NP)-based multiple sclerosis (MS) treatment influences microglial function. Background: Clinical investigation of MSC-NPs is aimed at promoting repair and regeneration in progressive MS patients. Recent results from a phase I trial demonstrated reversal of established disability after repeated intrathecal MSC-NP injection. Pre-clinical studies have described the trophic and immunomodulatory effects of MSC-NPs. Microglia play various roles in MS pathogenesis and may be affected by MSC-NP treatment. The presence of M1 activated microglia promotes inflammation and oligodendrocyte damage in MS, whereas M2 microglia regulate immune function and promote neuroprotection and CNS repair. Design/Methods: The BV-2 mouse microglial cell line was used to test microglial polarization into M1 or M2 by stimulating with GM-CSF/IFN-γ/LPS or M-CSF/IL-4/IL-13, respectively. MSC-NPs were expanded from bone marrow of MS patients (n=4) and co-cultured at various concentrations with stimulated or unstimulated BV-2 cells for 7 days. Microglial phenotype was determined by quantitative PCR for markers of M1 (NOS-2, CCL2) or M2 (Arg2, CD206, IL-10). Protein levels were determined by ELISA. To explore whether microglial markers could serve as biomarkers of therapeutic response, we analyzed cerebrospinal fluid (CSF) from clinical trial patients before and after intrathecal treatment with autologous MSC-NPs. Results: We observed a significant decrease in M1 and increase in M2-specific markers in microglial cells in response to co-culture with MSC-NPs. The extent of M1 to M2 shift was dose dependent and correlated with secretion of immunomodulatory factors by MSC-NPs such as TSG6, as well as release of extracellular vesicles. In MS patients treated with intrathecal MSC-NPs, we observed a significant decrease in CSF levels of M1 cytokine CCL2. Conclusions: These results suggest that MSC-NPs promote a beneficial shift in activated microglia and identify novel CSF biomarkers of stem cell-mediated neural repair. Study Supported by: Shubert Foundation Disclosure: Dr. Carling has nothing to disclose. Dr. Zanker has nothing to disclose. Dr. Sadiq has nothing to disclose. Dr. Harris has nothing to disclose.