Allogeneic MHC-mismatched microglia-like cell replacement as a therapeutic approach for multiple sclerosis.

BACKGROUND: Dysfunctional microglia contribute to the pathology of numerous neurological diseases. Depletion of harmful microglia and repopulation with healthy progenitors represents a new therapeutic option for neurodegenerative diseases with an urgent need for effective treatments. However, repopulation with patient-derived progenitors could result in similar dysfunction over time. We therefore propose obtaining microglia-like cells (MLCs) derived from healthy donors for allogeneic transplantation. We hypothesize that the immunosuppressive phenotype of MLCs, combined with the brain´s high immune tolerance, would enable effective engraftment. Additionally, the allogeneic origin of MLCs may increase immune tolerance, with additional therapeutic outcomes, particularly in multiple sclerosis (MS). METHODS: MLCs were generated from MHC-mismatched mouse strains in vitro and exposed to IL-10/IL-4/TGF-β or LPS/IFN-γ to induce specific immunophenotypes. Phagocytosis and T cell proliferation assays assessed MLC responses to pathogenic insults that could arise in autoimmune contexts. Microglial depletion was achieved using Cx3cr1CreER/−R26DTA/− mice or PLX3397 treatment. A protocol administering MLCs directly into the brain via the intracisterna magna was optimized to facilitate repopulation of the microglial niche. Repopulation with MHC-mismatched IL-10/IL-4/TGF-β-polarized MLCs was tested in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS, with immune profiling of cellular populations conducted using flow cytometry. RESULTS: BALB/c- and C3H-derived MLCs developed more pronounced anti-inflammatory profiles than did C57BL/6 MLCs, and promoted tolerogenic phenotypes when encountering MHC-mismatched C57BL/6 T cells. In vivo experiments demonstrated a partial repopulation of an emptied microglia-niche by pre-differentiated MLCs administered intracisternally (i.c) into the CNS. The adoptive transfer of MHC-mismatched MLCs led to enhanced immune tolerance mechanisms and the amelioration of disease progression in the EAE mouse model. CONCLUSIONS: Our findings support the therapeutic potential of anti-inflammatory MHC-mismatched MLCs in promoting immune tolerance within autoimmune neuropathologies. Specifically, disease progression was attenuated and tolerogenic mechanisms were activated in the MS mouse model. While a polarization protocol towards an anti-inflammatory phenotype confers MLCs with beneficial features in a pro-inflammatory disease context, the MHC-mismatch interaction within the host´s CNS promotes additional tolerogenic processes.