CD11c+CD88+CD317+ myeloid cells are critical mediators of persistent CNS autoimmunity

Background: Natalizumab, a humanized monoclonal antibody (mAb) against alpha4-integrin, reduces the number of dendritic cells (DC) in cerebral perivascular spaces in multiple sclerosis (MS). Selective deletion of α4-integrin in CD11c+ cells should curtail their migration to the CNS and ameliorate experimental autoimmune encephalomyelitis (EAE). Methods: We generated CD11c.Cre+/-ITGA4fl/fl C57/Bl6 mice to selectively delete α4-integrin in CD11c+ cells. Active immunization and adoptive transfer EAE models were employed. Multi-parameter flow cytometry was utilized to immunophenotype leukocytes. Single-cell RNA sequencing (scRNA-seq) was used to profile individual cells. Results: alpha4-integrin expression by CD11c+ cells was significantly reduced in primary and secondary lymphoid organs in CD11c.Cre+/-ITGA4fl/fl mice. In active EAE, a delayed disease onset was observed in CD11c.Cre+/-ITGA4fl/fl mice, during which CD11c+CD88+ cells were sequestered in the blood. Upon EAE onset, CD11c+CD88+ cells accumulated in the CNS and expressed CD317+. In adoptive transfer experiments, CD11c.Cre+/-ITGA4fl/fl mice had ameliorated clinical disease associated with diminished numbers of CNS CD11c+CD88+CD317+ cells. The transcription profile of CD11c+CD88+CD317+ cells placed them within previously defined microglia-like cells in human CSF. We show that activated, but not naive microglia expressed CD11c, CD88, and CD317. Finally, anti-CD317 treatment prior to clinical EAE substantially enhanced recovery. Conclusion: CD11c+CD88+CD317+ cells in the CNS promote inflammatory damage. Transcriptional analysis identifies CD11c+CD88+CD317+ cells as a unique myeloid subset in human CSF. The disease-propagating effects of these cells can be antagonized using anti-CD317 mAb.