Myelin-reactive CD8 T cells influence conventional dendritic cell subsets towards a mature and regulatory phenotype in experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS), an autoimmune demyelinating disease of the central nervous system, is modeled in mice as experimental autoimmune encephalomyelitis (EAE). While CD4 T cells, primarily Th1 and Th17 subsets, drive disease pathogenesis, the exact function of CD8 T cells remains unclear. We previously demonstrated that adoptively transferred myelin-reactive CD8 T cells (PLP-CD8) prevent EAE induction and suppress ongoing disease through the engagement of MHC Class-I in recipient mice. Here, we show that PLP-CD8 induce regulatory changes in both subsets of conventional dendritic cells (cDC1 and CD11b cDC) in vivo and in vitro. Adoptively transferred PLP-CD8 promoted both cDC subsets to adopt a mature and regulatory phenotype with an anti-inflammatory cytokine profile and a reduced capacity to support CD4 T cell proliferation. In vitro, PLP-CD8 induced similar phenotypic changes in both cDC subsets in an antigen-specific, dose-dependent manner. PLP-CD8 directly interacted with cDC1 and indirectly influenced CD11b cDC through paracrine signaling. Notably, direct interaction with PLP-CD8 had detrimental effects on CD11b cDC. Single-cell RNA sequencing revealed upregulation of key immunoregulatory genes, such as Foxo3, in both cDC subsets with enrichment of pathways involved in immune regulation and T cell differentiation. Our study highlights a novel mechanism in which myelin-reactive CD8 T cells directly interact with cDC1 and modulate CD11b cDC through paracrine mechanisms to induce mature, regulatory dendritic cells, which leads to inhibited CD4 T cell responses and reduced EAE pathogenesis.