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 by engaging MHC Class-I in recipient mice. In my dissertation, I show that PLP-CD8 induce regulatory changes in both subsets of conventional dendritic cells (cDC1 and cDC2) in the spleens of the recipient mice in vivo and in vitro. Adoptively transferred PLP-CD8 promoted both cDC subsets to upregulate costimulatory and regulatory markers reflecting 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 cDC2 through paracrine signaling. Notably, direct interaction with PLP-CD8 had detrimental effects on cDC2. However, the supernatant from this direct interaction did not cause similar changes in cDC2 and rather promoted a mature, regulatory profile reinforcing a contact-dependent negative effect of PLP-CD8 on cDC2. Single-cell RNA sequencing revealed upregulation of key immunoregulatory genes, such as Cd274 (PD-L1), Cd83, Mtor, Tgfb1 (TGF-β1) and Foxo3 with enrichment of immunoregulatory KEGG pathways predominantly in cDC2 but also in the cDC1 subset influenced by PLP-CD8. Our study highlights a novel mechanism in which myelin-reactive CD8+ T cells directly interact with cDC1 and modulate cDC2 through paracrine mechanisms to induce mature, regulatory dendritic cells, which leads to inhibited CD4+ T cell responses and reduced EAE pathogenesis.