Homologous MHC Antigens Induce cDC1-like Differentiation from Monocyte-Derived Dendritic Cells

Introduction/Rationale: Antitumor CD8+ T cell responses are orchestrated primarily by lineage-committed cDC1 dendritic cells (DC). However, data suggest that monocyte-derived DC loaded with homologous MHC antigens—bound MHC class I and II peptide epitopes sharing identical stretches of amino acid sequence, similarly elicit strong and durable CD8⁺ T-cell responses. Our clinical work further demonstrates that therapeutics based on this principle substantially extend survival in glioblastoma

Methods: Based on these critical observations, we used human and mouse moDCs to understand the mechanism(s) through which homologous MHC epitopes are detected and how signal transduction alters moDC phenotype.

Results: Here, we show that MHC peptide homology is sensed by the multi-aminoacyl tRNA synthetase (mARS) complex. We have demonstrated that the composition of aaRS within the mARS complex changes in accordance with the specific amino acids present in the sequence overlap region of bound MHC class I and class II peptides. To transmit the homology signal, the mARS complex relays information through mTORC1 via Rags, small GTP-binding proteins that act as intermediaries between amino acid sensors and the mTORC1 signaling pathway. Using RNAseq, RPPA, microscopy and western blot, we demonstrated a reduction in mTOR activation and phosphorylation of downstream targets p70S6K and cFos. In DCs, mTORC1 pathway is known to regulate IL-12 and IL-10 gene expression via NFkB. Using ChIPseq, we demonstrate significant enrichment of NFkB with IL-12a and reduced binding to IL-10 cis regulatory elements when moDC are loaded with homologous antigenic epitopes. Lastly, scRNAseq analysis of moDC loaded with homologous MHC antigens revealed enhancement of a cluster expressing cDC1 markers including Irf8, Batf3, Nfil3, Runx3, Id2, Ly75, Apol7c, Serpinb6b, Serpinb9, and costimulatory genes.

Conclusion: In sum, our work demonstrates that the loading of moDC with homologous MHC antigens induces skewing toward a cDC1-like phenotype.