Lymphatic-localized Treg-mregDC crosstalk limits antigen trafficking and restrains anti-tumor immunity [scRNA-seq]

Tumor microenvironment (TME) plays critical roles in both tumor progression and immunotherapeutic efficacy. Here using single-cell RNA sequencing (scRNA-seq), we described the TME heterogeneity and found a specific state of CCL22+ dendritic cell (mregDC) cross talk close to regulatory T cells (Treg). We analyzed cell–cell communication mediated by ligand–receptor interactions and finally found that mregDCs probably attract Treg cells via chemotaxis and physically interact with them in tumor. Within this cross talk, Treg cells received activation signals from mregDCs and upregulated suppressive and adhesion molecules, including PD-1, ICOS, CTLA-4 and OX-40, further enhancing their interaction with mregDCs. In turn, the association of Treg cells with mregDCs restrained the trafficking of tumor antigen-bearing dendritic cells to draining mesenteric lymph nodes and thus dampened the presentation of tumor antigens to initiate anti-tumor immune responses in a cell contact dependent manner. We analyzed the single cell transcriptomes of wild-type colon and Apc Min/+ colon tumor, a spontaneous mouse colorectal tumor model. Tumor single cell suspensions were enriched for immune cells and rapidly processed for analysis on the inDrops scRNA-seq platform. After filtering to exclude putative cell doublets and stressed or dead cells, a total of 23,922 cells passed the quality control, of which 14,445 were from tumor and the remaining 9,477 cells were from normal colon tissue.