Dendritic cells dysfunction in tumor-draining lymph nodes

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Abstract An effective anti-tumor response requires activation of both CD4 helper T cells (through MHC class II) and CD8 cytotoxic T cells (through MHC class I). Activation of tumor-specific CD4 and CD8 T cells depends on tumor antigen presentation by DCs. However, it is known that the tumor microenvironment largely suppresses immune responses. The focus of our study is to characterize the functional status of DCs in tumor-draining lymph nodes and to identify the mechanisms that lead to defective MHC class II presentation of tumor antigens. We injected either B16-F10 melanoma or MB49 bladder cancer adenocarcinoma cells into the flank of mice and isolated DCs from both tumor-draining lymph node (TDLN) and non-draining lymph nodes (NDLN) as our model system. Cross-presentation of OVA to OVA-specific CD8 T cells was not suppressed in TDLN in comparison to the NDLN either in vivo and ex vivo. However, both in vivo and ex vivo CD4 T cell activation by DCs from TDLNs was defective. Subset analysis revealed that both migratory and resident CD8-positive and CD8-negative DCs in TDLN show a less mature phenotype as compared to their counterparts isolated from NDLN. Examination of antigen uptake and processing also showed defects in DCs in TDLN. RNA-seq revealed many differences in gene expression between both resident and migratory DCs isolated from TDLN and NDLN. Characterized phenotypical and functional differences, confirmed by gene expression studies, may explain the dysfunction of DCs in tumor-bearing mice. Further analysis should enable moving towards “correcting” DC defects that would allow proper CD4 T cell priming to provide help to anti-tumor CD8 T cells.