Lymph node colonization promotes distant tumor metastasis through the induction of tumor-specific immune tolerance

Abstract

Abstract The majority of cancer deaths result from distant organ metastasis. Lymph nodes (LNs) are major sites of anti-tumor lymphocyte education, yet LN metastasis frequently precedes distant metastasis. Here, we find that LN metastasis represents a critical step in tumor progression by inducing tumor-specific immune tolerance, thus enabling further dissemination of tumors to distant organs. Using an in vivo passaging approach, we generated 300 cell lines exhibiting varying degrees of LN metastatic capacity. We show that the LN metastases promote distant organ metastasis in a manner that is tumor specific. Through organism-wide immune profiling by single cell sequencing, we identify multiple cellular mediators of tolerance. In particular, we find that LN metastases have the capacity to both resist NK cell cytotoxicity and induce regulatory T cells (Tregs). Adoptive transfer of Tregs from the LNs of mice bearing LN metastasis to naïve mice facilitates metastasis in a manner that Tregs from mice without LN metastases cannot. Additionally, these Tregs are induced in an antigen-specific manner. Using whole exome sequencing, we show LN metastases do not evolve through the acquisition of driver mutations, loss of neoantigens, loss of MHC class I, or decreases in melanoma antigens. Rather, by RNA-seq and ATAC-seq, we show that a conserved interferon signaling axis is upregulated in LN metastases and is rendered stable through epigenetic regulation of chromatin accessibility. Knockout studies reveal that these pathways are required for LN metastatic seeding, and we validate their significance in additional mouse models and patients. These findings demonstrate a critical role for LN metastasis in promoting tumor-specific immunosuppression. This work was supported by NIH grants U54 CA209971 and F32 CA189408.