Abstract PR013: Lymph node colonization promotes distant tumor metastasis through the induction of tumor-specific immune tolerance
Authors: Reticker-Flynn Nathan E. , Zhang Weiruo , Belk Julia A. , Basto Pamela A. , Gentles Andrew J. , Sunwoo John B. , Satpathy Ansuman K. , Plevritis Sylvia K. , Engleman Edgar G. 
Published: January 2023

Abstract
The majority of cancer-associated deaths result from distant organ metastasis, yet the mechanisms that enable this process remain poorly understood. For most solid tumors, colonization of regional or distant lymph nodes (LNs) typically precedes the formation of distant organ metastases, yet it remains unclear whether LN metastasis plays a functional role in disease progression. LNs are major sites of anti-tumor lymphocyte education, including in the context of immunotherapy, yet LN metastasis frequently correlates with further disease progression. Here, we find that LN metastasis represents a critical step in tumor progression through the capacity of such metastases to induce tumor-specific immune tolerance in a manner that promotes further dissemination of tumors to distant organs. Using an in vivo passaging approach of a non-metastatic syngeneic melanoma, we generated 300 unique cell lines exhibiting varying degrees of LN metastatic capacity. We show that the presence of these LN metastases enables distant organ seeding of metastases in a manner that the parental tumor cannot, and this effect is eliminated in mice lacking an adaptive immune response. Furthermore, this promotion of distant seeding by LN metastases is tumor specific. Using flow cytometry and single-cell sequencing to perform comprehensive immune profiling, 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). Furthermore, depletion of NK cells in vivo enables non-metastatic tumors to disseminate to LNs, and ablation of Tregs using FoxP3-DTR mice eliminates the occurrence of lymphatic metastases. 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, and we find that these Tregs are induced in an antigen-specific manner. Whole exome sequencing revealed that neither the metastatic proclivity nor immunosuppression evolve through the acquisition of driver mutations, loss of neoantigens, loss of MHC class I presentation, or decreases in melanoma antigen expression. 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 reprogramming of chromatin accessibility resulting from chronic exposure to interferons in vivo. Furthermore, using CRISPR/Cas9, we find that these pathways are required for LN metastatic seeding, and validate their conserved significance in additional mouse models of pancreatic ductal adenocarcinoma and head and neck squamous cell carcinoma and humans with LN metastatic disease. Together, these findings demonstrate a critical role for LN metastasis in promoting tumor-specific immunosuppression.
Citation Format: Nathan E. Reticker-Flynn, Weiruo Zhang, Julia A. Belk, Pamela A. Basto, Andrew J. Gentles, John B. Sunwoo, Ansuman K. Satpathy, Sylvia K. Plevritis, Edgar G. Engleman. Lymph node colonization promotes distant tumor metastasis through the induction of tumor-specific immune tolerance [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr PR013.