Abstract B019: Mapping the tumor-sentinel node immune migratome demonstrates a key role for CCR7+ dendritic cells in the successful response to immunoradiotherapy

Abstract Immune checkpoint inhibition has demonstrated no benefit when combined with chemoradiotherapy for locally advanced HNSCC, raising the possibility that standard therapies compromise the response to immunotherapy. To address this hypothesis, we previously demonstrated that ablating tumor draining lymphatics abolishes the response to immune-oncology therapy. Specifically, we defined that the response to immunotherapy is coordinated by interferon type-I signaling through the cDC1 population in tumor-draining lymph nodes. These findings support the premise that successful tumor responses to immuno-oncology therapies is predicated upon intact and functional, locoregional anatomy. Accordingly, we hypothesize that lymphatic-preserving, tumor-directed immune oncology therapy will promote antitumor immunity by enhancing surveillance along the tumor-immune-lymphatic axis. To explore this, we employ a novel mouse reporter model that allows precise spatiotemporal labeling of immune effector cells. Combined with sentinel lymph node mapping, our reporter model enables selective labeling of immune effectors within the tumor microenvironment and subsequent tracking and characterization of these cells as they migrate to the sentinel lymph node. This approach led us to define the “cancer immune migratome” - the repertoire of immune cells actively migrating from tumors to lymph nodes during an antitumor response. For precise cellular identification, we employed CITE-sequencing, which integrates single-cell RNA expression with surface protein markers, allowing us to comprehensively define the characteristics of migrating immune cells. This work represents the first characterization of immune cell populations migrating from the tumor to the sentinel lymph node, revealing the diversity and dynamics of these populations in antitumor immunity. We then develop a tumor-directed, lymphatic-sparing radiotherapy model to modulate the tumor immune microenvironment without inducing tumor regression. Sequential administration of tumor-directed radiotherapy followed by PD-1 checkpoint inhibition achieves complete and durable responses. Analysis of the cancer immune migratome during immunoradiotherapy revealed a crucial role for an activated population of CCR7+ dendritic cells. These migratory dendritic cells are reprogrammed, via rational sequencing of radiation and immunotherapy, from their canonical role in immune tolerance to actively drive antitumor immunity. This reprogramming enhances T cell priming, clonotypic expansion, and, ultimately, the successful tumor response to immunoradiotherapy. Disruption of sentinel lymphatic channels or selective blockade of CCR7+ DC entry into the SLN abrogates the response to immunoradiotherapy. Overall, this work supports rationally sequencing immune-sensitizing, lymphatic-preserving, tumor-directed radiotherapy followed by immune checkpoint inhibition to optimize tumor response. Our findings support a therapeutic strategy that enhances host response to immunotherapy by directing activated dendritic cells to sentinel lymph nodes. Citation Format: Robert Saddawi-Konefka, Riyam Al Msari, Shiqi Tang, Lauren Clubb, Santiago Fassardi, Riley Jones, Farhoud Faraji, Shiruyeh Schokrpur, Bryan S Yung, Michael M Allevato, Shawn M Jensen, Bernard A Fox, Richard Bell, J. Silvio Gutkind, Andrew Sharabi, Joseph A Califano. Mapping the tumor-sentinel node immune migratome demonstrates a key role for CCR7+ dendritic cells in the successful response to immunoradiotherapy [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B019.