The Tumor-Sentinel Lymph Node Immune Migratome Reveals a Key Role for Migratory CCR7+ Dendritic Cells in Response to Immunoradiotherapy [CITE-seq]

Surgical ablation or radiation of tumor-draining lymph nodes can eliminate the primary tumor response to immunotherapy, indicating that local tumor response to immunotherapy is mediated by tumor-draining lymph nodes. Here, we show that immunoradiotherapy efficacy is dependent on immune cell migration from tumor to sentinel lymph nodes. Using a tamoxifen-inducible reporter paired with CITE-sequencing in a murine model of oral cancer, we characterized tumor immune cellular migration through lymphatic channels to sentinel lymph nodes at single-cell resolution. Within a structured approach of sequential immunomodulatory radiotherapy and checkpoint inhibition, we demonstrate that lymphatic-sparing, tumor-directed radiotherapy followed by PD-1 inhibition achieves complete and durable tumor responses. Mechanistically, this treatment approach enhances activated, migratory CCR7+ dendritic cell surveillance across the tumor-sentinel lymph node axis, revealing a shift from their canonical role in promoting tolerance to driving antitumor immunity. Overall, this work supports rationally sequencing immune-sensitizing, lymphatic-preserving, tumor-directed radiotherapy followed by immune checkpoint inhibition to optimize the tumor response. By characterizing the tumor-sentinel lymph node immunomigratome that drives durable antitumor response, we reveal a therapeutic opportunity to enhance the response to immunotherapy by optimizing activated dendritic cell migration to tumor-draining sentinel nodes. Overall design: CITE-sequencing was performed on cells isolated from sentinel lymph node (sln) and tumors of mice treated with and without immunoradiotherapy (IRT) to characterize immune cell populations involved in antitumor surveillance