Sentinel lymph node-derived CD45⁺ cells combined with low-dose radiotherapy and PD-1 blockade as a next-generation adoptive cell therapy in head and neck cancer

Purpose: Head and neck squamous cell carcinoma (HNSCC) is the seventh most common cancer globally, representing roughly 6% of all malignancies. Each year it accounts for an estimated 660,000 new diagnoses and over 325,000 deaths, with incidence projected to rise by nearly 30% by 2030. Despite advances in surgery, radiation, and immunotherapy, patients with HPV-negative HNSCC continue to face poor outcomes, with five-year overall survival rates often below 55%. Adoptive cell therapy (ACT) in solid tumors remains limited by the scarcity of tumor-reactive T cells and their functional exhaustion after expansion. The sentinel lymph node (SLN), the initial site of tumor antigen presentation and T-cell priming, may provide a rich and minimally exhausted source of tumor-specific lymphocytes. Here, we evaluated the immunologic and therapeutic advantages of SLN-derived leukocytes over those from tumor tissue in an orthotopic model of HPV⁻ HNSCC. Methods: CD45⁺ immune cells isolated from donor SLNs, NSLNs, tumors, or SLNs preconditioned with low-dose tdRT (4 Gy) in the 4MOSC1 murine model were adoptively transferred into syngeneic tumor-bearing recipients to evaluate their therapeutic potential. Recipient groups included untreated controls, preconditioned mice with 4 Gy tdRT, or a single PD-1 blockade (PD1i) dose before ACT. Phenotypic and functional characterization was performed using flow cytometry, multiplex immunofluorescence, ELISA, and CITE-seq to evaluate cell populations, activation, exhaustion, clonal overlap, and tissue distribution. Results: SLN-CD45⁺ populations were enriched in activated CD4⁺/CD8⁺ T cells with elevated CD69, CD137, and IFN-gamma expression compared with tumor-derived counterparts. mIHC confirmed higher densities of activated T cells in SLN and tumor regions after SLN-CD45⁺ transfer. TCR analysis revealed substantial overlap between SLN and tumor clonotypes, suggesting selective enrichment of tumor-reactive clones. Functionally, ACT with SLN-CD45⁺ cells induced greater tumor regression and survival benefits than ACT from tumor source, even without lymphodepletion or expansion in culture. Notably, cryopreserved SLN-derived cells retained comparable efficacy to freshly isolated ones. Preconditioning recipients with 4 Gy tdRT or PD1i further improved intratumoral infiltration, activation, and persistence of transferred cells without added toxicity. Conclusions: The sentinel lymph node provides a potent, readily accessible reservoir of tumor-reactive immune cells for ACT. Combining SLN-derived ACT with tdRT and PD1i significantly enhances therapeutic efficacy in HPV⁻ HNSCC. These findings highlight the translational potential of leveraging tumor-draining lymphoid niches as tumor-primed immune reservoirs for next-generation ACT in solid tumors.