Abstract LB230: A prospective immunological analysis of head and neck squamous cell carcinoma in humans

Abstract Head and neck squamous cell carcinoma (HNSCC) is characterized by poor prognosis, with the 5-year survival rate being less than 50% for advanced HNSCC. Despite improvements in treatments, approximately half of HNSCC patients will recur. Clinical evidence suggests that patients with a higher density of TCF1+PD1+CD8+ T cells in the tumor prior to anti-PD1 treatment correlate with longer survival, though it is unknown whether this T cell subset remains in previously irradiated recurrent HNSCC tumors. This suggests that further analysis is needed to assess predictive biomarkers that correlate with outcomes in HNSCC patients. Thus, we conducted RNAseq on baseline tumors collected from standard of care HNSCC patients without a prior history of treatment to identify the major immune cell populations present in HNSCC tumors. RNAseq data highlighted functional T cell heterogeneity in HNSCC tumors and identified the presence of stem-like and effector T cell subsets which varied in composition across patient samples. Analysis further identified CCR5-CCL3 signaling corresponding to T cell-DC crosstalk, suggesting the formation of T cell-DC immune niches. We then utilized multiplex immunofluorescence (mIF) to analyze the tumor microenvironment (TME) of previously irradiated recurrent HNSCC tumors prior to concurrent reirradiation and nivolumab (anti-PD1) treatment. Analysis revealed that 70% of CD8+ T cells were PD1+ at the time of resection (N=30). On average, a higher density of TCF1-PD1+CD8+ effector T cells (median=63%, N=30) was observed compared to TCF1+PD1+CD8+ stem-like T cells (median=37%, N=30). Spatial distribution analysis further showed that TCF1+PD1+CD8+ stem-like T cells were localized significantly closer to MCH-II+ cells (p0. 0001) than TCF1-PD1+CD8+ effector T cells and correlated with immune niche density. Progressors had a lower density of both TCF1+PD1+CD8+ stem-like T cells and immune niche compared to non-progressors. A further analysis of the peripheral blood collected from these patients during concurrent reirradiation and nivolumab treatment was also conducted utilizing flow cytometry. When compared to the peripheral blood of the standard of care HNSCC patients receiving chemoradiotherapy, we observed an increased fold-change difference in Mo-MDSCs and activated CD8+CD38+HLADR+ T cells from baseline in the recurrent HNSCC patients at week 1 of radiation treatment not seen in the standard of care HNSCC patients. Our results suggest that previously irradiated recurrent HNSCC tumors maintain the stem-like CD8+ T cell population necessary for a robust anti-tumor response and that high density of both immune niche and TCF1+PD1+CD8+ T cells within the TME correlate with better outcomes in HNSCC patients. Our results also suggest that concurrent radiation and anti-PD1 immunotherapy impact circulating immune cell populations differently than chemoradiotherapy in HNSCC patients. Citation Format: Tarralyn Y. Clark, Erin Connolly, Jeromy Dooyema, Nabil Saba, Shlomo Koyfman, Haydn Kissick, Nicole C. Schmitt, Christine Lee-Poturalski, Timothy Chan, David Yu, Zachary S. Buchwald. A prospective immunological analysis of head and neck squamous cell carcinoma in humans abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86 (8Suppl): Abstract nr LB230.