536 Divergent cancer etiologies drive distinct B cell signatures and tertiary lymphoid structures in head and neck cancer

Background Current FDA-approved immunotherapies aim to reinvigorate CD8+ T cells, but the contribution of the humoral arm of the immune response in human cancer remains poorly understood. B cells within tissues can mediate anti-tumor immunity and regulate immune responses by presenting antigen and producing tumor-specific antibodies and immunomodulatory cytokines. Head and neck squamous cell carcinoma (HNSCC) can be induced by human papillomavirus (HPV+) and carcinogens such as tobacco and alcohol (HPV-), and the immune infiltrate is quite distinct in the two etiologies, in particular, increased B cells in HPV+ HNSCC patients. Further, increased B cells in HNSCC patients correlate with improved patient survival. Our study seeks to differentiate B cell phenotype, function and location in HPV+ and HPV- HNSCC to identify putative B cell-centric immunotherapeutic targets. Methods We utilized a multi-level approach to clearly categorize B cells in HNSCC patients. Single cell RNA sequencing (scRNAseq) was performed on CD45+ tumor infiltrating lymphocytes (TIL) from HPV+ and HPV- HNSCC patients. HNSCC TIL and PBL were stained via spectral cytometry (Cytek Aurora,25 parameters) for unbiased analysis of B cell subsets via computational spectral unmixing. Paraffin embedded slides from HNSCC primary tumors were utilized for multispectral immunofluorescence (mIF) to identify tertiary lymphoid structures (TLS) and identify differences in HPV+ and HPV- disease. Results We demonstrated distinct trajectories for B cells in HPV+ and HPV- disease. HPV- HNSCC tumors mainly contained memory B cells and plasma cells, while the B cells in HPV+ HNSCC were naive and germinal center (GC). Further, we quantified B cells and CD4+ T cells in TLS, and germinal center-like TLS were associated with improved outcome in HPV+ disease. We also observed that transcriptional and protein expression of Semaphorin A (SEMA4a) was restricted to GC B cells and increased on GC B cells in HNSCC patients compared to healthy tonsils. Additionally, we identified distinct waves of gene expression in GC B cells in HNSCC tumors, ultimately revealing a novel transitional state for GC B cells in the tumor microenvironment (TME). Conclusions Understanding B cell function in human cancers and how different TMEs influence B cells and TLS are important for devising novel therapeutic options for cancer patients. Ultimately, development of therapeutics to enhance B cell responses in the TME should be prioritized as a compliment to T-cell mediated therapies.