LB879 Friend or foe? Identification of MCPyV-specific B cells in Merkel cell carcinomas suggests a functional role in tumor immunity

Merkel cell carcinoma (MCC) is a rare and aggressive cancer of the skin with ∼30% mortality. Around 80% MCC tumors originate from integration polyomavirus (MCPyV) DNA into host genome, leading to expression viral T-antigen oncoprotein ultimately, tumorigenesis. Though PD-1 pathway blockade has significantly improved outcomes for advanced MCC, many patients do not benefit or develop resistance this immunotherapy. In recent years, tumor-infiltrating B cells have been generally associated better in MCC. immunity against presumed within situ lymphocyte maturation aggregates. These ‘tertiary lymphoid structures’ harbor germinal center that promote anti-tumor CD8 T responses collaboration CD4 follicular helper cells. However, mechanisms by which tumor antigen-specific sometimes antagonize difficult elucidate human tumors. The obligate all MCPyV-positive allows cancer-specific be studied across multiple patients. Using barcoded fluorescently labeled protein tetramer, we analyzed transcriptome, proteome, antibody sequences MCPyV-specific 13 digest samples using single-cell technologies. were identified both tumor-infiltrated lymph nodes Protein mRNA analyses revealed presence hallmarks antibody-secreting cells, indicating an ongoing response targeting virus-derived antigen. data suggest tumor-specific could novel approach improve efficacy