Response of B Cells Specific for Polyomavirus-Derived Oncoprotein Is Predictive of Merkel Cell Carcinoma Tumor Control

Merkel cell carcinomas (MCC) typically arise from the clonal integration of the Merkel cell polyomavirus. Immunogenic viral oncoproteins then lead to tumorigenesis. Oncoprotein-specific T cells are essential for anti-MCC immunity, but it is unclear whether B cells promote tumor control. In this study, we analyzed the frequency and phenotype of viral oncoprotein–specific and total B cells in blood samples from 47 patients with MCC and tumor samples from another 19 patients with MCC. The phenotype of blood B cells did not correlate with the outcomes of patients with MCC. In contrast, all 11 patients with robust oncoprotein-specific antibody-secreting and/or germinal center B cells in tumors experienced long-term MCC control. In vitro, B cells engineered to be specific for viral oncoproteins increased the sensitivity of oncoprotein-specific CD4^+ T cells by more than 50-fold. Together, our findings suggest that cancer-specific B cells promote antitumor immunity via increased responses by T cells and that cancer-specific augmentation of B cells could be therapeutically relevant.