A strong B cell response is part of the immune landscape in human high-grade serous ovarian metastases.
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PURPOSE: In high-grade serous ovarian cancer (HGSOC), higher densities of both B cells and the CD8+ T cell infiltrate were associated with a better prognosis. However, the precise role of B cells in the anti-tumor response remains unknown. As peritoneal metastases are often responsible for relapse, our aim was to characterize the role of B cells in the anti-tumor immune response in HGSOC metastases. EXPERIMENTAL DESIGN: Unmatched pre and post-chemotherapy HGSOC metastases were studied. B-cell localization was assessed by immunostaining. Their cytokines and chemokines were measured by multiplex assay and their phenotype was assessed by flow cytometry. Further in vitro and in vivo assays highlighted the role of B cells and plasma cell IgGs in the development of cytotoxic responses and dendritic cell activation. RESULTS: B cells mainly infiltrated lymphoid structures in the stroma of HGSOC metastases. There was a strong B-cell memory response directed at a restricted repertoire of antigens and production of tumor-specific IgGs by plasma cells. These responses were enhanced by chemotherapy. Interestingly, transcript levels of CD20 correlated with markers of immune cytolytic responses and immune complexes with tumor-derived IgGs stimulated the expression of the co-stimulatory molecule CD86 on antigen presenting cells. A positive role for B cells in the anti-tumor response was also supported by B cell depletion in a syngeneic mouse model of peritoneal metastasis. CONCLUSIONS: Our data showed that B cells infiltrating HGSOC omental metastases support the development of an anti-tumor response.