B cells sustain inflammation and predict response to immune checkpoint blockade in human melanoma

Tumor associated inflammation predicts response to immune checkpoint blockade in human melanoma. Established mechanisms that underlie therapy response and resistance center on anti-tumor T cell responses. Here we show that tumor-associated B cells are vital to tumor associated inflammation. Autologous B cells were directly induced by melanoma conditioned medium, expressed pro- and anti-inflammatory factors, and differentiated towards a plasmablast-like phenotype in vitro. We could identify this phenotype as a distinct cluster of B cells in an independent public single-cell RNA-seq dataset from melanoma tumors. There, plasmablast-like tumor-associated B cells showed expression of CD8+T cell-recruiting chemokines such as CCL3, CCL4, CCL5 and CCL28. Depletion of tumor associated B cells in metastatic melanoma patients by anti-CD20 immunotherapy decreased overall inflammation and CD8+T cell numbers in the human melanoma TME. Conversely, the frequency of plasmablast-like B cells in pretherapy melanoma samples predicted response and survival to immune checkpoint blockade in two independent cohorts. Tumor-associated B cells therefore orchestrate and sustain tumor inflammation, recruit CD8+ T effector cells and may represent a predictor for response and survival to immune checkpoint blockade in human melanoma.