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.
Immune-Checkpoint Blockade Opposes CD8+ T-cell Suppression in Human and Murine Cancer