Multiplexed imaging mass cytometry of the chemokine milieus in melanoma characterizes features of the response to immunotherapy

Intratumoral immune cells are crucial for tumor control and antitumor responses during immunotherapy. Immune cell trafficking into tumors is mediated by binding of specific immune cell receptors to chemokines, a class of secreted chemotactic cytokines. To broadly characterize chemokine expression and function in melanoma, we used multiplexed mass cytometry-based imaging of protein markers and RNA transcripts to analyze the chemokine landscape and immune infiltration in metastatic melanoma samples. Tumors that lacked immune infiltration were devoid of most of the profiled chemokines and exhibited low levels of antigen presentation and markers of inflammation. Infiltrated tumors were characterized by expression of multiple chemokines. CXCL9 and CXCL10 were often localized in patches associated with dysfunctional T cells expressing the B lymphocyte chemoattractant CXCL13. In tumors with B cells but no B cell follicles, T cells were the sole source of CXCL13, suggesting that T cells play a role in B cell recruitment and potentially in B cell follicle formation. B cell patches and follicles were also enriched with TCF7+ naïve-like T cells, a cell type that is predictive of response to immune checkpoint blockade. Our data highlight the strength of targeted RNA and protein codetection to analyze tumor immune microenvironments based on chemokine expression and suggest that the formation of tertiary lymphoid structures may be accompanied by naïve and naïve-like T cell recruitment, which may contribute to antitumor activity.