Microglial reprogramming enhances antitumor immunity and immunotherapy response in melanoma brain metastases

Melanoma is one of the solid tumor types with the highest risk of brain metastasis. However, the biology of melanoma brain metastasis and the contribution of the brain immune microenvironment to the responses to therapies remain insufficiently characterized. By using preclinical models and single-cell transcriptomics, we identify microglia, as critical regulators of melanoma biology in the brain. We show that activation of the Rela/NF-kB pathway in microglia promotes melanoma brain metastasis and that targeting this pathway elicits microglia reprogramming towards a pro-inflammatory phenotype that enhances anti-tumor immunity and reduces brain metastatic burden. Additionally, canonical and pro-inflammatory microglial markers in melanoma brain metastasis correlate with better responses to immune checkpoint inhibitors in patients and we show that Rela/NF-kB targeting improves responses to these therapies in the brain. Thus, we propose targeting Rela/NF-kB in activated microglia as a strategy to promote anti-tumor immunity and to improve the response to immune checkpoint inhibitors in melanoma brain metastasis.