Research ArticleCancer

T cell–induced CSF1 promotes melanoma resistance to PD1 blockade

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Science Translational Medicine  11 Apr 2018:
Vol. 10, Issue 436, eaan3311
DOI: 10.1126/scitranslmed.aan3311

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CSF1 curbs immunotherapy efficacy in melanoma

Although melanoma is one of the cancer types best targeted by checkpoint blockade, many patients are refractory to therapy. One likely culprit is the persistence of tumor-associated macrophages, which can be immunosuppressive. Neubert and colleagues examined patient samples and performed coculture experiments that implicated CD8+ T cell induction of tumor-derived CSF1, which could then promote immunosuppressive macrophages. Addition of CSF1 signaling blockade to anti-PD1 treatment improved responses in transplantable mouse melanoma models. These results uncover the biology of hurdles that still need to be overcome in immunotherapy, and also suggest a solution.

Abstract

Colony-stimulating factor 1 (CSF1) is a key regulator of monocyte/macrophage differentiation that sustains the protumorigenic functions of tumor-associated macrophages (TAMs). We show that CSF1 is expressed in human melanoma, and patients with metastatic melanoma have increased CSF1 in blood compared to healthy subjects. In tumors, CSF1 expression correlated with the abundance of CD8+ T cells and CD163+ TAMs. Human melanoma cell lines consistently produced CSF1 after exposure to melanoma-specific CD8+ T cells or T cell–derived cytokines in vitro, reflecting a broadly conserved mechanism of CSF1 induction by activated CD8+ T cells. Mining of publicly available transcriptomic data sets suggested co-enrichment of CD8+ T cells with CSF1 or various TAM-specific markers in human melanoma, which was associated with nonresponsiveness to programmed cell death protein 1 (PD1) checkpoint blockade in a smaller patient cohort. Combination of anti-PD1 and anti–CSF1 receptor (CSF1R) antibodies induced the regression of BRAFV600E-driven, transplant mouse melanomas, a result that was dependent on the effective elimination of TAMs. Collectively, these data implicate CSF1 induction as a CD8+ T cell–dependent adaptive resistance mechanism and show that simultaneous CSF1R targeting may be beneficial in melanomas refractory to immune checkpoint blockade and, possibly, other T cell–based therapies.

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