A Unique Signature for Cancer-Associated Fibroblasts in Melanoma Metastases.

Cancer-associated fibroblasts (CAFs) represent a central cell population of the tumor microenvironment (TME). Recently, single-cell RNA-sequencing (scRNA-seq) analyses of primary tumors of different cancer entities yielded different classifications of CAF subsets underscoring the heterogeneity of CAFs within the TME. Here, we analyzed the transcriptional signatures of approximately 8400 CAFs and normal fibroblasts by scRNA-seq and compared genetic profiles of CAFs from murine melanoma primary tumors to CAFs from corresponding melanoma lung metastases. This revealed distinct subsets for primary tumor and metastasis-specific CAF populations, respectively. Combined with the spatial characterization of metastasis CAFs at the RNA and protein level, scRNA analyses indicate tumor-dependent crosstalk between neutrophils and CAFs, mediated via SAA3 and IL1b-related signaling pathways, which can be recapitulated in vitro. Analyzing tissue sections of human patient samples, this interaction was found to be present in human melanoma metastasis. Taken together, our data highlight unique characteristics of metastasis CAFs with potential therapeutic impact for melanoma metastasis.