Single-cell RNA-sequencing of murine melanoma infiltrating immune cells in wild-type and miR-155 T cell conditional knockout mice

miR-155 has recently emerged as an important promoter of antitumor immunity through its functions in T lymphocytes. However, the impact of T cell expressed miR-155 on immune cell dynamics in solid tumors remains unclear. In the present study, we used single-cell RNA-sequencing to define the CD45+ immune cell populations within B16F10 murine melanoma tumors growing in either wild-type (WT) or miR-155 T cell conditional knockout (TCKO) mice at different timepoints. miR-155 was required for optimal T cell activation and reinforced the T cell response at the expense of infiltrating myeloid cells. Further, myeloid cells from tumors growing in TCKO mice were defined by an increase in wound healing genes and a decreased IFNg response gene signature. Finally, we found that miR-155 expression predicted a favorable outcome in human melanoma patients and was associated with a strong immune signature. Moreover, gene expression and histological analysis of the Cancer Genome Atlas (TCGA) data revealed that miR-155 expression also correlates with an immune-enriched subtype in 29 other human solid tumor types. Together, our study provides an unprecedented analysis of the cell types and gene expression signatures by immune cells within experimental melanoma tumors and elucidates miR-155’s role in coordinating this dynamic response.