Gubin et al. utilized single cell RNAseq and CyTOF to analyze the lymphoid and myeloid compartments in mice with T3 murine sarcoma that were treated with control, leading to tumor progression, or immune checkpoint therapy (ICT: anti-PD-1, anti-CTLA-4, or both), leading to tumor rejection. ICT reduced Tregs and activated and expanded NK cells, CD4+ T cells, and CD8+ T cells. This resulted in increased IFNγ, which led to maturation of monocytes into proinflammatory CX3CR1-CD206-iNOS+ macrophages in tumors that were ultimately rejected.
Although current immune-checkpoint therapy (ICT) mainly targets lymphoid cells, it is associated with a broader remodeling of the tumor micro-environment. Here, using complementary forms of high-dimensional profiling, we define differences across all hematopoietic cells from syngeneic mouse tumors during unrestrained tumor growth or effective ICT. Unbiased assessment of gene expression of tumor-infiltrating cells by single-cell RNA sequencing (scRNAseq) and longitudinal assessment of cellular protein expression by mass cytometry (CyTOF) revealed significant remodeling of both the lymphoid and myeloid intratumoral compartments. Surprisingly, we observed multiple subpopulations of monocytes/macrophages, distinguishable by the markers CD206, CX3CR1, CD1d, and iNOS, that change over time during ICT in a manner partially dependent on IFNgamma. Our data support the hypothesis that this macrophage polarization/activation results from effects on circulatory monocytes and early macrophages entering tumors, rather than on pre-polarized mature intratumoral macrophages.