Gsell, L.; Watson, S. S.; Sutevski, I.; Massara, M.; Soukup, K.; Eroglu, A.; Mold, J. E.; Joyce, J. A.; Hausser, J.

In cancer, improving diagnostics and therapeutic interventions can benefit from understanding the cellular and phenotypic heterogeneity of the tumor microenvironment (TME). In recent years, the TME has been profiled at an unprecedented level of detail by performing single-cell RNA sequencing (scRNAseq) on patient samples. However, from patient samples, studying the temporal dynamics of the TME using patient samples has been challenging. Interrogating the temporal dynamics of the TME is critical to understand how inter-tumor heterogeneity is organized into a temporally ordered sequence of causes and consequences in cellular events. Here we survey the temporal dynamics of the TME by performing longitudinal scRNAseq on mouse breast tumors at different progression time points of tumor progression. We reveal multi-cellular phenotypic dynamics that follow one out of three possible temporal patterns: stable colonization, wave-like, or progressive increase. In particular, IFN-responsive cancer cells, GzmB + cytotoxic T cells, as well as C1q macrophages, progressively increase in parallel with tumors progression. These findings establish the single-cell types and phenotypes in a progressing breast tumor, and determine when these cellular players enter and leave the TME.