A comprehensive single-cell map of T cell exhaustion-associated immune environments in human breast cancer
Abstract Immune checkpoint therapy in breast cancer remains restricted to triple negative patients, and long-term clinical benefit is rare. The primary aim of immune checkpoint blockade is to prevent or reverse exhausted T cell states, but the causes and implications of T cell exhaustion in breast tumors are not well understood. Here, we used single-cell transcriptomics combined with imaging mass cytometry to comprehensively study exhausted and non-exhausted immune environments in human breast tumors, with a focus on Luminal subtypes. We found that the presence of a PD-1high exhaustion-like T cell phenotype was indicative of an inflammatory immune environment with a characteristic cytotoxic profile and spatial features. Accumulation of natural killer T cells and increased myeloid cell activation in exhausted immune environments provide further support for tissue inflammation in these environments. Consistent with this, our comprehensive map of cellular interactions within the breast tumor microenvironment revealed elevated immunomodulatory, chemotactic, and cytokine signaling in exhausted environments. These data reveal fundamental differences between exhausted and non-exhausted immune environments within Luminal breast cancer, and show that expression of PD-1 and CXCL13 on T cells, and MHC-I – but not PD-L1 – on tumor cells are strong distinguishing features between these environments; these factors are potential new biomarkers for patient stratification.