Collagen-Bearing Exosomes from Breast Cancer-Associated Fibroblasts Promote T-cell Dysfunction.

Cancer-associated fibroblasts (CAF), a major component of the breast tumor microenvironment, drive immune evasion in various cancers by promoting T-cell exclusion and dampening T-cell activation. Previous studies have implicated CAF-derived soluble factors in mediating these immunosuppressive effects. In this study, we investigated whether exosomes secreted by CAFs could suppress T-cell activity. Inhibition of global exosome secretion in breast tumor-bearing mice significantly reduced tumor growth and increased tumor-infiltrating T cells with lower exhaustion marker expression. Conversely, administration of CAF-derived exosomes into tumors produced the opposite effects. Moreover, CAF exosomes associated with T cells in vivo and impaired T-cell activation and cytotoxic potential in ex vivo assays. Proteomic and biochemical analyses of T cells exposed to CAF exosomes revealed dampened early T-cell receptor signaling. Mass spectrometry identified an extracellular matrix (ECM) signature on CAF exosomes. Depleting type I and type V collagens from CAF exosomes restored T-cell proliferation, whereas overexpression of collagen in cancer cells led to its incorporation into exosomes, which suppressed T-cell activation. These findings suggest that a signaling bridge between CAF exosomes and T cells, mediated by collagen, promotes T-cell dysfunction, contributing to immune evasion in breast cancer. SIGNIFICANCE: Our data provide the first evidence that ECM proteins associate with mouse and human breast CAF-derived exosomes and directly impair T-cell activation and cytotoxicity. These findings suggest that signaling between collagen-rich CAF exosomes and T cells contribute to local and systemic T-cell dysfunction.