Tumor-Secreted Extracellular Vesicles Regulate T-Cell Costimulation and Can Be Manipulated To Induce Tumor-Specific T-Cell Responses.

Background & Aims: Colorectal cancer is a major cause of cancer-related deaths worldwide. Immune checkpoint blockade therapies are effective in 30%-60% of the microsatellite instable-high subtype. Unfortunately, most patients with colorectal cancer (>85%) have microsatellite stable tumors that do not respond. In this study, we aimed to decipher the underlying tumor-intrinsic mechanisms critical for improving immunotherapy in colorectal cancer.

Methods: We used human and mouse tumor samples, cell lines, human colorectal cancer organoids, and various syngeneic orthotopic mouse models of late-stage colorectal cancer to define the effects of tumor cell-secreted extracellular vesicles (EVs) on antitumor immune response.

Results: Our analyses of human colorectal cancer immune profiles and tumor-immune cell interactions showed that tumor-secreted EVs containing microRNA miR-424 suppressed the CD28-CD80/86 costimulatory pathway in tumor-infiltrating T cells and dendritic cells, leading to immune checkpoint blockade resistance. Modified tumor-secreted EVs with miR-424 knocked down enhanced T-cell-mediated antitumor immune response in colorectal cancer tumor models and increased the immune checkpoint blockade response. Intravenous injections of modified tumor-secreted EVs induced tumor antigen-specific immune responses and boosted the immune checkpoint blockade efficacy in colorectal cancer models that mimic aggressively progressing, late-stage disease.

Conclusions: Collectively, we show a critical role for tumor-secreted EVs in antitumor immune regulation and immunotherapy response, which could be developed as a novel treatment for immune checkpoint blockade-resistant colorectal cancer.