Combating small extracellular vesicle–mediated immunological barriers in the tumor microenvironment via strategically activatable PEGylated peptides

Tumor cell-derived small extracellular vesicles (TDEs) play a critical role in immune evasion, including the establishment of an immunosuppressive tumor microenvironment (TME), and form a substantial barrier to effective cancer immunotherapy. Here, we introduce the ExoPERM (pH-enabled rupture of exosome membranes) strategy, a pH-responsive system based on small extracellular vesicle (EV)-disrupting alpha-helical peptides that selectively target small EVs localized within the TME. By incorporating a pH-sensitive linker through PEGylation, this system ensures systemic stability while allowing the selective release of peptides within the mildly acidic TME. Mechanistic investigations revealed that the peptide preferentially ruptured small EVs at pH 6.5, effectively preventing EVs' PD-L1 interactions with PD-1 on CD8⁺ T cells and contributing to the restoration of their effector functions. Furthermore, this targeted disruption significantly attenuated TDE-induced activation of cancer-associated fibroblasts, thereby remodeling the dense fibrotic stroma that physically restricts immune cell penetration. In vivo studies have demonstrated enhanced CD8⁺ T-cell tumor infiltration and activation, notably when combined with immune checkpoint blockade or adoptive T-cell transfer. These synergistic effects were robustly validated across murine melanoma and colorectal cancer models, successfully converting immunologically cold tumors into T-cell-inflamed hot tumors. The ExoPERM strategy provides a promising option for overcoming TDE-mediated resistance in cancer, suggesting a distinct approach to small EV inhibition.