Modular engineered outer membrane vesicles for synergistic cancer immunotherapy via PD-L1 blockade and epigenetic reprogramming.

Immune checkpoint inhibitors have significantly improved therapeutic outcomes in advanced melanoma; however, their clinical efficacy is greatly limited by low overall response rates and the primary or acquired resistance. Here, we developed a SpyCatcher-engineered bacterial outer membrane vesicle (OMV) platform for the co-delivery of a PD-1/PD-L1 inhibitor, the D-PPA1 peptide, and the epigenetic regulator zebularine (Zeb). The resulting co-delivery system, OMV@PPA/Zeb, effectively blocked PD-1/PD-L1 interactions and markedly upregulated melanoma-associated antigens, including CD146 and TRP1, in melanoma cells. In a subcutaneous melanoma mouse model, OMV@PPA/Zeb substantially suppressed tumor growth without noticeable systemic toxicity. Moreover, OMV@PPA/Zeb significantly promoted the infiltration and activation of CD8+ T cells while reducing regulatory T cells (Tregs) within the tumor microenvironment. The potent antitumor immune response elicited by this platform contributed to its enhanced therapeutic efficacy against melanoma. Overall, this study provides a modular OMV-based strategy for combination immunotherapy in advanced tumors.