Engineered bacterial extracellular vesicles mediate pyroptosis to counteract m6A methylation-based immunosuppression after insufficient radiofrequency ablation of hepatocellular carcinoma

Insufficient radiofrequency ablation (IRFA) of hepatocellular carcinoma (HCC) leads to alterations in epigenetic properties such as <i>N</i> ⁶-methyladenosine (m⁶A) RNA methylation in tumor cells, which creates an immune-suppressive tumor microenvironment capable of promoting residual tumor growth and recurrence and affecting the efficacy of RFA. In this study, the constructed STM-Mn@OMVs, which were produced through the rational functionalisation of bacterial-derived OMVs with Mn²⁺ ions and the methylation inhibitor STM2457, were found to effectively activate antitumor immunity. Our study shows that STM-Mn@OMVs can effectively promote dendritic cells (DCs) maturation, T cell activation, and STING pathway activation after endocytosis by cells, thus promoting immune cell infiltration. The STM-Mn@OMVs were able to promote cellular pyroptosis and synergistically activate the STING pathway. Furthermore, STM-Mn@OMVs promoted the increase of M1 macrophage phenotype in tumor-associated macrophages (TAMs) by reducing the infiltration of immunosuppressive cell populations such as regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), thus reversing the suppressive immune microenvironment after IRFA to some extent. Ultimately, the growth of residual tumors was inhibited. In addition, the biosafety of STM-Mn@OMVs was demonstrated in this study. Therefore, the STM-Mn@OMVs constructed in this study have great potential for application in the field of RFA and immunotherapy for HCC.