Oncolytic viruses (OVs) represent a promising cancer immunotherapy modality; however, their clinical translation is significantly impeded by manufacturing complexities, biosafety concerns, pre-existing neutralizing antibodies, and viral genome engineering constraints. Here, we introduce Self-Amplifying mRNA-based Virus-like Vesicles In vivo Generation (SAMVIG), a versatile system enabling in vivo production of enveloped virus-like vesicles (VLVs). SAMVIG integrates an alphavirus RNA replicon, therapeutic payloads, and vesicular stomatitis virus glycoprotein within a single mRNA construct delivered via lipid nanoparticles. The system orchestrates multi-layered immune activation by combining dual antigen presentation, immune modulator co-expression, and VLV-mediated intercellular spread to elicit potent innate immune responses. This design leverages the advantages of mRNA technology and consolidates OV-like immunostimulatory functions while bypassing traditional OV constraints. Local and systemic administration of SAMVIG encoding tumor antigens significantly enhanced tumor-infiltrating lymphocyte recruitment and activation, resulting in robust antitumor efficacy across subcutaneous and metastatic tumor models. The modular architecture of SAMVIG facilitated seamless integration of checkpoint inhibitors (e.g., PD-1/PD-L1 inhibitor) and other functional proteins to substantially enhance therapeutic efficacy, without apparent payload length limitations. Coupled with its favorable safety profile observed in vivo, SAMVIG represents a versatile and customizable immunotherapy system that marks a paradigm shift in the field of oncolytic immunotherapy.
