Bowen Li

The advancement of mRNA‐based immunotherapies for cancer is highly dependent on the effective delivery of RNA payloads using ionizable lipid nanoparticles (LNPs). However, the clinical application of these therapies is hindered by variable mRNA expression among different cancer types and the risk of systemic toxicity. The transient expression profile of mRNA further complicates this issue, necessitating frequent dosing and thus increasing the potential for adverse effects. Addressing these challenges, we utilized a high‐throughput combinatorial method to synthesize and screen LNPs that efficiently deliver circular RNA (circRNA) to lung tumors. Our lead LNP, H1L1A1B3, demonstrated a fourfold increase in circRNA transfection efficiency in lung cancer cells over ALC‐0315, the industry‐standard LNPs, while providing potent immune activation. A single intratumoral injection of H1L1A1B3 LNPs, loaded with circRNA encoding interleukin‐12 (IL‐12), induced a robust immune response in a Lewis lung carcinoma model, leading to marked tumor regression. Immunological profiling of treated tumors revealed substantial increments in CD45 + leukocytes and enhanced infiltration of CD8 + T cells, underscoring the ability of H1L1A1B3 LNPs to modulate the tumor microenvironment favorably. These results highlight the potential of tailored LNP platforms to advance RNA drug delivery for cancer therapy, broadening the prospects for RNA immunotherapeutics. This article is protected by copyright. All rights reserved