Biomimetic mineralization-inspired formulation-adjuvant integrated circRNA nanovaccine against COVID-19

Abstract

Conventional RNA-based vaccines rely on lipid nanoparticles (LNPs) for delivery; however, concerns exist regarding the potential systemic toxicity of their chemical composition, and their immune-activating capabilities require further enhancement. Inspired by Mg²⁺ as a key ion for maintaining RNA secondary structure stability, we developed a one-pot method for directly synthesizing a circular RNA-based formulation-adjuvant integrated nanovaccine (CircRNA@FAiNVac) capable of delivering programmed circular RNA (circRNA) based on biomimetic mineralization principles. Specifically, during circRNA rolling circle transcription, the controllable crystallization of magnesium pyrophosphate (MgPPi) nanoparticles was achieved by enhancing the reaction kinetics between ribonucleotide triphosphates and Mg²⁺, thereby encapsulating circRNA within the nanoparticles and forming a protective carrier that also functions as an adjuvant. Based on the specific hydrolysis of MgPPi by pyrophosphatase, CircRNA@FAiNVac can efficiently release RNA intracellularly, thereby facilitating gene expression. Unlike LNPs, which often contain toxic excipients, the vector structure of CircRNA@FAiNVac consisted only of nucleic acid precursors and ions, exhibiting good biocompatibility and reducing adverse reactions. More importantly, CircRNA@FAiNVac possessed potent immune activation capabilities; its self-adjuvanting activity promoted multimodal immune activation, enhancing both humoral and cellular responses. Animal experiments confirmed that the innovative design of CircRNA@FAiNVac ensured stable and sustained autonomous expression of the SARS-CoV-2 receptor-binding domain, while the nanostructure activated multiple immune pathways, providing potent protection. The formulation-adjuvant integration strategy of CircRNA@FAiNVac based on biomimetic mineralization principles provides an alternative approach for the development of next-generation vaccines. Based on antigen sequence optimization, it enables rapid customized development of vaccines targeting variant strains.