A flexible, efficient, and scalable platform to produce circular RNAs as new therapeutics

Messenger RNA (mRNA) has recently emerged as a new drug modality with great therapeutic potential. However, linear mRNAs are relatively unstable and require base modification to reduce their immunogenicity, imposing a limitation to the broad application. The circular RNA (circRNA) presents a better alternative for prolonged expression of the proteins. However the in vitro circularization of RNA at industrial scale is technically challenging, and the direct comparison of efficacy between the circRNA and linear mRNA drugs is lacking. Here we developed a new self-catalyzed system to efficiently produce circRNAs in a co-transcriptional fashion. By rational sequence design, we can efficiently produce scarless circRNAs that do not contain foreign sequences. The resulting circRNAs are very stable and have low immunogenicity, enabling prolonged protein translation in different cells without cellular toxicity. The circRNAs encapsulated in lipid nanoparticles can be efficiently delivered into mice to direct robust protein expression with improved duration and efficiency. Finally, the circRNAs encoding RBD of SARS-CoV-2 S protein induced strong antibody productions, with neutralization antibody titers higher than the preclinical data from the linear mRNAs. Collectively, this study provided a general platform for efficient production of circRNAs with robust activity in directing protein production, demonstrating the potential of circRNAs as the new generation of mRNA therapy.