Although the use of RNAs has enormous therapeutic potential, these RNA-based therapies can trigger unwanted inflammatory responses by the activation of pattern recognition receptors (PRRs) and cause harmful side effects. In contrast, the immune activation by therapeutic RNAs can be advantageous for treating cancers. Thus, the immunogenicity of therapeutic RNAs should be deliberately controlled depending on the therapeutic applications of RNAs. In this study, we demonstrated that RNAs containing 2′fluoro (2′F) pyrimidines differentially controlled the activation of PRRs. The activity of RNAs that stimulate toll-like receptors 3 and 7 was abrogated by the incorporation of 2′F pyrimidine. By contrast, incorporation of 2′F pyrimidines enhanced the activity of retinoic acid-inducible gene 1-stimulating RNAs. Furthermore, we found that transfection with RNAs containing 2′F pyrimidine and 5′ triphosphate (5′ppp) increased cell death and interferon-β expression in human cancer cells compared with transfection with 2′hydroxyl 5′ppp RNAs, whereas RNAs containing 2′O-methyl pyrimidine and 5′ppp completely abolished the induction of cell death and cytokine expression in the cells. Our findings suggest that incorporation of 2′F and 2′O-methyl nucleosides is a facile approach to differentially control the ability of therapeutic RNAs to activate or limit immune and inflammatory responses depending on therapeutic applications.
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