In vitro-transcribed mRNAs encoding physiologically important proteins have considerable
potential for therapeutic applications. However, in its present form, mRNA is unfeasible
for clinical use because of its labile and immunogenic nature. Here, we investigated
whether incorporation of naturally modified nucleotides into transcripts would confer
enhanced biological properties to mRNA. We found that mRNAs containing pseudouridines
have a higher translational capacity than unmodified mRNAs when tested in mammalian
cells and lysates or administered intravenously into mice at 0.015-0.15 mg/kg doses.
The delivered mRNA and the encoded protein could be detected in the spleen at 1, 4,
and 24 hours after the injection, where both products were at significantly higher
levels when pseudouridine-containing mRNA was administered. Even at higher doses,
only the unmodified mRNA was immunogenic, inducing high serum levels of interferon-alpha
( IFN-alpha). These findings indicate that nucleoside modification is an effective
approach to enhance stability and translational capacity of mRNA while diminishing
its immunogenicity in vivo. Improved properties conferred by pseudouridine make such
mRNA a promising tool for both gene replacement and vaccination.
