Long-term in vivo imaging of translated RNAs for gene therapy

To determine the potential of RNA for transient expression, we followed its translational efficiency and expression kinetics in vivo in mouse skin. Three RNA species were delivered in vivo with differing 5′ and 3′ ends, as well as with different structures that are known to influence their translation fate, such as an internal ribosome entry site (IRES), a cap or a poly(A) tail. RNAs were transferred by electropermeabilization, and each encoded the firefly luciferase enzyme to allow monitoring of translational efficiency by in vivo bioluminescence imaging. We show that all types of naked RNAs delivered into mouse skin are efficient for transient protein expression in vivo. Expression could be achieved with some differences in efficiency and time course, using either capped/polyadenylated RNAs or RNAs containing HCV IRES structures with or without a poly(A) tail. Our data reveal expression occurring up to 2 weeks, suggesting that electroporated RNA has high stability in vivo, particularly capped and polyadenylated RNAs. Our study shows that RNA molecules are efficient tools for the transient expression of proteins in vivo and that they can be used for therapeutic purposes. Changes in RNA features may be used to modulate both expression efficiency and kinetics.