Fig. 1.

a In vitro transcribed mRNA is translated by ribosomes to yield proteins that can replace an absent or mutated protein [11]. b mRNA-based therapies introduce the in vitro transcribed (IVT) mature mRNA of a specific gene. A functional mRNA molecule comprises a 5’ cap structure, 5’ and 3’ UTRs, the coding sequence and a poly-A tail. Several modifications can be used to increase stability (green), modulate translation efficiency (grey) and/or decrease immunogenicity (orange). The use of (anti-reverse) capping analogues enhances protection against nuclease-mediated degradation and maintains the immune-modulatory capabilities of the 5’ cap structure. Careful consideration of the non-coding regions at the 5’ and 3’ end of the coding sequence and a 3’ poly-A tail of sufficient length (100–250 adenines) can further enhance stability and translational activity. Sequence and chemical modifications in the coding region can be applied to prevent TLR- and RIG1-activation and thus reduce immunogenicity [11, 28, 29]