Fig. 1

Design and in vivo administration of mRNA therapeutics. Left box: mRNA product design. mRNA consists of five in cis-acting structural elements: (1) a cap structure; (2) a 5′ untranslated region (UTR); (3) the coding sequence of the desired therapeutic protein; (4) a 3′ UTR and (5) a sequence of repeated adenine nucleotides forming a poly(A) tail. By using modified nucleotides and extensive purification processes, the innate immune stimulation characteristic of mRNA can be down-modulated. Nowadays, lipid-based nanoparticles (LNPs) are often used for the delivery of mRNA therapeutics by making use of microfluidic mixing devices. In such devices, an acidic aqueous solution of mRNA is rapidly mixed with an ethanol solution of lipids. By using LNPs, the mRNA is protected from degradation and is delivered to the cytosol. Optionally, specific targeting entities can be added to the surface of LNPs to direct the mRNA-LNP to specific tissues or cells. Right box: in vivo administration of the mRNA therapeutic. The systemic delivery of mRNA complexed in LNPs mainly target the liver due to the binding of apolipoprotein E and subsequent receptor-mediated uptake by hepatocytes. To circumvent predominant hepatic uptake and expression, the lipid composition of the LNP can be adjusted or specific targeting Abs can be added to the LNPs. Furthermore, upon local delivery by intradermal, intramuscular or subcutaneous administration of mRNA-LNPs, mainly expression at the site of injection has been observed. Abbreviations: UTR: untranslated region; LNP: lipid-based nanoparticles; TME: tumor microenvironment