Fig. 8

Obstacles in the clinical application of mRNA. a In vitro production of therapeutic mRNA involves a linear DNA template and RNA polymerase (T7), followed by purification; the mRNA consists of a 5′ cap, a 5′ UTR, an ORF that encodes the target protein, a 3′ UTR, and a poly(A) tail. b) Upon local or systemic administration, mRNA encounters various extracellular hurdles such as rapid breakdown by prevalent nucleases, removal through macrophage phagocytosis, and elimination via renal filtration. c A portion of mRNA that escapes from blood vessels can be taken up by cells. The majority of these internalized mRNAs get confined in endosomes and can be identified by endosomal and cytosolic RNA sensors, which ultimately decrease the mRNA's translation and stability. Enhancing the 5′ cap can boost the binding efficiency of cytoplasmic mRNAs to ribosomes, consequently increasing mRNA translation efficiency. Although the endosomal escape of bare and unaltered mRNA is difficult, it can be facilitated by employing mRNA carriers. Reprinted from [322] with permission from Springer Nature