Fig. 1.

mRNA vaccine structure and function. (a) mRNA vaccines have multiple components, each of which can be optimized for administration: a 5’ cap, untranslated regions at the 5’ and 3’ ends, a coding region containing the antigens of choice, and a poly-A tail. The BNT162b2 SARS-CoV-2 mRNA vaccine contains the sequence of the spike protein with mutations that maintain it in a pre-fusion conformation [24]. The poly-A tail of 100 residues has a stabilizing sequence (GCAUAUGACU) placed after the first 30 nucleotides. An experimental vaccine in trials by Moderna encodes the hemagglutinin of influenza A/Jiangxi-Donghu/346/2013 (H10N8) virus [96]. (b) Lipid nanoparticles are used to protect and deliver mRNA vaccines via injection into the deltoid muscle. Once inside cells, the mRNA is translated and the encoded viral protein is expressed, as well as processed into peptides and presented on MHC I molecules on the cell surface. Antigen-presenting cells can additionally internalize the expressed proteins and display viral peptides on MHC II molecules.