A capless hairpin-protected mRNA vaccine encoding the full-length Influenza A hemagglutinin protects mice against a lethal Influenza A infection

The success of mRNA vaccines in controlling the COVID 19 pandemic has confirmed the efficacy of synthetically synthesized mRNA in humans and has also provided a blueprint on how to design them in terms of molecular structure and cost. We describe a mRNA vector that, unlike linear mRNAs used in current vaccines/therapeutics, does not require a 5 ' cap to function. The described mRNA vector initiates translation from an internal ribosomal entry site (IRES) and contains specially designed self-folding secondary structures (hairpins) to protect the 5 ' end against degradation, dramatically improving its stability. The produced mRNA did not require any additional modifications for functionality. The 5 ' hairpins completely inhibited cap-dependent translation, and all vectors containing them required an IRES to express protein. When this capless mRNA vector was constructed to express the full-length Influenza A membrane protein hemagglutinin (HA), complexed with pre-formed lipid-based nanoparticles, and then injected into mice as a vaccine, it generated high titers of anti-HA antibodies and protected mice against a lethal dose of Influenza A.