13. Nucleic acid-based vaccines
Novel genetic engineering techniques have facilitated the use of nucleic
acids (DNA and RNA) as vaccine candidates. DNA-based vaccines are made
by inserting the encoding gene of a foreign antigen into the plasmid
DNA, while RNA-based vaccines are made up of mRNA expressing a microbial
antigen in a lipid nanoparticle coating. Finally, the expressed proteins
are delivered to the CD8+ T lymphocytes with the help
of MHC class Ι and induce robust T cell responses [27]. Although
plasmid DNA have been used as valuable expression platforms for decades,
the RNA is one of the emerging vehicles in vaccine development (Fig. 2)
[119]. Presently, 54 candidate (30 RNA-based and 24 DNA-based)
vaccines of this generation have been developed against SARS-CoV2, of
which only 8 DNA-based and 7 RNA-based vaccines have been licensed for
clinical trials [52].