Popular Vaccine, ,

mRNA vaccine is to transfer RNA to the cells of the body to express and produce protein antigens, so as to induce the body to produce an immune response against the antigen, thereby expanding the body’s immune capacity.

  1. Classification of mRNA vaccines

mRNA vaccines are categorized into non-replicating mRNA and self-amplifying mRNA. Self-amplifying mRNA not only encodes the target antigen but also the replication mechanism that enables intracellular RNA amplification and protein expression. Non-replicating mRNA vaccine only encodes target antigens and contain 5′ and 3′ untranslated regions (UTRs). They provide comprehensive stimulation of adaptability and innate immunity, namely in situ antigen expression and danger signal transmission, and have the following applications characteristics:

  • Induce “balanced” immune response, including humoral and cellular effectors and immune memory.
  • Combine different antigens without increasing the complexity of vaccine formulation.
  • Continuous improvement of immune potential can be achieved through repeated vaccination, and there is no or little immune response to the carrier.
  • Heat-stable mRNA vaccines required simplified transportation and storage of conditions.
  1. Features of mRNA vaccines

Compared with traditional vaccines, mRNA vaccines have simple production processes, fast development speeds, no need for cell culture, and low cost. Compared with DNA vaccines, mRNA vaccines do not need to enter the nucleus and there is no risk of integration into the host genome. The half-life can be adjusted by modification.

  Advantages Disadvantages
mRNA Vaccines Rapid research and development, vaccine production only takes 40 days. mRNA instability under physiological conditions, easy to degrade.
No need for any nuclear localization or signal transcription. Trigger an unnecessary immune response.
Will not integrate into the genome to avoid possible therapeutic mutations. The effectiveness of the safety nuclear remains to be verified.
  1. Improved strategies for the preparation of mRNA vaccines

Defects like poor stability of mRNA itself, liability to be degraded by nucleases in tissues, low cell entry efficiency, and low translation efficiency, limit the application of mRNA vaccines, and the stability of mRNA vaccines shaped by different delivery vehicles also plays a very critical role. Delivery vehicles can be divided into viral vectors and non-viral vectors (including liposomes, non-liposomes, viruses, and nanoparticles). Therefore, relevant improvement measures are needed. The followings are pharmacological improvement strategies for mRNA preparation.

  • Synthesize cap analogs or use capping enzymes to stabilize mRNA and increase protein translation by binding to eukaryotic translation initiation factor 4E (EIF4E).
  • Adjust the elements in the 5′-untranslated region (UTR) and 3′-UTR to stabilize mRNA and increase protein translation.
  • Adding Poly(A) tail can stabilize mRNA and increase protein translation.
  • Modified nucleosides to reduce innate immune activation and increase translation.
  • Treatment with RNase III and fast protein liquid chromatography (FPLC) purification can reduce immune activation and increase translation.
  • Optimize sequences or codons to increase translation.
  • Co-delivery of translation initiation factors and other methods to change translation and immunogenicity.
  1. Large-scale preparation of plasmid DNA

Plasmid DNA purification mainly removes contaminants such as RNA, open-circle DNA endotoxin, host protein, and host nucleic acid, and usually transforms recombinant plasmid into E. coli that undergoes high-density fermentation, then solid-liquid separation, and finally gets collected. The E. coli is then subjected to alkaline lysis, centrifugal solid-liquid separation and microfiltration clarification after lysis, ultrafiltration and concentration after clarification, and then chromatographic purification.