Review: mRNA delivery systems in vaccinations and COVID-19

ABSTRACT

mRNA vaccines open promising avenues for overcoming a variety of diseases due to their high therapeutic utilities, rapid growth capacities, and safe administration potentials. With the emergence of COVID-19, the use of mRNA vaccines has become even more widespread and far-reaching. However, for mRNA to be delivered to target cells and tissues, several obstacles must be overcome. For instance, naked mRNAs get easily and hastily degraded by ribonucleases in tissues and the bloodstream, and since mRNAs are large and polyanionic molecules, they cannot passively diffuse across cell membranes. Even though mRNAs are internalized by APCs, they must be able to reach the cytoplasm and escape endo-lysosomal traffic. Therefore, distinctive transport systems for efficient encapsulation of mRNAs using nanocarrier systems are required to ensure their delivery to cells’ cytoplasm. At this point, non-viral gene delivery systems such as polymers and lipids come to the fore, in which they can overcome the biological barriers and provide efficient delivery of mRNAs. Recently, mRNA vaccines have been used as a powerful weapon against COVID-19 pandemic which has affected the whole world since December 2019. This was clear by the emergence of Pfizer-BioNTech and Moderna vaccines, which offered mRNA vaccines with auspicious treatment abilities. A variety of carrying candidates have been utilized in such vaccines as polymers, metal nanoparticles, as well as LNPs, which each comes with its cons and pros in delivering mRNA. All of these mentioned points will be clarified and discussed in detail in this review paper.