The major disadvantages of traditional virus vaccines are time constraints in development and difficulties in large-scale production. Therefore, there is a need to develop stronger and more versatile vaccine platforms. mRNA vaccines constitute a promising alternative to traditional vaccine approaches due to their high potential, rapid development capacity, low cost production and safe administration potential. Stability and translation of mRNA are crucial for a successful RNA vaccine. It is critical to determine mRNA purity, stability, and protein yield during the translation process. Therefore, engineering the RNA sequence, such as modification of the 5' cap structure, extension of the poly (A) tail, editing nucleotide sequences in non-coding (UTR) and coding (ORF) regions, or incorporating modified nucleotides into the structure, makes synthetic mRNA more translatable. Two classes of non-replicating and self-amplifying mRNA are used as vaccines. While non-replicating mRNA only encodes protein antigens of interest, self-amplifying mRNA also encodes proteins required for RNA replication. The transfer and formulation of mRNA vaccines to cells is crucial for determining the kinetics of antigen expression, protein amount, and strength of immune response. In order to achieve this success, mRNA vaccines are given to cells in various formats such as lipid nanoparticles, polymers, peptides, and naked mRNA to develop the most effective transfer material. Recent technological advances have eliminated the low efficiency in in vivo transfer and translation and have made this vaccine platform widespread in preclinical and clinical trials against various infectious diseases and cancers. Over the past decade, major technological innovations have made mRNA a promising therapeutic tool in the fields of vaccine development and protein replacement therapy. Nowadays, antigens, neutralizing antibodies and proteins with immunostimulating activity have become coded by mRNA vaccines. Although many mRNA vaccines appear to be effective in preclinical and clinical studies, there are still some issues to be improved in terms of transfer efficiency, targeting to specific cell types, and the reliability of transfer devices. In this review, the latest developments and current challenges in the optimization, formulation and transfer of mRNA vaccines to cells with future development perspectives have been reviewed.
