In mRNA vaccines, mRNA encoding antigens enclosed in lipid nanoparticles (LNPs) are injected into the muscle to induce intracellular antigens, which are then secreted extracellularly and recognized by antigen-presenting cells, thereby conferring immunity. Therefore, if the extracellular secretion of antigen is increased, immunity can be efficiently acquired with a smaller amount of mRNA; thus contributing to the improvement of vaccine supply.
The secretory efficiency ranking of artificial and natural signal peptides has already been reported. In this study, we transfected HEK293 cells with a vector in which the N-terminal IL-6 signal peptide of NanoLuc® luciferase (Nluc) was replaced by the signal peptides with high secretory signal strength. The amount of Nluc secreted extracellularly at each signal peptide was determined by luciferase assays and Western blotting. As per the results, Nluc with the signal peptide of Cystatin S, a natural signal peptide, had the highest extracellular secretion. The Western blotting result was consistent with that of the luciferase assay. Our future studies will test those peptides on C2C12 skeletal muscle cells and HepG2 liver cells. We also plan in vivo validation of those peptides using mRNA-LNP.