Development of a novel-ionizable-lipid-based mRNA vaccine for broad protection against Streptococcus pneumoniae

Recently, messenger RNA (mRNA)-based vaccine technology has made significant advances in preventing pathogenic microbial infections. The composition and physicochemical properties of lipid nanoparticle (LNP) determine the delivery efficiency of mRNA vaccines. In this study, we synthesized a novel ionizable lipid, C14-192, featuring a 3-oxo-polyamine head group, which was used as a component for LNP to encapsulate and deliver mRNA. Analysis of <i>in vitro</i> and <i>in vivo</i> expression showed that C14-192-LNP-encapsulated luciferase mRNA exhibited high expression efficiency. To further assess the potential of the C14-192 LNP formulation for vaccine applications, we developed a prophylactic mRNA vaccine against <i>Streptococcus pneumoniae</i> (<i>S. pneumoniae</i>), based on the conserved and truncated pneumococcal histidine triad protein D (PhtD) and pneumolysin (Ply). The mRNA encoding the fusion construct exhibited the highest expression and secretion levels. In murine model, mRNA vaccine effectively prevented <i>S. pneumoniae</i> infection and colonization in the lungs and prevented severe lesions. Moreover, the vaccine demonstrated robust cross-protection against multiple serotypes of <i>S. pneumoniae</i> and provide effective protection against lethal infection. In conclusion, a novel ionizable lipid was successfully synthesized and applied in the development of a new prophylactic vaccine against <i>S. pneumoniae</i>.