Synergistic Effect of Nucleoside Modification and Ionizable Lipid Composition on Translation and Immune Responses to mRNA Vaccines

Lipid nanoparticle (LNP) structural components can impact the safety and immunogenicity of mRNA vaccines. Here we examine the mechanisms contributing to the performance of mRNA-LNP vaccines by exploring the impact of nucleoside modifications and LNP components on translational efficiency, innate immune activation, and immunogenicity, by employing in vitro (cell culture) and in vivo (mice and cynomolgus macaques) models. Our data reveal several molecular and immunological parameters affected by nucleoside modification. These include: i) a sequence-dependent increase in antigen expression; ii) decreased induction of genes associated with antiviral activity and RNA degradation in modified mRNA compared with unmodified mRNA; iii) reduced innate immune recognition of nucleoside-modified mRNA, accompanied by lower levels of inflammatory cytokines and chemokines in non-human primates; and iv) a synergistic effect of the mRNA and ionizable lipid composition on the immune activation triggered by the mRNA-LNP formulation. Our data show that changes in the LNP composition, independent from whether the mRNA is modified or unmodified, caused differential expression of genes associated with innate and antiviral immunity. For instance, modification of mRNA was able to silence the innate immune signatures more efficiently for certain LNPs but not others. We believe these findings offer valuable insights into mRNA vaccine function and offer strategies for enhancing vaccine efficacy and reducing the reactogenicity of next generation mRNA vaccines.