N1-methylpseudouridine enhances immunogenicity of RNA/lipidnanoparticle vaccines targeting SARS-CoV-2 spike and the model antigen ovalbumin

The recent success of RNA/lipid nanoparticle (LNP)-based vaccine
formulations in the clinic against SARS-CoV-2 and RSV has highlighted the
potential of this platform.  While RNA-LNP vaccines share the
fundamental principle of using lipid nanoparticles to deliver RNA
molecules into host cells to induce antigen expression and
antigen-specific immune responses, several factors including RNA type
(i.e., messenger, self-amplifying), RNA chemistry and/or nanoparticle
formulation can influence the vaccine’s stability, tolerability and
overall activity.  Although these differences may influence
clinical performance, the lack of head-to-head comparative studies limits
the ability to identify which factors have contributed most to the success
of the clinically approved vaccines. Herein, we evaluated the influence of
N1-methylpseudouridine incorporation into the RNA molecule on the overall
immunogenicity of RNA vaccines encoding either the pathogen derived
antigen SARS-CoV-2 spike or the model antigen ovalbumin.  Across
repeated in vivo mouse studies, we demonstrate that the replacement of
canonical uridine with N1-methylpseudouridine in the RNA molecules leads
to more immunogenic vaccine formulations, corresponding to higher
antigen-specific antibody titers as well as neutralizing
activity.  Both types of RNA vaccines induced antigen-specific T
cells, with the chemically modified RNA eliciting significantly higher
levels of spike-specific CD4+ T cells.  As such, the
incorporation of N1-methylpseudouridine can enhance vaccine
immunogenicity, providing insight into the activity of previously
evaluated formulations and supporting its continued use in vaccines under
development.