Rational design and evaluation of novel mRNA vaccines against MERS-CoV

AbstractTraditional strategies of vaccine development suffer from long-term and costly manufacture, and as a result,often fail to respond rapidly to newly emerging and reemerging infectious diseases. By contrast, messengerRNA (mRNA) is rising as a new technology platform to develop vaccines "on demand" against viral pathogens,offering attractive advantages such as cell-free production, non-viral delivery, as well as simple, fast and cost-effective manufacture. Further improvement upon mRNA's stability and translation efficiency, understanding oftheir immune mechanisms, and evaluation of their protective efficacy will facilitate the development of next-generation mRNA vaccine technologies against diverse viral pathogens. Middle-East respiratory syndrome(MERS) coronavirus (MERS-CoV) is a highly pathogenic, emerging infectious virus posing a continuous threatto public health worldwide. There are currently no MERS vaccines approved for use in humans. MERS-CoVspike (S) protein, particularly its receptor-binding domain (RBD), is an important vaccine target. We havepreviously shown that MERS-CoV RBD contains a critical neutralizing domain capable of inducing strongcross-neutralizing antibodies and protecting human dipeptidyl peptidase 4-transgenic (hDPP4-Tg) mice againstMERS-CoV infection with outstanding efficacy. However, production of subunit vaccines and other traditionalvaccines has limitations, such as low expression and complex purification. To address these unmetchallenges, we propose to rationally design and evaluate novel mRNA vaccines, using MERS-CoV as a modelpathogen and MERS-CoV S protein as a target antigen. We hypothesize that with appropriate modificationand optimization, MERS-CoV S protein RBD-based mRNA vaccines will demonstrate improved stability,increased translation efficiency, and enhanced immunogenicity in both mouse and non-human primates (NHP)models, with protective efficacy on par with the RBD-based subunit vaccine. The specific aims are to (1)rationally design MERS-CoV mRNA vaccines with improved stability and translation efficiency, (2) carefullyoptimize mRNA formulations and immunization regimens towards in-vivo evaluation of their immunogenicityand mode of action in wild-type mice, and (3) comprehensively evaluate protective efficacy of MERS-CoVmRNA vaccines and elucidate their protective mechanisms in hDPP4-Tg mice and NHPs. Of note, we will alsoexamine the utility of new technologies such as microfluidics and next-generation sequencing (NGS) analysisof B-cell response in mRNA vaccine development and evaluation. The long-term goal is to develop a safeand effective mRNA vaccine that is able to (1) maintain sufficient quantity and quality suitable for industrial-scale production, and (2) meet the WHO Target Product Profiles for rapid onset of immunity in outbreaksettings and long-term protection of people at high ongoing risk of MERS-CoV. Together, the proposed projectwill shed light on protective mechanisms of mRNA vaccines, and provide much-needed information andguidelines for developing mRNA vaccines against diverse viral pathogens with pandemic potential.