Elicitation of antibodies broadly neutralizing the porcine reproductive and respiratory syndrome virus (PRRSV) using reverse vaccinology

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Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen of swine. Unfortunately, the available live attenuated and inactivated vaccines provide only limited protection against symptomatic disease and cannot effectively prevent the spread of virulent field viruses in swine herds. Although a strong humoral immune response against homologous viral strains is elicited after vaccination, the achieved protection against genetically divergent viral strains is insufficient. Traditional vaccine approaches apparently cannot cover the large genetic variability of PRRSV comprising two separate species (PRRSV-1 and -2). The structure of PRRSV glycoproteins remains elusive to date, complicating the use of structure-based vaccine design to improve vaccine efficacy. In this project, we will apply reverse vaccinology approaches to fill these gaps. Using multi-color FACS with fluorescently labeled PRRSV glycoproteins and virions followed by state-of-the-art single B cell sequencing we will analyze the PRRSV-specific porcine antibody repertoire. Individual antibodies will be expressed recombinantly and the recombinant antibodies characterized with respect to their neutralization profile and potency as well as their cognate antigen. In parallel, we will build on our successful pipeline to identify PRRSV neutralization epitopes to focus on highly conserved epitopes targeted by broadly neutralizing antibodies that are of particular interest for vaccine design. For this purpose, we will immunize mice sequentially with PRRSV-1 and PRRSV-2 virions followed by isolation of memory B cells reacting with glycoproteins of both species and characterization of bnAbs as described above. We will also investigate interesting neutralizing antibodies generated in pigs or mice in this study with respect to their neutralization mechanism and whether the virus can escape these antibodies by mutation in a so-called "immune escape". Finally, we will structurally characterize the neutralizing antibody mAb18, which we have already identified in a proof-of-concept study to recognize PRRSV gp2, in complex with an epitope peptide and use the resulting structure to develop an epitope-focused vaccine. To this end, we will transfer this epitope to suitable "scaffold" proteins, produce a scaffold-based vaccine candidate in the form of nanoparticles and validate this candidate in a challenge trial in pigs. Taken together, this project will provide important insights into the immune response to PRRSV glycoproteins to facilitate informed vaccine design.