Neutralizing antibodies targeting PRRSV glycoproteins

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important pathogens in swine worldwide. PRRSV is an enveloped RNA virus that shares some characteristics with coronaviruses and is found exclusively in pigs. In pregnant sows, PRRSV causes abortions and in young animals, pneumonia. Vaccines based on life attenuated PRRS viruses are available, but they have undesirable side effects. The immune response following PRRSV vaccination is not fully understood, with the high genetic variability of PRRSV creating further problems. Based on the hypothesis that PRRSV glycoproteins contain conserved - i.e. invariant - epitopes for neutralizing antibodies, but are insufficiently stimulated by the porcine immune system, the goal is to identify such epitopes, and to develop a rational vaccine approach. In a first step, the repertoire of PRRSV-specific antibodies in pigs will be analyzed with respect to recognized PRRSV antigens and epitopes. For this purpose, specific memory B cells will be isolated from multiply immunized pigs and subsequently the variable regions of the expressed antibody genes will be determined by "next generation sequencing" on the single cell level. The immunoglobulin sequences determined in this way will then be fused with other genes and expressed as recombinant antibodies which will then be examined for their antiviral properties. The other part of the project focuses on the identification of potent PRRSV neutralization epitopes in the four glycoproteins of the viral envelope. For this purpose, mice are successively immunized with PRRSV-1 and PRRSV-2 virions, and weeks later the formed B - memory cells are isolated. Of interest are the antibodies of the B cells, which react with glycoproteins of both PRRSV species. The structure of a previously identified neutralizing antibody (mAb18) with the matching epitope in PRRSV GP2 will be elucidated by crystal structure analysis. The structural data obtained will be used to transfer the epitope into suitable "scaffold" proteins and validate a vaccine candidate in the form of nanoparticles in a porcine vaccination trial. The combination of antibody identification and structure elucidation of PRRSV glycoproteins with the embedded neutralizing epitopes enables a novel structure-based vaccine design.