Porcine Reproductive and Respiratory Syndrome Virus Engineered by Serine Substitution on the 44th Amino Acid of GP5 Resulted in a Potential Vaccine Candidate with the Ability to Produce High Levels of Neutralizing Antibody

SIMPLE SUMMARY: The slow and weak formation of neutralizing antibodies against the PRRSV is related to the N-linked glycosylation site surrounding the major epitope in the ectodomain of GP5 protein. To develop vaccine candidates that induce high levels of neutralizing antibodies, various previous studies have attempted to substitute the various glycosylation sites with other amino acids. In this study, we created a new vaccine candidate, vCSL1-GP5-N44S, by replacing the 44th asparagine amino with serine. In an animal trial, piglets inoculated with vCSL1-GP5-N44S showed no adverse effects and had a protective efficacy, including a high level of neutralizing antibodies after the challenge. Therefore, it has been demonstrated that substituting the 44th N-linked glycosylation site of the GP5 protein with serine is preferable among the various substitution. Additionally, vCSL1-GP5-N44S has shown its potential as a vaccine candidate. ABSTRACT: N-linked glycans covering GP5 neutralizing epitopes of porcine reproductive and respiratory syndrome virus (PRRSV) have been proposed to act as a sheath blocking the production of neutralizing antibodies. Herein, we genetically engineered PRRSV with serine (S) substitution on the 44th asparagine (N) on the GP5 ectodomain of PRRSV-2 lineage-1. To evaluate the recombinant PRRSV, in vivo experiments were performed in piglets. The recombinant virus group showed no viremia until 42 days post-inoculation (dpi), and the rectal temperature and average daily weight gain were in the normal range at the same time point as the negative control group. On the 42 dpi, both groups were challenged with the wild-type virus. The recombinant PRRSV group showed lower rectal temperature, viremia, and the lung lesions than that of the negative control group for 19 days post-challenge (dpc). Additionally, the recombinant virus induced 4.50 ± 3.00 (log(2)) and 8.25 ± 0.96 (log(2)) of neutralizing antibody before and after challenge, respectively. Taken together, this study confirmed that N44S substitution can create an infectious PRRSV that strongly induces neutralizing antibodies. In addition, the vCSL1-GP5-N44S mutant that we produced was confirmed to have potential as a vaccine candidate, showing good safety and protective effects in pigs.