Replication-Defective Porcine reproductive and respiratory syndrome (PRRSV) Vaccine

Investigator:

Overview

Porcine reproductive and respiratory syndrome (PRRS) is recognized by the pig industry worldwide as one of the most important swine diseases. Current vaccines against PRRS are far from ideal. New technologies have opened new approaches to vaccine discovery and our long-term goal is to develop a safe, effective and differential vaccine against PRRSV infection of pigs. Ultimately, recombinant PRRSV will be constructed, characterized and tested in vaccination trials in pigs.

Background

Porcine reproductive and respiratory syndrome (PRRS) is recognized by the pig industry worldwide as one of the most important swine diseases. PRRS is estimated to cost the U.S. industry approximately $560 million per year, and the cost of PRRS to the Canadian swine industry is estimated to be $100 million per year.

PRRS is caused by an enveloped, single-stranded positive-sense RNA virus (PRRSV). Current vaccines against PRRS are far from ideal. Licensed in Canada, a live attenuated vaccine cannot provide sterilizing immunity to PRRSV, and there are safety concerns because some of the PRRS outbreaks have been linked to the use of the live vaccine. In addition, this vaccine is not approved for use in pregnant females and breeding age boars, and the use of the vaccine is also discouraged in negative herds because it is impossible to differentiate vaccinated and infected swine.

The long-term goal of the project is to develop a safe, effective and differential vaccine against PRRSV infection of pigs. Recently established reverse genetics methods for PRRSV have opened new approaches to vaccine discovery. One of these approaches is the genetic inactivation of viruses by deleting an essential gene from the viral genome. The gene-deleted virus becomes replication-defective, and it grows only in the complementing cell line that provides the deleted-gene function in trans. Although the mutant virus is replication-defective, it is still able to enter host cells and produce viral proteins during a single cycle of replication inducing cell-mediated and humoral immune responses. Improved safety is a primary advantage of the replication-defective vaccine. In addition, pigs vaccinated with gene-deleted mutant virus can be easily differentiated from the naturally infected pigs.

Objectives

  1. Deletion of the N gene in the infectious cDNA clone of a North American PRRSV isolate (pVR-V7).
  2. Establishment of a complementing cell line and rescue of the N-gene deleted PRRSV.
  3. Characterization of in vitro growth of the N-gene deleted PRRSV and its genetic stability.
  4. Evaluation of immunogenicity, safety and protective efficacy of the N-gene deleted PRRSV vaccine in pigs.

Progress

We have accessed a full-length cDNA clone of PRRSV strain VR-2332 (pVR-V7) (Dr. Kay Faaberg, USDA). The virus has been rescued from the full-length clone after transfection of MARC-145 cells with the in vitro transcribed viral genomic RNA. Also, we established the MARC-145-based cell line stably expressing the N gene and made a deletion in the N gene encoded by pVR-V7. Currently, we are working on transfection of the complementing cell line with the N-gene deleted genomic RNA, rescuing and characterization of the mutant virus. Ultimately, mutant PRRSV will be tested in vaccination trials in pigs.