Production and immunogenicity of chimeric virus-like particles containing porcine reproductive and respiratory syndrome virus GP5 protein

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) poses a severe threat in swine industry and causes heavy economic losses worldwide. Currently, the available vaccines are the inactivated and attenuated virus vaccines, but the use of PRRSV in their production raises the issue of safety. We developed a chimeric virus-like particles (VLPs) vaccine candidate for PRRSV protection. The chimeric VLPs was composed of M1 protein from H1N1 influenza virus and a fusion protein, denoted as NA/GP5, containing the cytoplasmic and transmembrane domains of H1N1 virus NA protein and PRRSV GP5 protein. Vaccination of BALB/c mice with 10 μg of chimeirc VLPs by intramuscular immunization stimulated antibody responses to GP5 protein, and induced cellular immune response. The data suggested that the chimeric VLP vaccine candidate may provide a new strategy for further development of vaccines against PRRSV infection.

Introduction

Porcine reproductive and respiratory syndrome (PRRS) is a seriously viral disease causing losses to swine industry worldwide. It is characterized by severe reproductive failure in sows and respiratory distress in pigs of all ages [1], [2]. PRRS virus (PRRSV), as the causative agent of PRRS, is a member of the Arteriviridae family, which also includes lactate dehydrogenase-elevating virus (LDV), equine arteritis virus (EAV), and simian hemorrhagic fever virus (SHFV) [3]. PRRSV contains a positive-strand RNA genome which is approximately 15 kb in length. The PRRSV GP5 protein, which is one of the major antigens expressed on virion surfaces, is thought to be the most important target of neutralizing and protective antibodies [4], [5].

There are inactivated vaccines and attenuated vaccines in clinical application for PRRS prevention. It suggests that live vaccines might have the potential revert to strong virulence strain [6]. The inactivated vaccines cannot always provide solid protective immunity at herd level [7]. Recently, several experimental vaccines by expressing the major immunogenic protein(s) of PRRSV have been developed. Several systems have been used, including modified vaccinia virus ankara (MVA) [8], Mycobacterium bovis BCG [9], pseudorabies virus [10], [11], pseudotype baculovirus [12] and canine adenovirus [13]. An immunogenicity study of plant-made oral subunit vaccine against PRRSV was published lately [14].

As an alternative to conventional vaccine, non-infectious and self-assemble virus-like particles (VLPs) platform has been developed. By virtue of lacking the viral genome, VLPs are safer than virion-derived vaccines and elicit a robust and broad reactive immune response because VLPs not only faithfully mimic the overall structure of virion but also present conformational epitopes of surface proteins, which can be readily recognized and processed by antigen presenting cells such as dendritic cells capturing the antigens for presentation to both B and T lymphocytes [15], [16], [17]. An important application of VLPs is their use for the generation of immune responses against foreign protein epitopes by genetically fusing or chemically conjugating them to VLPs of different origins, resulting in so-called chimeric VLPs [18], [19]. For example, the anti-influenza A M2-HbcAg VLP vaccine has entered clinical trials [20].

Therefore, VLPs expressing PRRSV glycoproteins may be an attractive strategy for designing an effective PRRSV vaccine. In this study, we showed that the PRRSV GP5 protein was efficiently fused to the ectodomain of H1N1 influenza virus neuraminidase (NA) protein to obtain the fusion protein NA/GP5. And NA/GP5 fusion was incorporated efficiently into VLPs along with the influenza virus M1 protein to obtain chimeric VLPs. And we demonstrated that the chimeric VLPs could be prepared quantitatively and that immunization of BALB/c mice with the chimeric VLPs could stimulate robust immune responses.