Equine rhinitis A virus-like particle expressing DNA vaccine induces a virus neutralising immune response in mice

Equine rhinitis A virus (ERAV) is a respiratory pathogen of horses. Candidate vaccines to date have been hindered by low expression levels and the induction of non-neutralising antibodies. The immunodominant epitope of ERAV is conformational and is located within the quaternary structure of the capsid. This site should be retained in ERAV virus-like particles (VLPs) to stimulate the induction of neutralising antibodies. The immunogenicity of a plasmid-based DNA vaccine designed to express ERAV VLPs was assessed. The plasmid construct, pcD.P12A.3C, contained the capsid precursor (P1-2A) and the viral protease 3C, under the transcriptional control of a cytomegalovirus (CMV) promoter. Mature viral capsid proteins and VLPs were detected in vitro in transfected COS7 cells. Immunisation of BALB/c mice with pcD.P12A.3C induced virus neutralising antibodies and enhanced the virus neutralising antibody response to purified, UV-inactivated ERAV. This study further supports the use of DNA vaccines to elicit neutralising antibodies to complex antigenic proteins.