Vaccine 28 (2010) 3428–3434 Contents lists available at ScienceDirect Vaccine journal homepage: www.elsevier.com/locate/vaccine Marker vaccine potential of a foot-and-mouth disease virus with a partial VP1 G-H loop deletion V.L. Fowler ∗ , N.J. Knowles, D.J. Paton, P.V. Barnett Institute for Animal Health, Pirbright Laboratory, Ash Road, Surrey, GU24 0NF, UK article info Article history: Received 30 November 2009 Received in revised form 5 February 2010 Accepted 15 February 2010 Available online 1 March 2010 Keywords: Foot-and-mouth disease VP1 G-H loop Marker vaccine abstract Previous work in cattle and pigs demonstrated that protection against foot-and-mouth disease (FMD) could be achieved following vaccination with chimeric foot-and-mouth disease virus (FMDV) vaccines, in which the VP1 G-H loop had been substituted with that from another serotype. This indicated that the VP1 G-H loop may not be essential for the protection of natural hosts against FMDV. If this could be substantiated there would be potential to develop FMD marker vaccines, characterised by the absence of this region. Here, we investigate the serological responses to vaccination with a virus with a partial VP1 G-H loop deletion in order to determine the likelihood of achieving protection and the potential of this virus as a marker vaccine. Inactivated, oil adjuvanted, vaccines, consisting of chemically inactivated virus with or without a partially deleted VP1 G-H loop, were used to immunise cattle. Serum was collected on days 0, 7, 14 and 21 and antibody titres calculated using the virus neutralisation test (VNT) to estimate the likelihood of protection. We predict a good likelihood that cattle vaccinated with a vaccine characterised by a partial VP1 G-H loop would be protected against challenge with the same virus containing the VP1 G-H loop. We also present evidence on the potential of such a construct to act as a marker vaccine, when used in conjunction with a novel serological test. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Current foot-and-mouth disease (FMD) vaccines consist of chemically inactivated whole virus antigen that are formulated with either aluminium hydroxide/saponin or mineral oil adjuvant, depending on the target species [1]. Although these vaccines are capable of protecting animals from clinical disease they do not confer sterile immunity. The possibility of undisclosed infection in vaccinated animals necessitates methods to identify this and these rely on serological tests that can differentiate the immune response elicited by vaccination from that due to infection. Currently, this is achieved by purifying the vaccine antigen to remove FMD virus (FMDV) non-structural proteins (NSP) and then using detection of NSP antibodies as an indicator of infection [2]. However, vaccine preparations, depending on their source, can contain traces of NSP, reducing the specificity of the NSP assays [2]. Additionally, some vaccinated animals exposed to infection can become asymptomatic carriers, without an associated NSP serocon- version [3]. Therefore, there is a need for an additional and more reliable means of discriminating vaccinated and infected animals. ∗ Corresponding author. Tel.: +44 1483 232441; fax: +44 1483 232448. E-mail address: veronica.fowler@bbsrc.ac.uk (V.L. Fowler). Foot-and-mouth disease virus shares many structural features with that of other picornaviruses, for example the structural pro- teins VP1, VP2 and VP3 have their -barrel cores at essentially the same radius and orientation. However, unlike rhino- and enteroviruses, which have a ‘canyon’ or pit to prevent antibodies binding to their receptor binding site, FMDV has a relatively smooth surface with a prominent loop structure protruding from the cap- sid protein VP1, referred to as the G-H loop. The loop possesses an RGD binding site for attachment of the virus to integrin receptor molecules on the surface of susceptible cells [4]. Although the VP1 G-H loop has been regarded as an immunodominant antigenic site (site 1) on the viral capsid surface, there is considerable evidence to suggest that other antigenic sites are important in eliciting antibod- ies and protection against FMDV, not least that: (i) G-H loop peptide vaccines perform poorly in protecting target species such as cattle [5], (ii) pigs vaccinated with a chimeric vaccine virus possessing a serotype A backbone and a serotype C VP1 G-H loop were protected from challenge with serotype A virus but only partially protected from challenge with serotype C virus [6], (iii) cattle vaccinated with a virus which differed at sites other than the VP1 G-H loop from the challenge virus were also not protected from challenge [7], (iv) the proportion of antibody directed towards the VP1 G-H loop varies substantially in convalescent or vaccinated sera [8,9], (v) compe- tition of sera from the three main target species with monoclonal antibodies (MAbs) demonstrated that no one antigenic site (1, 2 0264-410X/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2010.02.074