Appendix 60 Significantly enhanced immune responses induced by a FMD DNA vaccine in swine using a protein antigen boost Yanmin Li1*, Catrina Stirling2, Haru Takamatsu2 and Paul Barnett1 1 FMD vaccine group, 2Porcine Immunology Group, Pirbright Laboratory, Institute for Animal Health, Ash Road, Woking, Surrey, GU24 0NF, UK. Abstract: Introduction: It has previously been shown that a FMD DNA vaccine containing the “empty capsid” cassette-structural protein precursor P1 and the non-structural proteins 2A, 3C and 3D (pCDNA3.1/P1-2A3C3D, P1) combined with an adjuvant plasmid expressing porcine granulocyte macrophage colony stimulating factor (poGM-CSF) induced neutralising antibodies to FMDV and conferred partial protection against live virus challenge in swine. Current studies are aimed at enhancing the immune responses from this DNA vaccine further in swine by incorporating a prime/boost vaccination strategy. Increasing the priming dose of FMD DNA vaccine (600 µg) and GMCSF (400 µg) and combining with a protein boost induced an average anti-FMDV antibody titre which was up to 30 times higher than that following conventional vaccination. Materials and Methods: Groups of pigs were immunised with P1 and poGM-CSF plasmids via the intramuscular/ intradermal route (i.m./i.d) once, twice or three times which was followed 3 weeks later by a protein boost of inactivated FMDV antigen and FMDV 3D protein via the i.m. or i.d. route. Results: FMDV specific immune responses were significantly increased following the protein antigen boost of the P1 DNA vaccinated pigs. Conclusion: FMDV P1 DNA vaccination followed by an inactivated FMDV antigen/3D boost could be a more efficient vaccination strategy in this model. Introduction: Vaccination with a DNA plasmid by various routes has been shown to elicit protective immune responses to the encoded antigen in a variety of animal models (Ulmer et al. 1993; Somasundaram et al. 1999; Lodmell et al. 1998). This novel approach is particularly attractive for several reasons: the antigen is endogenously synthesised and processed and therefore more closely mimics natural infection. This results in the antigen being presented via both MHC class I and class II pathways generating both humoral and cellular immune responses. The use of plasmid DNA as a vaccine can also trigger innate immunity in the host as an effect of the unmethylated CpG motifs in the bacterial plasmid backbone (Yankaucka et al., 1993; Wolff et al., 1992; Klinman et al., 2004). Additionally, DNA vaccines are non-infectious, easy to prepare, inexpensive, and are stable at room temperature reducing cold chain requirements (Babiuk et al., 2000; Gurunathan et al., 2000; Cichutek 2000). DNA vaccines have the potential to provide a more effective and cheaper vaccine for economically important domestic animals such as cattle and pigs and are particularly advantageous over the conventional FMD vaccine because they do not require high-security containment facilities for manufacture, and are easy to manipulate for incorporation of marker genes or covering against various serotypes and field isolates in an outbreak. The structural proteins of FMDV VP0, VP3 and VP1 were produced when the P1-2A precursor was cleaved by the viral protease 3C. One of each of these proteins can form into protomers and five protomers assemble into a pentamer. An icosahedral capsid particle is then assembled with twelve pentamers. When this capsid particle lacks the RNA genome, they are called “empty capsids” (Yafal and Palma, 1979; Rombaut et al., 1991; Abrams et al., 1995). It was found that empty capsid particles are capable of inducing antibody responses at a similar level to that induced by the whole virus (Rowlands et al., 1975; Grubman et al., 1985; Francis et al., 1985). Taking this observation together with the finding that the non-structural protein 3D stimulates a strong humoral and cellular immune response in the host (Foster et al., 1998), a P1 FMDV DNA vaccine was constructed containing an “empty capsid” gene cassette-P1-2A, 3C and 3D. Partial protection against homologous O1 Lausanne virus challenge was induced in pigs after three immunisations of this P1 plasmid. The antibody responses induced by this FMD DNA vaccine was improved by co-administration of a plasmid encoding porcine granulocyte macrophage colony stimulating factor (GM-CSF) (Cedillo-Barron et al., 2001). Furthermore, it has been found that increasing the amount of P1 plasmids and poGM-CSF DNA plasmids from 300 µg and 200 µg each to 600 µg and 400 µg respectively improved the immune response to FMDV in vaccinated pigs in a recent study performed in our group (unpublished data). This study was aimed at optimising this vaccination protocol to enhance the antibody and cellular responses induced by FMDV DNA immunisation of pigs by employing the prime/boost strategy, and simplifying the DNA vaccination protocol by reducing the injection intervals without decreasing the specific immune responses in vaccinated animals.
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