Abstract
Live herpesvirus-vectored vaccines are widely used in veterinary medicine to protect against many infectious diseases. In poultry, three strains of herpesvirus vaccines are used against Marek’s disease (MD). However, of these, only the herpesvirus of turkeys (HVT) has been successfully developed and used as a recombinant vaccine vector to induce protection against other avian viral diseases such as infectious bursal disease (IBD), Newcastle disease (ND) or avian influenza (AI). Although effective when administered individually, recombinant HVT vectors have limitations when combined in multivalent vaccines. Thus there is a need for developing additional viral vectors that could be combined with HVT in inducing protection against multiple avian diseases in multivalent vaccines. Gallid herpesvirus 3 (GaHV3) strain SB-1 is widely used by the poultry industry as bivalent vaccine in combination with HVT to exploit synergistic effects against MD. Here, we report the development and application of SB-1 as a vaccine vector to express the VP2 capsid antigen of IBD virus. A VP2 expression cassette was introduced into the SB-1 genome at three intergenic locations (UL3/UL4, UL10/UL11 and UL21/UL22) using recombineering methods on the full-length pSB-1 infectious clone of the virus. We show that the recombinant SB-1 vectors expressing VP2 induced neutralising antibody responses at levels comparable to that of commercial HVT-based VAXXITEKHVT+IBD vaccine. Birds vaccinated with the experimental recombinant SB-1 vaccine were protected against clinical disease after challenge with the very virulent UK661 IBDV isolate, demonstrating its value as an efficient viral vector for developing multivalent vaccines against avian diseases.
Highlights
Marek’s disease virus (MDV-1) or Gallid herpesvirus 2, belonging to the Mardivirus genus in the family Herpesviridae, is the causative agent of Marek’s disease (MD) characterised by rapid-onset lymphomatous tumours and paralytic symptoms due to neuronal infiltration of lymphocytes
The expression for IBDV VP2 was derived from a murine cytomegalovirus immediate early protein 2 promoter and the VP2 gene was derived from IBDV strain Faragher 52/70 with a SV40 early polyadenylation signal (Venugopal Nair, unpublished data)
Avian herpesvirus vaccines used against poultry diseases such as MD offer the additional advantage of being developed as potential viral vectors for inducing simultaneous protection against other avian diseases
Summary
Marek’s disease virus (MDV-1) or Gallid herpesvirus 2, belonging to the Mardivirus genus in the family Herpesviridae, is the causative agent of Marek’s disease (MD) characterised by rapid-onset lymphomatous tumours and paralytic symptoms due to neuronal infiltration of lymphocytes. The most successful and widely-used recombinant herpesvirus vaccine vector is the HVT strain which has been shown to be highly effective in protecting against a number of avian viral pathogens,[3,4,5,6] even in the presence of maternal antibodies.[7] individual recombinant HVT vaccines have proven to be extremely effective, combined use of more than one recombinant HVT vaccine has been shown to be less so. With these constraints on the use of HVT vectored vaccines, there is a need for developing other vector platforms that will not interfere, but rather complement the induction of protective responses against multiple antigens in the vaccine
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