Abstract
Marek’s disease virus (MDV) is a preferred vector in the construction of recombinant vaccines. However, bivalent vaccine based on MDV that confers full protection against both very virulent Marek’s and infectious bursal disease virus (IBDV) infections in chickens has not been produced. Here we developed a system utilizing overlapping fosmid DNAs transfection that rescues an MDV type 1 (MDV1) vaccine strain. Using this system, we inserted the IBDV VP2 gene at MDV1 genome sites UL41, US10 and US2. The VP2 protein was stably expressed in the recombinant MDV-infected cells and self-assembled into IBDV subviral particles. Insertion of the VP2 gene did not affect the replication phenotype of MDV in cell cultures, nor did it increase the virulence of the MDV vaccine strain in chickens. After challenge with very virulent IBDV, r814US2VP2 conferred full protection, whereas r814UL41VP2 and r814US10VP2 provided partial or no protection. All the three recombinant vaccines provided full protection against very virulent MDV challenge in chickens. These results demonstrated that r814US2VP2 could be used as a promising bivalent vaccine against both Marek’s and infectious bursal diseases in chickens.
Highlights
Are responsible for eliciting neutralizing antibodies[15]
10 sets of fosmid clones, each of which consisted of five- or six-fosmid combinations covering the entire Marek’s disease virus (MDV) genome, were transfected into primary CEFs (Table S1)
The transfection of set 2 resulted in the highest percent of plaques, this combination was used in further studies; virus rescued from this set was designated rMDV
Summary
Are responsible for eliciting neutralizing antibodies[15]. Considering its lower susceptibility to maternal antibodies and good safety, recombinant MDV1 vaccines expressing VP2 would be more desirable than the conventional IBDV live vaccines. After a decade of use, very virulent MDV (vvMDV) strains emerged and began to break through the HVT protection, prompting the introduction of a more effective bivalent vaccine that consisted of the MDV2 SB-1 strain plus HVT16. By the early 1990s, very virulent plus MDV (vv+MDV) strains began to emerge and overcome protection provided by bivalent vaccines[16]. The recombinant virus r814US2VP2 containing VP2 gene at US2 site confers full protection against vvMDV and vvIBDV infection in chickens. These results advance the development of efficient recombinant MDV vaccines and rapid manipulation of the viral genome for basic research
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