Search Results (6)

Herpesvirus of turkey (HVT) recombinant vector vaccines are widely used in the poultry industry. However, due to limitations in loading multiple foreign antigens into a single HVT vector, other viral vectors are urgently needed. Since chickens lack maternal immunity to duck enteritis virus (DEV), vector vaccines using DEV as a backbone are currently under study. Even though a recently developed DEV vector vaccine expressing the influenza hemagglutinin H5 of highly pathogenic avian influenza (DEV-H5) induces highly detectable anti-HA antibodies, safety issues hamper further vaccine development. In this work, tissue affinity and horizontal transmission in 1-day-old chickens were systematically evaluated after DEV-H5 vector vaccine inoculation. Sixty percent of DEV-H5-inoculated chickens died between day 2 and day 7 post-inoculation. The displayed clinical signs consisted of lethargy, anorexia, and diarrhea, and virus was shed in feces. Gross and/or histological lesions were recorded in the kidney, heart, intestine, liver, lung, and spleen. Moreover, DEV-H5 replication in intestinal cells caused an increment in interferon-α expression, while occluding junction proteins and ZO-1 expression were significantly upregulated. As a control, birds inoculated with a commercial recombinant turkey herpesvirus expressing the VP2 protein of the infectious bursal disease virus (HVT-VP2) vector vaccine showed neither clinical signs nor mortality. Overall, while the HVT-VP2 vaccine demonstrated complete safety in 1-day-old chickens, our potential DEV-H5 vaccine requires further attenuation for consideration as a vector vaccine candidate in chickens. Full article

Infectious bursal disease (IBD), caused by IBD virus (IBDV), is an extremely contagious immunosuppressive disease that causes major losses for the poultry industry worldwide. Recently, the novel variant IBDV (G2d) has been highly prevalent in Korea, but the current vaccines against this very virulent IBDV have limited efficacy against this novel variant. To develop a vaccine against this variant IBDV, a recombinant virus designated rHVT-VP2 was constructed by inserting the IBDV (G2d) VP2 gene into herpesvirus of turkeys (HVT) using CRISPR/Cas9 gene-editing technology. The PCR and sequencing results obtained showed that the recombinant virus rHVT-VP2 was successfully constructed. Vaccination with rHVT-VP2 generated IBDV-specific antibodies in specific pathogen-free chickens starting from 2 weeks post-immunization. Seven days after the challenge, the autopsy results showed that the bursa atrophy rates of the rHVT-VP2, HVT, vaccine A, and positive control groups were 0%, 100%, 60%, and 100%, respectively, and the BBIX values were 1.07 ± 0.22, 0.27 ± 0.05, 0.64 ± 0.33, and 0.32 ± 0.06, respectively. These results indicate that rHVT-VP2 can provide 100% protection against a challenge with the IBDV (G2d), whereas vaccine A only provides partial protection. In conclusion, vaccination with the recombinant virus rHVT-VP2 can provide chickens with effective protection against variant IBDV (G2d). Full article

Infectious bursal disease (IBD) represents a greatly transmissible viral disease found worldwide, causing significant health and production challenges in young chickens. The aim of this research was to assess the immune reaction induced by different vaccines targeting IBD. These vaccines included recombinant (Vac1; HVT-IBD vector), immune complex (Vac2; Bursa-Plex^®), and intermediate plus (Vac3; Bursine plus) IBD vaccines. Our assessment relied on serological and histopathological analyses, as well as the pattern of immune-related cytokine expression in the bursal tissue. The vaccinated groups, along with a control positive (CP) group, were subjected to a vvIBDV challenge on their 28th day of life, while the control negative (CN) group received a mock vaccination with PBS. Our study revealed that Vac1 resulted in the most favorable growth performance, as well as maintained normal liver and kidney function, mitigating the impact of IBDV infection. Serological analysis using VP2 ELISA kits indicated that Vac1 induced the strongest immunological response among all vaccines. Histopathological examination demonstrated that Vac1 caused minimal lymphoid depletion observed in the lymphoid organs, followed by Vac2. Analysis of cytokine expression profiles showed significant upregulation in all vaccinated groups, particularly Vac1, during the pre-challenge period. Following IBDV infection, Vac1 resulted in a noteworthy increase in the expression of IL2 and IFN-γ, Vac2 showed a significant upregulation in TNF-α and granzyme, and both Vac1 and Vac3 exhibited increased levels of IL1β and IL10. In conclusion, our study suggests that the various vaccines triggered immune responses against IBD through both humoral and cell-mediated immunity. However, recombinant followed by immune complex vaccines appeared to induce more robust immunity while also being safer for broiler chickens in contrast to the intermediate plus vaccine. Full article

Turkey herpesvirus (HVT) is widely used as an effective recombinant vaccine vector for expressing protective antigens of multiple avian pathogens from different loci of the HVT genome. These include the HVT029/031 (UL22–23) locus for the insertion of IBDV VP2 and the recently identified HVT005/006 locus as a novel site for expressing heterologous proteins. In order to compare the efficacy of recombinant vaccines with the HA gene at different sites, the growth curves and the HA expression levels of HVT-005/006-hCMV-HA, HVT-005/006-MLV-HA, and HVT-029/031-MLV-HA were first examined in vitro. While the growth kinetics of three recombinant viruses were not significantly different from those of parent HVT, higher expression of the HA gene was achieved from the HVT005/006 site than that from the HVT029/031 site. The efficacy of the three recombinant viruses against avian influenza H9N2 virus was also evaluated using one-day-old SPF chickens. Chickens immunized with HVT-005/006-MLV-HA or HVT-005/006-hCMV-HA displayed reduced virus shedding compared to HVT-029/031-MLV-HA vaccinated chickens. Moreover, the overall hemagglutination inhibition (HI) antibody titers of HVT-005/006-HA-vaccinated chickens were higher than that of HVT-029/031-HA-vaccinated chickens. However, HVT-005/006-MLV-HA and HVT-005/006-hCMV-HA did not result in a significant difference in the level of HA expression in vitro and provided the same protective efficacy (100%) at 5 days after challenge. In the current study, the results suggested that recombinant HVT005/006 vaccines caused better expression of HA than recombinant HVT029/031 vaccine, and that HVT-005/006-MLV-HA or HVT-005/006-hCMV-HA could be a candidate vaccine for the protection of chickens against H9N2 influenza. Full article

The increased virulence of infectious bursal disease virus (IBDV) is a threat to the chicken industry. The construction of novel herpesvirus of turkey-vectored (HVT) vaccines expressing VP2 of virulent IBDV may be a promising vaccine candidate for controlling this serious disease in chickens. We generated a novel infectious clone of HVT Fc-126 by inserting mini-F sequences in lieu of the glycoprotein C (gC) gene. Based on this bacterial artificial chromosome (BAC), a VP2 expression cassette containing the pMCMV IE promoter and a VP2 sequence from the virulent IBDV NJ09 strain was inserted into the noncoding area between the UL55 and UL56 genes to generate the HVT vector VP2 recombinant, named HVT-VP2-09. The recovered vectored mutant HVT-VP2-09 exhibited higher titers (p = 0.0202 at 36 h) or similar growth kinetics to the parental virus HVT Fc-126 (p = 0.1181 at 48 h and p = 0.1296 at 64 h). The high reactivation ability and strong expression of VP2 by HVT-VP2-09 in chicken embryo fibroblasts (CEFs) were confirmed by indirect immunofluorescence (IFA) and Western blotting. The AGP antibodies against IBDV were detected beginning at 3 weeks post-inoculation (P.I.) of HVT-VP2-09 in 1-day-old SPF chickens. Seven of ten chickens immunized with HVT-VP2-09 were protected post-challenge (P.C.) with the virulent IBDV NJ09 strain. In contrast, all chickens in the challenge control group showed typical IBD lesions in bursals, and eight of ten died P.C. In this study, we demonstrated that (i) a novel HVT BAC with the whole genome of the Fc-126 strain was obtained with the insertion of mini-F sequences in lieu of the gC gene; (ii) HVT-VP2-09 harboring the VP2 expression cassette from virulent IBDV exhibited in vitro growth properties similar to those of the parental HVT virus in CEF cells; and (iii) HVT-VP2-09 can provide efficient protection against the IBDV NJ09 strain. Full article

Herpesvirus of turkeys (HVT), used originally as a vaccine against Marek’s disease (MD), has recently been shown to be a highly effective viral vector for generation of recombinant vaccines that deliver protective antigens of other avian pathogens. Until the recent launch of commercial HVT-vectored dual insert vaccines, most of the HVT-vectored vaccines in the market carry a single foreign gene and are usually developed with slow and less efficient conventional recombination methods. There is immense value in developing multivalent HVT-vectored vaccines capable of inducing simultaneous protection against multiple avian pathogens, particularly to overcome the interference between individual recombinant HVT vaccines. Here we demonstrate the use of a previously developed CRISPR/Cas9 gene editing protocol for the insertion of ILTV gD-gI and the H9N2 AIV hemagglutinin expression cassettes into the distinct locations of the recombinant HVT-IBDV VP2 viral genome, to generate the triple insert HVT-VP2-gDgI-HA recombinant vaccine. The insertion, protein expression, and stability of each insert were then evaluated by PCR, immunostaining and Western blot analyses. The successful generation of the first triple insert recombinant HVT vaccine with the potential for the simultaneous protection against three major avian viral diseases in addition to MD is a major innovation in vaccination-based control of major poultry diseases. Full article