Oral vaccination against IBDV with plant-derived VP2

LUCERO, S.; GÓMEZ, E.; CHIMENO-ZOTH S.; CARBALLEDA, J.M.; GRAVISACO, M.J.; BERINSTEIN, A.

Congreso; Plant-Based Vaccines and Antibodies 2013; 2013

Introduction-Infectious Bursal Disease Virus (IBDV) is the etiological agent of an immunosuppressive and highly contagious disease that affects young birds causing important economic losses in the poultry industry. VP2 which contains the major neutralizing epitopes has been used for the development of subunit vaccines in a variety of heterologous platforms in order to attend to a new generation of vaccines as effective as the traditional virus based ones. We have previously demonstrated that VP2 transiently expressed in Nicotiana benthamiana is able to elicit a neutralizing antibody response in chickens when administered intramuscularly in a prime/boost scheme. We have also observed a decrease in T cells infiltration into the bursa after the challenge in those animals vaccinated with plant derived VP2, suggesting that humoral response prompted by the recombinant immunogen neutralizes totally or partially the entrance of IBDV. Given these antecedents and the fact that natural infections with IBDV occur by the oral route we decided to investigate whether VP2 produced in plants was also immunogenic when given orally to chickens. Objectives- the objectives of the present work were to transiently express the VP2 protein and to investigate whether this recombinant immunogen can be used as an oral vaccine in chickens. Materials and Methods- Transient expression was performed by the agroinfiltration of N. benthamiana leaves with a suspension of recombinant bacteria harboring the VP2 gene. VP2 protein expression was analyzed by Western blot utilizing an anti-VP2 polyclonal antibody raised in rabbit. Specific pathogen free chickens of 18 days old were randomly assigned to experimental groups. During 23 consecutive days chickens were fed with 1ml of plant extract containing 30 µg of VP2 (group 1), or a non-related antigen as control group (group 2). Animals of group 3 were vaccinated at day 0 with the commercial vaccine. All animals were weekly bled by the wing vein. Animals were challenged the last day of vaccination (23 day) by oral inoculation with 500 µl of classical IBDV strain LZD (6934 TCID50/ml). Five days later animals were euthanized and bursae were removed for lymphocyte isolation and flow cytometry analysis. Serum samples were evaluated for the presence of specific antibodies against IBDV with a commercial ELISA and they were evaluated for virus neutralizing activity using chicken embryo fibroblasts (CEFs). Results- Chickens orally vaccinated showed an immune response of specific antibodies with low titers with a the serum working dilution of 1/20, and three out of four chickens showed specific antibodies at 23 dpi. Animals vaccinated with VP2 barely developed a neutralizing response (titers of 1/16). After infection, IBDV replication in the bursa involves an infiltration of T cells into this organ and tissue damage. We have also investigated the frequency of T cells in the bursa of vaccinated animals after challenge with a high dose of a classical IBDV strain to determine if plant-derived VP2 elicited a protective immune response. Bursae of animals vaccinated with VP2 presented fewer infiltrating T cells compared to animals in the control group. Conclusion and Discussion- The immunogenicity and protective efficacy of an oral plant-based vaccine against IBDV were investigated. Although the humoral response was not as strong as we expected, it is worth to notice the fewer T cells infiltration presented in those animal vaccinated with VP2 that suggests an immune state of protection acquired by vaccination with the experimental immunogen.