Evaluation of intranasal vaccination with plant-derived VP2 against IBDV

LUCERO, MARÍA SOLEDAD; RICHETTA, MATÍAS; CHIMENO ZOTH, SILVINA; GRAVISACO, MARÍA JOSÉ; CARBALLEDA, JUAN MANUEL; DELGADO, FERNANDO; WIGDOROVITZ, ANDRÉS; BERINSTEIN, ANALÍA; GOMEZ, EVANGELINA

Lausanne

Conferencia; Plant-Based Vaccines, antibodies & Biologics; 2015

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. The structural protein 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 meet the needs of new generation 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. However, administration via injection is impractical, carries the risk of needle stick injury and is a less animal welfare friendly method. Mucosal vaccination is a noninvasive method and has several advantages over traditional systemic vaccines. Taking this into account 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 intranasally to chickens. Objectives- The objectives of the present work were to transiently express VP2 of IBDV in plants and to investigate whether this recombinant immunogen can be used as an intranasal vaccine in chickens. Materials and Methods-Transient expression was performed by the agroinfiltration of Nicotiana benthamiana plants 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. SPF chickens of 21 days old were randomly assigned to experimental groups. Nine animals in each group were intramuscularly (im.) or intranasally (in.) vaccinated with either plant extracts containing 6 ug of VP2, or plant extracts containing GFP as a non-related antigen, in a dose/boost scheme. Chickens were vaccinated at days 0 and 14 and they were bled by the wing vein every 10 days. Three weeks after boost, 6 animals of every group were challenged 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, histopathological observation and virus isolation. Serum samples were evaluated for the presence of specific antibodies against IBDV with a commercial ELISA and for virus neutralizing activity using chicken embryo fibroblasts (CEFs). Results- Animals inoculated im., but not in. with the experimental vaccine developed high titres of specific antibodies, with virus neutralizing activity. Negative groups did not present antibodies against IBDV. Also, bursae of animals vaccinated im. with VP2 presented few infiltrating T cells, low viral charge and normal morphology compared to animals in the control groups. However, chickens that received the immunogen via nasal route were not protected after challenge and their bursae were similar to those that received GFP. Conclusion and Discussion- The immunogenicity and protective efficacy of an in. plant-based vaccine against IBDV were investigated. This route proved to be ineffective in developing a humoral and protective response against viral challenge, at least, with the antigen concentration used in this experiment. However, we do not discard the possibility that a higher amount of VP2 given intranasally could be needed to elicit an immune response. Further investigations need to be done in order to find a better and more practical route of administration of the recombinant immunogen than the im. injection.