Development of a Prototype Chicken CD40-targeted Peptide Vaccine against Infectious Bursal Disease Virus (IBDv) in Chickens

Infectious bursal disease (IBD) is one of the biggest concerns for poultry farms because of significant economic losses due to high morbidity. Moreover, surviving birds are immunocompromised and susceptible to other pathogens. Although live and inactivated vaccines have been applied to minimize risk, massive losses are still occurring. Immunotherapy opens new horizons in the field of disease control through more effective and safer measures. One technique that gains importance is targeting CD40 with the immunogen of interest. This technique requires a smaller dose while also dramatically reducing response time. The goal of our research was to develop a vaccine complex that targets chCD40 with three synthetic IBD-VP2 peptides to protect young chickens from IBDV adverse effects. A live intermediate virulent virus strain (IBDV-D78) was used in overdose for the challenge test. The vaccine was also tested with regard to its ability to maintain the birds’ capacity to respond to the NDV vaccine because this is one of the most common commercially relevant programs. The first experiment aimed at assessing the dose and route of the IBDV live vaccine overdose challenge, which was expected to induce marked pathological changes. More than recommended vaccination doses (2x-8x) were applied either by oral or cloacal administration. Results indicated that cloacal challenge by 8x dose induced significant pathological changes by a marked reduction in the bursa of Fabricius (BF) weight, bursa to body weight ratio (BB), and anti-IBDV titer. In our second experiment, we examined the hypothesis that a single dose of subcutaneous immunization by chCD40 targeted VP2 peptide vaccine is able to provide protection against the immunosuppressive effects of the challenge. Challenge was either oral or intra-cloacal at 10x or 20x the recommended oral vaccine dose at day 24 of age. Ten days post-challenge, the different challenge modes reduced the weight of the bursa of Fabricius with 32%, 42%, 49%, and 58%, respectively, compared to controls. The peptide-based vaccine consisted of three different biotinylated VP2-derived synthetic fragments complexed with a biotinylated agonistic monoclonal anti-chicken CD40 antibody, using streptavidin as the central scaffold. Each bird received 50 micrograms of the respective peptide complexes (150 micrograms total) s.c at 14 days of age, i.e. ten days prior to challenge. Even with the maximum damaging challenge (20x cloacal), the vaccine prevented most of the damage caused by IBDV. The chCD40 targeted VP2 peptide vaccine significantly increased BB ratio, anti-IBDV titer and increased the Bu-1+ B-cell viability by 45%, in the circulation and by 63%, in the BF compared to challenged unvaccinated groups. In the final study, we assessed the capacity of the peptide vaccine to preserve subsequent NDV vaccine efficacy from the IBDV immunosuppression effects. Additionally, oral vaccination with chCD40 targeted VP2 peptide vaccine was evaluated as a practical mass vaccination method. Birds were vaccinated either orally or subcutaneously, ten days before the challenge. In the first trial, oral administration of the chCD40 targeted VP2 peptide vaccine at the same dose that used for s.c. injection was able to protect the NDV vaccine program significantly with the s.c route. At the same time, there was a moderate protection when oral vaccination was applied. However, when the oral dose was adjusted to 2x or 4x the s.c dose, the vaccine prevented B-cell depletion in the BF and circulatory B-cell numbers were not statistically different from the s.c vaccine or negative controls. Histopathologically, severe lymphocyte depletion in the bursal follicles and increased thickness of the interfollicular septae was observed in the IBDV challenged groups, but not in the vaccinated groups. Finally, the vaccine prevented IBDV-induced immunosuppression as judged by the response to subsequent vaccination against NDV. In conclusion, this CD40-targeted peptide delivery strategy may provide a safe and efficacious alternative to the currently used live IBDV vaccines