A novel plant-derived recombinant COBRA infectious bronchitis virus spike protein can elicit a strong immune response in chickens.

Infectious bronchitis virus (IBV) causes an acute respiratory disease in chickens of all ages, and is an economic burden on the global poultry industry. In severe cases, this virus can spread from the respiratory tract to urinary and reproductive organs, leading to kidney damage, poor egg quality, and high mortality rate of chickens. Among IBV glycoproteins, spike (S) is the major determinant of viral attachment to host receptors and induction of neutralizing antibodies. Rapid mutations were found within the S gene of numerous IBV strains presenting in multiple geographical locations. Since the early detection of IBV in the 1930s, no single control strategy has so far shown high efficacy in protecting chickens. The aim of this investigation was therefore to develop a novel S-subunit vaccine to prevent this disease. Using a design approach of Computationally Optimized Broadly Reactive Antigen (COBRA) and the Nicotiana benthamiana transient expression system, we have successfully generated a recombinant S protein comprising the most consensus amino acids of IBV strains circulating in Vietnam and surrounding areas. Importantly, our results showed that the plant-derived protein was able to induce a strong immune response in chickens with significantly high expression levels of IFN-γ, GZM-A, CD4, CD8 mRNAs in the peripheral blood. Remarkable titers of IgY specific antibodies were stably observed over a 5-week period post immunization by COBRA-S, which was in agreement with the reduction of clinical signs after virus challenge. This study contributes a potential direction to vaccine development coping with new IBV outbreaks in the future.