Derivation and characterization of a live attenuated equine influenza vaccine virus.

This research focuses on the development and analysis of a safe and potent live attenuated equine-2 influenza virus, which could be used as an intranasal vaccine. The team achieved this by artificially adapting a wild strain of equine-2 influenza virus to cold temperatures, then testing the derivative virus’s stability, safety, replication ability, and immunogenicity in ponies.

Methodology

• The researchers started with a wild-type equine-2 virus (A/Equine/Kentucky/1/91) and subjected it to a carefully controlled process of serial passaging in chicken eggs, gradually reducing the incubation temperature from 34°C to 26°C.
• At various stages, they extracted the virus-infected fluids from the eggs and tested them in a culture of Madin-Darby canine kidney (MDCK) cells at 34°C and 39.5°C. This was to identify if the virus had adapted to the colder temperature, by being able to replicate at 26°C in eggs and at 34°C in the cell culture, but not at 39.5°C.
• The research team focused on clones that displayed these characteristics along with stability, naming the most promising candidate P821.
• This virus clone was then administered intranasally to a group of eight healthy, seronegative ponies, around 18 months old, to study its safety, replication capability, and the immune response it triggered.

Results

• All randomly chosen clones from the 49th passage displayed a clear temperature-sensitive phenotype, revealing plaquing efficiencies of < 10(-6) (ratio of 39.5 C:34 C), and kept this trait even after five subsequent passages at 34°C in either eggs or cultured cells.
• The chosen candidate for the vaccine, clone P821, demonstrated the desired level of attenuation defined by the research team.
• This attenuated virus did not produce any adverse reactions or noticeable disease symptoms in ponies when administered intranasally.
• P821 was found to replicate in the upper respiratory tract of ponies and induced a strong serum antibody response, indicating successful immunity development.

Conclusions

• The research team successfully derived a live attenuated influenza vaccine virus through the cold adaptation of a wild equine-2 influenza virus, A/Equine/Kentucky/1/91, in embryonated chicken eggs.
• The candidate vaccine was shown to be safe, capable of replicating in the target host (ponies) and eliciting a robust immune response, making it a promising candidate for further study and potential use in preventing equine influenza.