Immunogenicity and efficacy of baculovirus-expressed and DNA-based equine influenza virus hemagglutinin vaccines in mice.

The research studied two different methods of vaccinating mice against equine influenza virus with a primary focus on the timing and efficacy of the vaccines. The two mechanisms used were hemagglutinin (HA) protein administered nasally and HA-encoding DNA administered using a gene gun. While both methods stimulated an immune response, the time between the initial and booster DNA vaccinations proved a key factor in determining the effectiveness of the vaccine.

Vaccine Development Approaches

• The research involved using two different methods for vaccination against the equine influenza virus in mice. The virus strain used was A/Equine/Kentucky/1/81 (H3N8), also known as Eq/KY.
• The first method involved the administration of hemagglutinin (HA) protein. This protein, crucial for the virus’s survival and infection, was synthesized in vitro, or outside a living organism, through the infection of insect cells via a recombinant baculovirus.
• The second vaccination approach was the administration of HA-encoding DNA. In this approach, plasmid DNA, carrying the gene for Eq/KY HA, was injected into mice via a gene gun.

Vaccine Immunogenicity and Efficacy

• Both vaccination approaches displayed different levels of immunity induced and protection from infection.
• The intranasal administration of HA protein induced virus-specific antibodies, detectable by enzyme-linked immunosorbent assay (ELISA). However, it didn’t trigger the production of virus neutralizing (VN) antibodies.
• The HA protein vaccine provided partial protection, but interestingly, when combined with cholera holotoxin, this vaccine failed to provide any protection, indicating potential interactive factors.
• On the other hand, the DNA-based vaccine induced not only virus-specific ELISA antibodies but also VN antibodies, suggesting a higher potential for virus neutralization.
• When this DNA vaccine was administered in two doses, three weeks apart, it didn’t completely prevent the infection. However, it seemed to aid in clearing off the infection more quickly than in unvaccinated mice.

Impact of Vaccination Timing

• A key finding from this research was the impact of the timing between the primary and booster doses of the DNA vaccine.
• When the second DNA vaccine was given nine weeks after the first, a significantly higher protection level was noted. This observation suggests that the time interval between initial and booster DNA vaccinations may play an important role in determining the efficacy of DNA vaccines.
• The study concluded that while the HA protein vaccine held potential, the results hinted at a possible influential factor for DNA vaccination success, specifically the spacing of vaccinations.