Immunization with pHKHA

The first step in determining whether a vaccine provides immunity to its host is to test the vaccine against challenge after a host is immunized with a vaccine, a virus is introduced into the host to see if the vaccine is effective. The virus that is used is one that the vaccine is supposed to provide immunity against. with a homologous virus. In this case, the pHKHA encodes for the HA of the HK97 virus, therefore, the HK97 virus would be the best choice for challenge. In addition to challenge with a homologous virus, the antigenic variant, CkHK97 was also used.

Methods

Mice were immunized with pHKHA via gene gun delivery of DNA: the plasmid DNA was affixed to 2.6mm gold beads, the DNA-coated gold particles (1mg) were then delivered into shaved abdominal areas of mice using a helium pulse gene gun. After 4 weeks, the mice were given a booster of the same dose. Ten days after receiving the boosters, the mice were challenged with 10-100mL 50% lethal doses (LD₅₀) of either HK97 or CkHK97, intranasally. The mice were observed daily for clinical signs, weight loss and mortality. On the fifth day postinfection, samples were taken for virus replication. (Serum samples were collected prebooster, prechallenge, and 10 days postchallenge for antibody analyses)

Results

Table 1. Protection against lethal H5N1 virus challenge induced from DNA encoding HA from HK97

Questions to Ponder

• Did immunization with pHKHA provide immunity against HK97? yes correct! The data above shows that pHKHA provided 100% protection against death. no incorrect: pHKHA provided 100% protection against death from HK97
• Did immunization with pHKHA provide immunity against CkHK97? yes correct! The data above shows that pHKHA provided 100% protection against death. no incorrect: pHKHA provided 100% protection against death from CkHK97
• Why use CkHK97? answer CkHK97 is an antigenic variant of HK97, thus protective immunity induced by pHKHA against CkHK97 suggests the possiblity of protection against other antigenic variant strains.
• What do these results suggest about the DNA vaccine? answer these results suggest that in an avian influenza pandemic, a DNA vaccine encoding an antigenically related HA might offer adequate protection until a genetically matched HA DNA vaccine could be made.

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