Use of DNA encoding influenza hemagglutinin as an avian influenza vaccine.

Recently, we demonstrated that direct inoculation of a hemagglutinin 7 (H7)-expressing DNA could vaccinate chickens against a lethal H7 influenza virus challenge. These experiments used a defective-retroviral-based vector to express H7 (p188) (Robinson et al., 1993). Here, we report protective immunizations using a non-retroviral-based vector for H7 expression (pCMV/H7). Unlike the previously used retroviral-based vector, this vector cannot be transmitted as an infectious agent (as a consequence of phenotypic mixing with exogenous or endogenous virus proteins). Vaccination was accomplished by inoculating young, immunocompetent chickens by each of three routes (intravenous, intraperitoneal, and intramuscular) with 100 micrograms of cesium chloride-purified pCMV/H7 DNA in saline. After two immunizations, birds were challenged via the nares with a lethal dose of a highly virulent chicken influenza virus of the H7 subtype. The results of five independent vaccine trials demonstrated protective immunizations in approximately 60% of the pCMV/H7 DNA-inoculated chickens. By contrast, only 3% of the chickens inoculated with control DNA survived the lethal challenge.