Efficacy of nucleoprotein and haemagglutinin antigens expressed in fowlpox virus as vaccine for influenza in chickens

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.

Recombinant fowlpox virus vaccines for poultry

The intensive poultry industries rely heavily upon the use of vaccines for disease control. Viral vector based vaccines offer new avenues for the development of vaccines for effective disease control in poultry. Techniques developed for the construction of recombinant vaccinia viruses have been readily adapted to the construction of recombinant viruses based on fowlpox virus (rFPV). The ability to insert several genes into the large genome of fowlpox may enable the development of multivalent vaccines and vaccines incorporating immune response modifiers such as lymphokines. Newcastle disease, avian influenza, infectious bursal disease and Marek's disease antigens expressed by rFPV have been shown to be effective vaccines in poultry. None appear, however, to provide a substantial improvement in vaccine efficacy. Recombinant FPV will be a valuable adjunct to conventional vaccines currently in widespread use. Whether rFPV or other vector based vaccines can circumvent the problems of vaccination in the presence of high maternally derived antibodies is yet to be resolved. The observation that avipoxvirus recombinants may be suitable for the vaccination of non-avian species provides an added dimension to vaccines based on FPV or other avipoxviruses. Recombinant FPV will find a useful role in poultry disease control when used in conjunction with conventional vaccines.

The cytolytic activity of pulmonary CD8+ lymphocytes, induced by infection with a vaccinia virus recombinant expressing the M2 protein of respiratory syncytial virus (RSV), correlates with resistance to RSV infection in mice

Previous studies demonstrated that the pulmonary resistance to respiratory syncytial virus (RSV) challenge induced by immunization with a recombinant vaccinia virus expressing the M2 protein of RSV (vac-M2) was significantly greater 9 days after immunization than at 28 days and was mediated predominantly by CD8+ T cells. In this study, we have extended these findings and sought to determine whether the level of CD8+ cytotoxic T-lymphocyte (CTL) activity measured in vitro correlates with the resistance to RSV challenge in vivo. Three lines of evidence documented an association between the presence of pulmonary CTL activity and resistance to RSV challenge. First, vac-M2 immunization induced pulmonary CD8+ CTL activity and pulmonary resistance to RSV infection in BALB/c (H-2d) mice, whereas significant levels of pulmonary CTL activity and resistance to RSV infection were not seen in BALB.K (H-2k) or BALB.B (H-2b) mice. Second, pulmonary CD8+ CTL activity was not induced by infection with other vaccinia virus-RSV recombinants that did not induce resistance to RSV challenge. Third, the peak of pulmonary CTL activity correlated with the peak of resistance to RSV replication (day 6), with little resistance being observed 45 days after immunization. An accelerated clearance of virus was not observed when mice were challenged with RSV 45 days after immunization with vac-M2. The results indicate that resistance to RSV induced by immunization with vac-M2 is mainly mediated by primary pulmonary CTLs and that this resistance decreases to very low levels within 2 months following immunization. The implications for inclusion of CTL epitopes into RSV vaccines are discussed in the context of these observations.

Protection against a lethal influenza virus challenge by immunization with a haemagglutinin-expressing plasmid DNA

Direct DNA inoculations have been used to demonstrate that in vivo transfections can be used to elicit protective immune responses. The direct inoculation of an H7 haemagglutinin-expressing DNA protected chickens against lethal challenge with an H7N7 influenza virus. Three-week-old chickens were vaccinated by inoculating 100 micrograms of plasma DNA by each of three routes (intravenous, intraperitoneal and subcutaneous). One month later, chickens were boosted with 100 micrograms of DNA by each of the three routes. At 1-2 weeks postboost, chickens were challenged via the nares with 100 lethal doses of an H7N7 virus. Low to undetectable levels of H7-specific antibodies were present postvaccination and boost. High titres of H7-specific antibodies appeared within 1 week of challenge. In a series of four experiments, 50% (28/56) of the DNA-vaccinated and < 2% (1/67) of the control chickens survived the challenge. This exceptionally simple method of immunization holds high promise for the development of subunit vaccines.

Recent advances in avian virology

Selected, recent research on the following avian diseases, and their causative viruses, has been reviewed: chicken anaemia, infectious bursal disease, turkey rhinotracheitis, avian nephritis, fowlpox, influenza, infectious bronchitis and turkey enteritis.