Enhancement of immunogenicity of recombinant antigens by production of a cytokine-antigen fusion protein for vaccination

Mucosal immunization of calves with recombinant bovine adenovirus-3 coexpressing truncated form of bovine herpesvirus-1 gD and bovine IL-6

Previous studies have suggested an important role of the cytokine adjuvant IL-6 in the induction of mucosal immune responses in animals, including mice. Here, we report the in vivo ability of bovine adenovirus (BAdV)-3 expressing bovine (Bo) IL-6, to influence the systemic and mucosal immune responses against bovine herpesvirus (BHV)-1 gDt in calves. To co-express both antigen and cytokine, we first constructed a recombinant BAdV-3 expressing chimeric gDt.BoIL-6 protein (BAV326). Secondly, we constructed another recombinant BAdV-3 simultaneously expressing gDt and BoIL-6 using IRES containing a bicistronic cassette gDt-IRES.IL-6, (BAV327). Recombinant proteins expressed by BAV326 and BAV327 retained antigenicity (gDt) and biological activity (BoIL-6). Intranasal immunization of calves with recombinant BAV326, BAV327 or BAV308 (gDt alone) resulted in demonstrable levels of gDt-specific IgG responses in sera and IgA response in nasal secretions, in all animals. In addition, all calves developed complement-independent neutralizing antibody responses against BHV-1. However, no significant difference could be observed in the induction of systemic or mucosal immune response in animals immunized with recombinant BAV326 or BAV327 co-expressing BoIL-6. Moreover, there was no difference in the protection against BHV-1 challenge particularly in the amount of virus excretion in the nasal cavity in calves immunized with BAV326, BAV327 or BAV308. These data suggest that the BoIL-6 had no modulating effect on the induction of gDt specific mucosal and systemic immune responses in calves.

DNA vaccination against influenza viruses: a review with emphasis on equine and swine influenza

The influenza virus vaccines that are commercially-available for humans, horses and pigs in the United States are inactivated, whole-virus or subunit vaccines. While these vaccines may decrease the incidence and severity of clinical disease, they do not consistently provide complete protection from virus infection. DNA vaccines are a novel alternative to conventional vaccination strategies, and offer many of the potential benefits of live virus vaccines without their risks. In particular, because immunogens are synthesized de novo within DNA transfected cells, antigen can be presented by MHC class I and II molecules, resulting in stimulation of both humoral and cellular immune responses. Influenza virus has been used extensively as a model pathogen in DNA vaccine studies in mice, chickens, ferrets, pigs, horses and non-human primates, and clinical trials of DNA-based influenza virus vaccines are underway in humans. Our studies have focused on gene gun delivery of DNA vaccines against equine and swine influenza viruses in mice, ponies and pigs, including studies employing co-administration of interleukin-6 DNA as an approach for modulating and adjuvanting influenza virus hemagglutinin-specific immune responses. The results indicate that gene gun administration of plasmids encoding hemagglutinin genes from influenza viruses is an effective method for priming and/or inducing virus-specific immune responses, and for providing partial to complete protection from challenge infection in mice, horses and pigs. In addition, studies of interleukin-6 DNA co-administration in mice clearly demonstrate the potential for this approach to enhance vaccine efficacy and protection.

Genetically engineered vaccines: an overview

Despite the early success demonstrated with the hepatitis B vaccine, no other recombinant engineered vaccine has been approved for use in humans. It is unlikely that a recombinant vaccine will be developed to replace an existing licensed human vaccine with a proven record of safety and efficacy. This is due to the economic reality of making vaccines for human use. Genetically engineered subunit vaccines are more costly to manufacture than conventional vaccines, since the antigen must be purified to a higher standard than was demanded of older, conventional vaccines. Each vaccine must also be subjected to extensive testing and review by the FDA, as it would be considered a new product. This is costly to a company in terms of both time and money and is unnecessary if a licensed product is already on the market. Although recombinant subunit vaccines hold great promise, they do present some potential limitations. In addition to being less reactogenic, recombinant subunit vaccines have a tendency to be less immunogenic than their conventional counterparts. This can be attributed to these vaccines being held to a higher degree of purity than was traditionally done for an earlier generation of licensed subunit vaccines. Ironically, the contaminants often found in conventional subunit vaccines may have aided in the inflammatory process, which is essential for initiating a vigorous immune response. This potential problem may be overcome by employing one of the many new types of adjuvants that are becoming available for use in humans. Recombinant subunit vaccines may also suffer from being too well-defined, because they are composed of a single antigen. In contrast, conventional vaccines contain trace amounts of other antigens that may aid in conferring an immunity to infectious agents that is more solid than could be provided by a monovalent vaccine. This problem can be minimized, where necessary, by creating recombinant vaccines that are composed of multiple antigens from the same pathogen. These issues are less of a concern with a live attenuated vaccine, since these vaccines are less costly, require fewer steps to manufacture, and elicit long-lived immunity after only a single dose. Unfortunately, live vaccines carry a higher risk of vaccine-induced complications in recipients that make their use in highly developed, litiginous countries unlikely. In lesser developed countries, where the prevalence of disease and the need for effective vaccines outweighs the risk associated with their administration, live vaccines may play an important role in human health. This review has attempted to make the reader aware of some of the current approaches and issues that are associated with the development of these vaccines. Genetically engineered vaccines hold great promise for the future, but the potential of these vaccines to improve human and animal health has yet to be fully realized.