Page 793 - Veterinary Immunology, 10th Edition

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FIG. 24.9 The structure of a typical DNA plasmid used for
vaccination purposes. In this case the plasmid codes for protective
antigens of West Nile virus. In addition to coding for the antigen in
question, the plasmid carries an antibiotic resistance marker so that
its fate may be traced.

This type of vaccine is used to protect horses against West Nile
virus infection. The commercial vaccine consists of a plasmid vector

engineered to express high levels of the virus envelope (E) and
premembrane (prM) proteins. In addition, the plasmid contains
gene promoters and marker genes. Upon injection together with a
biodegradable oil adjuvant, this plasmid enters cells and causes

them to express the viral protein. Other DNA vaccines have been
approved to prevent infectious hematopoietic necrosis in Atlantic
salmon and melanomas in dogs (Chapter 35). This approach has
also been applied experimentally to produce vaccines against avian

influenza, lymphocytic choriomeningitis, canine and feline rabies,
canine parvovirus, bovine viral diarrhea, feline immunodeficiency
virus, feline leukemia virus, pseudorabies, foot-and-mouth disease
virus, bovine herpesvirus-1, and Newcastle disease. Although

theoretically producing a response similar to that induced by
attenuated live vaccines, these nucleic acid vaccines are ideally
suited to protect against organisms that are difficult or dangerous
to grow in the laboratory. Some DNA vaccines can induce

immunity even in the presence of very high titers of maternal
antibody. Although the maternal antibodies block serological
responses, the development of strong memory responses is not
impaired.

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