Recombinant DNA technology for the preparation of subunit vaccines

Recombinant DNA technology appears to be on the verge of producing safe and effective protein vaccines for animal and human diseases. The procedure is applicable to most viruses because their isolated surface proteins generally possess immunogenic activity. Strategies used for the preparation and cloning of the appropriate genes depend on the characteristics of the viral genomes: whether DNA or RNA; their size, strandedness, and segmentation; and whether messenger RNA are monocistronic or polycistronic. Cloned surface proteins of foot-and-mouth disease and hepatitis B viruses are being tested for possible use as practical vaccines. Two doses of the cloned foot-and-mouth disease viral protein have elicited large amounts of neutralizing antibody and have protected cattle and swine against challenge exposure with the virus. Surface proteins have also been cloned for the viruses of fowl plague, influenza, vesicular stomatitis, rabies, and herpes simplex. Cloning is in progress for surface proteins of viruses causing canine parvovirus gastroenteritis, human papillomas, infectious bovine rhinotracheitis, Rift Valley fever, and paramyxovirus diseases. In addition, advances in recombinant DNA and other facilitating technologies have rekindled interest in the chemical synthesis of polypeptide vaccines for viral diseases. The bioengineering of bacterial vaccines is also under way. Proteinaceous pili of enterotoxigenic Escherichia coli are being produced in E coli K-12 strains for use as vaccines against neonatal diarrheal diseases of livestock.