Showing papers on "Anthrax vaccines published in 1993"

Expression of the protective antigen of Bacillus anthracis in attenuated Salmonella : a potential oral anthrax vaccine

Abstract: Anthrax is a disease of animals and man caused by Bacillus anthracis. The Protective Antigen (PA) of B. anthracis can induce protective immunity and is a candidate vaccine antigen, but current vaccines are not ideal. Live vaccine vectors, such as the aromatic amino acid Salmonella mutants, are capable of delivering antigens to the immune system and stimulating immune responses. The aim of this project was to develop a recombinant S. typhimurium expressing PA and to evaluate the protective immune responses generated in mice. Native PA was expressed at low levels in S. typhimurium. Various approaches to increasing expression were tried including changing the promoter, expressing the 63 kDa C-terminal fragment of PA as a fusion protein and expressing this fragment after a signal sequence. Altering the B. anthracis PA promoter to the E. coli lac promoter increased expression of PA which was exported with the B. anthracis signal sequence. The cytoplasmically located PA fragment was unstable and was not successfully exported by the signal sequence. The recombinant organisms were evaluated to select one for in vivo study. Many phagemids were unstable without ampicillin selection and an attempt to stabilise one with the cer region was not successful. Two constructs were chosen for animal work. Recombinant PA was shown to induce partial protection, comparable to native PA, when both were purified and administered with adjuvant. Mice were vaccinated intravenously with the live S. typhimurium constructs and subsequent challenged with virulent B. anthracis spores. The PA-expressing S. typhimuruon only colonised at low levels but induced partial protective responses. These protective responses occurred without detectable anti-PA antibody. This work showed that PA expressed by S. typhimurium can induce protective responses even when only low colonisation occurs. It shows the potential for this approach and suggests that further work to stabilise and increase the expression of PA would be worthwhile.