Development of recombinant Vibrio cholerae candidate vaccines

Cholera continues to be an important cause of illness and death in areas of the world where the disease is endemic and since the likelihood of widespread correction of inadequate sanitation in the near future is remote, vaccination remains the most practical approach to the prevention of the disease. The overall objective of the proposed project is the development of an effective vaccine against Vibrio cholerae infection using two alternative approaches: app1 involves the use of 1 cholerae ghosts (VCG) which are inactivated agents possessing inherent immunomodulatory activity. VCG are characterized by the absence of cytoplasmic contents and thus of all toxins including cholera toxin. We have shown that VCG can serve as a reliable vaccine delivery system induce serum antibodies following intraperitoneal immunization of mice. The use of VCG as vaccines and as carriers of heterologous antigens is a novel approach in vaccine development which has the advantage of eliminating the use of heat or chemical treatment for inactivation. Inactivate agents produced by heat or chemical treatment suffer from ill-defined molecular characteristics; such treatments have the potential to denature relevant immunological determinants. VCG can be produce inexpensively in large quantities by expression of a cloned phage lysis gene. Also, the VCG entity should have a direct stimulatory effect on the immune system which can aid in the immunogenic responses to inserted foreign antigens. The second approach, app2 involves the use of recombinant naturally occurring, non- toxigenic (NT) clinical isolates of V. cholerae as live cholera vaccine Most V. cholerae strains carry more than one type of toxin gene and it is difficult to eliminate all c them simultaneously. Live attenuated V. cholerae vaccines suffer from the theoretical drawback c genetic recombination or genetic reversal of the specific mutations associated with thei.r attenuation. The use of a recombinant derivative of a naturally occurring NT clinical isolate of V. cholerae offers several advantages as a live oral vaccine. In preliminary experiments, our NT strains were found t naturally lack the genes associated with toxigenicity. Our approach will circumvent the need t engineer toxigenic V. cholerae as live cholera vaccines. The results of this three-year study will enable us to evaluate comparatively, the safety, immunogenicity and protective abilities of these two, candidate vaccines and subsequently form the basis of future clinical trials.