Immunogenicity and protective capacity of inactivated "vibrio cholerae" whole cell vaccines

The effects of heat and chemical inactivants on the immunogenicity and protective capacity of V. cholerae was studied. ELISA systems, using whole cells of V. cholerae, purified LPS or flagella preparations as immobilized antigens were employed to measure serum antibody titers. The immune response to parenteral vaccination in rabbits with killed whole cell vaccines was dependent upon the inactivation procedure used. Cells inactivated by heat alone or in combination with phenol were found to be comparatively poor immunogens. Formalin, together with heating, produced a much superior immunogen. The concentration of formalin was found to be critical for production of an optimal immunogen. IgG-titers in all ELISA assays were between 10-fold to 100-fold higher when formalin-heat inactivated preparations were employed as compared to phenol-heat inactivated. Additionally, antibody produced in response to a formalin-heat inactivated preparation was capable of reacting with antigen determinants present on the cell surface of several heterologous strains of V. cholerae. The protection afforded by parenteral immunization with several inactivated preparations against live vibrio challenge was determined in the rabbit ileal loop model. A preparation prepared by heating alone offered no detectable protection while a phenol-heat inactivated preparation provided modest levels of protection (approximately 14-fold). In contrast, immunization with a formalin-heat inactivated preparation offered substantial protection (1,400-fold). These results demonstrate that a highly immunogenic inactivated V. cholerae whole cell vaccine can be prepared which provides significant protection against a live V. cholerae challenge.