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Development of 60Co-irradiated cholera vaccine

Yukio TAMURA and Tatsuo YAMAMOTO , ,
Dicision of Bacteriology Department of Infections Disease Control and International Medicine

Human intestinal mucosa possesses a potent specific immune system with secretory IgA production as the main constituent, and this system is different from the systemic immune system. The involvement of mucosal IgG, which may have bactericidal activity, has also been demonstrated. Therefore, the most rational means of prevention of bacterial infection is to establish mucosal immunity by strong induction of the mucosal specific immune responses to efficiently block the initial step of bacterial infection, i.e., blockage of colonization by pathogenic bacteria such as Vibrio cholerae O1 and O139, enterohemorrhagic Escherichia coli (O157), Helicobacter pylori, and Bacillus anthracis.

We have been developing 60Co-irradiated vaccines that are safe, easily developed, and exhibit a markedly higher protective effect on infection than the current inactivated vaccines. 60Co-irradiated vaccine is a new type of vaccine (new generation of inactivated vaccine) possessing properties of both live and inactivated vaccines.

60Co-irradiated cholera vaccine consists of killed bacteria, but the bacteria are motile rotating flagella in the intestinal tract and adhere to antigen-incorporating cells (M cells). The current inactivated cholera vaccine, so far reported, does not efficiently induce mucosal immunity without adjuvant, while 60Co-irradiated cholera vaccine strongly induces production of mucosal IgA and IgG without adjuvant. As the actions of 60Co-irradiated cholera vaccine, it is expected that mucosal IgA prevents bacterial colonization and neutralizes toxin, and IgG kills bacteria.

We have conducted animal experiments with the aim of developing a further effective 60Co-irradiated cholera vaccine by combining with an effective adjuvant. The same protocol is applicable to development of ,e.g., O157 vaccine and anthrax vaccine.

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