Mutants of Escherichia coli heat-labile enterotoxin and cholera toxin as mucosal adjuvants *

Mucosal vaccination has been getting more and more recognition because of its compliance and low risk of spreading infectious disease by contaminated syringes used in subcutaneous immunization. However, most vaccines are unable to induce immune responses when given mucosally, and require the use of strong adjuvant for effective delivery systems. Heat-labile enterotoxin (LT) and Cholera toxin(CT) are powerful mucosal adjuvants when co-administered with soluble antigens. But high toxicity hampers their use in humans. Thanks to the fine knowledge of the structure-function relationship of LT and CT, many nontoxic or low toxic mutants have been generated, part of them retain high adjuvanticity of mucosal immunization. Among these mutants, LTS63K, LTA72R, LTR192G and CTE29H, CTE112K have been widely investigated. LTS63K and CTE112K are fully non toxic, whereas LTA72R and CTE29H are low toxic, and LTR192G is nontoxic in vitro(it remains the same toxicity as wild type LT in vivo). These mutants are extremely active as mucosal adjuvants when co-administrated with a variety of antigens in different animal models. They will be investigated more widely and deeply in the future. Some of them will be tested soon in human bodies.