Genetically detoxified mutants of heat-labile toxin from Escherichia coli are able to act as oral adjuvants

Detoxified mutants of the Escherichia coil heat-labile toxin (LT) act as mu cosal adjuvants to intranasally presented coadministered antigens, Here, we compare the adjuvant activity of a panel of detoxified derivatives of LT, using both intranasal (i.n.) and oral (p.o.) routes of administration. The mutants used as adjuvants varied in sensitivity to proteases and toxicity. With keyhole limpet hemocyanin (KLH) as the bystander antigen, the immune r esponses to i.n. immunizations were consistently higher than the equivalent p.o.-delivered proteins. LT-G192, a mutant which demonstrates a 10-fold re duction in toxicity in vitro, demonstrated wild-type adjuvant activity both i.n. and p.o., inducing similar titers of KLH specific antibody in the ser a and immunoglobulin A in local mucosal secretions as wild-type LT, In line with previous data, the nontoxic holotoxoid LT-K63 induced intermediate im mune responses in both the serum and mucosal secretions which were lower th an those achieved with wild-type LT but at least 10-fold higher than those measured when the antigen was administered with LT-B, Although significant levels of local and systemic anti-KLH antibodies were induced following p.o . immunization with LT-K63, cellular proliferative responses to KLH was poo r or undetectable. In contrast, LT and LT-G192 induced significant T-cell r esponses to KLH following p.o. immunization. These proliferating cells secr eted both gamma interferon and interleukin-5, suggesting that the type of i mmune response induced following p.o. coimmunization with LT and purified p rotein is a mixed Th1/Th2 response.