Vaccine platform for infection or autoimmune diseases using an ETEC fimbrial scaffold
The expression of enterotoxigenic Escherichia coli (ETEC) fimbriae (colonization factor antigen I (CFA/I) or K99) on the surface of a Salmonella vaccine vector confers protection against ETEC challenge. Application of such fimbriae as a treatment for the proinflammatory disease, experimental autoimmune encephalomyelitis (EAE), or as a molecular scaffold for heterologous antigen expression by cloning enterohemorrhagic E. coli (EHEC) LPS peptide mimetics into the K99 fimbriae to produce a dual vaccine for ETEC/EHEC was investigated. The expression of CFA/I fimbriae by a Salmonella vaccine vector stimulates a biphasic T helper (Th) cell response and suppresses proinflammatory responses suggesting that CFA/I fimbriae may be protective against proinflammatory diseases. To test this hypothesis, SJL/J mice were vaccinated with Salmonella-CFA/I vaccine 1 or 4 wks prior to induction of EAE induced with encephalitogenic proteolipid protein (PLP) peptide, PLP₁₃₉-₁₅₁. Mice receiving Salmonella-CFA/I vaccine recovered completely from the mild acute clinical disease and showed only mild inflammatory infiltrates in the spinal cord. This protective effect was accompanied by a loss of encephalitogenic IFN-gamma secreting Th1 cells and replaced with increases in IL-4-, IL-10-, and IL-13- producing Th2 cells. These data suggest that Salmonella-CFA/I is an anti-inflammatory vaccine capable of suppressing proinflammatory cells to protect against EAE via immune deviation. To obtain an effective nasal vaccine for ETEC, the fanC gene of ETEC K99 major structural gene was cloned onto the reovirus adhesin, protein sigma1, which has been shown as an M cell targeting molecule. Although FanC/protein sigma1 fusion protein was successfully expressed, this vaccine failed to elicit immune responses against native FanC protein, presumably because of improper protein folding. Using K99 fimbriae as a molecular scaffold, a LPS peptide mimetic for EHEC was cloned into the fanH gene of K99 fimbriae minor structural gene to enable multiple antigenic peptide expression, resulting in an ETEC/EHEC dual vaccine. Insertion of peptide mimetic into fanH gene had no adverse effect on the formation of polymerized K99 fimbriae. However, various oral immunization regimens failed to induce the protective secretory IgA responses against the LPS mimetic peptide, although serum IgG antibodies were induced.