DNA immunisation against the CFA/I fimbriae of enterotoxigenic Escherichiacoli (ETEC)

The CFA/I fimbria promotes the attachment of enterotoxigenic Escherichia co li (ETEC) to the surface of human enterocytes. The generation of a protecti ve immune response requires the induction of antibodies able to block the C FA/I-mediated binding of ETEC to receptors located on the small intestine e pithelium or on the surface of human red blood cells, in hemagglutination t ests. An eukaryotic expression plasmid, pBLCFA, encoding the CFA/I gene und er the control of the human cytomegalovirus major immediate-early promoter was constructed as a prototype DNA vaccine against ETEC, pBLCFA-tranfected BHK-21 cells secreted a-peptide cross-reacting with a monoclonal antibody r aised against CFA/I subunits. BALB/c mice immunized intramuscularly with on e or two doses of purified pBLCFA developed CFA/I-specific serum antibodies for at least 52 Reeks, composed predominantly of the IgG1 subclass. pBLCFA -induced antibodies bind mainly to epitopes exposed on the surface of intac t,CFA/I fimbriae and do not react with immune recessive epitopes found in o ther ETEC fimbra sharing amino acid homologies,with CFA/I. Furthermore, pBL CFA-induced antibodies were able to block the adhesive properties of the CF A/I fimbriae,as evaluated by the ability to inhibit the hemagglutination pr omoted by CFA/I-expressing ETEC cells. These results suggest that secretion of CFA/I encoded by pBLCFA preserves important conformational epitopes req uired for the generation of protective antibodies against the adhesive prop erties of the CFA/I fimbriae and open new perspectives for the development of DNA vaccines against enteric bacterial pathogens. (C) 2000 Published by Elsevier Science Ltd.