New vaccine strategies against enterotoxigenic Escherichia coli. I: DNA vaccines against the CFA/I fimbrial adhesin

Stimulation of the mammalian immune system by administration of plasmid DNA has been shown to be an important approach for vaccine development against several pathogens. In the present study we investigated the use of DNA vac cines to induce immune responses against an enteric bacterial pathogen, ent erotoxigenic Escherichia coli (ETEC). Three plasmid vectors encoding coloni zation factor antigen I (CFA/I), an ETEC fimbrial adhesin, were constructed . Eukaryotic cells transfected with each of these plasmids expressed the he terologous antigen in different compartments: bound to the cytoplasmic memb rane (pRECFA), accumulated in the cytoplasm (pPolyCFA) or secreted to the o utside medium (pBLCFA). BALB/c mice were intramuscularly (im) inoculated wi th purified plasmid DNA and the systemic, cellular and secreted CFA/I-speci fic immune responses were analyzed. The results showed that all three DNA v accine formulations could elicit CFA/I-specific immune responses. Moreover, cellular location of the plasmid-encoded CFA/I seems to have an important role in the induced immune response. Taken together, these results indicate that DNA vaccines also represent a promising approach against enteric bact erial pathogens.