Phase 1 clinical trial of live attenuated Shigella dysenteriae type-1 DeltaicsA Deltaent Deltafep DeltastxA:HgR oral vaccine SC599 in healthy human adult volunteers.

Twenty-eight adults received between 10(2) and 10(8)colony forming units of live Shigella dysenteriae type-1 vaccine SC599, attenuated by deletion of invasion (icsA), iron chelation (ent, fep) and shiga toxin A-subunit (stxA) genes, followed by ciprofloxacin on day 4. Dose-independent diarrhea or change in bowel habit was seen in 3 subjects, without dysentery, vaccinaemia or serious adverse events. Hematology and biochemical parameters were unchanged. Doses of 10(5) or greater induced dose-independent SD1 lipopolysaccharide-specific antibody secreting cell (ASC) responses. Geometric mean number of IgA ASCs per 10(6) PBMCs for 10(5), 10(6), 10(7) and 10(8) groups were respectively 41, 8.8, 26 and 8.5. Serum antibody responses were seen in three subjects. SC599 appears immunogenic with maximum tolerated dose greater than 10(8)CFU.