Shigella flexneri 2a strain CVD 1207, with specific deletions in virG, sen, set, and guaBA, is highly attenuated in humans

A phase 1 clinical trial was conducted among 35 healthy adult volunteers to evaluate the safety, immunogenicity, and shedding of different doses of CV D 1207, a live attenuated Shigella flexneri 2a vaccine candidate with speci fic deletion mutations in virG, sen, set, and guaBA, CVD 1207 retains the a bility to invade epithelial cells but cannot effectively spread intercellul arly after invasion (Delta virG), does not produce enterotoxin (Delta sen a nd Delta set), and has limited proliferation in vivo (Delta guaBA). In a co nsecutive fashion, groups of three to seven subjects ingested a single oral dose of CVD 1207 at an inoculum of either 10(6), 10(7), 10(8), 10(9), or 1 0(10) CFU. CVD 1207 was remarkably well-tolerated at inocula as high as 10( 8) CFU, In comparison, one of 12 subjects who received 10(9) CFU experience d mild diarrhea and another experienced a single episode of emesis. One of five subjects who received 10(10) CFU experienced watery diarrhea and emesi s, All subjects who ingested doses of 10(8) to 10(10) CFU excreted the vacc ine; in 23 of 25, the duration of excretion was less than or equal to 3 day s. A dose-related, immunoglobulin A antibody-secreting cell (ASC) response to S. flexneri 2a O-specific lipopolysaccharide was seen, with geometric me an peak values of 6.1 to 35.2 ASCs/10(6) peripheral blood mononuclear cells (PBMC) among recipients of 10(7) to 10(10) CFU, The cytokine response to S higella-specific antigens observed in volunteers' PBMC following vaccinatio n suggested a Th1 pattern with stimulation of gamma interferon and absence of interleukin 4 (IL-4) or IL-5. CVD 1207 represents a Shigella live oral v accine strain prepared from wild-type S. flexneri 2a by rational use of rec ombinant DNA technology that achieves a remarkable degree of attenuation co mpared with earlier recombinant strains, even when administered at high dos age.