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Infect. Immun., Feb 1997, 452-456, Vol 65, No. 2
CO Tacket, MB Sztein, GA Losonsky, SS Wasserman, JP Nataro, R Edelman, D Pickard, G Dougan, SN Chatfield and MM Levine
A single-dose, oral Salmonella typhi vaccine strain has been sought as a
carrier or vector of cloned genes encoding protective antigens of other
pathogens. Such a hybrid vaccine, administered orally, would stimulate
immune responses both at the mucosal surface and in the systemic
compartment and would potentially provide protection against multiple
pathogens. S. typhi CVD 908 and CVD 906, which harbor deletions in aroC and
aroD, were further engineered by deletion in htrA to produce strains CVD
908-htrA and CVD 906-htrA, which are unable to sustain growth and are
severely impaired in their ability to survive in host tissues. These
strains were fed to humans at doses of 5 x 10(7) to 5 x 10(9) CFU with
buffer, and safety and immune responses were assessed. CVD 908-htrA and CVD
906-htrA were well tolerated in volunteers; mild diarrhea in 3 of 36
volunteers and mild fever in 1 volunteer were the only notable adverse
responses. The vaccine strains were not detected in blood cultures and only
transiently detected in stool. Serum immune responses to S. typhi
lipopolysaccharide and H antigens were observed in 75 to 100% of volunteers
who received 5 x 10(8) to 5 x 10(9) CFU, and cells secreting S.
typhi-specific antibodies were found in all volunteers after ingestion of
either strain. Sixty-three percent to 83% of volunteers developed
lymphoproliferative responses to S. typhi flagellar and particulate
antigens after the higher doses. These studies demonstrate the potential of
CVD 908-htrA as a live vector for the delivery of heterologous genes, and a
clinical trial of such a construct is planned.
Copyright © 1997, American Society for Microbiology
Safety of live oral Salmonella typhi vaccine strains with deletions in htrA and aroC aroD and immune response in humans
Department of Medicine, University of Maryland School of Medicine, Baltimore 21201, USA. ctacket@umppa1.ab.umd.edu
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