title: Safety and immunogenicity in humans of an attenuated Salmonella typhi vaccine vector strain expressing plasmid-encoded hepatitis B antigens stabilized by the Asd-balanced lethal vector system.
abstract: Attenuated Salmonella typhi organisms which express genes encoding protective antigens of other pathogens have been developed for use as experimental oral vaccines. A delta asd S. typhi strain attenuated by deletions in cya, crp, and cdt which contains hepatitis B core (HBc) and pre-S genes encoded on an Asd+ pBR-based plasmid vector was constructed. Healthy adult volunteers ingested a single dose of 5 x 10(5) to 5 x 10(8) CFU of strain chi4073 (delta cya delta crp delta cdt S. typhi Ty2), 6 x 10(7) or 1 x 10(9) CFU of strain chi4632(pYA3149), a further derivative of chi4073 deleted in asd and containing the Asd+ vector without the HBc-pre-S fusion, or 3 x 10(7) or 7 x 10(8) CFU of strain X4632(pYA3167), a derivative containing the vector with the HBc-pre-S fusion. Chi4073 was generally well tolerated by 22 volunteers. No volunteer had fever or positive blood cultures; 4 of 22 volunteers shed vaccine organisms in the stool in the first 48 h only. Two of 18 volunteers who received one of the plasmid-containing derivatives of chi4073 developed low-grade fevers on day 10 or 12 after ingestion. One of these volunteers had positive blood cultures on days 7 and 8. Seven of these 18 volunteers had vaccine organisms detected in their stools in the first 48 h only. Most volunteers developed S. typhi-specific serum responses and developed S. typhi-specific antibody-secreting cells. However, no volunteer developed serum antibody to hepatitis pre-S or pre-S-specific antibody-secreting cells. Although the parent strain chi4073 was well tolerated, induced immunoglobulin G seroconversion to S. typhi lipopolysaccharide in 80 to 100% of vaccinees and stimulated specific IgA-secreting lymphocytes in 80 to 100% of vaccinees given a single oral dose of 2 x 10(7) and 5 x 10(8) CFU, chi4073 derivatives containing the Asd+ vector with and without sequences encoding the HBc-pre-S fusion caused occasional febrile reactions at high doses and did not stimulate detectable immune responses to hepatitis B antigens.
authors.affiliation: Center for Vaccine Development, Department of Medicine, University of Maryland School of Medicine, Baltimore 21201, USA. ctacket@umppa1.ab.umd.edu
authors.forename: C O
authors.initials: CO
authors.lastname: Tacket
authors.forename: S M
authors.initials: SM
authors.lastname: Kelly
authors.forename: F
authors.initials: F
authors.lastname: Schödel
authors.forename: G
authors.initials: G
authors.lastname: Losonsky
authors.forename: J P
authors.initials: JP
authors.lastname: Nataro
authors.forename: R
authors.initials: R
authors.lastname: Edelman
authors.forename: M M
authors.initials: MM
authors.lastname: Levine
authors.forename: R
authors.initials: R
authors.lastname: Curtiss
mesh_terms: D000328:Adult; D000907:Antibodies, Bacterial / Q000097:blood; D001428:Bacterial Vaccines / Q000276:immunology*; D005822:Genetic Vectors; D006512:Hepatitis B Core Antigens / Q000235:genetics / Q000276:immunology*; D006514:Hepatitis B Surface Antigens / Q000235:genetics / Q000276:immunology*; D017325:Hepatitis B Vaccines / Q000009:adverse effects / Q000235:genetics / Q000276:immunology*; D006801:Humans; D009154:Mutation; D010957:Plasmids; D011498:Protein Precursors / Q000235:genetics / Q000276:immunology*; D012486:Salmonella typhimurium / Q000235:genetics* / Q000276:immunology*; D014613:Vaccines, Attenuated / Q000276:immunology; D014614:Vaccines, Synthetic / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D001428:Bacterial Vaccines; D006512:Hepatitis B Core Antigens; D006514:Hepatitis B Surface Antigens; D017325:Hepatitis B Vaccines; D011498:Protein Precursors; D014613:Vaccines, Attenuated; D014614:Vaccines, Synthetic; C050806:presurface protein 1, hepatitis B surface antigen