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Infection and Immunity, March 2000, p. 1196-1201, Vol. 68, No. 3
Center for Vaccine Development, Department of
Medicine, University of Maryland School of Medicine,
Baltimore,1 and University of
Maryland, College Park, University Health Center, College
Park,2 Maryland; and Peptide
Therapeutics Group plc, Cambridge,3
Evans Medical Limited, Liverpool,4 and
Medeva Group Research5 and
Imperial College of Science, Technology, and
Medicine,6 London, England
Received 21 September 1999/Accepted 30 November 1999
Salmonella enterica serovar Typhi strain CVD
908-htrA is a live attenuated strain which may be useful as
an improved oral typhoid vaccine and as a vector for cloned genes of
other pathogens. We conducted a phase 2 trial in which 80 healthy
adults received one of two dosage levels of CVD 908-htrA in
a double-blind, placebo-controlled, crossover study. There
were no differences in the rates of side effects among volunteers who
received high-dose vaccine (4.5 × 108 CFU),
lower-dose vaccine (5 × 107 CFU), or placebo in the
21 days after vaccination, although recipients of
high-dose vaccine (8%) had more frequent diarrhea than placebo recipients (0%) in the first 7 days. Seventy-seven percent and 46% of
recipients of high- and lower-dose vaccines, respectively, briefly
excreted vaccine organisms in their stools. All blood cultures were
negative. Antibody-secreting cells producing antilipopolysaccharide (LPS) immunoglobulin A (IgA) were detected in 100 and 92% of
recipients of high- and lower-dose vaccines, respectively. Almost half
the volunteers developed serum anti-LPS IgG. Lymphocyte
proliferation and gamma interferon production against serovar Typhi
antigens occurred in a significant proportion of vaccinees. This
phase 2 study supports the further development of CVD
908-htrA as a single-dose vaccine against typhoid fever
and as a possible live vector for oral delivery of other vaccine antigens.
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Phase 2 Clinical Trial of Attenuated
Salmonella enterica Serovar Typhi Oral Live Vector Vaccine
CVD 908-htrA in U.S. Volunteers

*
Corresponding author. Mailing address: Center for
Vaccine Development, Department of Medicine, University of Maryland
School of Medicine, 685 West Baltimore St., Baltimore, MD 21201. Phone: (410) 706-5328. Fax: (410) 706-4171. E-mail:
ctacket{at}medicine.umaryland.edu.
Present address: Microscience Ltd., London, England.
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