The Vaccine Candidate Vibrio cholerae 638 Is Protective against Cholera in Healthy Volunteers

Abstract

Vibrio cholerae 638 is a living candidate cholera vaccine strain attenuated by deletion of the CTX⌽ prophage from C7258 (O1, El Tor Ogawa) and by insertion of the Clostridium thermocellum endoglucanase A gene into the hemagglutinin/protease coding sequence. This vaccine candidate was previously found to be well tolerated and immunogenic in volunteers. This article reports a randomized, double-blind, placebo-controlled trial conducted to test short-term protection conferred by 638 against subsequent V. cholerae infection and disease in volunteers in Cuba. A total of 45 subjects were enrolled and assigned to receive vaccine or placebo. The vaccine contained 10 9 CFU of freshly harvested 638 buffered with 1.3% NaHCO 3 , while the placebo was buffer alone. After vaccine but not after placebo intake, 96% of volunteers had at least a fourfold increase in vibriocidal antibody titers, and 50% showed a doubling of at least the lipopolysaccharide-specific immunoglobulin A titers in serum. At 1 month after vaccination, five volunteers from the vaccine group and five from the placebo group underwent an exploratory challenge study with 10 9 CFU of ⌬CTX⌽ attenuated mutant strain V. cholerae 81. Only two volunteers from the vaccine group shed strain 81 in their feces, but none of them experienced diarrhea; in the placebo group, all volunteers excreted the challenge strain, and three had reactogenic diarrhea. An additional 12 vaccinees and 9 placebo recipients underwent challenge with 7 ؋ 10 5 CFU of virulent strain V. cholerae 3008 freshly harvested from a brain heart infusion agar plate and buffered with 1.3% NaHCO 3 . Three volunteers (25%) from the vaccine group and all from the placebo group shed the challenge agent in their feces. None of the 12 vaccinees but 7 volunteers from the placebo group had diarrhea, and 2 of the latter exhibited severe cholera (>5,000 g of diarrheal stool). These results indicate that at 1 month after ingestion of a single oral dose (10 9 CFU) of strain 638, volunteers remained protected against cholera infection and disease provoked by the wild-type challenge agent V. cholerae 3008. We recommend that additional vaccine lots of 638 be prepared under good manufacturing practices for further evaluation.

Contribution of Hemagglutinin/Protease and Motility to the Pathogenesis of El Tor Biotype Cholera

“…HapA has been shown to contribute to reactogenicity of live attenuated vaccines (3,13), but its role in cholera pathogenesis has not been established. Motility also has been shown to contribute to reactogenicity (32) and to affect the expression of virulence factors (14).…”

“…Inactivation of hapA increased adherence to mucin synthesized by HT29-18N2 cells (4), and expression of hapA was required for V. cholerae to penetrate a mucin-containing gel in vitro (42). Although analysis of hapA mutants in infant rabbits and suckling mice has not provided evidence that HapA is an essential virulence factor (11,18,36), HapA has been shown to contribute to reactogenicity of live attenuated cholera vaccine strains in humans (3,13).…”

Is cholera disease associated with poverty?

“…At the present, only one cholera vaccine, Dukoral, is internationally licensed and available [7], and mOROVAC (http://www.vabiotechvn.com) is used only in Vietnam [8]. Some vaccine projects are in development, such as the attenuated vaccines Peru 15, CVD 110, 111 and 112 strains [9] and 638 strain [10]) and the inactivated whole cells and subunit vaccines [11][12][13].…”

Role of the Histone-Like Nucleoid Structuring Protein in the Regulation of rpoS and RpoS-Dependent Genes in Vibrio cholerae

“…V. cholerae also secretes a Zn-dependent metalloprotease that displays a broad range of potentially pathogenic activities: hemagglutinin/protease (HA/protease), encoded by hapA (14,18,34,(59)(60)(61). HA/protease contributes to the reactogenicity of live cholera vaccine candidates and enhances enterotoxicity in the rabbit ileal loop model (4,15,51). Transcription of hapA requires the quorum-sensing regulator HapR (25), the cyclic AMP receptor protein (CRP) (3,49,31), and the alternative sigma factor S (RpoS), encoded by rpoS (49,62).…”