Sensitive microplate assay for detection of bactericidal antibodies to Vibrio cholerae O139

Safety and immunogenicity of the killed bivalent (O1 and O139) whole-cell cholera vaccine in the Philippines

The killed bivalent (O1 and O139) whole cell oral cholera vaccine (OCV) (Shanchol™) was first licensed in India in 2009 and World Health Organization pre-qualified in 2011. We assessed the safety and immunogenicity of this OCV in the Philippines. This was a phase IV, single-arm, descriptive, open-label study. We recruited 336 participants from 2 centers: 112 participants in each age group (1-4, 5-14 and ≥ 15 years). Participants received 2 OCV doses 14 d apart. Safety was monitored throughout the trial. Blood samples were collected at baseline (pre-vaccination) and 14 d after each dose. Serum vibriocidal antibody titers to V. cholerae O1 (El Tor Inaba and El Tor Ogawa) and O139 strains were assessed, with seroconversion defined as ≥ 4-fold increase from baseline in titers. No immediate unsolicited systemic adverse events/reactions were observed. Unsolicited systemic adverse events were mostly grade 1 intensity. One serious adverse event occurred after the first dose, but was unrelated to vaccination. High seroconversion rates (range 69-92%) were achieved against the O1 serotypes with a trend toward higher rates in the 1-4 y (86-92%) and 5-14 y (86-88%) age groups than the ≥ 15 y age group (69-83%). Lower seroconversion rates were achieved against the O139 serotype (35-70%), particularly in those aged ≥ 15 y (35-42%). The 2-dose regimen of the killed bivalent whole cell OCV was well-tolerated in this study conducted in the Philippines, a cholera-endemic country. Robust immune responses were observed even after a single-dose.

Safety and immunogenicity of escalating dosages of a single oral administration of peru-15 pCTB, a candidate live, attenuated vaccine against enterotoxigenic Escherichia coli and Vibrio cholerae

Enterotoxigenic Escherichia coli (ETEC) organisms are a leading cause of infectious diarrhea in developing countries. A live, attenuated cholera strain that expresses high levels of the nontoxic B subunit of cholera toxin, which might also serve as an ETEC protective antigen, was evaluated for safety, excretion, and immunogenicity in healthy volunteers. We enrolled four inpatient dose-escalation cohorts of 15 to 16 eligible subjects to randomly (3:1) receive a single oral dose of vaccine or placebo (buffer alone), evaluating 1 ×10(7), 1 ×10(8), 1 ×10(9), and 1 ×10(10) CFU of the vaccine. The vaccine was well tolerated, although some subjects experienced moderate diarrhea. The serum Inaba vibriocidal antibody response appeared to display a dose-response relationship with increasing dosages of vaccine, plateauing at the 10(9)-CFU dosage. The serum antitoxin (cholera toxin and heat-labile enterotoxin) antibody seroconversion rate (4-fold increase over baseline) also appeared to display a dose-response relationship. The vaccine strain was excreted in stool cultures, displaying a dose-response relationship. A single oral dose of Peru-15 pCTB at dosages up to 1 ×10(10) CFU was safe and immunogenic in this first-in-human trial. These encouraging data support the ongoing clinical development of this candidate combined cholera and ETEC vaccine. (This study has been registered at ClinicalTrials.gov under registration no. NCT00654108.).

Vibriocidal antibody responses to a bivalent killed whole-cell oral cholera vaccine in a phase III trial in Kolkata, India

BACKGROUND

During the development of a vaccine, identification of the correlates of protection is of paramount importance for establishing an objective criterion for the protective performance of the vaccine. However, the ascertainment of correlates of immunity conferred by any vaccine is a difficult task.

METHODS

While conducting a phase three double-blind, cluster-randomized, placebo-controlled trial of a bivalent killed whole-cell oral cholera vaccine in Kolkata, we evaluated the immunogenicity of the vaccine in a subset of participants. Randomly chosen participants (recipients of vaccine or placebo) were invited to provide blood samples at baseline, 14 days after the second dose and one year after the first dose. At these time points, serum geometric mean titers (GMT) of vibriocidal antibodies and seroconversion rates for vaccine and placebo arms were calculated and compared across the age strata (1 to 5 years, 5 to 15 years and more than 15 years) as well as for all age groups.

RESULTS

Out of 137 subjects included in analysis, 69 were vaccinees and 68 received placebo. There were 5•7 and 5•8 geometric mean fold (GMF) rises in titers to Vibrio cholerae Inaba and Ogawa, respectively at 14 days after the second dose, with 57% and 61% of vaccinees showing a four-fold or greater titer rise, respectively. After one year, the titers to Inaba and Ogawa remained 1•7 and 2•8 fold higher, respectively, compared to baseline. Serum vibriocidal antibody response to V. cholerae O139 was much lower than that to Inaba or Ogawa. No significant differences in the GMF-rises were observed among the age groups.

CONCLUSIONS

The reformulated oral cholera vaccine induced a statistically significant anti-O1 Inaba and O1 Ogawa vibriocidal antibody response 14 days after vaccination, which although declined after one year remained significantly higher than baseline. Despite this decline, the vaccine remained protective five years after vaccination.

Safety and immunogenicity assessment of an oral cholera vaccine through phase I clinical trial in Korea

The safety, tolerability and immunogenicity of an oral cholera vaccine (OCV) was assessed in adult Korean male through an open-label, non-comparative clinical study. Two doses of vaccine with an interval of 2 weeks were given to 20 healthy subjects. A total of 7 adverse events occurred in 6 subjects. However, no clinically significant change was observed in electrocardiograms, vital signs, physical examinations, and clinical laboratory tests. The immunogenicity of OCV was evaluated by serum vibriocidal assay where anti-Vibrio cholerae O1 and O139 antibodies were measured at day 0, 14, and 28 of vaccine administration. The antibody titers ranged from < 2.5-5,120 for V. cholerae O1 Inaba, < 2.5-10,240 for V. cholerae O1 Ogawa and < 2.5-480 for V. cholerae O139. In addition, the fold increase in antibody titers ranged from 1-4,096 for O1 Inaba, 1-8,192 for O1 Ogawa, and 1-384 for O139. The seroconversion rate was 95% and 45% for O1 and O139 antibodies, respectively. Our study clearly shows that administration of two doses of OCV at a 2 week-interval increases an appropriate level of antibody titer in the serum of healthy Korean adult males (Clinical Trial Number, NCT01707537).

Immunochemical characterization of synthetic hexa-, octa- and decasaccharide conjugate vaccines for Vibrio cholerae O:1 serotype Ogawa with emphasis on antigenic density and chain length

Cholera remains to be a global health problem without suitable vaccines for endemic control or outbreak relief. Here we describe a new parenteral vaccine based on neoglyco-conjugate of synthetic fragments of O-specific polysaccharide (O-SP) of Vibrio cholerae O1, serotype Ogawa. Hexa-, octa- and decasaccharides of the O-SP with carboxylic acid at the reducing end were chemically synthesized and conjugated to tetanus toxoid (TT). The conjugates prepared by a novel linking scheme consisted of 17-atom linker of hydrazide and alkyl bonds elicited robust serum IgG anti-LPS responses with vibriocidal activities in mice. There is a length dependence in immune response with decasaccharide conjugates elicited the highest anti-LPS IgG. There seems to be an indication that regardless of the carbohydrate chain length, a molar ratio of 230 ± 10 monosaccharide units per TT induced high antibody response. The conjugates also elicited cross-reactive antibodies to serotype Inaba. The formulation of the proposed cholera conjugate vaccine, similar to other licensed polysaccharide vaccine, is suitable for children immunization. A parenteral cholera vaccine could overcome the diminishing immunogenicity in most of oral vaccines due to the gastrointestinal complexity and environmental enteropathy in children living in impoverished environment and could be considered for global cholera immunization.

Vibriocidal assays to determine the antibody titer of patient sera samples

The vibriocidal titer assay can be used to detect antibodies against Vibrio cholerae in serum samples, serving as an indicator of prior infection and potential protection against cholera. The assay can be utilized in research and clinical settings to test the effectiveness of vaccines, and also in epidemiological studies relevant to cholera transmission and surveillance. This unit outlines the steps involved in conducting an easily interpreted colorimetric vibriocidal titer assay with a relatively short turnaround time for results of around 8 hr, with final result observations in 24 hr. The assay can also be easily scaled up or down to accommodate as many or as few serum samples available and is not V. cholerae strain specific.

Mucosal immunization with Vibrio cholerae outer membrane vesicles provides maternal protection mediated by antilipopolysaccharide antibodies that inhibit bacterial motility

Vibrio cholerae is the causative agent of cholera, a severe diarrheal disease that remains endemic in many parts of the world and can cause outbreaks wherever sanitation and clean water systems break down. Prevention of disease could be achieved through improved sanitation and clean water provision supported by vaccination. V. cholerae serogroup O1 is the major cause of cholera; O1 serotypes Inaba and Ogawa have similar disease burdens, while O139 is the only non-O1 serogroup to cause epidemics. We showed previously that immunization of adult female mice with purified V. cholerae outer membrane vesicles (OMVs) elicits an antibody response that protect neonates from oral V. cholerae challenge and that suckling from an immunized dam accounts for the majority of protection from V. cholerae colonization. Here we report that lipopolysaccharide (LPS) is the major OMV protective antigen. Mucosal immunization with OMVs from Inaba or Ogawa provides significant cross-serotype protection from V. cholerae colonization, although serotype-specific antigens are dominant. OMVs from O1 or O139 do not provide cross-serogroup protection, but by immunization with a mixture of O1 and O139 OMVs, cross-serogroup protection was achieved. Neonatal protection is not associated with significant bacterial death but may involve inhibition of motility, as antibodies from OMV-immunized mice inhibit V. cholerae motility in vitro, with trends that parallel in vivo protection. Motility assays also reveal that a higher antibody titer is required to immobilize O139 compared to O1, a phenotype that is O139 capsule dependent.

A randomized, placebo-controlled trial of the bivalent killed, whole-cell, oral cholera vaccine in adults and children in a cholera endemic area in Kolkata, India

OBJECTIVES

An effective vaccine against cholera has been used for public health purposes in Vietnam since the 1990s. This vaccine was reformulated to meet WHO requirements. We assessed the safety and immunogenicity of the reformulated bivalent (Vibrio cholerae 01 and 0139) killed whole cell oral vaccine in a cholera endemic area in Kolkata, India.

DESIGN

Double-blind, randomized, placebo controlled trial.

SETTING

The trial was conducted in the clinical trial ward of the Infectious Diseases Hospital in Kolkata, India.

PARTICIPANTS

The participants were 101 healthy adults (males and non-pregnant females) aged 18-40 years and 100 healthy children (males and non-pregnant females) aged 1-17 years.

INTERVENTIONS

Participants were randomized to receive either the bivalent killed whole cell oral cholera vaccine or placebo (killed oral Escherichia coli K12).

OUTCOME MEASURES

For safety: proportion of subjects with adverse events during the duration of study participation. For immunogenicity: Proportion of subjects who had a > or = 4-fold rise in serum vibriocidal antibody titers 14 days after the second dose of vaccine or placebo.

RESULTS

Adverse reactions were observed with similar frequency among vaccine and placebo recipients in both age groups. Among adults 4% of vaccine and 8% of placebo recipients and among children 4% of vaccine and 2% of placebo recipients had at least one adverse event within 28 days of the first dose of the vaccine. Following immunization, 53% of adult and 80% of children vaccinees showed a > or = 4 fold rise in serum V. cholerae O1 vibriocidal antibody titers. A less pronounced response to V. cholerae O139 vibriocidal antibody titers post-immunization was noted among vaccinees.

CONCLUSIONS

We found the vaccine to be safe and immunogenic in a cholera-endemic area in India.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00119197.