Anti-O-specific polysaccharide (OSP) immune responses following vaccination with oral cholera vaccine CVD 103-HgR correlate with protection against cholera after infection with wild-type Vibrio cholerae O1 El Tor Inaba in North American volunteers

Abstract

Background: Cholera is an acute voluminous dehydrating diarrheal disease caused by toxigenic strains of Vibrio cholerae O1 and occasionally O139. A growing body of evidence indicates that immune responses targeting the O-specific polysaccharide (OSP) of V. cholerae are involved in mediating protection against cholera. We therefore assessed whether antibody responses against OSP occur after vaccination with live attenuated oral cholera vaccine CVD 103-HgR, and whether such responses correlate with protection against cholera.

Methodology: We assessed adult North American volunteers (n = 46) who were vaccinated with 5 × 108 colony-forming units (CFU) of oral cholera vaccine CVD 103-HgR and then orally challenged with approximately 1 × 105 CFU of wild-type V. cholerae O1 El Tor Inaba strain N16961, either 10 or 90 days post-vaccination.

Principal findings: Vaccination was associated with induction of significant serum IgM and IgA anti-OSP and vibriocidal antibody responses within 10 days of vaccination. There was significant correlation between anti-OSP and vibriocidal antibody responses. IgM and IgA anti-OSP responses on day 10 following vaccination were associated with lower post-challenge stool volume (r = -0.44, P = 0.002; r = -0.36, P = 0.01; respectively), and none of 27 vaccinees who developed a ≥1.5 fold increase in any antibody isotype targeting OSP on day 10 following vaccination compared to baseline developed moderate or severe cholera following experimental challenge, while 5 of 19 who did not develop such anti-OSP responses did (P = 0.01).

Conclusion: Oral vaccination with live attenuated cholera vaccine CVD 103-HgR induces antibodies that target V. cholerae OSP, and these anti-OSP responses correlate with protection against diarrhea following experimental challenge with V. cholerae O1.

Trial registration: ClinicalTrials.gov NCT01895855.

Conflict of interest statement

Jakub K. Simon, Douglas Haney, Michael Lock, Marc Gurwith were employed by PaxVax, Inc. Wilbur H. Chen, Caroline E. Lyon, Beth D. Kirkpatrick, Mitchell Cohen, Myron M. Levine received research funding from PaxVax, Inc. Myron M. Levine is the patent holder of CVD 103-HgR. Jakub K. Simon is currently employed by Merck & Co. All other authors report no potential conflicts.

Figures

Fig 1. Serum IgM, IgA and IgG responses targeting V. cholerae O1 Inaba or Ogawa OSP in vaccine recipients of CVD 103-HgR.

Figure only contains results for samples collected prior to wild type experimental V. cholerae challenge. Day 0 is pre-vaccination and other dates are timed from vaccination. In total, 46 vaccinees are included until day 10, then 20 vaccinees until day 90. X axis indicates the time points of samples while Y-axis denotes OSP-specific antibody responses. Each single dot indicates an individual OSP antibody value, horizontal bars indicate the geometric mean (GM), and error bars indicate 95% confidence intervals. P values represent significant differences of the mean between groups. Asterisks represent differences in responder frequency in Fisher’s exact test (*** P ≤ 0.001, ** P ≤ 0.01). We defined a responder as having a ≥1.5-fold increase in anti-OSP units after vaccination compared to pre-vaccination value. Responder frequency is represented in parenthesis on x-axis.

Fig 2. Serum antibody responses against OSP in vaccinees of day 10 challenged group.

Serum IgM, IgA and IgG responses targeting V. cholerae O1 Inaba or Ogawa OSP in recipients (n = 26) of oral cholera vaccine CVD 103-HgR who were then experimentally challenged with wild type V. cholerae O1 Inaba N16961 10 days after vaccination (denoted by top arrows). Day 0 is pre-vaccination and other dates are timed from vaccination. X axis indicates the time points of samples, while Y-axis denotes OSP-specific antibody responses. Each single dot indicates an individual OSP antibody value, horizontal bars indicate the geometric mean (GM), and error bars indicate 95% confidence intervals. P values represent differences of the mean between groups. Asterisks represent significant differences in responder frequency in Fisher’s exact test (*** P ≤ 0.001, ** P ≤ 0.01). We defined a responder as having a ≥1.5-fold increase in anti-OSP units compared to pre-vaccination value. Responder frequency is represented in parenthesis on x-axis.

Fig 3. Serum antibody responses against OSP in vaccinees of day 90 challenged group.

Serum IgM, IgA and IgG responses targeting V. cholerae O1 Inaba or Ogawa OSP in recipients (n = 20) of oral cholera vaccine CVD 103-HgR who were then experimentally challenged with wild type V. cholerae O1 Inaba N16961 90 days after vaccination (denoted by top arrows). Day 0 is pre-vaccination and other dates are timed from vaccination. X axis indicates the time points of samples, while Y-axis denotes OSP-specific antibody responses. Each single dot indicates an individual OSP antibody value, horizontal bars indicate the geometric mean (GM), and error bars indicate 95% confidence intervals. P values represent differences of the mean between groups. Asterisks represent significant differences of responder frequency in Fisher’s exact test (*** P ≤ 0.001, ** P ≤ 0.01). We defined a responder as having a ≥1.5-fold increase in anti-OSP units compared to pre-vaccination value. Responder frequency is represented in parenthesis on x-axis.

Fig 4. Serum IgM, IgA and IgG antibody responses targeting V. cholerae O1 Inaba and Ogawa OSP 10 days after oral vaccination.

The figure shows the OSP specific antibodies responses 10 days after vaccination in volunteers who developed moderate (≥3L) or severe (≥5L) diarrhea versus no diarrhea following wild type V. cholerae O1 Inaba experimental infection 10 or 90 days after vaccination. X axis indicates the time points of samples while Y-axis denotes OSP specific antibody responses. Each single dot indicates an individual OSP antibody value, horizontal bars indicate the geometric mean (GM), and error bars indicate 95% confidence intervals. Responders were defined as having an increase in kinetic ELISA units ≥ 1.5 fold on day 10 post-vaccination compared with day 0 pre-vaccination. Asterisk indicates statistical significant difference (* P ≤ 0.05) of responder frequency between no diarrhea versus moderate/severe diarrhea group in Fisher’s exact test.

Fig 5. Correlation between fold increase of Inaba OSP specific antibody responses and cumulative diarrheal volume.

X axis represents the fold-increase (day 10 to day 0) of IgM, IgA, and IgG responses against V. cholerae O1 Inaba OSP and Y axis represents cumulative diarrhea following experimental challenge with wild type V. cholerae O1 Inaba 10 or 90 days post vaccination with Inaba CVD 103-HgR. Dashed horizontal lines mark moderate (3L) or severe (5L) diarrheal values. Dashed vertical line denotes 1.5-fold anti-OSP antibody value change (day 10 post-vaccination compared to day 0 pre-vaccination).