Phase 1 Evaluation ofVibrio choleraeO1, Serotype Inaba, Polysaccharide-Cholera Toxin Conjugates in Adult Volunteers

Abstract

Conjugate vaccines were prepared by binding hydrazine-treated lipopolysaccharide (DeALPS) from Vibrio cholerae O1, serotype Inaba, to cholera toxin (CT) variants CT-1 and CT-2. Volunteers (n ‫؍‬ 75) were injected with either 25 g of DeALPS, alone or as a conjugate, or the licensed cellular vaccine containing 4 ؋ 10 9 organisms each of serotypes Inaba and Ogawa per ml. No serious adverse reactions were observed. mean titer (1,249), followed by DeALPS-CT-2 (588) and DeALPS-CT-1 (330). The correlation coefficient between IgG anti-LPS and 2-mercaptoethanol (2-ME)-resistant vibriocidal antibodies was 0.81 (P ‫؍‬ 0.0004). Convalescent sera from cholera patients had a mean vibriocidal titer of 2,525 that was removed by treatment with 2-ME. The vibriocidal activities of sera from all vaccine groups and from the patients were absorbed (>75%) by LPS but not by either CT-1 or CT-2. Conjugate-induced IgG vibriocidal antibodies persisted longer than those elicited by the whole-cell vaccine. Both conjugates, but not the cellular vaccine, elicited IgG anti-CT. DeALPS alone did not elicit serum LPS or vibriocidal antibodies in mice and only low levels of immunoglobulin M (IgM) anti-LPS in the volunteers. Recipients of the cellular vaccine had the highest IgM anti-LPS levels, but the difference was not statistically significant from that elicited by the conjugates. The conjugates elicited the highest levels of IgG anti-LPS (DeALPS-CT-2 > DeALPS-CT-1 > cellular vaccine). Both conjugates and the cellular vaccine elicited vibriocidal antibodies: after 8 months, recipients of cellular vaccine had the highest geometric

Immunological properties of complex conjugates based on Vibrio cholerae O1 Ogawa lipopolysaccharide antigen

“…Conjugate vaccine constructed from native detoxified Inaba LPS injected into mice, together with adjuvant, elicited the formation of specific vibriocidal antibodies to a lesser degree than did commercial whole cell vaccine [10]. Similar results were seen when the Inaba conjugate formulation was used to immunize human volunteers [11].…”

The ABCs (Antibody, B Cells, and Carbohydrate Epitopes) of Cholera Immunity: Considerations for an Improved Vaccine

“…Another isotype of antibody that could protect against cholera is V. cholerae LPS-specific serum IgG, which is made in response to V. cholerae infection (144,187,188). The concept that IgG is protective against cholera was put forth by the Robbins group (87,88). In support of this perspective, parenteral vaccination with killed WC V. cholerae induced protective anti-LPS antibodies in older individuals (161).…”

“…The conjugates were not as immunogenic, nor did they induce vibriocidal responses as effectively as native Inaba LPS. A similar approach was used to prepare conjugates for a phase 1 trial of adults (88) wherein partially deacylated LPS conjugated to CT was compared to the licensed killed, dual serotype, oral cholera vaccine. The efficacy of two 25 µg doses (subcutaneous) of the conjugate vaccine given 6 weeks apart was compared to two doses of the oral vaccine also given 6 weeks apart.…”

“…The protective potential of anti-LPS antibodies in humans, while not directly tested, is supported by early vaccine trials that demonstrated some protection resulting from Ogawa or Inaba LPS vaccines delivered parenterally (12,13,161,164). Robbins' group tested an Inaba V. cholerae detoxified LPS-based conjugate vaccine in a phase 1 clinical trial and demonstrated vibriocidal antibody in sera of vaccinees (88). The next human cholera vaccine trials of LPS subunit vaccines require a more comprehensive experimental design and should include experimental groups that have not been previously exposed to V. cholerae, as well a group with prior oral exposure to V. cholerae that have a range of anti-V. cholerae LPS antibody titers.…”

Acid-detoxified Inaba lipopolysaccharide (pmLPS) is a superior cholera conjugate vaccine immunogen than hydrazine-detoxified lipopolysaccharide and induces vibriocidal and protective antibodies

“…One reason protection may wane for young children immunized with kW-C cholera vaccines is the lack of robust recruitment of B-cell memory to either LPS or other unknown Vc antigens (Patel et al, 2012). To address this problem, several groups constructed Vc LPS-based conjugate vaccines (Kabir, 1987;Gupta et al, 1992;Gupta et al, 1998;Chernyak et al, 2002;Meeks et al, 2004;Grandjean et al, 2009). An early conclusion based on this literature, detoxified LPS, pmLPS and DetAcLPS, were poorly immunogenic by themselves for BALB/c mice (Gupta et al, 1992;Grandjean et al, 2009).…”