Safety and immunogenicity of intramuscularly administered CS6 subunit vaccine with a modified heat-labile enterotoxin from enterotoxigenic Escherichia coli

Abstract

Introduction Enterotoxigenic Escherichia coli (ETEC) is a common cause of infectious diarrhoea and a leading cause of morbidity and mortality in children living in resource-limited settings. It is also the leading cause of travellers’ diarrhoea among civilian and military travellers. Its dual importance in global public health and travel medicine highlights the need for an effective vaccine. ETEC express colonization factors (CFs) that mediate adherence to the small intestine. An epidemiologically prevalent CF is coli surface antigen 6 (CS6). We assessed the safety and immunogenicity of a CS6-targeted candidate vaccine, CssBA, co-administered intramuscularly with the double-mutant heat-labile enterotoxin, dmLT [LT(R192G/L211A)]. Methods This was an open-label trial. Fifty subjects received three intramuscular injections (Days 1, 22 and 43) of CssBA alone (5 µg), dmLT alone (0.1 µg) or CssBA (5, 15, 45 µg) + dmLT (0.1 and 0.5 µg). Subjects were actively monitored for adverse events for 28 days following the third vaccination. Antibody responses (IgG and IgA) were characterized in the serum and from lymphocyte supernatants (ALS) to CS6 and the native ETEC heat labile enterotoxin, LT. Results Across all dose cohorts, the vaccine was safe and well-tolerated with no vaccine-related severe or serious adverse events. Among vaccine-related adverse events, a majority (98%) were mild with 79% being short-lived vaccine site reactions. Robust antibody responses were induced in a dose-dependent manner with a clear dmLT adjuvant effect. Response rates in subjects receiving 45 µg CssBA and 0.5 µg dmLT ranged from 50 to 100% across assays. Conclusion This is the first study to demonstrate the safety and immunogenicity of CssBA and/or dmLT administered intramuscularly. Co-administration of the two components induced robust immune responses to CS6 and LT, paving the way for future studies to evaluate the efficacy of this vaccine target and development of a multivalent, subunit ETEC vaccine.

Intradermal fractional-dose inactivated polio vaccine (fIPV) adjuvanted with double mutant Enterotoxigenic Escherichia coli heat labile toxin (dmLT) is well-tolerated and augments a systemic immune response to all three poliovirus serotypes in a randomized placebo-controlled trial

“…Our primary endpoint was safety and no significant or serious adverse events (AE) with the addition of intradermal dmLT to fIPV were identified. This adds to prior clinical data which has shown a favorable safety profile for oral, sublingual, intramuscular, and intradermal administration of dmLT both alone and in combination with various antigens [22] , [23] , [24] , [44] . While a degree of increased local reactogenicity was observed, including mild induration, hyperpigmentation, and pruritis at the injection site, these were not unexpected.…”

“…The dose of 0.47 µg was chosen following preclinical toxicology assessments of intradermal dmLT in combination with IPV which showed this dose to be both immunogenic and well-tolerated in animal models (unpublished data). Additionally, preclinical and clinical work assessing the use of dmLT as an injectable adjuvant for Enterotoxigenic Escherichia coli (ETEC) vaccines has similarly found doses of 0.5 µg to be immunogenic with limited local reactogenicity [22] , [31] . dmLT was produced according to good manufacture practice (GMP) specification by IDT Biologika Corporation and supplied by PATH in the form of 500 μg lyophilized cake in 3 mL vials (lot 001-0816) and maintained at −20 °C during transport and storage at the clinical site for up to 12 months prior to use.…”

“…To facilitate the complete removal of OPV and final polio eradication, an effective adjuvanted IPV which stimulates mucosal immune responses and curtails poliovirus shedding and transmission would be ideal [20] . The double mutant [LT(R192G/L211A)] Enterotoxigenic Escherichia coli heat labile toxin (dmLT) adjuvant has been extensively studied for safety and systemic and mucosal immunogenicity in animals and humans both alone and admixed with other (non-IPV) vaccines by oral, sublingual, intramuscular and intradermal routes [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] . Derived from an enteric bacteria ( Escherichia coli ), dmLT appears to have a unique ability to stimulate mucosal immune responses in pre-clinical models, even when admistered at anatomically distant sites [20] , [26] , [27] , [28] .…”

Controlled Human Infection Models To Accelerate Vaccine Development

“…Parenteral delivery of the CfaE adhesin by the intradermal route with mLT induced strong serum and mucosal responses to the adhesin and reduced the severity and incidence of ETEC illness in a CHIM involving challenge with the H10407 strain of ETEC. In addition, intramuscular immunization with CssBA and mLT was also highly immunogenic, inducing both systemic and mucosal immunity as well (296). Funding is currently being sought for a follow-on immunization and challenge study with this antigen-adjuvant combination.…”

“…Previous work with double-mutant heat-labile toxin (dmLT) from enterotoxigenic Escherichia coli (ETEC) (R192G/L211A) has demonstrated that it is a potent adjuvant when administered orally (591,592) and that it also has the potential to stimulate mucosal immunity of parenterally co-administered antigens, including IPV (593). This effect has been established in mouse (594) and nonhuman primate preclinical models (Norton B., personal communication) and in a recent ETEC subunit vaccine Phase 1 clinical study (595).…”