Safety and immunogenicity in humans of enterotoxigenic Escherichia coli double mutant heat-labile toxin administered intradermally

Abstract

Enterotoxigenic Escherichia coli (ETEC) diarrhea is associated with a high burden of disease globally, for which no licensed vaccine is available. A Phase 1, double-blind, dose-escalation (0.1-2.0 µg) study was conducted to evaluate the safety and immunogenicity of double mutant heat-labile toxin LTR192G/L211A (dmLT) delivered intradermally (ID) to healthy adults. Subjects received up to three immunizations at three-week intervals. The vaccine was safe, although it induced mild local and some gastrointestinal adverse events, as well as frequent hyperpigmentation at the injection site. High levels of serum IgG and IgA, LT neutralizing antibodies, and IgG and IgA antibodies in lymphocyte supernatant were elicited post-vaccination, most prominently at the largest dose (2.0 μg). Rates of responses were the highest in subjects who received the largest dose (2.0 μg) and multiple immunizations. The ETEC dmLT vaccine was safe and highly immunogenic, inducing long-lasting systemic and mucosal responses when administered by the ID route. Trial registration Clinical Trials NCT02531685.

Fig. 1. Distribution of participants.

Of the original 246 participants screened, 100 were enrolled in seven cohorts to receive increasing dosages of dmLT ID (Cohorts 1-4), placebo, or in one to three vaccinations of highest tolerable dose, 2.0 µg of dmLT (Cohorts 5A-C).

Fig. 2. Solicited Adverse Events by vaccination cohort.

Prevalence and severity of solicited symptoms by cohort at any time point after first vaccination.

Fig. 3. Geometric Mean Fold-rise (GMFR) of serum antibody responses in vaccinees and placebo participants.

a Immunoglobulin (Ig) G and (b) IgA antibody responses in serum to dmLT in vaccinees and placebo by dosage of dmLT and number of vaccinations (represented by the vertical red lines). GMFR are represented by line while the percentage of responders (FR ≥ 4) is represented by bar plots. Subjects who received 2.0 µg of dmLT were classified based on number of vaccinations received, rather than initial randomization.

Fig. 4. Geometric Mean Fold-rise (GMFR) of neutralizing antibody responses in vaccinees and placebo participants.

LT neutralizing antibody in vaccinees and placebo by dosage of dmLT and number of vaccinations (represented by vertical red lines). GMFR are represented by line while the percentages of responders (FR ≥ 4) are represented by bar plots. Subjects who received 2.0 µg of dmLT were classified based on number of vaccinations received, rather than initial randomization.

Fig. 5. Geometric Mean Fold-rise (GMFR) of antibodies in lymphocyte supernatants (ALS) in vaccinees and placebo participants.

a Immunoglobulin (Ig) G and b IgA antibody responses in ALS to dmLT in vaccinees and placebo by dosage of dmLT and number of vaccinations (represented by vertical red lines). GMFR are represented by line while the percentages of seroconversion (FR ≥ 2) are represented by bar plots. Subjects who received 2.0 µg of dmLT were classified based on number of vaccinations received, rather than initial randomization.

Fig. 6. Generalized estimating equation (GEE) analysis comparison between serum and ALS antibody titers.

Data represent maximum titers after each dose, as applicable, and after final vaccination for all cohorts. Effect estimate (β), standard error (SE) and p value significance (p) reported for each comparison.