Putative correlates of protection against shigellosis assessing immunomarkers across responses to S. sonnei investigational vaccine.

Shigella spp. are a leading bacterial cause of diarrhea. No widely licensed vaccines are available and there is no generally accepted correlate of protection. We tested a S. sonnei Generalized Modules for Membrane Antigen (GMMA)-based vaccine (1790GAHB) in a phase 2b, placebo-controlled, randomized, controlled human infection model study (NCT03527173) enrolling healthy United States adults aged 18-50 years. We report analyses evaluating immune responses to vaccination, with the aim to identify correlates of risk for shigellosis among assessed immunomarkers. We found that 1790GAHB elicited S. sonnei lipopolysaccharide specific α4ß7+ immunoglobulin (Ig) G and IgA secreting B cells which are likely homing to the gut, indicating the ability to induce a mucosal in addition to a systemic response, despite parenteral delivery. We were unable to establish or confirm threshold levels that predict vaccine efficacy facilitating the evaluation of vaccine candidates. However, serum anti-lipopolysaccharide IgG and bactericidal activity were identified as potential correlates of risk for shigellosis.

Complement-mediated serum bactericidal activity of antibodies elicited by the Shigella sonnei GMMA vaccine in adults from a shigellosis-endemic country: Exploratory analysis of a Phase 2a randomized study.

Shigella is associated with a significant burden of disease worldwide among individuals of all ages and is the major cause of moderate and severe diarrhea in children under five years of age in low- and middle-income countries. Several candidate vaccines against Shigella species are currently under clinical development. The investigational 1790GAHB vaccine against Shigella sonnei is based on GMMA (Generalized Modules for Membrane Antigens) technology. The vaccine was well tolerated and induced high antibody levels in early-phase clinical trials in both Shigella-endemic and non-endemic settings. The present analysis assessed the bactericidal activity of antibodies induced by 1790GAHB in healthy Kenyan adults during a phase 2a, controlled, randomized study (NCT02676895). Participants received two doses of 1790GAHB 4 weeks apart containing either 1.5/25 µg or 6/100 µg O antigen/protein, or active comparator vaccines (Control). Serum bactericidal activity (SBA) against S. sonnei was assessed at pre-vaccination (D1), 28 days post-first dose (D29) and 28 days post-second dose (D57), using a luminescence-based assay. Most participants had SBA titers above the lower limit of quantification of the assay at D1. SBA geometric mean titers increased 3.4-fold in the 1.5/25 µg group and 6.3-fold in the 6/100 µg group by D29 and were maintained at D57. There was no increase in SBA geometric mean titers in the Control group. A strong correlation was observed between SBA titers and anti-S. sonnei lipopolysaccharide serum immunoglobulin G antibody concentrations (Pearson correlation coefficient = 0.918), indicating that SBA can effectively complement enzyme-linked immunosorbent assay data by indicating the functionality of 1790GAHB-induced antibodies.

GMMA Technology for the Development of Safe Vaccines: Meta-Analysis of Individual Patient Data to Assess the Safety Profile of Shigella sonnei 1790GAHB Vaccine in Healthy Adults, with Special Focus on Neutropenia.

INTRODUCTION: Shigellosis is a major health concern among children < 5 years of age from developing countries, and there are no widely available vaccines to prevent it. The GMMA-based 1790GAHB investigational vaccine against Shigella sonnei was well tolerated and immunogenic in phase 1 and 2 studies conducted in healthy adults from Shigella endemic and non-endemic populations. Based on pooled data of five individual trials, we assessed the association between vaccine administration and the risk of neutropenia as well as the overall safety profile of 1790GAHB. METHODS: The risk ratio (RR) of neutropenia was evaluated between participants receiving 1790GAHB (vaccinees) and active comparator/placebo (controls) using different ethnicity-specific absolute neutrophil count (ANC) thresholds established to define neutropenia. Safety was assessed in terms of solicited, unsolicited, and serious adverse events (AEs). RESULTS: Of the 279 participants, 11 (5.5%) vaccinees and 4 (5.0%) controls had ANC below the appropriate threshold within 7 days post-vaccination. RR was 0.96 [95% confidence interval (CI) 0.54-1.70]. When neutrophil counts of participants of African descent were measured against an ethnicity non-specific threshold, they resulted in neutropenia episodes in 30 (37.0%) vaccinees and 16 (30.2%) controls, while only 2 (2.5%) vaccinees and 1 (1.9%) control had neutropenia when the ethnicity-specific threshold was applied. RRs were 0.98 (95% CI 0.75-1.28) and 1.30 (95% CI 0.1-17.6), respectively. Solicited and unsolicited AEs were slightly more frequent among vaccinees than controls. No serious AEs, other than neutropenia cases, were recorded in the vaccine group. CONCLUSION: By applying the appropriate threshold, no increased risk of neutropenia was identified in vaccinees compared with the controls. The frequency of neutropenia events varied drastically when ethnicity-appropriate thresholds were applied. This observation highlights the importance of selecting appropriate cut-off values according to the correct population reference. Overall, the 1790GAHB vaccine demonstrated an acceptable safety profile.