Exploring the Role of GMMA Components in the Immunogenicity of a 4-Valent Vaccine against Shigella

Abstract

Shigellosis is the leading cause of diarrheal disease, especially in children of low- and middle-income countries, and is often associated with anti-microbial resistance. Currently, there are no licensed vaccines widely available against Shigella, but several candidates based on the O-antigen (OAg) portion of lipopolysaccharides are in development. We have proposed Generalized Modules for Membrane Antigens (GMMA) as an innovative delivery system for OAg, and a quadrivalent vaccine candidate containing GMMA from S. sonnei and three prevalent S. flexneri serotypes (1b, 2a and 3a) is moving to a phase II clinical trial, with the aim to elicit broad protection against Shigella. GMMA are able to induce anti-OAg-specific functional IgG responses in animal models and healthy adults. We have previously demonstrated that antibodies against protein antigens are also generated upon immunization with S. sonnei GMMA. In this work, we show that a quadrivalent Shigella GMMA-based vaccine is able to promote a humoral response against OAg and proteins of all GMMA types contained in the investigational vaccine. Proteins contained in GMMA provide T cell help as GMMA elicit a stronger anti-OAg IgG response in wild type than in T cell-deficient mice. Additionally, we observed that only the trigger of Toll-like Receptor (TLR) 4 and not of TLR2 contributed to GMMA immunogenicity. In conclusion, when tested in mice, GMMA of a quadrivalent Shigella vaccine candidate combine both adjuvant and carrier activities which allow an increase in the low immunogenic properties of carbohydrate antigens.

Towards establishing a correlate of protection against shigellosis: assessing immunological endpoints across immune responses to the Shigella sonnei 1790GAHB GMMA investigational vaccine

“…This is in line with previous preclinical observations that showed anti-OAg antibodies are the main drivers of SBA against OAg-positive Shigella strains, while antibodies not targeting OAg are functional against OAg-negative bacteria. 44,45 The anti-Shigella LPS speci c IgG avidity analysis suggested an association between S. sonnei LPS speci c total IgG avidity and protection from shigellosis. Antibody avidity was similar between 1790GAHB and placebo recipients regardless of the challenge outcome, suggesting that this association is not impacted by vaccination and that this immunomarker may be a suitable CoP.…”

Functional assays to evaluate antibody-mediated responses against Shigella: a review

“…The ELISA is very simple, can be automated to increase throughput and operator independency, and can be easily transferred to different labs including those with low level of technology. Flow cytometry is instead commonly used to assess serum binding to whole Shigella instead of single antigens ( Mancini et al., 2023 ).…”

“…Non-differentiated cells like THP-1 monocytes are not able to kill and only provide indication of antibody-mediated internalization of targets. In contrast, by using more specialized cells (e.g., primary neutrophils, differentiated HL-60, differentiated THP-1 macrophages) it is possible to evaluate killing efficiency of serum ( Butler et al., 2019 ; Mancini et al., 2023 ). Complement is commonly added to the assay to evaluate concerted FcγRs- and CR-mediated uptake and killing (although it is not always necessary to induce internalization and/or killing) ( Mancini et al., 2023 ).…”

“…Flow cytometry-based OPA with THP-1 monocytes and neutrophils from whole blood were used to evaluate opsonophagocytosis of beads coated with antigens of interest, and not whole Shigella ( Bernshtein et al., 2022 ) Interestingly, while SBA and OPKA results usually correlated with each other and with respect to symptoms severity, OPA assays with specific antigens provided new insights, as contrarily to SBA and OPKA titers, OAg- and IpaB-antibodies negatively correlated with symptoms severity ( Bernshtein et al., 2022 ). Finally, classical OPKA was used by our group to evaluate the immune response of mice immunized with candidate GMMA-based vaccine ( Mancini et al., 2023 ).…”

Nanoparticles and Other Nanostructures and the Control of Pathogens: From Bench to Vaccines

“…The study by F. Mancini et al [26] proposes a vaccine substrate to protect against Shigella sonnei and Shigella flexneri which are causative agents of severe diarrhea, mainly in developing countries, and may present antibiotic resistance. In the study, it is stated, "O-antigen-based vaccines may not be the best solution if one refers to the former Salmonella typhi vaccine, which is almost devoid of a protective effect."…”