GMMA and Glycoconjugate Approaches Compared in Mice for the Development of a Vaccine against Shigella flexneri Serotype 6

Abstract

Shigella infections are one of the top causes of diarrhea throughout the world, with Shigella flexneri being predominant in developing countries. Currently, no vaccines are widely available and increasing levels of multidrug-resistance make Shigella a high priority for vaccine development. The serotype-specific O-antigen moiety of Shigella lipopolysaccharide has been recognized as a key target for protective immunity, and many O-antigen based candidate vaccines are in development. Recently, the Generalized Modules for Membrane Antigens (GMMA) technology has been proposed as an alternative approach to traditional glycoconjugate vaccines for O-antigen delivery. Here, these two technologies are compared for a vaccine against S. flexneri serotype 6. Genetic strategies for GMMA production, conjugation approaches for linkage of the O-antigen to CRM197 carrier protein, and a large panel of analytical methods for full vaccine characterization have been put in place. In a head-to-head immunogenicity study in mice, GMMA induced higher anti-O-antigen IgG than glycoconjugate administered without Alhydrogel. When formulated on Alhydrogel, GMMA and glycoconjugate elicited similar levels of persistent anti-O-antigen IgG with bactericidal activity. Glycoconjugates are a well-established bacterial vaccine approach, but can be costly, particularly when multicomponent preparations are required. With similar immunogenicity and a simpler manufacturing process, GMMA are a promising strategy for the development of a vaccine against Shigella.

Effect of O-Antigen Chain Length Regulation on the Immunogenicity of Shigella and Salmonella Generalized Modules for Membrane Antigens (GMMA)

“…We have previously verified that OAg length does not play a major role on the immune response elicited by S. flexneri 6 GMMA and that even short OAg chains are able to induce a high and functional anti-OAg specific immune response, similar to that induced by long OAg chains [ 6 ]. In this study, we extended the investigation to S. sonnei , S. flexneri 2a, and S .…”

“…GMMA are outer membrane exosomes released from Gram-negative bacteria genetically engineered to increase blebbing (e.g., through deletion of the tolR gene) and reduce reactogenicity, usually by modifying the lipid A acylation pattern (e.g., through the deletion of the htrB and msbB genes) [ 4 , 5 ]. GMMA display the OAg in an outer membrane context and have been proven to be non-inferior compared to equivalent glycoconjugate vaccines in preclinical studies [ 6 , 7 ]. Moreover, GMMA can be produced at high yields and using a simple and robust process of manufacturing, potentially leading to affordable vaccines [ 8 ].…”

“…OAg repeating units can also be assembled into high molecular-mass capsules (Group 4 Capsules, G4C) if an additional G4C operon is present [ 20 ]. The introduction of mutations in the OAg locus or in the G4C operon results in a loss of specific polysaccharide populations on the bacterial surface [ 21 , 22 ], and consequently on GMMA [ 6 ].…”

“…We have previously performed studies in mice with S. flexneri serotype 6 GMMA differing in OAg length and found no major impact of the OAg length on the induced immune response [ 6 ]. Here, we extended the investigation to different OAg structures displayed by S. sonnei , S. flexneri 2a, and S. Typhimurium GMMA.…”

Short Vi-polysaccharide abrogates T-independent immune response and hyporesponsiveness elicited by long Vi-CRM197conjugate vaccine

“…We suggest that the approach presented in this study can be expanded to other conjugated polysaccharides, where the polysaccharide still retains the correct epitopes but loses its T-independent induction ability and consequently creates a pure T-dependent antigen. We recently described this approach for the synthesis of a glycoconjugate vaccine against Shigella flexneri 6 ( 39 ). There are other examples in the literature suggesting that saccharides of shorter chain length, as opposed to higher molecular weight polysaccharides, may be better able to elicit T cell-dependent antibody responses ( 36 , 40 – 42 ).…”