A Synthetic Carbohydrate Conjugate Vaccine Candidate against Shigellosis: Improved Bioconjugation and Impact of Alum on Immunogenicity

Abstract

Conjugation chemistry is among the most important parameters governing the efficacy of glycoconjugate vaccines. High robustness is required to ensure high yields and batch to batch reproducibility. Herein, we have established a robust bioconjugation protocol based on the thiol-maleimide addition. Major variables were determined and acceptable margins were investigated for a synthetic pentadecasaccharide-tetanus toxoid conjugate, which is a promising vaccine candidate against Shigella flexneri serotype 2a infection. The optimized process is applicable to any thiol-equipped hapten and provides an efficient control of the hapten:carrier ratio. Moreover, comparison of four S. flexneri 2a glycoconjugates only differing by their pentadecasaccharide:tetanus toxoid ratio confirmed preliminary findings indicating that hapten loading is critical for immunogenicity with an optimal ratio here in the range of 17 ± 5. In addition, the powerful influence of alum on the immunogenicity of a Shigella synthetic carbohydrate-based conjugate vaccine candidate is demonstrated for the first time, with a strong anti-S. flexneri 2a antibody response sustained for more than one year.

A modular synthetic route to size-defined immunogenicHaemophilus influenzaeb antigens is key to the identification of an octasaccharide lead vaccine candidate

“…After establishing the immunological cross-reactivity of the sPRP constructs with PRP-directed antibodies, immunization studies with sPRP-CRM197 glycoconjugates were initiated. Mindful of the fact that proper conjugation chemistry is key to efficient glycoconjugate production, 31 and the importance of choosing a linker that induces minimal undesired immunogenic responses, 32 the well-established thiol–maleimide coupling method was chosen 17 , 24 , 33 , 34 The sPRP oligosaccharides were conjugated to CRM197, a carrier protein that has been successfully used in commercial vaccines and immunological studies in conjunction with a variety of antigens. 17 , 24 , 33 , 34 The amine group of the linker of sPRP oligosaccharide 1 was reacted with commercially available dithiobis(succinimidyl propionate) (DSP) in phosphate buffer (pH 7.4) at room temperature ( Scheme 5 ).…”

A tale of two bacterial enteropathogens and one multivalent vaccine

“…Although many Shigella vaccine strategies have been pursued (reviewed in Ashkenazi & Cohen, 2013;Barry et al, 2013;Levine et al, 2007;Mani, Wierzba, & Walker, 2016), the current leading approaches include the following: (a) parenteral vaccines that deliver chemically purified or synthetic Shigella OPS antigens as conjugates to carrier proteins, genetic bioconjugates (Riddle et al, 2016) bohydrate antigens that were conjugated to a protein carrier (Phalipon et al, 2006;Phalipon et al, 2009;van der Put et al, 2016). These vaccine candidates have been demonstrated to be safe and immunogenic in volunteers (Cohen et al, 2017) and are advancing to evaluation using the controlled human infection model.…”

Role of antigen specific T and B cells in systemic and mucosal immune responses in ETEC and Shigella infections, and their potential to serve as correlates of protection in vaccine development

“…When functionality of the serum antibodies was evaluated in adults who received the S. sonnei-rEPA vaccine, 78% of the responders had specific S. sonnei IgG exhibiting strong serum bactericidal activity. A synthetic carbohydrate-based conjugate vaccine, SF2a-TT15 against S. flexneri 2a was designed and constructed at Institut Pasteur [47,48] aiming to obtain a more immunogenic vaccine conferring protection against shigellosis in children younger than 3 years of age. In a phase I study recently completed in Israel, the SF2a-TT15 conjugate vaccine induced a stronger serum IgG response as compared with the 1st generation of detoxified O-specific polysaccharidebased S. flexneri 2a-rEPA conjugate [49,Cohen D et al,unpublished data].…”