Investigation of the protective properties of glycosylphosphatidylinositol-based vaccine candidates in aToxoplasma gondiimouse challenge model

Abstract

Vaccination against the ubiquitous parasite Toxoplasma gondii would provide the most efficient prevention against toxoplasmosis-related congenital, brain and eye diseases in humans. We investigated the immune response elicited by pathogen-specific glycosylphosphatidylinositol (GPI) glycoconjugates using carbohydrate microarrays in a BALB/c mouse model. We further examined the protective properties of the glycoconjugates in a lethal challenge model using the virulent T. gondii RH strain. Upon immunization, mice raised antibodies that bind to the respective GPIs on carbohydrate microarrays, but were mainly directed against an unspecific GPI epitope including the linker. The observed immune response, though robust, was unable to provide protection in mice when challenged with a lethal dose of viable tachyzoites. We demonstrate that anti-GPI antibodies raised against the here described semi-synthetic glycoconjugates do not confer protective immunity against T. gondii in BALB/c mice.

Parasite Carbohydrate Vaccines

“…Synthetic carbohydrates with defined carrier protein binding sites are advantageous for generating well-defined glycoconjugates with predictable conjugation sites. To minimize the immunogenicity of the linker (Buskas et al, 2004; Gotze et al, 2015) short linkers with no functional groups are best used to ensure that immune responses against the desired antigen epitope are not detrimentally affected. The processing of the linker after uptake by APCs is also an important consideration, to allow for the release of vaccine oligosaccharide and peptide moieties for antigenic display.…”

“…Immunization did not provide protection for mice in the lethal challenge model. Furthermore, the induced antibodies failed to exhibit any significant effect on the inflammatory response for either group (Gotze et al, 2015). Analysis of the immune response indicates that antibody induction was directed away from the desired carbohydrate side branch of the TgGPI, and more toward the linker used to attach the carbohydrate to the carrier protein.…”

“…Analysis of the immune response indicates that antibody induction was directed away from the desired carbohydrate side branch of the TgGPI, and more toward the linker used to attach the carbohydrate to the carrier protein. In a potential next step, the formulation has to be adjusted (Gotze et al, 2015). …”

Glycan Arrays: From Basic Biochemical Research to Bioanalytical and Biomedical Applications

“…The specific reaction between maleimide groups on the slide and thio-functionalized glycans is a reliable alternative to amine/NHS coupling and has also been used for glycodendrimers (22,41,42) (Figure 3a). Epoxy slides can react with compounds presenting amines and thiols (43,44). Glycans without a linker but with a free reducing end can be coupled covalently and site-specifically to surfaces presenting hydrazides or oxyamines (45,46) (Figure 3b).…”

“…Anti-GPI antibodies are highly sensitive biomarkers to detect Toxoplasma gondii infections and to discriminate between acute and latent infections (43). The biomarker antibody target GPIs, when used as CRM 197 conjugates, did not induce protective immunity in mice even though glycan arrays showed that antibodies were induced (44).…”