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Crawford C, Guazzelli L, McConnell SA, McCabe O, d’Errico C, Greengo SD, Wear MP, Jedlicka AE, Casadevall A, Oscarson S. Synthetic Glycans Reveal Determinants of Antibody Functional Efficacy against a Fungal Pathogen. ACS Infect Dis 2024; 10:475-488. [PMID: 37856427 PMCID: PMC10862557 DOI: 10.1021/acsinfecdis.3c00447] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Indexed: 10/21/2023]
Abstract
Antibodies play a vital role in the immune response to infectious diseases and can be administered passively to protect patients. In the case of Cryptococcus neoformans, a WHO critical priority fungal pathogen, infection results in antibodies targeting capsular glucuronoxylomannan (GXM). These antibodies yield protective, non-protective, and disease-enhancing outcomes when administered passively. However, it was unknown how these distinct antibodies recognized their antigens at the molecular level, leading to the hypothesis that they may target different GXM epitopes. To test this hypothesis, we constructed a microarray containing 26 glycans representative of those found in highly virulent cryptococcal strains and utilized it to study 16 well-characterized monoclonal antibodies. Notably, we found that protective and non-protective antibodies shared conserved reactivity to the M2 motif of GXM, irrespective of the strain used in infection or GXM-isolated to produce a conjugate vaccine. Here, only two antibodies, 12A1 and 18B7, exhibited diverse trivalent GXM motif reactivity. IgG antibodies associated with protective responses showed cross-reactivity to at least two GXM motifs. This molecular understanding of antibody binding epitopes was used to map the antigenic diversity of two Cryptococcus neoformans strains, which revealed the exceptional complexity of fungal capsular polysaccharides. A multi-GXM motif vaccine holds the potential to effectively address this antigenic diversity. Collectively, these findings underscore the context-dependent nature of antibody function and challenge the classification of anti-GXM epitopes as either "protective" or "non-protective".
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Affiliation(s)
- Conor
J. Crawford
- Centre
for Synthesis and Chemical Biology, University
College Dublin, Belfield D04 V1W8, Dublin 4, Ireland
- Department
of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205, United States
| | - Lorenzo Guazzelli
- Centre
for Synthesis and Chemical Biology, University
College Dublin, Belfield D04 V1W8, Dublin 4, Ireland
| | - Scott A. McConnell
- Department
of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205, United States
| | - Orla McCabe
- Centre
for Synthesis and Chemical Biology, University
College Dublin, Belfield D04 V1W8, Dublin 4, Ireland
| | - Clotilde d’Errico
- Centre
for Synthesis and Chemical Biology, University
College Dublin, Belfield D04 V1W8, Dublin 4, Ireland
| | - Seth D. Greengo
- Department
of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205, United States
| | - Maggie P. Wear
- Department
of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205, United States
| | - Anne E. Jedlicka
- Department
of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205, United States
| | - Arturo Casadevall
- Department
of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205, United States
| | - Stefan Oscarson
- Centre
for Synthesis and Chemical Biology, University
College Dublin, Belfield D04 V1W8, Dublin 4, Ireland
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Abstract
The structural complexity of glycans poses a serious challenge in the chemical synthesis of glycosides, oligosaccharides and glycoconjugates. Glycan complexity, determined by composition, connectivity, and configuration far exceeds what nature achieves with nucleic acids and proteins. Consequently, glycoside synthesis ranks among the most complex tasks in organic synthesis, despite involving only a simple type of bond-forming reaction. Here, we introduce the fundamental principles of glycoside bond formation and summarize recent advances in glycoside bond formation and oligosaccharide synthesis.
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Affiliation(s)
- Conor J Crawford
- Department of Biomolecular Systems, Max Planck Institute for Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam, Germany.
| | - Peter H Seeberger
- Department of Biomolecular Systems, Max Planck Institute for Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam, Germany.
- Institute for Chemistry and Biochemistry, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
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Crawford CJ, Wear MP, Smith DFQ, d'Errico C, McConnell SA, Casadevall A, Oscarson S. A glycan FRET assay for detection and characterization of catalytic antibodies to the Cryptococcus neoformans capsule. Proc Natl Acad Sci U S A 2021; 118:e2016198118. [PMID: 33514659 PMCID: PMC7865134 DOI: 10.1073/pnas.2016198118] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Classic antibody functions include opsonization, complement activation, and enhancement of cellular antimicrobial function. Antibodies can also have catalytic activity, although the contribution of catalysis to their biological functions has been more difficult to establish. With the ubiquity of catalytic antibodies against glycans virtually unknown, we sought to advance this knowledge. The use of a glycan microarray allowed epitope mapping of several monoclonal antibodies (mAbs) against the capsule of Cryptococcus neoformans From this, we designed and synthesized two glycan-based FRET probes, which we used to discover antibodies with innate glycosidase activity and analyze their enzyme kinetics, including mAb 2H1, the most efficient identified to date. The validity of the FRET assay was confirmed by demonstrating that the mAbs mediate glycosidase activity on intact cryptococcal capsules, as observed by a reduction in capsule diameter. Furthermore, the mAb 18B7, a glycosidase hydrolase, resulted in the appearance of reducing ends in the capsule as labeled by a hydroxylamine-armed fluorescent (HAAF) probe. Finally, we demonstrate that exposing C. neoformans cells to catalytic antibodies results in changes in complement deposition and increased phagocytosis by macrophages, suggesting that the antiphagocytic properties of the capsule have been impaired. Our results raise questions over the ubiquity of antibodies with catalytic activity against glycans and establish the utility of glycan-based FRET and HAAF probes as tools for investigating this activity.
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Affiliation(s)
- Conor J Crawford
- Centre for Synthesis and Chemical Biology, University College Dublin, Dublin 4, Ireland
- Department of Molecular Microbiology and Immunology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
| | - Maggie P Wear
- Department of Molecular Microbiology and Immunology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
| | - Daniel F Q Smith
- Department of Molecular Microbiology and Immunology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
| | - Clotilde d'Errico
- Centre for Synthesis and Chemical Biology, University College Dublin, Dublin 4, Ireland
| | - Scott A McConnell
- Department of Molecular Microbiology and Immunology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
| | - Arturo Casadevall
- Department of Molecular Microbiology and Immunology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205
| | - Stefan Oscarson
- Centre for Synthesis and Chemical Biology, University College Dublin, Dublin 4, Ireland;
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Crawford CJ, Oscarson S. Convergent total synthesis of Cryptococcus neoformans serotype B capsule repeating motif. Carbohydr Res 2020; 497:108150. [PMID: 32932031 DOI: 10.1016/j.carres.2020.108150] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 09/02/2020] [Accepted: 09/02/2020] [Indexed: 11/27/2022]
Abstract
Cryptococcus neoformans is an opportunistic fungal pathogen, which is a frequent cause of a life-threatening meningitis in immunocompromised individuals. We report the first total synthesis of the serotype B heptasaccharide repeating motif. The use of di- and trisaccharide building blocks enabled a concise convergent synthesis of the protected 6-O-acetylated repeating motif in three steps. Glycosylations gave total 1,2-trans selectivity, despite the absence of a neighboring participating group. Using our recently disclosed catalyst pre-tuning strategy global deprotection gave the desired 6-O-acetylated heptasaccharide with no saturation by-products, overall in four steps 31% yield. The serotype B glucuronoxylomannan (GXM) glycans accessed in this study will increase the structurally diversity of our GXM microarray, allowing further steps towards the development of semi-synthetic vaccines against cryptococcal infections.
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Affiliation(s)
- Conor J Crawford
- Centre for Synthesis and Chemical Biology, University College Dublin, Belfield, Dublin, Ireland.
| | - Stefan Oscarson
- Centre for Synthesis and Chemical Biology, University College Dublin, Belfield, Dublin, Ireland
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Crawford C, Oscarson S. Optimized Conditions for the Palladium-Catalyzed Hydrogenolysis of Benzyl and Naphthylmethyl Ethers: Preventing Saturation of Aromatic Protecting Groups. European J Org Chem 2020. [DOI: 10.1002/ejoc.202000401] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Conor Crawford
- School of Chemistry; University College Dublin; Belfield 4 Dublin Ireland
| | - Stefan Oscarson
- School of Chemistry; University College Dublin; Belfield 4 Dublin Ireland
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MacCalman TE, Phillips-Jones MK, Harding SE. Glycoconjugate vaccines: some observations on carrier and production methods. Biotechnol Genet Eng Rev 2020; 35:93-125. [PMID: 32048549 DOI: 10.1080/02648725.2019.1703614] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Glycoconjugate vaccines use protein carriers to improve the immune response to polysaccharide antigens. The protein component allows the vaccine to interact with T cells, providing a stronger and longer-lasting immune response than a polysaccharide interacting with B cells alone. Whilst in theory the mere presence of a protein component in a vaccine should be sufficient to improve vaccine efficacy, the extent of improvement varies. In the present review, a comparison of the performances of vaccines developed with and without a protein carrier are presented. The usefulness of analytical tools for macromolecular integrity assays, in particular nuclear magnetic resonance, circular dichroism, analytical ultracentrifugation and SEC coupled to multi-angle light scattering (MALS) is indicated. Although we focus mainly on bacterial capsular polysaccharide-protein vaccines, some consideration is also given to research on experimental cancer vaccines using zwitterionic polysaccharides which, unusually for polysaccharides, are able to invoke T-cell responses and have been used in the development of potential all-polysaccharide-based cancer vaccines.A general trend of improved immunogenicity for glycoconjugate vaccines is described. Since the immunogenicity of a vaccine will also depend on carrier protein type and the way in which it has been linked to polysaccharide, the effects of different carrier proteins and production methods are also reviewed. We suggest that, in general, there is no single best carrier for use in glycoconjugate vaccines. This indicates that the choice of carrier protein is optimally made on a case-by-case basis, based on what generates the best immune response and can be produced safely in each individual case.Abbreviations: AUC: analytical ultracentrifugation; BSA: bovine serum albumin; CD: circular dichroism spectroscopy; CPS: capsular polysaccharide; CRM197: Cross Reactive Material 197; DT: diphtheria toxoid; Hib: Haemophilius influenzae type b; MALS: multi-angle light scattering; Men: Neisseria menigitidis; MHC-II: major histocompatibility complex class II; NMR: nuclear magnetic resonance spectroscopy; OMP: outer membrane protein; PRP: polyribosyl ribitol phosphate; PSA: Polysaccharide A1; Sa: Salmonella; St.: Streptococcus; SEC: size exclusion chromatography; Sta: Staphylococcus; TT: tetanus toxoid; ZPS: zwitterionic polysaccharide(s).
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Affiliation(s)
- Thomas E MacCalman
- National Centre for Macromolecular Hydrodynamics, University of Nottingham, Nottingham, UK
| | - Mary K Phillips-Jones
- National Centre for Macromolecular Hydrodynamics, University of Nottingham, Nottingham, UK
| | - Stephen E Harding
- National Centre for Macromolecular Hydrodynamics, University of Nottingham, Nottingham, UK.,Kulturhistorisk Museum, University of Oslo, Oslo, Norway
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Micoli F, Costantino P, Adamo R. Potential targets for next generation antimicrobial glycoconjugate vaccines. FEMS Microbiol Rev 2018; 42:388-423. [PMID: 29547971 PMCID: PMC5995208 DOI: 10.1093/femsre/fuy011] [Citation(s) in RCA: 114] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 03/13/2018] [Indexed: 12/21/2022] Open
Abstract
Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated. This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.
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Affiliation(s)
- Francesca Micoli
- GSK Vaccines Institute for Global Health (GVGH), Via Fiorentina 1, 53100 Siena
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Guazzelli L, McCabe O, Oscarson S. Synthesis of part structures of Cryptococcus neoformans serotype C capsular polysaccharide. Carbohydr Res 2016; 433:5-13. [PMID: 27423877 DOI: 10.1016/j.carres.2016.06.012] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Revised: 06/27/2016] [Accepted: 06/28/2016] [Indexed: 11/19/2022]
Abstract
Cryptococcus neoformans is a fungal pathogen that can cause life-threatening infections in immunocompromised patients. The development of a vaccine based on the capsular polysaccharide of C. neoformans is still an open challenge due to the heterogeneity of the capsular polysaccharide and the difficulty of identifying protective epitopes. Therefore, construction of structurally defined part structures of the C. neoformans GXM capsule is in great demand. Herein is presented the synthesis of a 3-O-naphthalenylmethyl protected trisaccharide thioglycoside building block which is present in C. neoformans serotype C polysaccharide. Its property as a donor in a glycosylation reaction with a model acceptor has been evaluated together with its behaviour as an acceptor following removal of the temporary protecting group. The heavily branched hexasaccharide was obtained in good yields and excellent α-selectivity. The frame shifted octasaccharide structural triad motif for serotype C was also prepared following the same building block strategy. For the first time this structural motif, which is the most substituted amongst the four C. neoformans serotypes, was prepared. Three synthesized C. neoformans serotype C fragments of varying size, from penta-up to octasaccharide, were deprotected and will be included in unique glycoarrays to further investigate the possibility to develop a synthetic vaccine against this pathogen.
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Affiliation(s)
- Lorenzo Guazzelli
- School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland.
| | - Orla McCabe
- School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland
| | - Stefan Oscarson
- School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland
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Guazzelli L, Ulc R, Oscarson S. Synthesis of a Glucuronic Acid-Containing Thioglycoside Trisaccharide Building Block and Its Use in the Assembly of Cryptococcus Neoformans Capsular Polysaccharide Fragments. ChemistryOpen 2015; 4:729-39. [PMID: 27308199 PMCID: PMC4906494 DOI: 10.1002/open.201500143] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Indexed: 11/27/2022] Open
Abstract
As part of an ongoing project aimed at identifying protective capsular polysaccharide epitopes for the development of vaccine candidates against the fungal pathogen Cryptococcus neoformans, the synthesis and glycosylation properties of a naphthalenylmethyl (NAP) orthogonally protected trisaccharide thioglycoside, a common building block for construction of serotype B and C capsular polysaccharide structures, were investigated. Ethyl (benzyl 2,3,4‐tri‐O‐benzyl‐β‐d‐glucopyranosyl‐ uronate)‐(1→2)‐[2,3,4‐tri‐O‐benzyl‐β‐d‐xylopyranosyl‐(1→4)]‐6‐O‐benzyl‐3‐O‐(2‐naphthalenylmethyl)‐1‐thio‐α‐d‐mannopyranoside was prepared and used both as a donor and an acceptor in glycosylation reactions to obtain spacer equipped hexa‐ and heptasaccharide structures suitable either for continued elongation or for deprotection and printing onto a glycan array or conjugation to a carrier protein. The glycosylation reactions proceeded with high yields and α‐selectivity, proving the viability of the building block approach also for construction of 4‐O‐xylosyl‐containing C. neoformans CPS structures.
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Affiliation(s)
- Lorenzo Guazzelli
- School of Chemistry and Chemical Biology University College Dublin Belfield 4 Dublin Ireland
| | - Rebecca Ulc
- School of Chemistry and Chemical Biology University College Dublin Belfield 4 Dublin Ireland
| | - Stefan Oscarson
- School of Chemistry and Chemical Biology University College Dublin Belfield 4 Dublin Ireland
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