13 research outputs found
Total synthesis of a Streptococcus pneumoniae serotype 12F CPS repeating unit hexasaccharide
The Gram-positive bacterium Streptococcus pneumoniae causes severe disease
globally. Vaccines that prevent S. pneumoniae infections induce antibodies
against epitopes within the bacterial capsular polysaccharide (CPS). A better
immunological understanding of the epitopes that protect from bacterial
infection requires defined oligosaccharides obtained by total synthesis. The
key to the synthesis of the S. pneumoniae serotype 12F CPS hexasaccharide
repeating unit that is not contained in currently used glycoconjugate vaccines
is the assembly of the trisaccharide
β-D-GalpNAc-(1→4)-[α-D-Glcp-(1→3)]-β-D-ManpNAcA, in which the branching points
are equipped with orthogonal protecting groups. A linear approach relying on
the sequential assembly of monosaccharide building blocks proved superior to a
convergent [3 + 3] strategy that was not successful due to steric constraints.
The synthetic hexasaccharide is the starting point for further immunological
investigations
Sequential Linkage of Carbohydrate Antigens to Mimic Capsular Polysaccharides: Toward Semisynthetic Glycoconjugate Vaccine Candidates against Streptococcus pneumoniae Serotype 14
Vaccines based on isolated polysaccharides successfully protect humans from bacterial pathogens such as Streptococcus pneumoniae. Because polysaccharide production and isolation can be technically challenging, glycoconjugates containing synthetic antigens are an attractive alternative. Typically, the shortest possible oligosaccharide antigen is preferable as syntheses of longer structures are more difficult and time-consuming. Combining several protective epitopes or polysaccharide repeating units as blocks by bonds other than glycosidic linkages would greatly reduce the synthetic effort if the immunological response to the polysaccharide could be retained. To explore this concept, we bridged the well-understood and immunologically potent RU of S. pneumoniae serotype 14 (ST14) with an aliphatic spacer and conjugated it to the carrier protein CRM197. Mice immunized with the spacer-bridged glycan conjugates produced high levels of specific antibodies after just one or two vaccine doses, while the tetrasaccharide repeating unit alone required three doses. The antibodies recognized specifically ST14 CPS, while no significant antibody levels were raised against the spacer or unrelated CPS. Synthetic vaccines generated antibodies with opsonic activity. Mimicking polysaccharides by coupling repeating unit antigens via an aliphatic spacer may prove useful also for the development of other glycoconjugate vaccine candidates, thereby reducing the synthetic complexity while enhancing a faster immune response
1,3-Dibromo-5,5-dimethylhydantoin as promoter for glycosylations using thioglycosides
1,3-Dibromo-5,5-dimethylhydantoin (DBDMH), an inexpensive, non-toxic and stable reagent, is a competent activator of thioglycosides for glycosidic bond formation. Excellent yields were obtained when triflic acid (TfOH) or trimethylsilyl trifluoromethanesulfonate (TMSOTf) were employed as co-promoters in solution or automated glycan assembly on solid phase
Deciphering Antigenic Determinants of <i>Streptococcus pneumoniae</i> Serotype 4 Capsular Polysaccharide using Synthetic Oligosaccharides
<i>Streptococcus pneumoniae</i> is a major cause of mortality
and morbidity worldwide. More than 90 <i>S. pneumoniae</i> serotypes are distinguished based on the structure of their primary
targets to the human immune system, the capsular polysaccharides (CPSs).
The CPS of the prevalent serotype 4 (ST4) is composed of tetrasaccharide
repeating units and is included in existing pneumococcal vaccines.
Still, the structural antigenic determinants that are essential for
protective immunity, including the role of the rare and labile cyclic <i>trans</i>-(2,3) pyruvate ketal modification, remain largely
unknown. Molecular insights will support the design of synthetic subunit
oligosaccharide vaccines. Here, we identified the key antigenic determinants
of ST4 CPS with the help of pyruvated and nonpyruvated synthetic repeating
unit glycans. Glycan arrays revealed oligosaccharide antigens recognized
by antibodies in the human reference serum. Selected depyruvated ST4
oligosaccharides were used to formulate neoglycoconjugates and immunologically
evaluated in mice. These oligosaccharides were highly immunogenic,
but the resulting antiglycan antibodies showed only limited binding
to the natural CPS present on the bacterial surface. Glycan array
and surface plasmon resonance analysis of murine polyclonal serum
antibodies as well as monoclonal antibodies revealed that terminal
sugars are important in directing the immune responses. The pyruvate
modification on the oligosaccharide is needed for cross-reactivity
with the native CPS. These findings are an important step toward the
design of oligosaccharide-based vaccines against <i>S. pneumoniae</i> ST4
Sequential Linkage of Carbohydrate Antigens to Mimic Capsular Polysaccharides: Toward Semisynthetic Glycoconjugate Vaccine Candidates against Streptococcus pneumoniae Serotype 14
Synthesis, Liposomal Formulation, and Immunological Evaluation of a Minimalistic Carbohydrate-α-GalCer Vaccine Candidate
Fully
synthetic glycan-based vaccines hold great potential as preventive
and therapeutic vaccines against infectious diseases as well as cancer.
Here, we present a two-component platform based on the facile conjugation
of carbohydrate antigens to α-galactosylceramide (α-GalCer)
to yield fully synthetic vaccine candidates. Formulation of the cancer-associated
Tn antigen glycolipid model vaccine candidate into liposomes of different
sizes and subsequent immunization of mice generated specific, high-affinity
antibodies against the carbohydrate antigen with characteristics of
T cell-dependent immunity. Liposome formulation elicited more reproducible
glycan immunity than a conventional glycoconjugate vaccine bearing
the same glycan antigen did. Further evaluation of the immune response
revealed that the size of the liposomes influenced the glycan antibody
responses toward either a cellular (Th1) or a humoral (Th2) immune
phenotype. The glycolipid vaccine platform affords strong and robust
antiglycan antibody responses <i>in vivo</i> without the
need for an external adjuvant
Development of an Efficacious, Semisynthetic Glycoconjugate Vaccine Candidate against <i>Streptococcus pneumoniae</i> Serotype 1
Infections
with <i>Streptococcus pneumoniae</i> are a
major health burden. Glycoconjugate vaccines based on capsular polysaccharides
(CPSs) successfully protect from infection, but not all pneumococcal
serotypes are covered with equal potency. Marketed glycoconjugate
vaccines induce low levels of functional antibodies against the highly
invasive serotype 1 (ST1), presumably due to the obscuring of protective
epitopes during chemical activation and conjugation to carrier proteins.
Synthetic oligosaccharide antigens can be designed to carry linkers
for site-selective protein conjugation while keeping protective epitopes
intact. Here, we developed an efficacious semisynthetic ST1 glycoconjugate
vaccine candidate. A panel of synthetic oligosaccharides served to
reveal a critical role of the rare aminosugar, 2-acetamido-4-amino-2,4,6-trideoxy-d-galactose (d-AAT), for ST1 immune recognition. A
monovalent ST1 trisaccharide carrying d-AAT at the nonreducing
end induced a strong antibacterial immune response in rabbits and
outperformed the ST1 component of the multivalent blockbuster vaccine
Prevenar 13, paving the way for a more efficacious vaccine
Total Synthesis of a Densely Functionalized Plesiomonas shigelloides Serotype 51 Aminoglycoside Trisaccharide Antigen
Plesiomonas
shigelloides, a pathogen
responsible for frequent outbreaks of severe travelers’ diarrhea,
causes grave extraintestinal infections. Sepsis and meningitis due
to P. shigelloides are associated with
a high mortality rate as antibiotic resistance increases and vaccines
are not available. Carbohydrate antigens expressed by pathogens are
often structurally unique and are targets for developing vaccines
and diagnostics. Here, we report a total synthesis of the highly functionalized
trisaccharide repeating unit <b>2</b> from P.
shigelloides serotype 51 from three monosaccharides.
A judicious choice of building blocks and reaction conditions allowed
for the four amino groups adorning the sugar rings to be installed
with two <i>N</i>-acetyl (Ac) groups, rare acetamidino (Am),
and d-3-hydroxybutyryl (Hb) groups. The strategy for the
differentiation of amino groups in trisaccharide <b>2</b> will
serve well for the syntheses of other complex glycans
Development of an Efficacious, Semisynthetic Glycoconjugate Vaccine Candidate against <i>Streptococcus pneumoniae</i> Serotype 1
Infections
with <i>Streptococcus pneumoniae</i> are a
major health burden. Glycoconjugate vaccines based on capsular polysaccharides
(CPSs) successfully protect from infection, but not all pneumococcal
serotypes are covered with equal potency. Marketed glycoconjugate
vaccines induce low levels of functional antibodies against the highly
invasive serotype 1 (ST1), presumably due to the obscuring of protective
epitopes during chemical activation and conjugation to carrier proteins.
Synthetic oligosaccharide antigens can be designed to carry linkers
for site-selective protein conjugation while keeping protective epitopes
intact. Here, we developed an efficacious semisynthetic ST1 glycoconjugate
vaccine candidate. A panel of synthetic oligosaccharides served to
reveal a critical role of the rare aminosugar, 2-acetamido-4-amino-2,4,6-trideoxy-d-galactose (d-AAT), for ST1 immune recognition. A
monovalent ST1 trisaccharide carrying d-AAT at the nonreducing
end induced a strong antibacterial immune response in rabbits and
outperformed the ST1 component of the multivalent blockbuster vaccine
Prevenar 13, paving the way for a more efficacious vaccine
Synthesis, Liposomal Formulation, and Immunological Evaluation of a Minimalistic Carbohydrate-α-GalCer Vaccine Candidate
Fully
synthetic glycan-based vaccines hold great potential as preventive
and therapeutic vaccines against infectious diseases as well as cancer.
Here, we present a two-component platform based on the facile conjugation
of carbohydrate antigens to α-galactosylceramide (α-GalCer)
to yield fully synthetic vaccine candidates. Formulation of the cancer-associated
Tn antigen glycolipid model vaccine candidate into liposomes of different
sizes and subsequent immunization of mice generated specific, high-affinity
antibodies against the carbohydrate antigen with characteristics of
T cell-dependent immunity. Liposome formulation elicited more reproducible
glycan immunity than a conventional glycoconjugate vaccine bearing
the same glycan antigen did. Further evaluation of the immune response
revealed that the size of the liposomes influenced the glycan antibody
responses toward either a cellular (Th1) or a humoral (Th2) immune
phenotype. The glycolipid vaccine platform affords strong and robust
antiglycan antibody responses <i>in vivo</i> without the
need for an external adjuvant