Tomasz Lipinski

In vivo supramolecular templating enhances the activity of multivalent ligands: A potential therapeutic against the Escherichia coli O157 AB5 toxins

We demonstrate that interactions between multimeric receptors and multivalent ligands are dramatically enhanced by recruiting a complementary templating receptor such as an endogenous multimeric protein but only when individual ligands are attached to a polymer as preorganized, covalent, heterobifunctional pairs. This effect cannot be replicated by a multivalent ligand if the same recognition elements are independently arrayed on the scaffold. Application of this principle offers an approach to create high-avidity inhibitors for multimeric receptors. Judicious selection of the ligand that engages the templating protein allows appropriate effector function to be incorporated in the polymeric construct, thereby providing an opportunity for therapeutic applications. The power of this approach is exemplified by the design of exceptionally potent Escherichia coli Shiga toxin antagonists that protect transgenic mice that constitutively express a human pentraxin, serum amyloid P component.

Enhanced Immunogenicity of a Tricomponent Mannan Tetanus Toxoid Conjugate Vaccine Targeted to Dendritic Cells via Dectin-1 by Incorporating β-Glucan

In a previous attempt to generate a protective vaccine against Candida albicans, a β-mannan tetanus toxoid conjugate showed poor immunogenicity in mice. To improve the specific activation toward the fungal pathogen, we aimed to target Dectin-1, a pattern-recognition receptor expressed on monocytes, macrophages, and dendritic cells. Laminarin, a β-glucan ligand of Dectin-1, was incorporated into the original β-mannan tetanus toxoid conjugate providing a tricomponent conjugate vaccine. A macrophage cell line expressing Dectin-1 was employed to show binding and activation of Dectin-1 signal transduction pathway by the β-glucan–containing vaccine. Ligand binding to Dectin-1 resulted in the following: 1) activation of Src family kinases and Syk revealed by their recruitment and phosphorylation in the vicinity of bound conjugate and 2) translocation of NF-κB to the nucleus. Treatment of immature bone marrow–derived dendritic cells (BMDCs) with tricomponent or control vaccine confirmed that the β-glucan–containing vaccine exerted its enhanced activity by virtue of dendritic cell targeting and uptake. Immature primary cells stimulated by the tricomponent vaccine, but not the β-mannan tetanus toxoid vaccine, showed activation of BMDCs. Moreover, treated BMDCs secreted increased levels of several cytokines, including TGF-β and IL-6, which are known activators of Th17 cells. Immunization of mice with the novel type of vaccine resulted in improved immune response manifested by high titers of Ab recognizing C. albicans β-mannan Ag. Vaccine containing laminarin also affected distribution of IgG subclasses, showing that vaccine targeting to Dectin-1 receptor can benefit from augmentation and immunomodulation of the immune response.

Synthesis and Immunogenicity of a Glycopolymer Conjugate

A protective β-mannan trisaccharide epitope from the Candida albicans cell wall phosphomannan has been synthesized and activated for copolymerization with acrylamide. The resulting glycopolymer displayed 33 trisaccharide haptens and was derivatized for conjugation to the immunogenic carrier protein, chicken serum albumin. The resulting conjugate achieves a high degree of oligosaccharide substitution while limiting the sites of substitution on the protein. The murine immune response against this conjugate was compared with the response to a trisaccharide-tetanus toxoid conjugate vaccine. The glycopolymer was shown to induce a more robust immune response with higher trisaccharide-specific antibody titers and with a significantly larger proportion of responding mice developing antibodies that bound the target, native cell wall antigen of C. albicans.

Synthesis and Immunochemical characterization of S‐linked Glycoconjugate Vaccines against Candida albicans

Replacement of the glycosidic oxygen atom by a sulphur atom is a promising technique for creating glycoconjugates with increased resistance to hydrolysis by endogenous glycosidases. The synthesis and antigenic properties of two distinct (1-->2)-beta-mannan trisaccharides with inter residue-S-linked mannopyranose residues are described. Syntheses were based on an oxidation-reduction strategy to construct the O-linked beta-mannopyranoside bonds and a SN2 inversion to provide 1-thio-beta-mannopyranoside residues. Subsequently the allyl trisaccharide glycosides were subjected to photo addition with cysteine amine and coupled to tetanus toxoid and bovine serum albumin with good efficiency via an adipic acid tether. Rabbit immunization studies revealed that the antibodies elicited by the two glycoconjugates were able to recognize the corresponding O-linked trisaccharide epitope conjugated to BSA and the native cell wall antigen of Candida albicans.

A structurally diversified linker enhances the immune response to a small carbohydrate hapten

The tether employed to covalently attach β-mannan disaccharide glycoconjugates influences the specificity of rabbit antibodies that protect against Candida albicans. Two glycoconjugates containing (1 → 2)-β-mannan disaccharides linked to chicken serum albumin (CSA) either via a structurally uniform or via a stereodiversified spacer were prepared and evaluated in immunization trials in mice and rabbits. Immunization with conjugate vaccine possessing a structurally diversified linker induced higher IgG titers against Candida albicans cell wall phosphomannan than a conjugate with a structurally uniform linker. These results suggest that affinity maturation and the specific antibody response can be shifted towards recognition of the desired hapten by employing a linker with diversified configuration.

Synthesis of Monomeric and Dimeric Repeating Units of the Zwitterionic Type 1 Capsular Polysaccharide from Streptococcus pneumoniae

Zwitterionic polysaccharides (ZPSs) from Bacteroides fragilis and Streptococcus pneumoniae display unique T-cell activities. The first synthesis of a hexasaccharide representing two repeating units of the zwitterionic capsular polysaccharide from S. pneumoniae type 1 (Sp1) is reported. Key elements of the approach are stereoselective construction of 1,4-cis-alpha-galactose linkages based on a reactive trichloroacetimidate donor that incorporates a 6-O-acetyl group, which may contribute to the high alpha selectivity in glycosylation. After assembly of the fully protected hexasaccharide from five monosaccharide synthons 2-4, 24 and 25, selective deprotection of the primary hydroxyl groups of the four galactose residues followed by oxidation to the corresponding uronic acids provides hexasaccharide 19. The trisaccharide counterpart 1 was synthesized in similar fashion from three synthons, 2-4. This approach employed both conventional and dehydrative glycosylation methodologies and avoids the use of poorly reactive uronic acid derived glycosyl donors and acceptors.

A β-mannan trisaccharide conjugate vaccine aids clearance of Candida albicans in immunocompromised rabbits.

A β-(1 → 2)-linked mannose trisaccharide epitope that is the optimal inhibitor of two protective monoclonal antibodies specific for the Candida albicans cell wall phosphomannan was used to create a synthetic conjugate vaccine. Two injections of the trisaccharide-tetanus toxoid conjugate administered with alum induced a robust secondary antibody response in rabbits with trisaccharide specific IgG ELISA titers in excess of 1:100,000. Fluorescent labeling studies demonstrated these antibodies (i) recognized the cell wall β-mannan of C. albicans on hyphae and budding cells and (ii) C. albicans incubated with immune sera bound complement factor C3. The synthetic conjugate vaccine but not the carrier protein, tetanus toxoid reduced Candida load in vaccinated rabbits subsequently rendered leukocytopenic by injection of cyclophosphamide and then challenged with live C. albicans. These data support the contention that antibody mediated immunity plays a role in combating C. albicans infections and suggests that a surprisingly simple, readily accessible synthetic conjugate vaccine may have therapeutic potential.

Synthesis of antifungal vaccines by conjugation of β-1,2 trimannosides with T-cell peptides and covalent anchoring of neoglycopeptide to tetanus toxoid.

Selective strategies for the construction of novel three component glycoconjugate vaccines presenting Candida albicans cell wall glycan (β-1,2 mannoside) and polypeptide fragments on a tetanus toxoid carrier are described. The first of two conjugation strategies employed peptides bearing an N-terminal thiopropionyl residue for conjugation to a trisaccharide equipped with an acrylate linker and a C-terminal S-acetyl thioglycolyl moiety for subsequent linking of neoglycopeptide to bromoacetylated tetanus toxoid. Michael addition of acrylate trisaccharides to peptide thiol under mildly basic conditions gave a mixture of N- and C- terminal glyco-peptide thioethers. An adaptation of this strategy coordinated S-acyl protection with anticipated thioester exchange equilibria. This furnished a single chemically defined fully synthetic neoglycopeptide conjugate that could be anchored to a tetanus toxoid carrier and avoids the introduction of exogenous antigenic groups. The second strategy retained the N-terminal thiopropionyl residue but replaced the C-terminal S-acetate functionality with an azido group that allowed efficient, selective formation of neoglycopeptide thioethers and subsequent conjugation of these with propargylated tetanus toxoid, but introduced potentially antigenic triazole linkages.

Designing a Candida albicans Conjugate Vaccine by Reverse Engineering Protective Monoclonal Antibodies

Candida albicans is a human commensal fungus typically found in the vulvovaginal and gastrointestinal tracts, and the oropharyngeal cavity. Under opportunistic conditions, the interaction between host and fungus can become pathogenic leading to candidiasis (Mochon and Cutler 2005). Cutaneous/mucocutaneous and hematogenously disseminated candidiasis are the two main forms in which the disease manifests. The most common forms of mucocutaneous candidiasis are vulvovaginitis and oral thrush, neither of which is considered life-threatening. Candida infections have the potential to significantly compromise the health of immunocompromised patients (Dreizen 1984), including cancer patients with myelosuppression (Bodey 1986), a condition involving decreased bone marrow activity, T-cell deficient individuals (Mochon and Cutler 2005), women with chronic or recurring vulvovaginitis (Foxman et al. 2000), and HIV/AIDS patients with esophageal candidiasis (Dreizen 1984). Hematogenously disseminated candidiasis is the life-threatening form of the disease (Anttile et al. 1994; Komshian et al. 1989), and may involve the kidney, liver, spleen, heart, lung, and central nervous system (Mochon and Cutler 2005).