The synthesis and preliminary immunological evaluation of a dual-adjuvant SARS-CoV-2 RBD vaccine: Covalent integration of TLR7/8 and iNKT cell agonists.

Covalently linking an adjuvant to an antigenic protein enhances its immunogenicity by ensuring a synergistic delivery to the immune system, fostering a more robust and targeted immune response. Most adjuvant-protein conjugate vaccines incorporate only one adjuvant due to the difficulties in its synthesis. However, there is a growing interest in developing vaccines with multiple adjuvants designed to elicit a more robust and targeted immune response by engaging different aspects of the immune system for complex diseases where traditional vaccines fall short. Here, we pioneer the synthesis of a dual-adjuvants protein conjugate Vaccine 1 by assembling a toll-like receptor 7/8 (TLR7/8) agonist, an invariant natural killer T cell (iNKT) agonist with a clickable bicyclononyne (BCN). The BCN group can bio-orthogonally react with azide-modified severe acute respiratory syndrome coronavirus-2 receptor-binding domain (SARS-CoV-2 RBD) trimer antigen to give the three-component Vaccine 1. Notably, with a mere 3 µg antigen, it elicited a balanced subclass of IgG titers and 20-fold more IgG2a than control vaccines, highlighting its potential for enhancing antibody-dependent cellular cytotoxicity. This strategy provides a practicable way to synthesize covalently linked dual immunostimulants. It expands the fully synthetic self-adjuvant protein vaccine that uses a single adjuvant to include two different types of adjuvants.

Unfolding Protein-Based Hapten Coupling via Thiol-Maleimide Click Chemistry: Enhanced Immunogenicity in Anti-Nicotine Vaccines Based on a Novel Conjugation Method and MPL/QS-21 Adjuvants.

Vaccines typically work by eliciting an immune response against larger antigens like polysaccharides or proteins. Small molecules like nicotine, on their own, usually cannot elicit a strong immune response. To overcome this, anti-nicotine vaccines often conjugate nicotine molecules to a carrier protein by carbodiimide crosslinking chemistry to make them polymeric and more immunogenic. The reaction is sensitive to conditions such as pH, temperature, and the concentration of reactants. Scaling up the reaction from laboratory to industrial scales while maintaining consistency and yield can be challenging. Despite various approaches, no licensed anti-nicotine vaccine has been approved so far due to the susboptimal antibody titers. Here, we report a novel approach to conjugate maleimide-modified nicotine hapten with a disulfide bond-reduced carrier protein in an organic solvent. It has two advantages compared with other approaches: (1) The protein was unfolded to make the peptide conformation more flexible and expose more conjugation sites; (2) thiol-maleimide "click" chemistry was utilized to conjugate the disulfide bond-reduced protein and maleimide-modified nicotine due to its availability, fast kinetics, and bio-orthogonality. Various nicotine conjugate vaccines were prepared via this strategy, and their immunology effects were investigated by using MPL and QS-21 as adjuvants. The in vivo study in mice showed that the nicotine-BSA conjugate vaccines induced high anti-nicotine IgG antibody titers, compared with vaccines prepared by using traditional condensation methods, indicating the success of the current strategy for further anti-nicotine or other small-molecule vaccine studies. The enhancement was more significant by using MPL and QS-21 than that of traditional aluminum adjuvants.

Harnessing the potential of de-sulfated heparin for targeted drug delivery: A three-component approach exemplified by conjugation with galactose and paclitaxel.

Heparin, an anticoagulant with a century-long history of use, has been investigated over the past decade as a potential drug delivery vehicle. Despite its safety and efficacy, its interactions with many proteins through specific sulfate patterns can complicate drug delivery by mediating diverse biological functions. Here, we present the synthesis of a three-component drug delivery system comprising de-sulfated heparin as the carrier, galactose as the targeting moiety, and paclitaxel as the therapeutic drug. Removal of sulfates eliminated most of its anticoagulant effects in all intermediates. Through coupling with galactose and paclitaxel, the system improved the solubility of the drug and achieved selective targeting and efficient drug delivery to HepG2 cells, a liver carcinoma cell line with high galactose receptor expression. While the three-component system exhibited a slightly higher IC50 value than native paclitaxel, demonstrating its efficacy as a drug carrier, the IC50 value for the normal human liver cell line QSG7701 was significantly higher, indicating its selectivity and safety. Our study introduces a novel approach utilizing desulfated heparin as a carrier, warranting further investigation to unlock its potential in targeted drug delivery strategies.

Strategic development of a self-adjuvanting SARS-CoV-2 RBD vaccine: From adjuvant screening to enhanced immunogenicity with a modified TLR7 agonist.

Adjuvants enhance the body's immune response to a vaccine, often leading to better protection against diseases. Monophosphoryl lipid A analogues (MPLA, TLR4 agonists), α-galactosylceramide analogues (NKT cell agonists), and imidazoquinoline compounds (TLR7/8 agonists) are emerging novel adjuvants on market or under clinical trials. Despite significant interest in these adjuvants, a direct comparison of their adjuvant activities remains unexplored. We initially assessed the activities of various adjuvants from three distinct categories using the SARS-CoV-2 RBD trimer antigen. TLR4 and TLR7/8 agonists are discovered to elicit robust IgG2a/2b antibodies, which is crucial for eliciting antibody dependent cytotoxicity. While α-galactosylceramide analogs induced mainly IgG1 antibody. Then, because of the flexibility of the TLR7/8 agonist, we designed and synthesized a tri-component self-adjuvanting SARS-CoV-2 RBD vaccine, featuring a covalent TLR7 agonist and targeting mannoside. Animal studies indicated that this vaccine generated antigen-specific humoral immunity. Yet, its immunogenicity seems compromised, indicating the complexity of the vaccine.

Chemoenzymatic synthesis and immunological evaluation of sialyl-Thomsen-Friedenreich (sTF) antigen conjugate to CRM197.

sTF (sialyl-Thomsen-Friedenreich) is a type of tumor-associated carbohydrate antigens (TACAs) and is highly expressed in various human malignancies. To validate if sTF could be a valuable molecular target for future cancer vaccine development, in this work the sTF antigen was prepared by adopting a strategy combining chemical and enzymatic methods, and then was covalently conjugated to a carrier protein, CRM197. The preliminary immunological evaluation, performed on BALB/c mice, revealed that the sTF-CRM197 conjugate elicited high titers of specific IgG antibodies. FACS experiments showed that the antisera induced by sTF-CRM197 conjugate could specifically recognize and bind to sTF-positive cancer cells T-47D. Furthermore, the conjugate mediated effective and specific antibody-mediated complement-dependent cytotoxicity (CDC).

Characterization of pneumococcal serotype 7F in vaccine conjugation.

Streptococcus pneumoniae is a highly invasive bacterial pathogen that can cause a range of illnesses. Pneumococcal capsular polysaccharides (CPS) are the main virulence factors that causes invasive pneumococcal disease (IPD). Pneumococcal CPS serotype 7F along with a few other serotypes is more invasive and likely to cause IPD. Therefore, 7F is a target for pneumococcal vaccine development, and is included in the two recently approved multi-valent pneumococcal conjugated vaccines, i.e. VAXNEUVANCE and PREVNAR 20.To support process and development of our 15-valent pneumococcal conjugated vaccine (PCV15), chromatographic methods have been developed for 7F polysaccharide and conjugate characterization. A size-exclusion chromatography (SEC) method with UV, light scattering and refractive index detections was employed for concentration, size and conformation analysis. A reversed-phase ultra-performance liquid chromatography (RP-UPLC) method was used for analysis of conjugate monosaccharide composition and degree of conjugation. The collective information obtained by these chromatographic analysis provided insights into the pneumococcal conjugate and conjugation process.

Exonuclease III Can Efficiently Cleave Linear Single-Stranded DNA: Reshaping Its Experimental Applications in Biosensors.

Exonuclease III (Exo III) has been generally used as a double-stranded DNA (dsDNA)-specific exonuclease that does not degrade single-stranded DNA (ssDNA). Here, we demonstrate that Exo III at concentrations above 0.1 unit/µL can efficiently digest linear ssDNA. Moreover, the dsDNA specificity of Exo III is the foundation of many DNA target recycling amplification (TRA) assays. We demonstrate that with 0.3 and 0.5 unit/µL Exo III, the degradation of an ssDNA probe, free or fixed on a solid surface, was not discernibly different, regardless of the presence or absence of target ssDNA, indicating that Exo III concentration is critical in TRA assays. The study has expanded the Exo III substrate scope from dsDNA to both dsDNA and ssDNA, which will reshape its experimental applications.

Efficient synthesis of α-galactosylceramide and its C-6 modified analogs.

The synthesis of α-galactosylceramide (KRN7000) and its C-6 modified analogs remains a challenge due to the difficult α-1,2-cis-glycosidic bond. A non-participating benzyl (Bn) protecting group has been commonly used to favor the α-glycosylation product. Here, we report the α-selective glycosylation by using a bulky 4,6-O-di-tert-butylsilylene (DTBS) galactosyl donor, regardless of the 2-benzoyl (Bz) participating group. Compared with Bn, Bz groups can be selectively removed in basic conditions without impacting the C-6 azide modification. The azide has the potential for clicking with alkyne or being easily transformed to other functional groups.

Self-Assembled TLR7/8 Agonist-Mannose Conjugate as An Effective Vaccine Adjuvant for SARS-CoV-2 RBD Trimer.

Small synthetic TLR7/8-agonists can be used as vaccine adjuvants to enhance cell and humoral-mediated immune responses to specific antigens. Despite their potency, after local injection they can be dispersed to undesired body parts causing high reactogenicity, limiting their clinical applications. Here we describe a vaccination strategy that employs the covalent conjugate of a mannose and TLR7/8 agonist as a vaccine adjuvant to take advantage of mannose binding C-type lectins on dendritic cells to enhance the vaccine's immunogenicity. The mannose-TLR7/8 agonist conjugate can self-assemble into nanoparticles with the hydrophilic mannose on the outside and hydrophobic TLR7/8 agonist inside. Although its ability to stimulate HEK-BlueTM hTLR7/8 cells dropped, it can efficiently stimulate mouse bone marrow-derived dendritic cells as indicated by the up-regulation of CD80 and CD86, and higher cytokine expression levels of TNF-α, IL6, and IL-12p70 than the native TLR7/8 agonist. In vivo, vaccination using the SARS-CoV-2 RBD trimer as the antigen and the conjugate as the adjuvant induced a significantly higher amount of IgG2a. These results suggest that the mannose-TLR7/8-agonist conjugate can be used as an effective vaccine adjuvant.

Monitoring bromide loss in bromoacetyl-derivatized polyribosylribitol polysaccharide in Haemophilus influenzae type b for PedvaxHIB® by capillary electrophoresis and NMR spectroscopy.

PedvaxHIB® is an effective pediatric vaccine for protecting infants from invasive gram-negative bacterium Haemophilus influenzae type b. It is a highly purified capsular polysaccharide, polyribosylribitol phosphate that is covalently linked to an outer membrane protein complex of Neisseria meningitidis. PRP is first derivatized with an organic linker, followed by the coupling of a butadiamine group, and then at the end terminal, a bromoacetyl group is attached for conjugation with thiolated OMPC. The stability of the bromide group in derivatized PRP is monitored by two different methods, capillary electrophoresis and NMR spectroscopy. The loss of the bromide group is detected by measuring the amount of free bromide ion liberated using capillary electrophoresis and by observing a change in amide proton peaks near the bromide group using NMR. The two methods give similar rate hydrolysis results, therefore both can be employed as quick stability tools for bromoacetylation PRP content during manufacturing.

Aptamer-based Cas14a1 biosensor for amplification-free live pathogenic detection.

CRISPR-Cas systems have been employed to detect a large variety of pathogenic microorganisms by simply changing the guide RNA sequence. However, these platforms usually rely on nucleic acid extraction and amplification to achieve good sensitivity. Herein, we developed a new platform for the highly specific and sensitive detection of live staphylococcus aureus (S. aureus) based on an Aptamer-based Cas14a1 Biosensor (ACasB), without the need for nucleic acid extraction or amplification. First, the S. aureus specific aptamer was hybrid with a blocker DNA. After the live S. aureus was added, the blocker can be released upon bacteria-aptamer binding. Finally, the released blocker can activate Cas14a1 protein by binding with the sgRNA to generate a change of fluorescent intensity. The ACasB indicates high specificity and sensitivity: it can directly distinguish 400 CFU/ml live S. aureus cells. Comparable to qPCR, the Cas14a1-aptamer biosensor can detect S. aureus with 100% accuracy in complex samples. Therefore, this ACasB for the on-site detection of live S. aureus can broaden its applications in food safety and environmental monitoring.

Conjugate of structurally reassigned pneumococcal serotype 31 polysaccharide with CRM197 elicited potent immune response.

Around 100 Streptococcus pneumonia (Spn) serotypes have been discovered, 90% of the severe diseases in children are caused by 13 serotypes. With the success of pneumococcal bacterial polysaccharide conjugate vaccines (PCVs), the burden of pneumococcal disease has been significantly reduced. Serotype 31 is a non-vaccine serotype and has increased in prevalence. By using Nuclear Magnetic Resonance (NMR) as the primary tool, we report the revised serotype 31 polysaccharide (s-31-ps) structure as [→3)-ß-D-Galf-(5/6-OAc)-(1 â†’ 3)-ß-D-Galp-(1 â†’ 3)-ß-L-Rhap-(2-OAc)-(1 â†’ 2)-α-L-Rhap-(1 â†’ 4)-ß-D-GlcpA-(1→]n. Furthermore, the reductive amination-conjugate of serotype 31 polysaccharide and cross reacting material (CRM197) protein was prepared in organic solvent (N,N-dimethylformamide, DMF) instead of water. The reaction is faster, and the DMF conjugate elicited comparable immune responses with the aqueous conjugate. S-31-ps conjugate vaccine has the potential of being included in the next-generation PCV vaccines.

New Insights for Biosensing: Lessons from Microbial Defense Systems.

Microorganisms have gained defense systems during the lengthy process of evolution over millions of years. Such defense systems can protect them from being attacked by invading species (e.g., CRISPR-Cas for establishing adaptive immune systems and nanopore-forming toxins as virulence factors) or enable them to adapt to different conditions (e.g., gas vesicles for achieving buoyancy control). These microorganism defense systems (MDS) have inspired the development of biosensors that have received much attention in a wide range of fields including life science research, food safety, and medical diagnosis. This Review comprehensively analyzes biosensing platforms originating from MDS for sensing and imaging biological analytes. We first describe a basic overview of MDS and MDS-inspired biosensing platforms (e.g., CRISPR-Cas systems, nanopore-forming proteins, and gas vesicles), followed by a critical discussion of their functions and properties. We then discuss several transduction mechanisms (optical, acoustic, magnetic, and electrical) involved in MDS-inspired biosensing. We further detail the applications of the MDS-inspired biosensors to detect a variety of analytes (nucleic acids, peptides, proteins, pathogens, cells, small molecules, and metal ions). In the end, we propose the key challenges and future perspectives in seeking new and improved MDS tools that can potentially lead to breakthrough discoveries in developing a new generation of biosensors with a combination of low cost; high sensitivity, accuracy, and precision; and fast detection. Overall, this Review gives a historical review of MDS, elucidates the principles of emulating MDS to develop biosensors, and analyzes the recent advancements, current challenges, and future trends in this field. It provides a unique critical analysis of emulating MDS to develop robust biosensors and discusses the design of such biosensors using elements found in MDS, showing that emulating MDS is a promising approach to conceptually advancing the design of biosensors.

trans Single-Stranded DNA Cleavage via CRISPR/Cas14a1 Activated by Target RNA without Destruction.

As a CRISPR-Cas system (clustered regularly interspaced short palindromic repeats and CRISPR associated proteins), Cas14a1 can cis/trans cleave single-stranded DNA (ssDNA). Here, we describe an unreported capacity of Cas14a1: RNA can trigger the trans ssDNA cleavage. This Cas14a1-based RNA-activated detection platform (Amplification, Transcription, Cas14a1-based RNA-activated trans ssDNA cleavage, ATCas-RNA) has an outstanding specificity for the detection of target RNAs with point mutation resolution, which is better than that of the Cas14a1-based ssDNA-activation. Using ATCas-RNA via a fluorophore quencher-labeled ssDNA reporter (FQ), we were able to detect 1 aM pathogenic nucleic acid within 1 h, and achieve 100 % accuracy with 25 milk samples. This platform can serve as a new tool for high-efficiency nucleic acid diagnostics. Importantly, this work can expand our understanding of Cas14a1 and inspire further mechanisms and applications of Class-2 Cas systems.

Paramagnetic Tag for Glycosylation Sites in Glycoproteins: Structural Constraints on Heparan Sulfate Binding to Robo1.

An enzyme- and click chemistry-mediated methodology for the site-specific nitroxide spin labeling of glycoproteins has been developed and applied. The procedure relies on the presence of single N-glycosylation sites that are present natively in proteins or that can be engineered into glycoproteins by mutational elimination of all but one glycosylation site. Recombinantly expressing glycoproteins in HEK293S (GnT1-) cells results in N-glycans with high-mannose structures that can be processed to leave a single GlcNAc residue. This can in turn be modified by enzymatic addition of a GalNAz residue that is subject to reaction with an alkyne-carrying TEMPO moiety using copper(I)-catalyzed click chemistry. To illustrate the procedure, we have made an application to a two-domain construct of Robo1, a protein that carries a single N-glycosylation site in its N-terminal domains. The construct has also been labeled with 15N at amide nitrogens of lysine residues to provide a set of sites that are used to derive an effective location of the paramagnetic nitroxide moiety of the TEMPO group. This, in turn, allowed measurements of paramagnetic perturbations to the spectra of a new high affinity heparan sulfate ligand. Calculation of distance constraints from these data facilitated determination of an atomic level model for the docked complex.

Detection of mucopolysaccharidosis III-A (Sanfilippo Syndrome-A) in dried blood spots (DBS) by tandem mass spectrometry.

BACKGROUND: With ongoing efforts to develop improved treatments for Sanfilippo Syndrome Type A (MPS-IIIA), a disease caused by the inability to degrade heparan sulfate in lysosomes, we sought to develop an enzymatic activity assay for the relevant enzyme, sulfamidase, that uses dried blood spots (DBS). METHODS: We designed and synthesized a new sulfamidase substrate that can be used to measure sulfamidase activity in DBS using liquid chromatography-tandem mass spectrometry (LC-MS/MS). RESULTS: Sulfamidase activity was readily detected in DBS using the new substrate and LC-MS/MS. Sulfamidase activity showed acceptable linearity proportional to the amount of enzyme and reaction time. Sulfamidase activity in 238 random newborns was well elevated compared to the range of activities measured in DBS from 8 patients previously confirmed to have MPS-IIIA. CONCLUSIONS: This is the first report of an assay capable of detecting sulfamidase in DBS. The new assay could be useful in diagnosis and potentially for newborn screening of MPS-IIIA.

A Traveling Wave Ion Mobility Spectrometry (TWIMS) Study of the Robo1-Heparan Sulfate Interaction.

Roundabout 1 (Robo1) interacts with its receptor Slit to regulate axon guidance, axon branching, and dendritic development in the nervous system and to regulate morphogenesis and many cell functions in the nonneuronal tissues. This interaction is known to be critically regulated by heparan sulfate (HS). Previous studies suggest that HS is required to promote the binding of Robo1 to Slit to form the minimal signaling complex, but the molecular details and the structural requirements of HS for this interaction are still unclear. Here, we describe the application of traveling wave ion mobility spectrometry (TWIMS) to study the conformational details of the Robo1-HS interaction. The results suggest that Robo1 exists in two conformations that differ by their compactness and capability to interact with HS. The results also suggest that the highly flexible interdomain hinge region connecting the Ig1 and Ig2 domains of Robo1 plays an important functional role in promoting the Robo1-Slit interaction. Moreover, variations in the sulfation pattern and size of HS were found to affect its binding affinity and selectivity to interact with different conformations of Robo1. Both MS measurements and CIU experiments show that the Robo1-HS interaction requires the presence of a specific size and pattern of modification of HS. Furthermore, the effect of N-glycosylation on the conformation of Robo1 and its binding modes with HS is reported. Graphical Abstract ᅟ.

Controlled Chemoenzymatic Synthesis of Heparan Sulfate Oligosaccharides.

A chemoenzymatic approach has been developed for the preparation of diverse libraries of heparan sulfate (HS) oligosaccharides. It employs chemically synthesized oligosaccharides having a chemical entity at a GlcN residue, which in unanticipated manners influences the site of modification by NST, C5-Epi/2-OST and 6-OST1 /6-OST3 , thus resulting in oligosaccharides differing in N/O-sulfation and epimerization pattern. The enzymatic transformations defined fine substrate requirements of NST, C5-Epi, 2-OST, and 6-OST.

Cell-Surface Glyco-Engineering by Exogenous Enzymatic Transfer Using a Bifunctional CMP-Neu5Ac Derivative.

Cell-surface engineering strategies that permit long-lived display of well-defined, functionally active molecules are highly attractive for eliciting desired cellular responses and for understanding biological processes. Current methodologies for the exogenous introduction of synthetic biomolecules often result in short-lived presentations, or require genetic manipulation to facilitate membrane attachment. Herein, we report a cell-surface engineering strategy that is based on the use of a CMP-Neu5Ac derivative that is modified at C-5 by a bifunctional entity composed of a complex synthetic heparan sulfate (HS) oligosaccharide and biotin. It is shown that recombinant ST6GAL1 can readily transfer the modified sialic acid to N-glycans of glycoprotein acceptors of living cells resulting in long-lived display. The HS oligosaccharide is functionally active, can restore protein binding, and allows activation of cell signaling events of HS-deficient cells. The cell-surface engineering methodology can easily be adapted to any cell type and is highly amenable to a wide range of complex biomolecules.

Heparan Sulfate Microarray Reveals That Heparan Sulfate-Protein Binding Exhibits Different Ligand Requirements.

Heparan sulfates (HS) are linear sulfated polysaccharides that modulate a wide range of physiological and disease-processes. Variations in HS epimerization and sulfation provide enormous structural diversity, which is believed to underpin protein binding and regulatory properties. The ligand requirements of HS-binding proteins have, however, been defined in only a few cases. We describe here a synthetic methodology that can rapidly provide a library of well-defined HS oligosaccharides. It is based on the use of modular disaccharides to assemble several selectively protected tetrasaccharides that were subjected to selective chemical modifications such as regioselective O- and N-sulfation and selective de-sulfation. A number of the resulting compounds were subjected to enzymatic modifications by 3-O-sulfotransferases-1 (3-OST1) to provide 3-O-sulfated derivatives. The various approaches for diversification allowed one tetrasaccharide to be converted into 12 differently sulfated derivatives. By employing tetrasaccharides with different backbone compositions, a library of 47 HS-oligosaccharides was prepared and the resulting compounds were used to construct a HS microarray. The ligand requirements of a number of HS-binding proteins including fibroblast growth factor 2 (FGF-2), and the chemokines CCL2, CCL5, CCL7, CCL13, CXCL8, and CXCL10 were examined using the array. Although all proteins recognized multiple compounds, they exhibited clear differences in structure-binding characteristics. The HS microarray data guided the selection of compounds that could interfere in biological processes such as cell proliferation. Although the library does not cover the entire chemical space of HS-tetrasaccharides, the binding data support a notion that changes in cell surface HS composition can modulate protein function.