Importance of Carrier Protein-polysaccharide Conjugation

Conjugation of carrier proteins to polysaccharide antigens is an effective strategy to enhance the immunogenicity of poorly immunogenic polysaccharides. This conjugation method has been successfully applied to the development of polysaccharide conjugate vaccines. Through covalent linkage, the protein antigen on the polysaccharide is improved and the immunogenicity of the polysaccharide is enhanced. This involves the selection of carrier proteins and polysaccharide antigens as well as conjugation techniques.

Fig.1 Production of conjugate vaccines. (Ihssen, et al., 2010)

One-stop Solutions for Polysaccharide Conjugation at CD BioGlyco

As a professional company for polysaccharide-carrier protein conjugation, CD BioGlyco provides carrier protein design, polysaccharide antigen production, and polysaccharide conjugation technology services.

Carrier proteins carry human T-cell epitopes and convert T-cell-independent immune responses to polysaccharides into T-helper cell responses would be suitable carriers for polysaccharide-conjugated vaccines. However, the availability of such carrier proteins is limited. Therefore, it is crucial to develop new vaccine carriers in addition to the traditional protein carriers. The production of polysaccharide antigens presents technical challenges that require attention. Moreover, the conjugation technology based on physical and chemical principles plays a vital role in the successful preparation of conjugates.

Several factors influence the immunogenicity of polysaccharide conjugates, including the sugar length, sugar amount, sugar type, charge of the non-reducing end, conjugation chemistry, and linker used for conjugation. The optimal immune response varies depending on the specific vaccine candidate, requiring an appropriate sugar length. It is important for the sugar size to adequately represent the natural antigenic epitope. Furthermore, the addition of adjuvants is considered to enhance the immunogenicity of polysaccharide conjugate vaccines. In the process of designing polysaccharide conjugates, we will consider the following points:

• Investigate the impact of polysaccharide size and conjugate size on the immune response.
• Evaluate the immune mechanism underlying the modification of immune response by carrier proteins.
• Comprehend the fundamental immune mechanisms involved in polysaccharide antigen competition.
• Explore and utilize advanced analytical tools to assess different properties of polysaccharide conjugate vaccines.
• Examine the influence of conjugation chemistry on immunogenicity.

Fig.2 Factors to consider when designing polysaccharide conjugates. (CD BioGlyco)

Case Study: One-Stop Solutions for Quadrivalent Meningococcal Polysaccharide and BSA Conjugation

• Objective

To perform polysaccharide and BSA conjugation.

• Introduction & Project Background

Polysaccharide-protein conjugate vaccines represent a vital cornerstone in modern immunology, enabling weak polysaccharide antigens to trigger a robust, long-lasting T-cell dependent immune response by linking them to an appropriate carrier protein.

In this project, CD BioGlyco was contracted by a prominent client to prepare four distinct types of meningococcal polysaccharides alongside bovine serum albumin (BSA), and subsequently conjugate the BSA carrier protein to each of the individual meningococcal polysaccharides. The core objective was to perform high-efficiency polysaccharide and BSA conjugation to support the client's research requirements. To achieve this, each of the four meningococcal polysaccharides had to be activated separately and then successfully coupled to the carrier BSA.

• CD BioGlyco's Technical Solution & Approach

To fulfill the client's strict requirements for quality and purity, we implemented a reliable conventional method for chemical coupling and downstream processing. The full one-stop solution was performed across four meticulous procedural stages:

1. Preparation of the Carrier Protein (BSA) Solution
   • The BSA intended for labeling was dialyzed in a 50 mM carbonate buffer consisting of 0.015 M Na₂CO₃ and 0.035 M NaHCO₃ at pH 9.6.
   • This dialysis process included two fluid changes, during which the final BSA concentration was precisely adjusted to 5 mg/mL.
   • Interferences were prevented by ensuring that all reagents containing free amino groups, such as Tris and NH⁴⁺, were entirely removed from the solution.
2. Chemical Oxidation and Activation of Polysaccharides
   • For each batch, 1 mg of polysaccharides was weighed and fully dissolved in 100 μL of ddH₂O.
   • Separately, an oxidizing solution was prepared by dissolving 21 mg of NaIO₄ in 1 mL of ddH₂O.
   • Next, 100 μL of the prepared NaIO₄ solution was slowly mixed with 100 μL of the polysaccharide solution, and the reaction was allowed to stand at 4°C for 30 minutes.
   • To quench the oxidation, 2 µL of ethylene glycol was slowly added to the oxidized polysaccharide solution, which then stood at room temperature in the dark for 30 minutes.
3. Labeling and Conjugation
   • The newly oxidized polysaccharide solution was directly added into the pre-treated BSA solution.
   • The conjugation reaction was maintained at room temperature for a duration of 2 hours.
4. Stabilization and Purification
   • To stabilize the conjugated link, a reducing solution was made by dissolving 0.4 mg of NaBH₄ in 20 µL of ddH₂O.
   • The entire reduction solution was added directly into the reaction mixture and left to stand at 4°C for 2 hours, with gentle shaking applied once every 30 minutes.
   • Finally, the mixture was dialyzed overnight in a PBS buffer (pH 7.2) and stored at -20°C.

• Rigorous Quality Control & Results Validation

By utilizing our state-of-the-art glycobiochemistry platform, all target products were successfully synthesized and verified. The quality control of the four final conjugates was confirmed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and a UV-Vis full wavelength scan.

1. Multi-Method Characterization Profiles

• SDS-PAGE Analysis
  Successful molecular shifting and conjugate formation were observed across all lines. The lane configurations were mapped with Line 1 as the Marker, Line 2 as the Meningococcal polysaccharide A-BSA conjugate, Line 3 as the Meningococcal polysaccharide C-BSA conjugate, Line 4 as the Meningococcal polysaccharide W-BSA conjugate, Line 5 as the Meningococcal polysaccharide Y-BSA conjugate, and Line 6 as the control BSA carrier protein.

Fig.3 SDS-PAGE of conjugates. (CD BioGlyco)

• UV-Vis Full Wavelength Scan

Spectral analysis confirmed the characteristic profiles of the conjugates, traced as Cyan for the Meningococcal polysaccharide A-BSA conjugate, Green for the Meningococcal polysaccharide W-BSA conjugate, Yellow for the Meningococcal polysaccharide C-BSA conjugate, and Purple for the Meningococcal polysaccharide Y-BSA conjugate.

Fig.4 UV-Vis full wavelength scan. (CD BioGlyco)

The combined data explicitly demonstrated that all four separate polysaccharide strains were successfully conjugated to the carrier protein, and the high-purity target products were obtained.

2. Final Delivered Specifications

The four high-quality conjugates were successfully validated and delivered to the client with the following technical parameters:

• Meningococcal Polysaccharide A-BSA Conjugate

Delivered at a size/volume of 350 μL with a concentration of 3 mg/mL, in a 10 mM PBS buffer, stored at -20°C in the dark to avoid repeated freezing and thawing.

• Meningococcal Polysaccharide C-BSA Conjugate

Delivered at a size/volume of 350 μL with a concentration of 3.3 mg/mL, in a 10 mM PBS buffer, stored at -20°C in the dark to avoid repeated freezing and thawing.

• Meningococcal Polysaccharide W-BSA Conjugate

Delivered at a size/volume of 350 μL with a concentration of 3.2 mg/mL, in a 10 mM PBS buffer, stored at -20°C in the dark to avoid repeated freezing and thawing.

• Meningococcal Polysaccharide Y-BSA Conjugate

Delivered at a size/volume of 350 μL with a concentration of 3.1 mg/mL, in a 10 mM PBS buffer, stored at -20°C in the dark to avoid repeated freezing and thawing.

• Demonstrating CD BioGlyco's Superior Capabilities

This successful quadrivalent conjugation project showcases our robust, reliable, and highly adaptive capabilities in carbohydrate-protein chemistry. Our custom one-stop solutions for polysaccharide conjugation streamline the entire workflow, from expert material preparation and chemical activation to comprehensive purification and rigorous analytical quality control.

Advantages of Us

• We attach great importance to the materials required for conjugation, not only providing protein carrier design services but also polysaccharide antigen production services.
• We provide comprehensive technical support for polysaccharide-protein conjugation.
• A professional Glyco™ Vaccine Development Platform
• Comprehensive and reliable after-sales service

CD BioGlyco aims to provide customers with unparalleled support for the Development of Carbohydrate-based Vaccines. We provide integrated one-stop solutions for polysaccharide conjugation. For decades, we have won the trust of global scientists with high-quality products, services, and technical support. If you are interested in our services, please contact us for more details without any hesitation.

Reference:

1. Ihssen, J.; et al. Production of glycoprotein vaccines in Escherichia coli. Microbial cell factories. 2010, 9: 1-13.