First characterization of immunogenic conjugates of Vi negative Salmonella Typhi O-specific polysaccharides with rEPA...

Area of Science:

• Immunology
• Vaccinology
• Microbiology

Background:

• Typhoid fever poses a significant health burden, particularly in developing countries.
• Existing Vi polysaccharide-based conjugate vaccines are effective against Vi-positive Salmonella Typhi but not Vi-negative strains.
• Novel vaccine candidates are needed to combat Vi-negative S. Typhi infections.

Purpose of the Study:

• To synthesize and evaluate novel polysaccharide-protein conjugates derived from Vi-negative S. Typhi as potential vaccine candidates.
• To compare the immunogenicity of conjugates prepared using different carrier proteins (HSA, rEPA) and conjugation methods (reductive amination, ADH linker).

Main Methods:

• Synthesis of four different S. Typhi outer surface polysaccharide (OSP) conjugates using recombinant exoprotein A (rEPA) or human serum albumin (HSA) as carriers.
• Conjugation strategies included direct reductive amination and an adipic acid dihydrazide (ADH) linker.
• Immunization of mice with synthesized conjugates and assessment of antibody titers.

Main Results:

• Conjugates prepared via direct reductive amination (OSP-HSA and OSP-rEPA) elicited significantly higher antibody titers compared to OSP alone (P=0.0001 and P≤0.0001, respectively).
• Conjugates utilizing the ADH linker (OSP_ADH-HSA and OSP_ADH-rEPA) showed insignificant antibody responses (P=0.1684 and P=0.3794, respectively).
• The OSP-rEPA conjugate demonstrated superior immunogenicity compared to OSP-HSA.

Conclusions:

• Direct reductive amination is a more effective method for preparing S. Typhi OSP glycoconjugates.
• Recombinant exoprotein A (rEPA) is a superior carrier protein compared to human serum albumin (HSA) for S. Typhi OSP conjugates.
• The OSP-rEPA conjugate is a promising candidate for an efficacious typhoid vaccine and warrants further clinical evaluation.