Development and Validation of a Functional Antibody Assay for Evaluating Protein-Based Pneumococcal Vaccines

Area of Science:

• Microbiology
• Immunology
• Vaccine Development

Background:

• Streptococcus pneumoniae (Spn) causes severe invasive diseases like meningitis and pneumonia.
• Current polysaccharide vaccines have limitations including serotype replacement.
• Pneumococcal surface protein A (PspA) is a promising antigen for new protein-based vaccines.

Purpose of the Study:

• To establish a standardized functional antibody assay for PspA-based vaccines.
• To overcome limitations in current antibody detection methods for pneumococcal vaccines.

Main Methods:

• Modified the multiplex opsonophagocytic killing assay (MOPA) for PspA.
• Selected and developed a target strain panel using PCR and ELISA.
• Optimized MOPA by extending phagocytic reaction time and confirmed specificity via competitive inhibition assays.

Main Results:

• The assay showed high linearity (R² ≥ 0.98) and acceptable precision (CV ≤ 30% repeatability, CV ≤ 50% intermediate precision).
• Preclinical and clinical serum samples demonstrated potent bactericidal activity against diverse PspA families, irrespective of capsule type.

Conclusions:

• A standardized framework was provided for developing and assessing protein-based pneumococcal vaccines.
• The assay facilitates the evaluation of functional antibodies against PspA, crucial for vaccine efficacy.