Epitope-Specific Serological Assays for RSV: Conformation Matters

Area of Science:

• Immunology
• Vaccinology
• Virology

Background:

• Respiratory syncytial virus (RSV) poses significant health risks, particularly to vulnerable populations.
• Effective RSV vaccines depend on antibodies targeting the fusion (F) protein, which has distinct pre-fusion (pre-F) and post-fusion (post-F) conformations.
• The pre-F conformation exposes critical antigenic sites not present on post-F, making it a key target for neutralizing antibodies.

Purpose of the Study:

• To investigate the impact of F protein conformation and antibody competition on assays measuring neutralizing antibody responses.
• To optimize assays for quantifying antibodies targeting specific antigenic sites on the RSV F protein.
• To inform the interpretation of clinical trial outcomes and the definition of serological correlates of protection for RSV vaccines.

Main Methods:

• Development and optimization of monoclonal antibody competition ELISAs.
• Evaluation of D25-competing antibodies (DCA) targeting antigenic site Ø on pre-F.
• Comparison of palivizumab-competing antibody (PCA) readouts on both pre-F and post-F substrates.

Main Results:

• Antibodies targeting adjacent antigenic sites can influence DCA and PCA assay readouts.
• Cross-competition from non-targeted sites significantly confounds PCA measurements when using a post-F substrate.
• Assay limitations necessitate careful consideration when interpreting immune monitoring data from RSV vaccine trials.

Conclusions:

• Measuring DCA and PCA levels can help delineate antibody roles at different F protein sites.
• Assay caveats are critical for accurate interpretation of immune responses in RSV vaccine development.
• Refined assay methodologies are essential for defining robust correlates of protection against RSV.