Quantitative and epitope-specific antigenicity analysis of the human papillomavirus 6 capsid protein in aqueous solution or when adsorbed on particulate adjuvants

Human papillomavirus (HPV) 6 is a human pathogen which causes genital warts. Recombinant virus-like particle (VLP) based antigens are the active components in prophylactic vaccines to elicit functional antibodies. The binding and functional characteristics of a panel of 15 murine monoclonal antibodies (mAbs) against HPV6 was quantitatively assessed. Elite conformational indicators, recognizing the conformational epitopes, are also elite viral neutralizers as demonstrated with their viral neutralization efficiency (5 mAbs with neutralization titer below 4 ng/mL) in a pseudovirion (PsV)-based system. The functionality of a given mAb is closely related to the nature of the corresponding epitope, rather than the apparent binding affinity to antigen. The epitope-specific antigenicity assays can be used to assess the binding activity of PsV or VLP preparations to neutralizing mAbs. These mAb-based assays can be used for process monitoring and for product release and characterization to confirm the existence of functional epitopes in purified antigen preparations. Due to the particulate nature of the alum adjuvants, the vaccine antigen adsorbed on adjuvants was considered largely as “a black box” due to the difficulty in analysis and visualization. Here, a novel method with fluorescence-based high content imaging for visualization and quantitating the immunoreactivity of adjuvant-adsorbed VLPs with neutralizing mAbs was developed, in which antigen desorption was not needed. The facile and quantitative in situ antigenicity analysis was amendable for automation. The integrity of a given epitope or two non-overlapping epitopes on the recombinant VLPs in their adjuvanted form can be assessed in a quantitative manner for cross-lot or cross-product comparative analysis with minimal manipulation of samples.