Epitope clustering analysis for vaccine-induced human antibodies in relationship to a panel of murine monoclonal antibodies against HPV16 viral capsid.

Human papillomavirus (HPV) type 16 is the most common type implicated as the etiological agent that causes cervical cancer. The marketed prophylactic vaccines against HPV infection are composed of virus-like particles (VLPs) assembled from the recombinant major capsid protein L1. Elicitation of functional and neutralizing antibodies by vaccination is the mode of action by which the vaccines prevent the viral infection. In this study, a panel of murine mAbs against HPV16 L1 were generated and comprehensively characterized with respect to their mapping to the epitope spectrum on the viral capsid. These mAbs were categorized into five epitope bins by two different methods based on the pairwise cross-inhibition and competition with human polyclonal antibodies. In addition, a preliminary demonstration of the spatial relationship of the epitopes recognized by these mAbs was performed using a cross-blocking assay with a well-characterized human mAb, 26D1. Interestingly, two mAbs recognizing different epitopes were found to act synergistically in the pseudovirion-based neutralization assay (PBNA). To facilitate cross-lab and cross-study comparison, the international standard (IS) serum 05/134 was used to calibrate the mAbs as well as the human serum samples from the HPV16/18 vaccine recipients. The neutralizing mAbs, particularly those that recognizing immunodominant epitopes, would be useful in developing epitope-specific assays for monitoring the vaccine production process and for serological assessment.