Optimization and validation of a high throughput method for detecting neutralizing antibodies against human papillomavirus (HPV) based on pseudovirons.

The pseudoviron-based neutralization assay is accepted as the gold standard to evaluate the functional humoral immune response against HPV. The goal of this study was to develop and optimize a human papillomavirus (HPV) neutralization assay using HPV pseudovirons with Gaussia luciferase (Gluc) as the reporter gene. For this purpose, high-titers Gluc pseudovirons were generated by cotransfecting 293TT cells with HPV structural genes and Gluc expressing plasmids. Six types of neutralizing monoclonal antibodies, vaccines immunized serum samples and WHO international antibody standard were used to validate the new developed assay. The ideal circumstances of the assay were identified for cell counts (30,000/well for 96-well plate), pseudoviron inoculating size (100 times RLU above background) and incubation time (72 hr). The sensitivity of the Gluc assay was comparable to secreted alkaline phosphatase (SEAP) assay and higher than the green florescent protein (GFP) assay. The non-specific background for different types of sample was significantly different (rabbit sera > human sera > mouse sera, P < 0.01). The non-specific neutralization effects were not attributed to IgG antibody. The cutoff value for this assay was determined as 50% inhibition at a dilution of 1:40. Without requirements of sample dilution and different incubation times at different temperature before processing, the detection time was shortened from more than 90 min to less than 5 min for a 96-well plate compared with the SEAP-based assay. With the advantages of short detection time and easy-to-use procedure, the newly developed assay is more suitable for large sero-epidemiological studies or clinical trials and more amenable to automation.