Evolution of type-specific immunoassays to evaluate the functional immune response to Gardasil: a vaccine for human papillomavirus types 16, 18, 6 and 11.

Epidemiological studies and clinical trials of vaccines depend on the accurate measurement of antibodies within the polyclonal response to infection or vaccination. The assay currently used to measure the antibody response to vaccination with GARDASIL [Quadrivalent Human Papillomavirus (Types 6, 11, 16, 18) Recombinant Vaccine]--a quadrivalent vaccine used against human papillomavirus (HPV) types 6, 11, 16, and 18--is a competitive Luminex assay (cLIA) that uses multiplex technology to detect type-specific neutralizing antibodies against all four HPV types in a single serum sample. Here we describe how the cLIA was developed, as well as how the monoclonal antibodies (mAbs), used as competitors in the assay, were characterized. An enzyme-linked immunosorbent assay (ELISA) was used to screen eight previously-identified mAbs for their ability to bind to HPV virus-like particles (VLPs) in a type-specific and conformation-dependent manner. Four of these mAbs, H6.M48, K11.B2, H16.V5, and H18.J4, met our specifications and were shown to have the potential to neutralize HPV infection in hemagglutination inhibition and pseudovirus neutralization assays. The competitive immunoassay format was able to distinguish type-specific antibodies in the sera of nonhuman primates vaccinated with HPV VLPs, whereas a traditional direct-bind ELISA could not. In addition, the serum antibodies measured by the competitive assay are known to be neutralizing, whereas the ELISA does not distinguish neutralizing and nonneutralizing antibodies in a serum sample. By detecting antibodies to neutralizing epitopes, the competitive assay both demonstrates sero-conversion and provides a potential functional link between sero-conversion and protective immunity in response to vaccination with GARDASIL.