Characterization of serum antibodies from women immunized with Gardasil: A study of HPV-18 infection of primary human keratinocytes.

•Gardasil-immunized sera or IgG possesses strong extracellular neutralization.•FcRn expressed on primary human keratinocytes (PHKs) mediates the uptake of IgG.•Bound or intracellular Gardasil-immunized IgG does not neutralize HPV virions.•Neutralization window of the immune sera is limited to 4h in early passage PHKs.•Growth characteristics of PHKs affect the neutralization window from 4h to 16h.