Human papillomavirus type 31 life cycle: methods for study using tissue culture models.

The life cycle of human papillomaviruses (HPVs) has been difficult to study in tissue culture owing to its dependence on epithelial differentiation. In this chapter several methods are described to imitate the important steps in the HPV life cycle. Normal human keratinocytes (NHKs) harvested from neonatal foreskins were transfected with HPV type 31 genomes in order to generate stable cell lines containing episomal copies of HPV genomes. HPV-positive keratinocyte cultures were maintained in E medium in the presence of mitomycin C-treated J2 3T3 fibroblast feeders. Finally, the keratinocytes were induced to undergo epithelial differentiation in semisolid medium to provoke viral late functions like genomic amplification and late transcription.