KLF4 and cervical squamous intraepithelial neoplasia: To investigate if KLF4 had any role in regulating the HPV life cycle, lentiviruses expressing shRNAs against KLF4 were used to transiently infect CIN-612 cells, which are derived from a cervical biopsy and stably maintain HPV-31 episomes without expressing drug resistance markers[39].