A Human Papillomavirus Related to Human Papillomavirus MM7/LVX82 Produces Distinct Histological Abnormalities in Human Foreskin Implants Grown as Athymic Mouse Xenografts

Abstract

Studies of human papillomaviruses (HPVs) are hampered by the lack of a conventional culture system because HPV completes its life cycle only in fully differentiated human tissue. To overcome this obstacle, the athymic mouse xenograft system has been used to study the pathogenesis of HPV 11 and to develop neutralizing assays for vaccine development. Recently, HPV 40 has been produced in this system, and HPV 16 has been produced using mice with severe combined immune deficiency. To identify and characterize additional genital HPV types for similar studies, condylomata acuminata lesions containing a high copy number of HPV and detectable L1 major capsid protein were used to prepare infectious virus stocks. Human foreskin fragments were infected with the virus preparations and implanted under the renal capsules of athymic mice. After 5 months of growth, implant tissue was removed and processed for studies to detect HPV infection. Evidence of HPV infection was noted in some of the implants, but in contrast to HPV 11-infected epithelium, the implants derived from the new virus preparations contained a lesser degree of acanthosis, less developed koilocytosis, and a reduced number of preserved nuclei in the hyperkeratotic material within the cyst lining. The L1 consensus region was amplified by polymerase chain reaction from implant DNA and sequenced. Alignment of the amplified sequences with those in the HPV sequence database showed that the 452-bp amplimer was closely related but not identical to HPV LVX82 and HPV MM7 (also called Pap 291). The entire 7.9-kb genome was amplified by polymerase chain reaction and cloned. The presence of virions of the new isolate (named HPV IU) in the implants was verified by immunohistochemical detection of L1 major capsid protein and by demonstration of virion particles by electron microscopy. A second extract was made from one of the new implants and used to successfully propagate HPV IU. These experiments demonstrate that experimental infection of human epithelium with the new isolate, HPV IU, is associated with histological abnormalities that differ in potentially important ways from the changes observed in experimental HPV 11 infection.