Interferon induces morphologic reversion with elimination of extrachromosomal viral genomes in bovine papillomavirus-transformed mouse cells

Bovine delta papillomavirus E5 oncoprotein negatively regulates the cGAS-STING signaling pathway in cattle in a spontaneous model of viral disease

Persistent infection and tumorigenesis by papillomaviruses (PVs) require viral manipulation of various cellular processes, including those involved in innate immune responses. The cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING) pathway has emerged as an essential innate immune sensing system, that recognizes DNA and trigger potent antiviral effector responses. In this study, we found that bovine PV (BPV) E5 protein, the major oncoprotein of bovine delta PVs, interacts with STING but not with cGAS in a spontaneous BPV infection of neoplastic urothelial cells of cattle. Real-time RT-PCR revealed a significant reduction in both cGAS and STING transcripts in E5-expressing cells. Furthermore, western blot (WB) analysis failed to detect any variation in the expression of interferon-inducible protein 16 (IFI16), an upstream effector of the STING pathway. A ternary complex composed of E5/STING/IFI16 was also observed. Co-immunoprecipitation studies showed that STING interacts with a protein network composed of total and phosphorylated TANK-binding kinase 1 (TBK1), total and phosphorylated interferon regulatory factor 3 (IRF3), IRF7, IKKα, IKKβ, IKKϵ, ELKS, MEKK3, and TAK1. RT-qPCR revealed a significant reduction in TBK1 mRNA levels in BPV-infected cells. WB analysis revealed significantly reduced expression levels of pTBK1, which is essential for the activation and phosphorylation of IRF3, a prerequisite for the latter to enter the nucleus to activate type 1 IFN genes. WB also revealed significantly down-expression of IKKα, IKKβ, IKKϵ, and overexpression of IRF7, ELKS, MEKK3, and TAK1in BPV-positive urothelial cells compared with that in uninfected healthy cells. Phosphorylated p65 (p-p65) was significantly reduced in both the nuclear and cytosolic compartments of BPV-infected cells compared with that in uninfected urothelial cells. Our results suggest that the innate immune signaling pathway mediated by cGAS-STING is impaired in cells infected with BPV. Therefore, effective immune responses are not elicited against these viruses, which facilitates persistent viral infection and subsequent tumorigenesis.

Bovine Delta Papillomavirus E5 Oncoprotein Interacts With TRIM25 and Hampers Antiviral Innate Immune Response Mediated by RIG-I-Like Receptors

Persistent infection and tumourigenesis by papillomaviruses (PVs) require viral manipulation of various of cellular processes, including those involved in innate immune responses. Herein, we showed that bovine PV (BPV) E5 oncoprotein interacts with a tripartite motif-containing 25 (TRIM25) but not with Riplet in spontaneous BPV infection of urothelial cells of cattle. Statistically significant reduced protein levels of TRIM25, retinoic acid-inducible gene I (RIG-I), and melanoma differentiation-associated gene 5 (MDA5) were detected by Western blot analysis. Real-time quantitative PCR revealed marked transcriptional downregulation of RIG-I and MDA5 in E5-expressing cells compared with healthy urothelial cells. Mitochondrial antiviral signalling (MAVS) protein expression did not vary significantly between diseased and healthy cells. Co-immunoprecipitation studies showed that MAVS interacted with a protein network composed of Sec13, which is a positive regulator of MAVS-mediated RLR antiviral signalling, phosphorylated TANK binding kinase 1 (TBK1), and phosphorylated interferon regulatory factor 3 (IRF3). Immunoblotting revealed significantly low expression levels of Sec13 in BPV-infected cells. Low levels of Sec13 resulted in a weaker host antiviral immune response, as it attenuates MAVS-mediated IRF3 activation. Furthermore, western blot analysis revealed significantly reduced expression levels of pTBK1, which plays an essential role in the activation and phosphorylation of IRF3, a prerequisite for the latter to enter the nucleus to activate type 1 IFN genes. Our results suggested that the innate immune signalling pathway mediated by RIG-I-like receptors (RLRs) was impaired in cells infected with BPVs. Therefore, an effective immune response is not elicited against these viruses, which facilitates persistent viral infection.

Aristocratic human papillomavirus drove cervical cancer: a study of the therapeutic potential of the combination of interferon with zinc

Human papillomavirus (HPV) infection is related to cancer growth of vaginal, cervical, vulva, penile, anogenital, and non-genital oropharyngeal sites. HPV, as a sexually transmitted virus, infects all sexes similarly but with more significant pathological risks in women. This accounts for high mortality due to late detection and poor prognosis. The initial development and eventual progress of this cancer type depend entirely on three main oncogenes E5, E6 and E7, constitutively expressed to lead to carcinogenesis. Despite an opportunity for pharmacological therapy, there is still a shortage of medical treatment that may remove HPV from infected lesions. This study offers a concise summary of the nature of the issue and the current status of work on potential lead molecules and therapeutic approaches that show the capacity of HPV therapies to counteract the roles of deregulation of E5, E6, and E7.

Roles of APOBEC3A and APOBEC3B in Human Papillomavirus Infection and Disease Progression

The apolipoprotein B messenger RNA-editing, enzyme-catalytic, polypeptide-like 3 (APOBEC3) family of cytidine deaminases plays an important role in the innate immune response to viral infections by editing viral genomes. However, the cytidine deaminase activity of APOBEC3 enzymes also induces somatic mutations in host genomes, which may drive cancer progression. Recent studies of human papillomavirus (HPV) infection and disease outcome highlight this duality. HPV infection is potently inhibited by one family member, APOBEC3A. Expression of APOBEC3A and APOBEC3B is highly elevated by the HPV oncoproteins E6 and E7 during persistent virus infection and disease progression. Furthermore, there is a high prevalence of APOBEC3A and APOBEC3B mutation signatures in HPV-associated cancers. These findings suggest that induction of an APOBEC3-mediated antiviral response during HPV infection may inadvertently contribute to cancer mutagenesis and virus evolution. Here, we discuss current understanding of APOBEC3A and APOBEC3B biology in HPV restriction, evolution, and associated cancer mutagenesis.

Host cell restriction factors that limit transcription and replication of human papillomavirus

The life cycle of human papillomaviruses (HPV) is tightly regulated by the differentiation state of mucosal and cutaneous keratinocytes. To counteract viral infection, constitutively expressed cellular factors, which are defined herein as restriction factors, directly mitigate viral gene expression and replication. In turn, some HPV gene products target these restriction factors and abrogate their anti-viral effects to establish efficient gene expression and replication programs. Ironically, in certain circumstances, this delicate counterbalance between viral gene products and restriction factors facilitates persistent infection by HPVs. This review serves to recapitulate the current knowledge of nuclear restriction factors that directly affect the HPV infectious cycle.

Development of a Novel Marker Gene Based Assay System for Detection and Evaluation of Antiviral Agents with Activity against Papillomaviruses

A novel assay system has been developed in which expression of a human tissue-plasminogen activator (t-PA) gene, carried on a recombinant papillomavirus vector, is used as a marker for the presence of bovine papillomavirus type 1 (BPV-1) within transformed mouse C127 cells. This provides a relatively quick and simple means of identifying and evaluating agents with anti-papillomavirus activity. Using this system the antiviral activity and cytotoxicity of interferon and retinoic acid, have been investigated. After seven subcultures in the presence of 200 Units ml−1 mouse α and β interferon, t-PA expression was completely inhibited, with a concurrent alteration in cellular morphology, and restoration of contact inhibition. In accordance with the problems encountered with interferon therapy of human papillomavirus infections, these effects were dependent on the continued presence of interferon, its removal leading to a rapid return of t-PA expression, and reversion of cells to the transformed phenotype. In comparison, 2.0 μg ml−1 retinoic acid partially reduced t-PA expression (this effect was largely maintained even after removal of the inhibiting compound) but did not affect the transformed cell phenotype. These results are discussed in relation to other in vitro studies and also to the clinical treatment of human papillomavirus (HPV) disease.

Recent Insights into the Control of Human Papillomavirus (HPV) Genome Stability, Loss, and Degradation

Most human papillomavirus (HPV) antiviral strategies have focused upon inhibiting viral DNA replication, but it is increasingly apparent that viral DNA levels can be chemically controlled by approaches that promote its instability. HPVs and other DNA viruses have a tenuous relationship with their hosts. They must replicate and hide from the DNA damage response (DDR) and innate immune systems, which serve to protect cells from foreign or “non-self” DNA, and yet they draft these same systems to support their life cycles. DNA binding antiviral agents promoting massive viral DNA instability and elimination are reviewed. Mechanistic studies of these agents have identified genetic antiviral enhancers and repressors, antiviral sensitizers, and host cell elements that protect and stabilize HPV genomes. Viral DNA degradation appears to be an important means of controlling HPV DNA levels in some cases, but the underlying mechanisms remain poorly understood. These findings may prove useful not only for understanding viral DNA persistence but only in devising future antiviral strategies.

Activation of NF-κB by human papillomavirus 16 E1 limits E1-dependent viral replication through degradation of E1

NF-κB is a family of transcription factors that regulate gene expression involved in many processes, such as the inflammatory response and cancer progression. Little is known about associations of NF-κB with the human papillomavirus (HPV) life cycle. We have developed a tissue culture system to conditionally induce E1-dependent replication of the human papillomavirus 16 (HPV16) genome in human cervical keratinocytes and found that expression of HPV16 E1, a viral helicase, results in reduction of IκBα and subsequent activation of NF-κB in a manner dependent on helicase activity. Exogenous expression of a degradation-resistant mutant of IκBα, which inhibits the activation of NF-κB, enhanced E1-dependent replication of the viral genome. Wortmannin, a broad inhibitor of phosphoinositide 3-kinases (PI3Ks), and, to a lesser extent, VE-822, an ATR kinase inhibitor, but not KU55933, an ATM kinase inhibitor, suppressed the activation of NF-κB and augmented E1-dependent replication of the HPV16 genome. Interestingly, the enhancement of E1-dependent replication of the viral genome was associated with increased stability of E1 in the presence of wortmannin as well as the IκBα mutant. Collectively, we propose that expression of E1 induces NF-κB activation at least in part through the ATR-dependent DNA damage response and that NF-κB in turn limits E1-dependent replication of HPV16 through degradation of E1, so that E1 and NF-κB may constitute a negative feedback loop.

IMPORTANCE

A major risk factor in human papillomavirus (HPV)-associated cancers is persistent infection with high-risk HPVs. To eradicate viruses from infected tissue, it is important to understand molecular mechanisms underlying the establishment and maintenance of persistent infection. In this study, we obtained evidence that human papillomavirus 16 (HPV16) E1, a viral DNA helicase essential for amplification of the viral genomes, induces NF-κB activation and that this limits E1-dependent genome replication of HPV16. These results suggest that NF-κB mediates a negative feedback loop to regulate HPV replication and that this feedback loop could be associated with control of the viral copy numbers. We could thus show for the first time that NF-κB activity is involved in the establishment and maintenance of persistent HPV infection.

Immunomodulators in warts: Unexplored or ineffective?

Cutaneous warts are known to be recurrent and often resistant to therapy. Resistant warts may reflect a localized or systemic cell mediated immune (CMI) deficiency to HPV. Many modalities of treatment are in use; most of the provider-administered therapies are destructive and cause scarring, such as cryotherapy, chemical cauterisation, curettage, electrodessication and laser removal. Most patient-applied agents like podophyllotoxin have the risk of application-site reactions and recurrence. Thus immunotherapy is a promising modality which could lead to resolution of warts without any physical changes or scarring and in addition would augment the host response against the causative agent, thereby leading to complete resolution and decreased recurrences. Immunomodulators can be administered systemically, intralesionally or intradermally, and topically. A few agents have been tried and studied extensively such as cimetidine and interferons; others are new on the horizon, such as Echinacea, green tea catechins and quadrivalent HPV vaccine, and their efficacy is yet to be completely established. Though some like levamisole have shown no efficacy as monotherapy and are now used only in combination, other more recent agents require large and long term randomized placebo-controlled trials to clearly establish their efficacy or lack of it. In this review, we focus on the immunomodulators that have been used for the treatment of warts and the studies that have been conducted on them.

Interferon treatment of human keratinocytes harboring extrachromosomal, persistent HPV-16 plasmid genomes induces de novo viral integration

Interferons (IFNs) have been used to treat epithelial lesions caused by human papillomavirus (HPV) persistence. Here, we exposed primary human keratinocytes (HFKs) immortalized by persistently replicating HPV-16 plasmid genomes to increasing levels of IFN-γ. While untreated HFKs retained replicating HPV-16 plasmids for up to 60-120 population doublings, IFN led to rapid HPV-16 plasmid loss. However, treated cultures eventually gave rise to outgrowth of clones harboring integrated HPV-16 genomes expressing viral E6 and E7 oncogenes from chimeric virus-cell mRNAs similar to those in cervical and head and neck cancers. Surprisingly, every HPV-16 integrant that arose after IFN exposure stemmed from an independent integration event into a different cellular gene locus, even within parallel cultures started from small cell inocula and cultured separately for ≥ 25 doublings to permit the rise and expansion of spontaneous integrants. While IFN treatment conferred a growth advantage upon preexisting integrants added to mixed control cultures, our results indicate that IFN exposure directly or indirectly induces HPV-16 integration, rather than only selects preexisting, spontaneous integrants that appear to be much less frequent. We estimate that IFN exposure increased integration rates by ≥ 100-fold. IFN-induced HPV-16 integration involved a wide range of chromosomal loci with less apparent selection for recurrent insertions near genes involved in cancer-related pathways. We conclude that IFNs and other potential treatments targeting high-risk HPV persistence that disrupt viral genome replication may promote increased high-risk HPV integration as a step in cancer progression. Therapies against high-risk HPV persistence thus need to be evaluated for their integration-inducing potential.

Inactivation of p53 rescues the maintenance of high risk HPV DNA genomes deficient in expression of E6

The human papillomavirus DNA genome undergoes three distinct stages of replication: establishment, maintenance and amplification. We show that the HPV16 E6 protein is required for the maintenance of the HPV16 DNA genome as an extrachromosomal, nuclear plasmid in its natural host cell, the human keratinocyte. Based upon mutational analyses, inactivation of p53 by E6, but not necessarily E6-mediated degradation of p53, was found to correlate with the ability of E6 to support maintenance of the HPV16 genome as a nuclear plasmid. Inactivation of p53 with dominant negative p53 rescued the ability of HPV16 E6STOP and E6SAT mutant genomes to replicate as extrachromosomal genomes, though not to the same degree as observed for the HPV16 E6 wild-type (WT) genome. Inactivation of p53 also rescued the ability of HPV18 and HPV31 E6-deficient genomes to be maintained at copy numbers comparable to that of HPV18 and HPV31 E6WT genomes at early passages, though upon further passaging copy numbers for the HPV18 and 31 E6-deficient genomes lessened compared to that of the WT genomes. We conclude that inactivation of p53 is necessary for maintenance of HPV16 and for HPV18 and 31 to replicate at WT copy number, but that additional functions of E6 independent of inactivating p53 must also contribute to the maintenance of these genomes. Together these results suggest that re-activation of p53 may be a possible means for eradicating extrachromosomal HPV16, 18 or 31 genomes in the context of persistent infections.

Human papillomaviruses (HPVs) infect epithelial tissues. HPVs that infect mucosal epithelia cause infectious lesions in the anogenital tract and oral cavity. HPV infections are normally cleared by the immune system; however, in rare cases, infections can persist for years. Persistent infections by certain HPVs place one at a high risk of developing carcinomas of the cervix, other anogenital tissues, and the head/neck region. These HPVs are responsible for over 5% of all human cancers. For an HPV infection to persist, the viral circular genome must be maintained, i.e. replicated and inherited during cell division. In this study we define the mechanism by which the viral gene E6 contributes to the maintenance of the HPV genome. We demonstrate that E6 must inactivate the cellular factor, p53, for the viral genome to be maintained. Significantly, p53, is inactivated in many types of human cancers and because much research has been done on p53, promising new drugs have been identified that can re-activate p53. If such drugs can re-activate the p53 that has been inactivated by E6, then we hypothesize that these drugs could be used to cure patients with persistent HPV infections and thereby reduce their risk of developing HPV associated cancers.

The inhibitory action of P56 on select functions of E1 mediates interferon's effect on human papillomavirus DNA replication

The interferon (IFN)-induced protein P56 inhibits human papillomavirus (HPV) DNA replication by binding to HPV E1, which has several distinct functions in initiating viral DNA replication. Here, we determined that P56 inhibited HPV type 18 (HPV18) E1's DNA helicase activity, E2 binding, and HPV Ori sequence-specific DNA binding but not nonspecific DNA binding. We observed that deletion of a single amino acid, F399, produced an E1 mutant that could not bind P56. This E1 mutant retained its ability to support Ori DNA replication, but this activity was not inhibited by IFN, demonstrating that P56 is the principal executor of the anti-HPV action of IFN.

The role of inflammation in HPV carcinogenesis

The role of inflammation in human papillomavirus (HPV) infection and disease is complex since it involves responses capable of preventing initial infections, clearing those ongoing as well as promoting persistence and progression of associated lesions. Avoiding the immune response has been considered a key aspect of HPV persistence which is the main factor leading to HPV-related neoplasia. HPVs have evolved different ways of targeting immune signaling pathways. Moreover, host inflammatory response may promote lesion progression and affect tumor fate by diverse mechanisms including the direct participation of inflammatory cells. In this review, we discuss the interplay between HPV oncogenic proteins and an array of inflammatory responses that ultimately may lead to cancer.

Interferon for the treatment of genital warts: a systematic review

Background

Interferon has been widely used in the treatment of genital warts for its immunomodulatory, antiproliferative and antiviral properties. Currently, no evidence that interferon improves the complete response rate or reduces the recurrence rate of genital warts has been generally provided. The aim of this review is to assess, from randomized control trials (RCTs), the efficacy and safety of interferon in curing genital warts.

Methods

We searched Cochrane Sexually Transmitted Diseases Group's Trials Register (January, 2009), Cochrane Central Register of Controlled Trials (2009, issue 1), PubMed (1950-2009), EMBASE (1974-2009), Chinese Biomedical Literature Database (CBM) (1975-2009), China National Knowledge Infrastructure (CNKI) (1979-2009), VIP database (1989-2009), as well as reference lists of relevant studies. Two reviewers independently screened searched studies, extracted data and evaluated their methodological qualities. RevMan 4.2.8 software was used for meta-analysis

Results

12 RCTs involving 1445 people were included. Among them, 7 studies demonstrated the complete response rate of locally-used interferon as compared to placebo for treating genital warts. Based on meta-analysis, the rate of Complete response of the two interventions differed significantly (locally-used interferon:44.4%; placebo:16.1%). The difference between the two groups had statistical significance (RR 2.68, 95% CI 1.79 to 4.02, P < 0.00001). 5 studies demonstrated the complete response rate of systemically-used interferon as compared to placebo for treating genital warts. Based on meta-analysis, the rate of Complete response of the two interventions had no perceivable discrepancy (systemically-used interferon:27.4%; placebo:26.4%). The difference between the two groups had no statistical significance (RR1.25, 95% CI 0.80 to 1.95, P > 0.05). 7 studies demonstrated the recurrence rate of interferon as compared to placebo for treating genital warts. Based on meta-analysis, the recurrence rate of the two interventions had no perceivable discrepancy(interferon 21.1%; placebo: 34.2%). The difference between the two groups had no statistical significance (RR0.56, 95% CI 0.27 to 1.18, P > 0.05). However, subgroup analysis showed that HPV-infected patients with locally administered interferon were less likely than those given placebo to relapse, but that no significant difference in relapse rates was observed between systemic and placebo. The reported adverse events of interferon were mostly mild and transient, which could be well tolerated.

Conclusion

Interferon tends to be a fairly well-tolerated form of therapy. According to different routes of administration, locally-used interferon appears to be much more effective than both systemically-used interferon and placebo in either improving the complete response rate or reducing the recurrence rate for the treatment of genital warts.

Human papillomaviruses and the interferon response

Human papillomaviruses (HPV) are small DNA viruses that target stratified keratinocytes for infection. A subset of HPV types infect epithelia in the genital tract and are the causative agents of cervical as well as other anogenital cancers. Interferon treatment of existing genital HPV lesions has had mixed results. While HPV proteins down-regulate the expression of interferon-inducible genes, interferon treatment ultimately induces their high-level transcription after a delay. Cells containing complete HPV genomes that are able to undergo productive replication upon differentiation are sensitive to interferon-induced growth arrest, while cells from high-grade cancers that only express E6 and E7 are resistant. Recent studies indicate this sensitivity is dependent upon the binding of the interferon-inducible factor, p56, to the E1 replication protein. The response to interferon by HPV proteins is complex and results from the action of multiple viral proteins.

Interferon-beta treatment increases human papillomavirus early gene transcription and viral plasmid genome replication by activating interferon regulatory factor (IRF)-1

Interferons (IFNs) have been used to treat mucosal lesions caused by human papillomavirus (HPV) infection, such as intraepithelial precursor lesions to cancer of the uterine cervix, genital warts or recurrent respiratory papillomatosis, to potentially reduce or eliminate replicating HPV plasmid genomes. Mucosal HPVs have evolved mechanisms that impede IFN-β synthesis and downregulate genes induced by IFN. Here we show that these HPV types directly subvert a cellular transcriptional response to IFN-β as a potential boost in infection. Treatment with low levels of human IFN-β induced initial amplification of HPV-16 and HPV-11 plasmid genomes and increased HPV-16 or HPV-31 DNA copy numbers up to 6-fold in HPV-immortalized keratinocytes. IFN treatment also increased early gene transcription from the major early gene promoters in HPV-16, HPV-31 and HPV-11. Furthermore, mutagenesis of the viral genomes and ectopic interferon regulatory factor (IRF) expression in transfection experiments using IRF-1 ^−/− , IRF-2 ^−/− and dual knockout cell lines determined that these responses are due to the activation of IRF-1 interaction with a conserved interferon response element demonstrated in several mucosal HPV early gene promoters. Our results provide a molecular explanation for the varying clinical outcomes of IFN therapy of papillomatoses and define an assay for the modulation of the HPV gene program by IFNs as well as other cytokines and signaling molecules in infection and therapy.

Cellular factors are required to activate bovine papillomavirus-1 early gene transcription and to establish viral plasmid persistence but are not required for cellular transformation

Transcription from the major upstream early gene promoter, P89, of bovine papillomavirus (BPV)-1 is detectable in transfected cells lacking viral gene products yet also responds to viral E2 proteins. In contrast to human papillomaviruses (HPVs), the BPV upstream regulatory region (URR) functions as a transcriptional enhancer in epithelial cells and fibroblasts of bovine, murine or human origin. Mutations of Sp1 and/or two novel transcriptional enhancer factor (TEF)-1 sites within the 5' URR of the intact BPV-1 genome dramatically reduced P89-initiated mRNA levels, leading to decreased BPV-1 plasmid amplification and inefficient formation of transformed cell foci. However, cell lines transformed with wt or mutant BPV-1 genomes contained similar levels of unintegrated BPV-1 DNA, P89 mRNA and E2-dependent transactivation. We conclude that cellular factors necessary for activating viral early gene transcription, establishment of viral plasmid replication and cell immortalization are not required during the maintenance phase of BPV-1 infection.

Interferon-inducible protein, P56, inhibits HPV DNA replication by binding to the viral protein E1

Type I interferon (IFN) inhibits, by an unknown mechanism, the replication of human papillomaviruses (HPV), which are major human pathogens, Here, we present evidence that P56 (a protein), the expression of which is strongly induced by IFN, double-stranded RNA and viruses, mediates the anti-HPV effect of IFN. Ectopic expression of P56 inhibited HPV DNA replication and its ablation in IFN-treated cells alleviated the inhibitory effect of IFN on HPV DNA replication. Protein-protein interaction and mutational analyses established that the antiviral effect of P56 was mediated by its direct interaction with the DNA replication origin-binding protein E1 of several strains of HPV, through the tetratricopeptide repeat 2 in the N-terminal region of P56 and the C-terminal region of E1. In vivo, the interaction with P56, a cytoplasmic protein, caused translocation of E1 from the nucleus to the cytoplasm. In vitro, recombinant P56, or a small fragment derived from it, inhibited the DNA helicase activity of E1 and E1-mediated HPV DNA replication. These observations delineate the molecular mechanism of IFN's antiviral action against HPV.

Papillomaviruses and interferon

Papillomaviruses are infectious agents which cause benign tumours, or warts, of cutaneous, uterine cervical and laryngeal epithelia. These infections are very common, yet no uniformly effective therapy exists. Current treatments do not selectively inhibit viral processes but destroy the infected epithelial cells. Since interferons have antiviral effects in vivo and in vitro, it was hypothesized that they might be useful for treating papillomavirus-induced conditions. Interferons have now been demonstrated to be effective in several forms of papillomavirus infection. In vitro, chronic treatment of bovine papillomavirus-transformed cells led to the loss of the papillomavirus genomes and return of the cells to a normal morphology. In humans, interferons have been used for treating laryngeal papillomatosis, cutaneous and anogenital warts and epidermodysplasia verruciformis. Partial and total remissions have been achieved with both intralesional and systemic administration. Ongoing studies aim to identify which conditions are most responsive, the optimal dosage and regimen and the most effective class of interferon. The mechanisms by which these responses occur are unknown, but are thought to depend on interferon inducing specific cellular proteins.

Organization and expression of the genome of bovine papillomavirus type 1

The viral mRNAs present in C127 cells transformed by bovine papillomavirus type 1 (BPV-1) have been mapped by a variety of techniques, including S1 nuclease analysis, Northern blot analysis, primer extension and electron microscopic heteroduplex analysis. The results reveal a very complex mRNA pattern, comprising at least five types of spliced cytoplasmic mRNAs. Both unspliced and partially processed nuclear RNA species have also been identified. The transforming region of BPV-1 contains several promoter regions. A major cap site is located at coordinate 1 and another putative cap site at coordinate 31. A third candidate cap site maps around coordinate 39.

Selection of cervical keratinocytes containing integrated HPV16 associates with episome loss and an endogenous antiviral response

Integration of high-risk human papillomavirus (HRHPV) into the host genome is a key event in cervical neoplastic progression. Integration is associated with deregulated expression of the viral oncogenes E6 and E7 and acquisition of a selective growth advantage for cells containing integrants. Overexpression of the viral transcriptional regulator E2 from heterologous promoters has an inhibitory effect on transcription from integrated HRHPV. Therefore, we hypothesized that loss of E2-expressing episomes from cells in which integration had previously occurred would be required for such cells to gain a growth advantage. Using the unique W12 model of cervical squamous carcinogenesis, we show that cells containing integrated HPV16 reproducibly emerged during long-term culture when there had been a rapid fall in episome numbers. During the period of emergence, it is possible to isolate single-cell clones containing an intracellular mixture of the integrant being selected and episomes at reduced load. The lower level of E2 expression seen in such cells is associated with partial inhibition of transcription from the HPV16 integrant. Full deregulation is not observed until complete loss of E2-expressing episomes occurs. Microarray analysis showed that episome loss was closely associated with endogenous activation of antiviral response genes that are also inducible by the type I IFN pathway. Taken together, our results indicate that episome loss, associated with induction of antiviral response genes, is a key event in the spontaneous selection of cervical keratinocytes containing integrated HPV16. We conclude that cervical carcinogenesis requires not only HRHPV integration, but also loss of inhibitory episomes.

Inhibition of E2 binding to Brd4 enhances viral genome loss and phenotypic reversion of bovine papillomavirus-transformed cells

The bovine papillomavirus E2 protein tethers the viral genomes to mitotic chromosomes in dividing cells through binding to the C-terminal domain (CTD) of Brd4. Expression of the Brd4-CTD competes the binding of E2 to endogenous Brd4 in cells. Here we extend our previous study that identified Brd4 as the E2 mitotic chromosome receptor to show that Brd4-CTD expression released the viral DNA from mitotic chromosomes in BPV-1 transformed cells. Furthermore, stable expression of Brd4-CTD enhanced the frequency of morphological reversion of BPV-1 transformed C127 cells resulting in the complete elimination of the viral DNA in the resulting flat revertants.

Papillomavirus virus-like particles induce cytokines characteristic of innate immune responses in plasmacytoid dendritic cells

Human papillomavirus (HPV) virus-like particles (VLP) are being extensively tested as vaccines for the prevention of HPV-associated cervical cancer. Dendritic cells (DC) acquire and present antigens, initiating innate and adaptive immune responses. It has been shown previously that DC of the myeloid lineage are capable of generating adaptive immune responses to HPV VLP in vitro. However, the capacity of plasmacytoid DC (pDC) to acquire HPV VLP and the nature of the immune response generated have not been reported. In this study we found that freshly isolated as well as CpG-matured pDC bind papillomavirus VLP and that internalization occurs preferentially in the immature pDC. In contrast to myeloid DC, pDC did not undergo phenotypic maturation upon exposure to HPV16 VLP. However, HPV16 VLP induced pDC to secrete of IFN-alpha and IL-6, both cytokines that play a role in the generation of antibody responses, as well as TNFalpha and IL-8. Given that VLP do not contain viral nucleic acids, these results indicate that viral capsids alone may be capable of inducing cytokine production by pDC. Finally, CpG-activated pDC, but not pDC exposed to HPV16 VLP, activated lymphocytes to secrete IL-10 and low levels of IFN-gamma. Together these findings suggest a possible immunogenic effect of pDC in the setting of VLP vaccination.

Long-term effect of interferon on keratinocytes that maintain human papillomavirus type 31

The long-term effects of interferon treatment on cell lines that maintain human papillomavirus type 31 (HPV-31) episomes have been examined. High doses and prolonged interferon treatment resulted in growth arrest of HPV-positive cells, with a high percentage of cells undergoing apoptosis. These effects were not seen with interferon treatment of either normal human keratinocytes or cells derived from HPV-negative squamous carcinomas, which exhibited only slight decreases in their rates of growth. Within 2 weeks of the initiation of treatment, a population of HPV-31-positive cells that were resistant to interferon appeared consistently and reproducibly. The resistant cells had growth and morphological characteristics similar to those of untreated cells. Long-term interferon treatment of HPV-positive cells also resulted in a reduction in HPV episome levels but did not significantly decrease the number of integrated copies of HPV. Cells that maintained HPV genomes lacking E5 were sensitive to interferon, while cells expressing only the E6/E7 genes were resistant. In contrast, cells that expressed E2 from a tetracycline-inducible promoter were found to be significantly more sensitive to interferon treatment than parental cells. This suggests that at least a portion of the sensitivity to interferon could be mediated through the E2 protein. These studies indicate that cells maintaining HPV episomes are highly sensitive to interferon treatment but that resistant populations arise quickly.

Human papillomavirus infections: epidemiology, pathogenesis, and therapy

BACKGROUND

Human papillomaviruses (HPV) are common human pathogens and are classified into more than 80 different types. These viruses produce benign warts in many cases and aggressive squamous cell carcinomas in other cases.

OBJECTIVE

The goal of this review is to update the reader on the epidemiology, pathogenesis, and therapy of HPV infections. Nonanogenital warts are transmitted by skin-to-skin contact while anogenital warts are usually transmitted sexually. Both types of warts produce much morbidity but rarely undergo malignant transformation. They are commonly treated with surgical or cytodestructive therapy, but immunomodulatory agents, such as imiquimod, have been proven to be very effective in anogenital warts and are being evaluated in nonanogenital warts. Other types of HPV have marked oncogenic potential such that over 99% of all cervical cancers and over 50% of other anogenital cancers are due to infection with oncogenic HPV. Many cofactors, such as cigarette smoking, genetics, and helper viruses, have potential roles in HPV oncogenesis, but their relative contributions are poorly understood. Other control measures for warts and HPV-associated cancers are under study, but the greatest future potential may be from the development of prophylactic and therapeutic vaccines.

CONCLUSIONS

Infection with HPV is very prevalent as are the clinical manifestations of this family of pathogens. Improved therapies for warts (e.g., imiquimod) have recently become available. Vaccines for HPV offer hope for future interventions for warts as well as for prevention of anogenital malignancies.

Impaired angiogenic balance and suppression of tumorigenicity in HeLa cells chronically exposed to interferon-alpha

We have previously reported that IFNalpha-chronic treatment for 41 days induced a partial phenotype reversion on HeLa cells along with a down-regulation of HPV18 mRNA levels. However, tumorigenicity of these cells in nude mice was unchanged. Interestingly, after 1 year of IFNalpha-chronic exposition, HeLa cells failed to induce s.c. tumors when injected into nude mice. In such experimental conditions both HPV18 DNA integration pattern and viral DNA copy number present in HeLa cells remained intact in the nontumorigenic phenotype cells. As result of the treatment with IFNalpha, HeLa cells rendered more resistant to lysis mediated by activated natural killer cells in vitro. Furthermore, IFNalpha-chronic treatment was able to induce VEGF and decrease bFGF mRNA expression, suggesting a potential effect on the angiogenic behavior of these tumoral cells. Thus, long-term treatment of HeLa cells with IFNalpha can accomplish a reversion of the malignant phenotype by a sequential multistep mechanism, in which the antiangiogenic effect of IFNalpha could be one of the contributing events.

Human papillomavirus infections: epidemiology, pathogenesis, and host immune response

Human papillomaviruses (HPVs) are ubiquitous and often cause lesions on the skin that come to the attention of the dermatologist. Skin lesions, or warts, often occur on the hands or soles of the feet and can cause embarrassment or discomfort. Genital HPV infections are transmitted by sexual contact. Infections associated with some HPV types have a high risk of progressing to carcinoma. This review discusses the molecular biology and genetics of human papillomaviruses and provides an overview of the virology, pathology, clinical manifestations, and host immune response to infection.

A novel drug screening assay for papillomavirus specific antiviral activity

Discovery and development of human papillomavirus (HPV) specific antiviral agents have been hampered by the lack of an in vitro assay permissive to HPV replication. An experimental assay system for monitoring HPV-11 DNA replication has been optimized for use as a papillomavirus antiviral drug screening tool. Cloned HPV DNA was introduced into SCC-4 cells by electroporation and viral DNA replication monitored by Southern blot. Kinetic studies demonstrated an increased HPV genome copy number with time. Viral DNA replicated as episomal, unit length genome and remained episomal after multiple passages. These data suggested the basis for an in vitro replication assay for evaluating the antiviral activity of potential chemotherapeutic agents directly on HPV. This model was used to investigate antiviral activities of current anti-HPV therapies such as 5-fluorouracil (5-FU) and alpha-interferon (alpha-IFN) and potential therapies such as sodium butyrate, 5-bromo-20-deoxyuridine (BrdU) and antisense oligonucleotides. HPV- 11 replication is significantly inhibited by BrdU and sodium butyrate; however 5-FU and alpha-IFN did not give consistent dose response results. Finally, ISIS 2105, a 20-mer phosphorothioate antisense oligonucleotide, which targets HPV-11 E2 gene product, showed potent antiviral activity in this assay with an IC50 of approximately 70 nM.

Modulation of human papillomavirus type 16 mRNA in cervical invasive carcinoma patients by interferon-alpha therapy

Mechanisms by which interferon produces papilloma regression remain largely unknown. We analyzed biopsies from three cervical invasive carcinoma patients treated with interferon-alpha (IFN-alpha) administered both topically and i.m. for 15 days. All specimens contained human papillomavirus (HPV-16) DNA as determined by polymerase chain reaction using specific HPV-16 E7 primers. Interestingly, in two patients. HPV-16 mRNA expression was reduced (44% and 67%, respectively) after IFN treatment. Upregulation of 2-5 A synthetase and PKR mRNA levels were indicative of the IFN effect. A larger study should be initiated to see whether IFN-alpha modulates the HPV-16 mRNA levels in tumor biopsies from cervical carcinoma patients.

Randomised double-blind trial of recombinant interferon-beta for condyloma acuminatum

OBJECTIVE

To evaluate the safety and efficacy of two intralesional doses of recombinant human interferon-beta (r-hIFN-beta: Rebif, Ares Serono), given 3 times a week for 3 weeks, in the treatment of condyloma acuminatum.

DESIGN

A randomised, double-blind, within-patient, placebo-controlled study.

SUBJECTS

25 patients (24 males, 1 female) with a history of condyloma acuminatum. Twenty had failed previous treatment for condyloma acuminatum. In each patient, 3 distinct lesions were selected for treatment. Each selected lesion was randomly assigned to receive intralesionally one of the following: r-hIFN-beta 33,000 IU/day, r-hIFN-beta 1 x 10(6) IU/day, or matching placebo.

SETTING

Institut Alfred Fournier, Paris, France.

OUTCOME MEASURES

Response was evaluated colposcopically at the end of treatment (day 22) and 5 weeks later (month 2). Complete response (CR) was defined as disappearance of the treated lesion. Partial response (PR) was defined as at least a 50% reduction in size, but not disappearance of the treated lesion.

RESULTS

The higher dose of 1 x 10(6) IU achieved significantly more complete and partial remissions than placebo, both by the end of treatment, and 5 weeks later.

CONCLUSIONS

r-hIFN-beta appears to be safe and effective when administered intralesionally to patients with condyloma acuminatum. Most of the treated patients had failed previous treatments and were therefore a resistant population.

Adjuvant interferon for anal condyloma. A prospective, randomized trial

PURPOSE

The aim of this study was to determine whether interferon combined with surgical excision and fulguration could reduce the unacceptably high rate of recurrence of anal condyloma seen after surgical extirpation.

METHODS

Forty-three patients with anal condyloma were prospectively randomized into two groups. Group I (n = 25) patients underwent surgical excision and fulguration immediately followed by an injection of 500,000 IU (0.1 ml) of interferon alfa-n3 into each quadrant of the anal canal. Group II (n = 18) patients underwent surgical excision and fulguration but then received four injections (0.1 ml) of saline into each quadrant of the anal canal.

RESULTS

After a mean follow-up of 3.8 months, 10 of 43 (23 percent) patients developed recurrent anal condyloma. Only 3 of 25 (12 percent) interferon-treated patients had recurrences vs. 7 recurrences in 18 (39 percent) saline-treated patients (P = 0.046). Interferon was particularly effective in reducing recurrences in patients whose condylomata were present for more than six months (P = 0.04) and those condylomata that contained human papillomavirus DNA subtype 6/11 (P = 0.05).

CONCLUSION

Adjuvant interferon treatment can reduce the high recurrence rate of anal condyloma seen after surgical extirpation.

Double-blind, randomized clinical trial on the effect of interferon-beta in the treatment of condylomata acuminata

A randomized, double-blind, placebo-controlled trial was conducted to assess interferon-beta efficacy and safety in the treatment of anogenital condylomatous lesions. One hundred patients received a daily intramuscular injection of either interferon-beta (IFN-beta) (2 MIU/day) or placebo for 10 days. Of 94 evaluable patients, the complete response rate observed 8 weeks after treatment was significantly higher in the group receiving IFN-beta, as compared to the placebo-treated group (51% vs 28.9%, P < 0.05). After one year, 24 patients (100%) out of 24 complete responders to IFN-beta who attended for follow-up remained free of lesions. Twelve of 13 patients with complete response to placebo (92.3%) remained free of lesions after one year. Side effects were mild and no significant analytical changes were observed. In conclusion, interferon-beta is an effective and safe treatment for long-term eradication of anogenital condylomatous lesions.

Partial phenotypic reversion of HeLa cells by long-term interferon-alpha treatment

Human papillomaviruses (HPV) are associated with malignant cervical neoplasia. Several HPV-related diseases have been shown to be sensitive to interferon (IFN) treatment. HeLa cells contain and express the HPV type 18 genome and were used as a model for the evaluation of the viral expression regulation and the effect on the malignant phenotype during IFN treatment. Cells were treated continuously with 200 IU/ml IFN-alpha 2b or natural leukocyte INF-alpha for six passages (42 days). Some IFN-induced changes were observed: decrease of HPV-18 mRNA expression, changes of cell morphology, and reduction of clonogenicity in soft agar. Tumorigenicity in nude mice was not modified. Other targets of the IFN system were analyzed, and an increase of the 2',5'-oligoadenylate synthetase mRNA level and a down-regulation of type I IFN receptor were found. These results demonstrate that long-term IFN-alpha treatment induces a partial phenotypic reversion of HeLa cells to a more differentiated stage were down-regulation of HPV-18 expression could play a central role. It therefore confirms that the IFN-alpha treatment may be therapeutically useful in cervix cancer produced by HPV-18.

Inhibition of growth, transformation, and expression of human papillomavirus type 16 E7 in human keratinocytes by alpha interferons

We used a model system of normal human keratinocytes (HKc) and HKc immortalized with human papillomavirus type 16 DNA (HKc/HPV16) to investigate the effects of alpha interferons (IFN-alpha) on the growth of HPV16-immortalized human epithelial cells, on HPV16-mediated immortalization of normal HKc, and on HPV16 gene expression. Normal HKc and HKc/HPV16 were treated with several recombinant human IFN-alpha subtypes (IFN-alpha B, IFN-alpha D, and IFN-alpha B/D). These IFN-alpha subtypes inhibited proliferation of both normal HKc and HKc/HPV16 in a dose-dependent fashion; however, although 1,000 to 10,000 U of IFN-alpha per ml were required to inhibit growth of normal HKc, HKc/HPV16 were substantially growth inhibited by 100 U/ml. In addition, 100 U of IFN-alpha B/D per ml inhibited transformation of normal HKc by HPV16 DNA. Northern (RNA) blot analysis showed no effect of IFN-alpha on the mRNA levels of the HPV16 E6 and E7 open reading frames. However, immunofluorescence studies of the HPV16 E6 and E7 proteins with anti-E6 and anti-E7 monoclonal antibodies showed significant inhibition of E7 protein expression in cells treated with IFN-alpha, whereas E6 protein expression was not altered. The inhibition of E7 protein expression in cells treated with IFN-alpha was further confirmed by Western immunoblot analysis. These results suggest that IFN-alpha may inhibit HPV16-mediated transformation of HKc and proliferation of HKc/HPV16 through an inhibition of HPV16 E7 protein expression.

Superficial laser vulvectomy

Skillful laser ablation can remove any volume of human papillomavirus-associated vulvar disease but cannot prevent reactivation of the surrounding latent viral reservoir during postoperative healing. Conversely, interferon and 5-fluorouracil are relatively ineffective as primary therapies in clearing bulky lesions. In this study of 71 assessable patients, topical 5-fluorouracil and systemic interferon injections were used postoperatively. Success rates within the adjuvant 5-fluorouracil and laser alone arms were essentially the same (9 of 18 vs 8 of 20). In contrast, outcome in the interferon group was significantly better than that for the other two arms combined (27 of 33 [82%] vs 17 of 38 [45%]; chi 2 10.31; p less than 0.002). Moreover, 18 of 21 failures (86%) in the first two arms and 3 of 6 failures (50%) in the interferon arm were "rescued" from the need for a second laser surgical procedure by crossover to either the 1 or 3 MIU interferon regimen. Results from this open-label, randomized clinical trial suggest that even a relatively low dose of recombinant interferon, used in combination with effective surgical debulking, can markedly reduce the risk of postoperative recurrence.

A bovine papillomavirus E1-related protein binds specifically to bovine papillomavirus DNA

The E1 open reading frame of bovine papillomavirus (BPV) was expressed as a RecA-E1 fusion protein in Escherichia coli. The bacterially expressed RecA-E1 protein exhibited sequence-specific DNA binding activity; strong binding to the region from nucleotides 7819 to 93 on the BPV genome (designated region A) and weak binding to the adjacent region from nucleotides 7457 to 7818 (region B) were observed. The interaction between the BPV-derived RecA-E1 protein and region A appeared to be highly specific for BPV DNA, as no comparable binding was detected with heterologous papillomavirus DNAs. Binding to region A was eliminated by digestion of region A at the unique HpaI site, which suggests that the RecA-E1 binding site(s) was at or near the HpaI recognition sequence. Binding to region B but not region A was observed when nuclear extracts from ID13 cells were used as a source of E1 proteins. The absence of region A binding by ID13 extracts may reflect a negative regulation of E1 DNA binding activity.

Efficacy of interferons on bowenoid papulosis and other precancerous lesions

Preliminary results of an open randomized trial of recombinant interferon gamma in patients suffering from bowenoid papulosis are described. Recombinant interferon gamma was given subcutaneously to 12 patients at a daily dose of 4 X 10(6) I.U. by injection. Four patients each were assigned to one of three treatment groups consisting of continuous therapy (group A) with three subcutaneous injections per week for 13 weeks; intermittent block therapy (group B) with four six-week cycles consisting of five injections on days 1, 3, 5, 7, and 9 of each cycle; and intermittent single-dose therapy (group C) with six four-week cycles consisting of only one subcutaneous injection on day one of each cycle. At the twenty-sixth week after onset of therapy, complete responses were seen in three of four patients of treatment group A, whereas in the treatment groups B and C only one patient, respectively, responded partially. These results suggest that in contrast to condylomata acuminata bowenoid papulosis lesions respond better to continuous than to intermittent interferon gamma injections.

Human papillomavirus infections of the genital tract

Infection of the genital tract by HPV is a sexually transmitted disease of increasing prevalence. The association of HPV infection with genital tract malignancies is of great concern, and further studies are needed to clarify this association. Few investigators believe at this time that proof of a direct causative role exists for HPV in these cancers, but indirect evidence of such a role is abundant. There are many clinical forms of HPV infection of the genital tract, and few clinicians can easily recognize them all. Treatment of condyloma acuminatum is difficult and frustrating. Cryotherapy with liquid nitrogen is the safest and most effective therapy for most forms of condyloma acuminatum. Recurrence of condyloma acuminatum is common with all presently used forms of therapy, probably owing to latent HPV infection in normal-appearing skin. No form of treatment is ideal for all forms of condyloma acuminatum, but without continued efforts to find better therapeutic modalities and preventative measures, the epidemic of genital HPV infection will continue unchecked.

Antigen presentation and T-cell activation in epidermodysplasia verruciformis

Aberrant immune responses may play a role in the susceptibility of patients with epidermodysplasia verruciformis to human papilloma virus (HPV). We examined the stimulatory capacity of antigen-presenting cells from HPV-infected skin and peripheral blood T-cell responses of patients with epidermodysplasia verruciformis. The percentage of Langerhans cells in relation to total epidermal cells in suspension was slightly reduced in HPV-infected lesions, relative to apparently clinically uninfected epidermis. In addition, the morphologic appearance of Langerhans cells was altered in lesional epidermal sheets. Despite these abnormalities, Langerhans cells were functionally intact in their capacity to present alloantigens to T cells and, in fact, the epidermis of HPV-infected lesions demonstrated enhanced antigen-presenting activity in three of four patients tested. The antigen-presenting activity was entirely abrogated by removal of Langerhans cells and was not associated with increased activity of cytokines with stimulatory activity for the thymocyte co-stimulation assay. Although epidermodysplasia verruciformis T cells were unresponsive to autologous HPV-infected epidermis, they responded well to mitogens, allogeneic mononuclear leukocytes, and allogeneic epidermal cells. Epidermodysplasia verruciformis T cells were inhibited in their capacity to respond to allogeneic epidermal cells when they were simultaneously exposed to autologous epidermal cells from HPV-infected lesional epidermis, but not to normal-appearing epidermis. Thus, although Langerhans cell activity is intact in epidermodysplasia verruciformis, these individuals fail to respond to autologous papillomas, which may, at least in part, be explained by an interaction between papillomal epidermal cells and autologous T cells that results in an inhibited response.

Intralesional interferon alfa-2b for the treatment of genital warts

A randomized, double-blind, placebo-controlled study has been conducted, and intralesional interferon alfa-2b was tested in the treatment of genital warts. This study design was to give 1 million units interferon alfa-2b intralesionally into the base of each of five external genital warts per patient, on a Monday-Wednesday-Friday treatment schedule for 3 weeks (total of nine injections). Forty-two patients were entered (20 randomized to receive interferon and 22 placebo injections). There were 43.8% of patients on the interferon treatment arm of the double-blind portion of the study who had complete disappearance of all warts, with an additional 25% of patients showing greater than 50% shrinkage of visible warts. On the placebo arm 14.3% showed a complete response, with an additional 14.3% showing greater than 50% shrinkage. This difference between interferon and placebo treatment was statistically significant (p less than 0.03). We conclude that intralesional interferon alfa-2b has significant activity in the treatment of genital warts.

Human papillomaviruses and carcinomas

The recognition of multiple types of human papillomaviruses has resulted in remarkable progress in the detection of persisting viral nucleic acid sequences in carcinomas. The consistent transcription in tumors of two early open reading frames, E6 and E7, with few exceptions (Lehn et al., 1985), indicates a role for the products of these genes in the induction and/or maintenance of the transformed state. A number of studies have shown that in vitro transformation can be achieved by transfection of E6/E7 DNA, and proteins encoded by these DNA sequences can be demonstrated in primary human keratinocytes immortalized by this DNA (Kaur et al., 1989). Mutagenesis experiments are needed to determine the absolute requirement for and function of these genes in transformation. A preferential association of some types with benign lesions while others may be frequently found in malignant tumors has been observed. HPV types 5 and 8 in epidermodysplasia verruciformis patients and types 16, 18, 31, 33, etc. in genital lesions are most frequently associated with progression to malignancy, whereas other types, such as HPV-6,-10, -11, and -20, are regularly identified in benign warts. Such distinctions are not absolute but provide the initial steps toward establishing a causal role for some human papillomaviruses in carcinomas. The need for well-designed epidemiological studies in concert with optimum molecular and serologic evaluations is evident (Armstrong et al., 1988). The data from human and animal studies indicate that papillomaviruses contribute significantly to the development of many, if not all, carcinomas, but we do not yet have a clear understanding of the importance of other interacting viral, chemical, or cellular factors. The application of gene cloning and non-stringent hybridization (Law et al., 1979) has provided us with an apparently ever-increasing catalog of human papillomaviruses. More effort is now required to establish their prevalence, the natural history of infection, and the mechanism of neoplastic transformation.