The human papillomavirus E7 protein is able to inhibit the antiviral and anti-growth functions of interferon-alpha

Preimmunization with Listeria-vectored cervical cancer vaccine candidate strains can establish specific T-cell immune memory and prevent tumorigenesis

BACKGROUND

Although HPV prophylactic vaccines can provide effective immune protection against high-risk HPV infection, studies have shown that the protective effect provided by them would decrease with the increased age of vaccination, and they are not recommended for those who are not in the appropriate age range for vaccination. Therefore, in those people who are not suitable for HPV prophylactic vaccines, it is worth considering establishing memory T-cell immunity to provide long-term immune surveillance and generate a rapid response against lesional cells to prevent tumorigenesis.

METHODS

In this study, healthy mice were preimmunized with LM∆E6E7 and LI∆E6E7, the two Listeria-vectored cervical cancer vaccine candidate strains constructed previously by our laboratory, and then inoculated with tumor cells 40 d later.

RESULTS

The results showed that preimmunization with LM∆E6E7 and LI∆E6E7 could establish protective memory T-cell immunity against tumor antigens in mice, which effectively eliminate tumor cells. 60% of mice preimmunized with vaccines did not develop tumors, and for the remaining mice, tumor growth was significantly inhibited. We found that preimmunization with vaccines may exert antitumor effects by promoting the enrichment of T cells at tumor site to exert specific immune responses, as well as inhibiting intratumoral angiogenesis and cell proliferation.

CONCLUSION

Altogether, this study suggests that preimmunization with LM∆E6E7 and LI∆E6E7 can establish memory T-cell immunity against tumor antigens in vivo, which provides a viable plan for preventing tumorigenesis and inhibiting tumor progression.

Immunotherapy that leverages HPV-specific immune responses for precancer lesions of cervical cancer

Cervical cancer and its precursor lesion, cervical intraepithelial neoplasia (CIN), are caused by high-risk human papillomavirus (HPV) viral infection and are highly susceptible to host immunity targeting of HPV viral proteins, which include both foreign antigens and cancer antigens expressed by tumors. Immunotherapy that induces Th1 immunoreactivity against viral proteins is expected to take advantage of this immunological regression mechanism. However, although cancer immunotherapies for cervical cancer and CIN have been developed over the past several decades, none have been commercialized. Most of these immunotherapies target the viral cancer proteins E6 and E7, which are generally the same. The reasons for the underdevelopment of HPV-targeted immunotherapy differ depending on whether the target is invasive cancer or CIN. We here summarize the developmental history of cancer immunotherapy for CIN and discuss strategies for solving the problems that led to this underdevelopment. We note that CIN is a mucosal lesion and propose that inducing mucosal immunity may be the key.

Deciphering the role of HPV-mediated metabolic regulation in shaping the tumor microenvironment and its implications for immunotherapy in HNSCC

Head and neck squamous cell carcinoma (HNSCC), as a complex and variable malignancy, poses a significant threat to human health. Since the intricate association between HPV and HNSCC emerged, its role within the TME has garnered extensive attention. HPV+HNSCC exhibits distinct immunological characteristics within the TME, intricately intertwined with mechanisms of immune evasion. HPV employs multifaceted pathways to intervene in metabolic regulation within the TME, exerting influence over immune cell functionality and neoplastic cell genesis. Furthermore, the heightened immune reactivity exhibited by HPV+HNSCC within the TME augments responses to immune interventions such as immune checkpoint inhibitors. Therefore, amidst the current limitations of therapeutic approaches, immunotherapy stands as a promising strategy to overcome the conventional confines of treating HNSCC. This article comprehensively outlines the impact of HPV on the inception and progression of HNSCC while discussing the amalgamation of metabolic regulation within the TME and immunotherapeutic strategies. By intervening in the reciprocal interactions between HPV and HNSCC within the TME, the potential to modulate the efficacy of immune-based treatments becomes evident. Concurrently, a synthesis of pertinent biomarker development is summarized. Such endeavors hold paramount significance for personalized therapeutic approaches and the more effective management of HNSCC patients.

The Interaction of Human Papillomavirus Infection and Prostaglandin E2 Signaling in Carcinogenesis: A Focus on Cervical Cancer Therapeutics

Chronic infection by high-risk human papillomaviruses (HPV) and chronic inflammation are factors associated with the onset and progression of several neoplasias, including cervical cancer. Oncogenic proteins E5, E6, and E7 from HPV are the main drivers of cervical carcinogenesis. In the present article, we review the general mechanisms of HPV-driven cervical carcinogenesis, as well as the involvement of cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) and downstream effectors in this pathology. We also review the evidence on the crosstalk between chronic HPV infection and PGE2 signaling, leading to immune response weakening and cervical cancer development. Finally, the last section updates the current therapeutic and preventive options targeting PGE2-derived inflammation and HPV infection in cervical cancer. These treatments include nonsteroidal anti-inflammatory drugs, prophylactic and therapeutical vaccines, immunomodulators, antivirals, and nanotechnology. Inflammatory signaling pathways are closely related to the carcinogenic nature of the virus, highlighting inflammation as a co-factor for HPV-dependent carcinogenesis. Therefore, blocking inflammatory signaling pathways, modulating immune response against HPV, and targeting the virus represent excellent options for anti-tumoral therapies in cervical cancer.

The Creation of the Suppressive Cancer Microenvironment in Patients with HPV-Positive Cervical Cancer

The development of malignancy is closely connected with the process of cancer microenvironment remodeling. As a malignancy develops, it stimulates the creation of the suppressive microenvironment of the tumor through the presence of cells that express membrane proteins. These proteins are secreted into the cancer microenvironment, where they enable tumor growth. In patients with cancer of the cervix, the development of the disease is also linked to high-risk HPV (hr-HPV) infection. Such infections are common, and most clear spontaneously; however, a small percentage of these infections can persist and progress into precancerous cervical intraepithelial neoplasia and invasive cervical carcinoma. Consequently, it is assumed that the presence of hr-HPV infection alone is not sufficient for the development of cancer. However, chronic HPV infection is associated with the induction of the remodeling of the microenvironment of the epithelium. Furthermore, the local microenvironment is recognized as a cofactor that participates in the persistence of the HPV infection and disease progression. This review presents the selected immune evasion mechanisms responsible for the persistence of HPV infection, beginning with the delay in the virus replication process prior to the maturation of keratinocytes, the shift to the suppressive microenvironment by a change in keratinocyte immunomodulating properties, the alteration of the Th1/Th2 polarization of the immune response in the microenvironment, and, finally, the role of HLA-G antigen expression.

HPV-mediated Cervical Cancer: A Systematic review on Immunological Basis, Molecular Biology and Immune evasion mechanisms

BACKGROUND

Human papillomavirus (HPV), one of the most frequently transmitted viruses globally, causing several malignancies including cervical cancer.

AIM

Owing to their unique pathogenicity HPV viruses can persist in the host organism for a longer duration than other virus types, to complete their lifecycle. During its association with the host, HPV causes various pathological conditions affecting the immune system by evading the host immune- mechanisms leading to the progression of various diseases, including cancer.

METHOD

To date, ~ 150 serotypes were identified, and certain high-risk HPV types are known to be associated with genital warts and cervical cancer. As of now, two prophylactic vaccines are in use for the treatment of HPV infection, however, no effective antiviral drug is available for HPV-associated disease/infections. Numerous clinical and laboratory studies are being investigated to formulate an effective and specific vaccine again HPV infections and associated diseases.

RESULT

As the immunological basis of HPV infection and associated disease progress persist indistinctly, deeper insights on immune evasion mechanism and molecular biology of disease would aid in developing an effective vaccine.

CONCLUSION

Thus this review focuses, aiming a systematic review on the immunological aspects of HPV-associated cervical cancer by uncovering immune evasion strategies adapted by HPV.

Immunohistochemical Detection of Human Papillomavirus 16 E7 Oncoprotein in Cervical Lesions

Almost all cervical cancer is associated with persistent infection of high-risk (hr) human papillomavirus (HPV) like HPV16. The E7 oncoprotein encoded by hrHPV plays a crucial role in carcinogenesis. The present study aimed to establish a reliable protocol of immunohistochemistry stains to detect HPV16 E7 protein in formalin-fixed and paraffin-embedded tissue specimens of various cervical lesions. Firstly, the HPV16 E7 gene was inserted into a prokaryotic expression vector pGEX-4T2. Then the recombinant plasmid pGEX-4T2-(HPV16-E7) was transformed into Escherichia coli JM109. The fusion protein containing a GST tag was purified, and New Zealand white rabbits were immunized to produce the HPV16 E7 polyclonal antibody. The anti-HPV16 E7 antibody was verified by western blotting and immunofluorescence stains, and applied in 182 HPV16 DNA-positive cervical tissue specimens and matched 36 HPV DNA-negative specimens by immunohistochemistry. Furthermore, A positive correlation between HPV16 E7 protein expression and malignancy grade was observed. But there is no relationship between HPV16 E7 protein expression and tumor sizes, tumor differentiation, lymph node metastasis, International Federation of Gynecology and Obstetrics (FIGO) stage, or lymphovascular space invasion in cervical cancer. These findings provide a basis for further research focusing on the role of HPV E7 protein in various HPV-related diseases.

Biology of HPV Mediated Carcinogenesis and Tumor Progression

Human papillomavirus (HPV) is a ubiquitous DNA virus that infects squamous epithelia. Though HPV only encodes 8 genes, it is capable of causing cellular transformation and ultimately cancer in host cells. In this article we review the classification of HPV viruses, their genetic structure and life cycle, viral gene biology, and provide an overview of the role of HPV in cancer. We explain how the viral life cycle can lead to integration of viral DNA into the host genome leading to increased cell cycle progression, decreased apoptosis, altered DNA repair, and chromosomal instability. We describe the multifaceted roles of the canonical oncogenes E6 and E7 in promoting tumorigenesis and the important role of other viral genes in regulating cancer development. We also review how the virus actively suppresses innate and adaptive immunity to evade immune detection and promote a pro-tumorigenic microenvironment. The biology presented here will serve as a foundation to the other chapters in this edition and we hope it will incite enthusiasm for continued research on this fascinating virus that causes significant morbidity and mortality worldwide.

Virus-Driven Carcinogenesis

Cancer arises from the accumulation of genetic and epigenetic alterations. Even in the era of precision oncology, carcinogens contributing to neoplastic process are still an important focus of research. Comprehensive genomic analyses have revealed various combinations of base substitutions, referred to as the mutational signatures, in cancer. Each mutational signature is believed to arise from specific DNA damage and repair processes, including carcinogens. However, as a type of carcinogen, tumor viruses increase the cancer risk by alternative mechanisms, including insertional mutagenesis, viral oncogenes, and immunosuppression. In this review, we summarize virus-driven carcinogenesis to provide a framework for the control of malignant cell proliferation. We first provide a brief overview of oncogenic viruses and describe their implication in virus-related tumors. Next, we describe tumor viruses (HPV, Human papilloma virus; HBV, Hepatitis B virus; HCV, Hepatitis C virus; EBV, Epstein-Barr virus; Kaposi sarcoma herpesvirus; MCV, Merkel cell polyoma virus; HTLV-1, Human T-cell lymphotropic virus, type-1) and tumor virus-related cancers. Lastly, we introduce emerging tumor virus candidates, human cytomegalovirus (CMV), human herpesvirus-6 (HHV-6) and adeno-associated virus-2 (AAV-2). We expect this review to be a hub in a complex network of data for virus-associated carcinogenesis.

Functional Interfaces, Biological Pathways, and Regulations of Interferon-Related DNA Damage Resistance Signature (IRDS) Genes

Interferon (IFN)-related DNA damage resistant signature (IRDS) genes are a subgroup of interferon-stimulated genes (ISGs) found upregulated in different cancer types, which promotes resistance to DNA damaging chemotherapy and radiotherapy. Along with briefly discussing IFNs and signalling in this review, we highlighted how different IRDS genes are affected by viruses. On the contrary, different strategies adopted to suppress a set of IRDS genes (STAT1, IRF7, OAS family, and BST2) to induce (chemo- and radiotherapy) sensitivity were deliberated. Significant biological pathways that comprise these genes were classified, along with their frequently associated genes (IFIT1/3, IFITM1, IRF7, ISG15, MX1/2 and OAS1/3/L). Major upstream regulators from the IRDS genes were identified, and different IFN types regulating these genes were outlined. Functional interfaces of IRDS proteins with DNA/RNA/ATP/GTP/NADP biomolecules featured a well-defined pharmacophore model for STAT1/IRF7-dsDNA and OAS1/OAS3/IFIH1-dsRNA complexes, as well as for the genes binding to GDP or NADP+. The Lys amino acid was found commonly interacting with the ATP phosphate group from OAS1/EIF2AK2/IFIH1 genes. Considering the premise that targeting IRDS genes mediated resistance offers an efficient strategy to resensitize tumour cells and enhances the outcome of anti-cancer treatment, this review can add some novel insights to the field.

The head and neck cancer genome in the era of immunotherapy

The recent success of immunotherapy in head and neck squamous cell carcinoma (HNSCC) has necessitated a new perspective on the cancer genome. Here we review recent advances in the carcinogenesis and molecular genetics of HNSCC with an eye on their implications for cancer immunity. Newer sequencing technologies have recently facilitated dissection of the complex interaction between the HPV virus, tumor, host factors, and the tumor microenvironment (TME) that help shed light on how the immune system interacts with head and neck malignancies.

HPV post-infection microenvironment and cervical cancer

Human papillomavirus (HPV) is the most common sexually transmitted virus worldwide. More than 99% of cervical cancer cases are associated with certain types of HPVs, termed high-risk types. In addition to the well-known transformative properties, HPVs-infected cells actively instruct the local milieu and create a supportive post-infection microenvironment (PIM), which is becoming recognized as a key factor for the viral persistence, propagation, and malignant progression. The PIM is initiated and established via a complex interplay among virus-infected cells, immune cells, and host stroma, as well as their derived components including chemokines, cytokines, extracellular vesicles, and metabolites. In this review, we summarize the current understanding of these key components, characteristics, and effects of the PIM, and highlights the prospect of targeting the PIM as a potential strategy to improve therapeutic outcomes for cervical cancer.

The Interplay between Antiviral Signalling and Carcinogenesis in Human Papillomavirus Infections

Human papillomaviruses (HPV) are the causative agents of the most common sexually transmitted infection worldwide. While infection is generally asymptomatic and can be cleared by the host immune system, when persistence occurs, HPV can become a risk factor for malignant transformation. Progression to cancer is actually an unintended consequence of the complex HPV life cycle. Different antiviral defence mechanisms recognize HPV early in infection, leading to the activation of the innate immune response. However, the virus has evolved several specific strategies to efficiently evade the antiviral immune signalling. Here, we review and discuss the interplay between HPV and the host cell innate immunity. We further highlight the evasion strategies developed by different HPV to escape this cellular response and focus on the correlation with HPV-induced persistence and tumorigenesis.

Increased High-Risk Human Papillomavirus Viral Load Is Associated With Immunosuppressed Microenvironment and Predicts a Worse Long-Term Survival in Cervical Cancer Patients

OBJECTIVES

To evaluate the correlation between tumor-infiltrating lymphocytes (TILs) and the viral load of high-risk human papillomavirus (HR-HPV) in cervical cancer patients.

METHODS

A total of 62 cervical cancer patients were recruited during 1993-1994 and assigned into four groups treated with radiotherapy alone or radiotherapy combined with chemotherapy and/or thermotherapy. Ki67+ tumor cells, CD4+, CD8+, FoxP3+, OX40+ and granzyme B+ TILs were detected by immunohistochemistry. The viral load of HR-HPV in biopsy tissues before therapy was detected by in situ hybridization.

RESULTS

The patients with high HPV viral load showed a significantly lower 15-year survival rate and an advanced International Federation of Gynecology and Obstetrics (FIGO) stage and increased recurrence rate. The distribution of Ki67+ tumor cells, FoxP3+ TILs, and CD8+/FoxP3+ ratio was obviously different between low and high HPV viral load groups. A worse clinical outcome was also implicated with increased HPV viral load tested by Cox regression analysis.

CONCLUSIONS

Patients with increased HR-HPV viral load tend to be resistant to therapy with decreased immune surveillance in the immune microenvironment. Thus, HR-HPV viral load would influence the local immune microenvironment, and then further affect the survival of cervical cancer patients.

Human Papillomavirus 16 E6 and E7 Synergistically Repress Innate Immune Gene Transcription

Human papillomaviruses (HPV) are causative agents in 5% of all cancers, including the majority of anogenital and oropharyngeal cancers. Downregulation of innate immune genes (IIGs) by HPV to promote the viral life cycle is well documented; E6 and E7 are known repressors of these genes. More recently, we demonstrated that E2 could also repress IIGs. These studies have been carried out in cells overexpressing the viral proteins, and to further investigate the role of individual viral proteins in this repression, we introduced stop codons into E6 and/or E7 in the entire HPV16 genome and generated N/Tert-1 cells stably maintaining the HPV16 genomes. We demonstrate that E6 or E7 individually is not sufficient to repress IIG expression in the context of the entire HPV16 genome; both are required for a synergistic repression. The DNA damage response (DDR) is activated by HPV16 irrespective of E6 and E7 expression, presumably due to viral replication; E1 is a known activator of the DDR. In addition, replication stress was apparent in HPV16-positive cells lacking E6 and E7, manifested by attenuated cellular growth and activation of replication stress genes. These studies led us to the following model. Viral replication per se can activate the DDR following infection, and this activation is a known inducer of IIG expression, which may induce cellular senescence. To combat this, E6 and E7 synergistically combine to manipulate the DDR and actively repress innate immune gene expression promoting cellular growth; neither protein by itself is able to do this.IMPORTANCE The role of human papillomavirus 16 (HPV16) in human cancers is well established; however, to date there are no antiviral therapeutics that are available for combatting these cancers. To identify such targets, we must enhance the understanding of the viral life cycle. Innate immune genes (IIGs) are repressed by HPV16, and we have reported that this repression persists through to cancer. Reversal of this repression would boost the immune response to HPV16-positive tumors, an area that is becoming more important given the advances in immunotherapy. This report demonstrates that E6 and E7 synergistically repress IIG expression in the context of the entire HPV16 genome. Removal of either protein activates the expression of IIGs by HPV16. Therefore, gaining a precise understanding of how the viral oncogenes repress IIG expression represents an opportunity to reverse this repression and boost the immune response to HPV16 infections for therapeutic gain.

Decreased local immune response and retained HPV gene expression during chemoradiotherapy are associated with treatment resistance and death from cervical cancer

More than one-third of patients with locally advanced cervical cancer do not respond to chemoradiation therapy (CRT). We aimed to characterize the transcriptional landscape of paired human cervical tumors before and during CRT in order to gain insight into the evolution of treatment response and to elucidate mechanisms of treatment resistance. We prospectively collected cervical tumor biopsies from 115 patients both before and 3 weeks into CRT. RNA-sequencing, Gene Set Enrichment Analysis and HPV gene expression were performed on 20 paired samples that had adequate neoplastic tissue mid-treatment. Tumors from patients with no evidence of disease (NED) at last follow-up had enrichment in pathways related to the immune response both pretreatment and mid-treatment, while tumors from patients dead of disease (DOD) demonstrated enrichment in biosynthetic and mitotic pathways but not in immune-related pathways. Patients DOD had decreased expression of T-cell and cytolytic genes and increased expression of PD-L2 mid-treatment compared to patients NED. Histological and immunohistochemical analysis revealed a decrease in tumor-associated lymphocytes (TAL) during CRT in all patients but tumors from patients DOD had a significantly more pronounced decrease in TALs and CD8+ cells mid-treatment, which was validated in a larger mid-treatment cohort. Finally, patients DOD retained more HPV E6/E7 gene expression during CRT and this was associated with increased expression of genes driving mitosis, which was corroborated in vitro. Our results suggest that decreased local immune response and retained HPV gene expression may be acting together to promote treatment resistance during CRT in patients with cervical cancer.

Papillomavirus Immune Evasion Strategies Target the Infected Cell and the Local Immune System

Persistent infection with human papillomavirus (HPV) initiates ~5% of all human cancers, and particularly cervical and oropharyngeal cancers. HPV vaccines prevent HPV infection, but do not eliminate existing HPV infections. Papillomaviruses induce hyperproliferation of epithelial cells. In this review we discuss how hyperproliferation renders epithelial cells less sensitive to immune attack, and impacts upon the efficiency of the local immune system. These observations have significance for the design of therapeutic HPV cancer immunotherapies.

Current strategies against persistent human papillomavirus infection (Review)

Human papillomavirus (HPV) is the most common sexually transmitted infection, exhibiting a tropism for the epidermis and mucosae. The link between persistent HPV infection and malignancies involving the anogenital tract as well as the head and neck has been well‑established, and it is estimated that HPV‑related cancers involving various anatomical sites account for 4.5% of all human cancers. Current prophylactic vaccines against HPV have enabled the prevention of associated malignancies. However, the sizeable population base of current infection in whom prophylactic vaccines are not applicable, certain high‑risk HPV types not included in vaccines, and the vast susceptible population in developing countries who do not have access to the costly prophylactic vaccines, put forward an imperative need for effective therapies targeting persistent infection. In this article, the life cycle of HPV, the mechanisms facilitating HPV evasion of recognition and clearance by the host immune system, and the promising therapeutic strategies currently under investigation, particularly antiviral drugs and therapeutic vaccines, are reviewed.

Human Papillomavirus 16 E2 Regulates Keratinocyte Gene Expression Relevant to Cancer and the Viral Life Cycle

Human papillomaviruses (HPVs) are causative agents in ano-genital and oropharyngeal cancers. The virus must reprogram host gene expression to promote infection, and E6 and E7 contribute to this via the targeting of cellular transcription factors, including p53 and pRb, respectively. The HPV16 E2 protein regulates host gene expression in U2OS cells, and in this study, we extend these observations into telomerase reverse transcriptase (TERT) immortalized oral keratinocytes (NOKs) that are capable of supporting late stages of the HPV16 life cycle. We observed repression of innate immune genes by E2 that are also repressed by the intact HPV16 genome in NOKs. Transcriptome sequencing (RNA-seq) data identified 167 up- and 395 downregulated genes by E2; there was a highly significant overlap of the E2-regulated genes with those regulated by the intact HPV16 genome in the same cell type. Small interfering RNA (siRNA) targeting of E2 reversed the repression of E2-targeted genes. The ability of E2 to repress innate immune genes was confirmed in an ano-genital immortalized keratinocyte cell line, N/Tert-1. We present the analysis of data from The Cancer Genome Atlas (TCGA) for HPV16-positive and -negative head and neck cancers (HNC) suggesting that E2 plays a role in the regulation of the host genome in cancers. Patients with HPV16-positive HNC with a loss of E2 expression exhibited a worse clinical outcome, and we discuss how this could, at least partially, be related to the loss of E2 host gene regulation.IMPORTANCE Human papillomavirus 16 (HPV16)-positive tumors that retain expression of E2 have a better clinical outcome than those that have lost E2 expression. It has been suggested that this is due to a loss of E2 repression of E6 and E7 expression, but this is not supported by data from tumors where there is not more E6 and E7 expression in the absence of E2. Here we report that E2 regulates host gene expression and place this regulation in the context of the HPV16 life cycle and HPV16-positive head and neck cancers (the majority of which retain E2 expression). We propose that this E2 function may play an important part in the increased response of HPV16-positive cancers to radiation therapy. Therefore, host gene regulation by E2 may be important for promotion of the HPV16 life cycle and also for the response of HPV16-positive tumors to radiation therapy.

Modulation of radiation sensitivity and antitumor immunity by viral pathogenic factors: Implications for radio-immunotherapy

Several DNA viruses including Human Papillomavirus (HPV), Epstein-Barr virus (EBV), and Human cytomegalovirus (HCMV) are mechanistically associated with the development of human cancers (HPV, EBV) and/or modulation of the immune system (HCMV). Moreover, a number of distinct mechanisms have been described regarding the modulation of tumor cell response to ionizing radiation and evasion from the host immune system by viral factors. There is further accumulating interest in the treatment with immune-modulatory therapies such as immune checkpoint inhibitors for malignancies with a viral etiology. Also, patients with HPV-positive tumors have a significantly improved prognosis that is attributable to increased intrinsic radiation sensitivity and may also arise from modulation of a cytotoxic T cell response in the tumor microenvironment (TME). In this review, we will highlight recent advances in the understanding of the biological basis of radiation response mediated by viral pathogenic factors and evasion from and modulation of the immune system by viruses.

Genital warts treatment: Beyond imiquimod

Genital warts are one of the most common sexually transmitted diseases worldwide. The disease is a result of infection with low-risk types of human papillomaviruses, mostly type 6 and 11. Current therapies for genital warts are mainly ablative, or alternatively topical application of imiquimod cream and sinecatechin (polyphenon E) ointment to the warts. However, low patient compliance and high recurrence rate are significant problems for the treatment of genital warts by imiquimod and ablative therapies. We summarise recent literature in this area and propose combining imiquimod with other therapies to increase the efficacy of imiquimod.

The etiologic spectrum of head and neck squamous cell carcinoma in young patients

Head and neck squamous cell carcinoma (HNSCC), accounting for more than 80% in head and neck malignancies, kills thousands of people a year in the world. Despite most of the patients are more than 45, and the occurrences of head and neck cancer shows a decreasing trend; however, horribly, the incidences of the patients under 45 years old is steadily increasing. Hence, it's of vital importance to get more pathogen information about risk factors of HNSCC in children and young adults. This review outlines the etiologic spectrum of HNSCC, especially oral/oropharyngeal squamous cell carcinoma, in patients under 45 years of age.

Immunopathogenesis of HPV-Associated Cancers and Prospects for Immunotherapy

Human papillomavirus (HPV) infection is a causative factor for various cancers of the anogenital region and oropharynx, and is supposed to play an important cofactor role for skin carcinogenesis. Evasion from immunosurveillance favors viral persistence. However, there is evidence that the mere presence of oncogenic HPV is not sufficient for malignant progression and that additional tumor-promoting steps are required. Recent studies have demonstrated that HPV-transformed cells actively promote chronic stromal inflammation and conspire with cells in the local microenvironment to promote carcinogenesis. This review highlights the complex interplay between HPV-infected cells and the local immune microenvironment during oncogenic HPV infection, persistence, and malignant progression, and discusses new prospects for diagnosis and immunotherapy of HPV-associated cancers.

Immunomodulatory and antitumor effects of type I interferons and their application in cancer therapy

During the last decades, the pleiotropic antitumor functions exerted by type I interferons (IFNs) have become universally acknowledged, especially their role in mediating interactions between the tumor and the immune system. Indeed, type I IFNs are now appreciated as a critical component of dendritic cell (DC) driven T cell responses to cancer. Here we focus on IFN-α and IFN-β, and their antitumor effects, impact on immune responses and their use as therapeutic agents. IFN-α/β share many properties, including activation of the JAK-STAT signaling pathway and induction of a variety of cellular phenotypes. For example, type I IFNs drive not only the high maturation status of DCs, but also have a direct impact in cytotoxic T lymphocytes, NK cell activation, induction of tumor cell death and inhibition of angiogenesis. A variety of stimuli, including some standard cancer treatments, promote the expression of endogenous IFN-α/β, which then participates as a fundamental component of immunogenic cell death. Systemic treatment with recombinant protein has been used for the treatment of melanoma. The induction of endogenous IFN-α/β has been tested, including stimulation through pattern recognition receptors. Gene therapies involving IFN-α/β have also been described. Thus, harnessing type I IFNs as an effective tool for cancer therapy continues to be studied.

An oral keratinocyte life cycle model identifies novel host genome regulation by human papillomavirus 16 relevant to HPV positive head and neck cancer

Many aspects of the HPV life cycle have been characterized in cervical cell lines (W12, CIN612) and in HPV immortalized primary foreskin keratinocytes. There is now an epidemic of HPV positive oropharyngeal cancers (HPV16 is responsible for 80-90% of these); therefore increased understanding of the HPV16 life cycle in oral keratinocytes is a priority. To date there have been limited reports characterizing the HPV16 life cycle in oral keratinocytes. Using TERT immortalized "normal" oral keratinocytes (NOKs) we generated clonal cell lines maintaining the HPV16 genome as an episome, NOKs+HPV16. Organotypic raft cultures demonstrated appropriate expression of differentiation markers, E1^E4 and E2 expression along with amplification of the viral genome in the upper layers of the epithelium. Using this unique system RNA-seq analysis revealed extensive gene regulation of the host genome by HPV16; many of the changes have not been observed for HPV16 before. The RNA-seq data was validated on a key set of anti-viral innate immune response genes repressed by HPV16 in NOKs+HPV16. We show that the behavior of these NOKs+HPV16 lines is identical to HPV16 immortalized human tonsil keratinocytes with regards innate gene regulation. Finally, using The Cancer Genome Atlas (TCGA) data we examined gene expression patterns from HPV positive and negative head and neck cancers and demonstrate this innate immune gene signature set is also downregulated in HPV positive cancers versus negative. Our system provides a model for understanding HPV16 transcriptional regulation of oral keratinocytes that is directly relevant to HPV positive head and neck cancer.

ISG15 inhibits cancer cell growth and promotes apoptosis

Cervical cancer is one of the most common causes of cancer-related mortality in women in developing countries. Interferon (IFN)-α has been widely used in the treatment of various types of cancer, including cervical cancer, and IFN-stimulated gene 15 (ISG15), an ubiquitin-like protein, is upregulated by IFN-α treatment. The anti-virus and antitumor effects of ISG15 have been reported; however, its mechanism of action have not yet been fully elucidated. In this study, HeLa cells were used as a model system to investigate the roles of ISG15 in IFN-α-mediated cancer cell growth inhibition and induction of apoptosis. The results revealed that both p53 and p21 were upregulated in HeLa cells treated with IFN-α or in the HeLa cells overexpressing ISG15. In addition, the expression levels of ubiquitin-like modifier-activating enzyme 7 (UBA7, also known as UBE1L; ISG15 E1-activating enzyme), UBCH8 (ISG15 E2-conjugating enzyme) and HERC5 (ISG15 E3-ligase) were elevated in the HeLa cells treated with IFN-α. The levels of p53 in the HeLa cells were attenuated by transient transfection with small interfering RNA (siRNA) targeting ISG15 (ISG15-siRNA). Cell viability was inhibited by both IFN-α treatment and ISG15 overexpression. However, these effects were significantly diminished when p53 was knocked down, suggesting that the effects of inhibitory effects of ISG15 on HeLa cell growth and the induction of apoptosis were p53-dependent. Taken together, these results suggest the existence of the IFN-α/ISG15/p53 axis in cervical cancer cells and any strategies manipulating the levels of ISG15 may thus prove to be effective in the treatment of cervical cancer.

Molecular mechanisms of HPV mediated neoplastic progression

Human Papillomavirus is the major etiological agent in the development of cervical cancer but not a sufficient cause. Despite significant research, the underlying mechanisms of progression from a low-grade squamous intraepithelial lesion to high grade squamous intraepithelial lesion are yet to be understood. Deregulation of viral gene expression and host genomic instability play a central role in virus-mediated carcinogenesis. Key events such as viral integration and epigenetic modifications may lead to the deregulation of viral and host gene expression. This review has summarized the available literature to describe the possible mechanism and role of viral integration in mediating carcinogenesis. HPV integration begins with DNA damage or double strand break induced either by oxidative stress or HPV proteins and the subsequent steps are driven by the DNA damage responses. Inflammation and oxidative stress could be considered as cofactors in stimulating viral integration and deregulation of cellular and viral oncogenes during the progression of cervical carcinoma. All these events together with the host and viral genetic and epigenetic modifications in neoplastic progression have also been reviewed which may be relevant in identifying a new preventive therapeutic strategy. In the absence of therapeutic intervention for HPV-infected individuals, future research focus should be directed towards preventing and reversing of HPV integration. DNA damage response, knocking out integrated HPV sequences, siRNA approach, modulating the selection mechanism of cells harboring integrated genomes and epigenetic modifiers are the possible therapeutic targets.

Management of locally advanced HPV-related oropharyngeal squamous cell carcinoma: where are we?

HPV-related (HPV+) oropharyngeal cancer (OPC) has a better prognosis compared to HPV unrelated (HPV-) OPC. This review summarizes and discusses several of the controversies regarding the management of HPV+ OPC, including the mechanism of its treatment sensitivity, modern surgical techniques, chemotherapy regimens, and treatment de-intensification protocols. We also discuss and reconsider potential adverse prognostic factors such as tumor EGFR expression, tumor hypoxia, and patient smoking history, as well as the significance of retropharyngeal adenopathy. Finally, we discuss elective nodal treatment of uninvolved lymph node stations. While this review does not exhaust all controversies related to the management of HPV+ OPC, it aims to highlight some of the most clinically relevant ones.

High-risk human papillomavirus targets crossroads in immune signaling

Persistent infections with a high-risk type human papillomavirus (hrHPV) can progress to cancer. High-risk HPVs infect keratinocytes (KCs) and successfully suppress host immunity for up to two years despite the fact that KCs are well equipped to detect and initiate immune responses to invading pathogens. Viral persistence is achieved by active interference with KCs innate and adaptive immune mechanisms. To this end hrHPV utilizes proteins encoded by its viral genome, as well as exploits cellular proteins to interfere with signaling of innate and adaptive immune pathways. This results in impairment of interferon and pro-inflammatory cytokine production and subsequent immune cell attraction, as well as resistance to incoming signals from the immune system. Furthermore, hrHPV avoids the killing of infected cells by interfering with antigen presentation to antigen-specific cytotoxic T lymphocytes. Thus, hrHPV has evolved multiple mechanisms to avoid detection and clearance by both the innate and adaptive immune system, the molecular mechanisms of which will be dealt with in detail in this review.

Genomic landscape of human papillomavirus-associated cancers

Recent next-generation sequencing studies have generated a comprehensive overview of the genomic landscape of human papillomavirus (HPV)-associated cancers. This review summarizes these findings to provide insight into the tumor biology of these cancers and potential therapeutic opportunities for HPV-driven malignancies. In addition to the tumorigenic properties of the HPV oncoproteins, integration of HPV DNA into the host genome is suggested to be a driver of the neoplastic process. Integration may confer a growth and survival advantage via enhanced expression of viral oncoproteins, alteration of critical cellular genes, and changes in global promoter methylation and transcription. Alteration of cellular genes may lead to loss of function of tumor suppressor genes, enhanced oncogene expression, loss of function of DNA repair genes, or other vital cellular functions. Recurrent integrations in RAD51B, NR4A2, and TP63, leading to aberrant forms of these proteins, are observed in both HPV-positive head and neck squamous cell carcinoma (HNSCC) and cervical carcinoma. Additional genomic alterations, independent of integration events, include recurrent PIK3CA mutations (and aberrations in other members of the PI3K pathway), alterations in receptor tyrosine kinases (primarily FGFR2 and FGFR3 in HPV-positive HNSCC, and ERBB2 in cervical squamous cell carcinoma), and genes in pathways related to squamous cell differentiation and immune responses. A number of the alterations identified are potentially targetable, which may lead to advances in the treatment of HPV-associated cancers.

Immune therapy for human papillomaviruses-related cancers

Human papillomaviruses (HPVs) are a large family of double strand DNA viruses comprising more than 180 types. Infection with HPV is very common and it is associated with benign and malignant proliferation of skin and squamous mucosae. Many HPVs, considered low-risk such as HPV 6 and 11, produce warts; while high-risk viruses, such as HPVs 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, and 58, induce tumors. About 5% of all cancers in men and women are associated with HPV infection. Because there are not antiviral drugs for HPV infection, current therapies for low-risk HPV infections involve physical removal of the lesion by cryotherapy, trichloracetic acid, laser, or surgical removal. Surgical procedures are effective in the treatment of pre-cancerous lesions, however after these procedures, many recurrences appear due to new re-infections, or to failure of the procedure to eliminate the HPV. In addition, HPV can inhibit recognition of malignant cells by the immune system, leading to the development of cancer lesions. When this occurs, radiotherapy and chemotherapy are then used. Unfortunately, about 50% of the HPV-cancer patients still die. In the past decade, a better knowledge of the natural history of the virus-host interaction and of the immune response against this viral infection has brought new therapeutic strategies geared to modulate the immune system to generate an efficient virus-specific cytotoxic response. Novel HPV protein-expressing vaccines have shown some significant clinical efficacy and systemic HPV-specific cytotoxic T cell responses. This review will describe the current status of the several therapeutic strategies used to treat HPV-induced lesions, and discuss the various new therapies now being tested.

Human Papillomavirus (HPV)-associated Oral Cancers and Treatment Strategies

Human papillomavirus (HPV) is known to be associated with several types of human cancer, including cervical, vulvar, vaginal, penile, anal, and head-and-neck cancers. Among these cancers, HPV-associated head-and-neck cancers, inclusive of oropharyngeal squamous cell carcinoma (OSCC) and oral cavity squamous cell carcinomas (OCSCC), have recently risen dramatically in men under 50 years old. Within 20 years, the percentage of HPV-positive OSCC in total OSCC went from less than 20% to more than 70% in the United States and some European countries. This article reviews the incidence trend and pathogenesis of HPV-associated head-and-neck cancers as well as current treatment modalities for the disease.

The interplay between HPV and host immunity in head and neck squamous cell carcinoma

Persistent infection with human papillomavirus (HPV) type 16 is a major risk factor for the development of head and neck squamous cell carcinoma (HNSCC), in particular oropharyngeal squamous cell carcinoma (OPSCC). The oropharyngeal epithelium differs from the mucosal epithelium at other commonly HPV16-infected sites (i.e., cervix and anogenital region) in that it is juxtaposed with the underlying lymphatic tissue, serving a key immunologic function in the surveillance of inhaled and ingested pathogens. Therefore, the natural history of infection and immune response to HPV at this site may differ from that at other anatomic locations. This review summarizes the literature concerning the adaptive immune response against HPV in the context of HNSCC, with a focus on the T-cell response. Recent studies have shown that a broad repertoire of tumor-infiltrating HPV-specific T-cells are found in nearly all patients with HPV-positive tumors. A systemic response is found in only a proportion of these. Furthermore, the local response is more frequent in OPSCC patients than in cervical cancer patients and HPV-negative OPSCC patients. Despite this, tumor persistence may be facilitated by abnormalities in antigen processing, a skewed T-helper cell response, and an increased local prevalence of T-regulatory cells. Nonetheless, the immunologic profile of HPV-positive vs. HPV-negative HNSCC is associated with a significantly better outcome, and the HPV-specific immune response is suggested to play a role in the significantly better response to therapy of HPV-positive patients. Immunoprofiling may prove a valuable prognostic tool, and immunotherapy trials targeting HPV are underway, providing hope for decreasing treatment-related toxicity.

The papillomavirus E7 proteins

E7 is an accessory protein that is not encoded by all papillomaviruses. The E7 amino terminus contains two regions of similarity to conserved regions 1 and 2 of the adenovirus E1A protein, which are also conserved in the simian vacuolating virus 40 large tumor antigen. The E7 carboxyl terminus consists of a zinc-binding motif, which is related to similar motifs in E6 proteins. E7 proteins play a central role in the human papillomavirus life cycle, reprogramming the cellular environment to be conducive to viral replication. E7 proteins encoded by the cancer-associated alpha human papillomaviruses have potent transforming activities, which together with E6, are necessary but not sufficient to render their host squamous epithelial cell tumorigenic. This article strives to provide a comprehensive summary of the published research studies on human papillomavirus E7 proteins.

The invisible enemy - how human papillomaviruses avoid recognition and clearance by the host immune system

Human papillomavirus (HPV) needs to persist in squamous epithelia for a certain amount of time to complete its reproductive cycle. Therefore, the virus has evolved multiple immune evasion strategies. The interplay of these immune evasion mechanisms with the host immune system decides whether a HPV infection is cleared or becomes persistent. Clearance of HPV-induced lesions is mediated by a cellular immune response, consisting of both cytotoxic T lymphocyte and T helper cell responses. Persistent HPV infection, on the other hand, is the single most important risk factor for the development of HPV-associated premalignant lesions and HPV-driven cancers. This article reviews the immune evasion mechanisms employed by high-risk HPVs to escape host immune recognition and attack.

Papillomavirus E5: the smallest oncoprotein with many functions

Papillomaviruses (PVs) are established agents of human and animal cancers. They infect cutaneous and mucous epithelia. High Risk (HR) Human PVs (HPVs) are consistently associated with cancer of the uterine cervix, but are also involved in the etiopathogenesis of other cancer types. The early oncoproteins of PVs: E5, E6 and E7 are known to contribute to tumour progression. While the oncogenic activities of E6 and E7 are well characterised, the role of E5 is still rather nebulous. The widespread causal association of PVs with cancer makes their study worthwhile not only in humans but also in animal model systems. The Bovine PV (BPV) system has been the most useful animal model in understanding the oncogenic potential of PVs due to the pivotal role of its E5 oncoprotein in cell transformation. This review will highlight the differences between HPV-16 E5 (16E5) and E5 from other PVs, primarily from BPV. It will discuss the targeting of E5 as a possible therapeutic agent.

Therapeutic targets in head and neck squamous cell carcinoma: identification, evaluation, and clinical translation

Head and neck squamous cell carcinoma (HNSCC) encompasses a diverse group of malignancies originating in the oral cavity, oropharynx, larynx and hypopharynx. Although treatment modalities have improved, carefully designed biomarker-driven clinical trials will yield the best opportunities to enhance HNSCC therapy options in the future. Due to the heterogeneous nature of HNSCC, discovering a "silver bullet" for the treatment of HNSCC is unlikely. Consequently, impactful HNSCC clinical trials will require multiple assay platforms and expanded technical expertise. In this review, we will outline pathways critical to HNSCC oncogenesis and highlight signaling nodes within these pathways that represent biomarkers for prognosis and potential targeted therapies. All treatment modalities are subject to mechanisms of resistance; thus, lessons learned from HNSCC investigations and studies of similar targeted agents in other pertinent malignancies will be discussed.

The tug-of-war between dendritic cells and human chronic viruses

The human immune system is under constant challenge from many viruses, some of which the body is successfully able to clear. Other viruses have evolved to escape the host immune responses and thus persist, leading to the development of chronic diseases. Dendritic cells are professional antigen-presenting cells that play a major role in both innate and adaptive immunity against different pathogens. This review focuses on the interaction of different chronic viruses with dendritic cells and the viruses' ability to exploit this critical cell type to their advantage so as to establish persistence within the host.

Regulation of immune responses to HPV infection and during HPV-directed immunotherapy

The recent development of vaccines prophylactic against human papillomavirus (HPV) infection has the potential to reduce the incidence of cervical cancer globally by up to 70% over the next 40 years, if universal immunization is adopted. As these prophylactic vaccines do not alter the natural history of established HPV infection, immunotherapies to treat persistent HPV infection and associated precancers would be of benefit to assist with cervical cancer control. Efforts to develop immuno-therapeutic vaccines have been hampered by the relative non-immunogenicity of HPV infection, by immunoregulatory processes in skin, and by subversion of immune response induction and immune effector functions by papillomavirus proteins. This review describes HPV-specific immune responses induced by viral proteins, their regulation by host and viral factors, and highlights some conclusions from our own recent research.

Prevention and treatment of papillomavirus-related cancers through immunization

Cervical and other anogenital cancers are initiated by infection with one of a small group of human papillomaviruses (HPV). Virus-like particle-based vaccines have recently been developed to prevent infection with two cancer-associated HPV genotypes (HPV16, HPV18) and have been ∼95% effective at preventing HPV-associated disease caused by these genotypes in virus-naive subjects. Although immunization induces virus-neutralizing antibody sufficient to prevent infection, persistence of antibody as measured by current assays does not appear necessary to maintain protection over time. Investigators have not identified a reliable surrogate immunological marker of protection against disease following immunization. The prophylactic vaccines are not therapeutic for existing infection. Trials of HPV-specific immunotherapy have shown some efficacy for existing disease, although animal modeling suggests that a combination of immunization and local enhancement of innate immunity may be necessary for optimal therapeutic outcome. HPV prophylactic vaccines are the first vaccines designed to prevent a human cancer and are the practical outcome of a global collaborative effort between basic and applied scientists, clinicians, and industry.

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.

Local hyperthermia could induce antiviral activity by endogenous interferon-dependent pathway in condyloma acuminata

Local hyperthermia has been successfully used in the treatment of viral warts by mechanisms that have largely remained unclear. Using an organotypic culture system, we found that hyperthermia at 42 °C and 45 °C could induce a significant increase in the transcriptional expression of interferon (IFN)-α, IFN-β and IFN-γ, in a temperature-dependent manner in condyloma acuminata (CA), but not in normal skin. Accordingly, local hyperthermia could enhance the expression of 2'-5' oligoadenylate synthase and double-stranded RNA (dsRNA)-dependent protein kinase, two antiviral enzymes downstream of the IFN-dependant pathway. Hyperthermia led to an increase in IFN-α/β receptor transcripts, and an increase in the levels in phospho-Stat1 and phospho-Stat2 in CA, though it had no influence on the levels of Jak1, Tyk2, Stat1 and Stat2 transcriptional expression. Local hyperthermia was proved effective in treating human papillomavirus-infected skin. These results suggested that hyperthermia took effect partly by inducing the expression of local endogenous IFN and partly by subsequent IFN-induced antiviral activity via Jak-STATs signalling pathway in CA.

Expression of human papillomavirus type 16 E7 oncoprotein alters keratinocytes expression profile in response to tumor necrosis factor-alpha

Acute expression of E7 oncogene from human papillomavirus (HPV) 16 or HPV18 is sufficient to overcome tumor necrosis factor (TNF)-alpha cytostatic effect on primary human keratinocytes. In the present study, we investigated the molecular basis of E7-induced TNF resistance through a comparative analysis of the effect of this cytokine on the proliferation and global gene expression of normal and E7-expressing keratinocytes. Using E7 functional mutants, we show that E7-induced TNF resistance correlates with its ability to mediate pRb degradation and cell transformation. On the other hand, this effect does not depend on E7 sequences required to override DNA damage-induced cell cycle arrest or extend keratinocyte life span. Furthermore, we identified a group of 66 genes whose expression pattern differs between normal and E7-expressing cells upon cytokine treatment. These genes are mainly involved in cell cycle regulation suggesting that their altered expression may contribute to sustained cell proliferation even in the presence of a cytostatic stimulus. Differential expression of TCN1 (transcobalamin I), IFI44 (Interferon-induced protein 44), HMGB2 (high-mobility group box 2) and FUS [Fusion (involved in t(12;16) in malignant liposarcoma)] among other genes were further confirmed by western-blot and/or real-time polymerase chain reaction. Moreover, FUS upregulation was detected in HPV-positive cervical high-grade squamous intraepithelial lesions when compared with normal cervical tissue. Further evaluation of the role of such genes in TNF resistance and HPV-associated disease development is warranted.

Therapeutic vaccines against human papillomavirus and cervical cancer

Cervical cancer and its precursor intra-epithelial lesions are linked to infection by a subset of so-called "highrisk" human papillomavirus types, which are estimated to infect nearly four hundred million women worldwide. Two prophylactic vaccines have been commercialized recently targeting HPV16 and 18, the most prevalent viral types found in cervical cancer, which operate through induction of capsid-specific neutralizing antibodies. However, in patients with persistent infection these vaccines have not been found to protect against progression to neoplasia. Attempts are being made to develop therapeutic vaccines targeting nonstructural early viral proteins. Among these, E6 and E7 are the preferred targets, since they are essential for induction and maintenance of the malignant phenotype and are constitutively expressed by the transformed epithelial cells. Here are reviewed the most relevant potential vaccines based on HPV early antigens that have shown efficacy in preclinical models and that are being tested in clinical studies, which should determine their therapeutic capacity for eradicating HPV-induced premalignant and malignant lesions and cure cervical cancer.

Molecular mechanisms of human papillomavirus-induced carcinogenesis

Approximately 20% of all cancers are associated with infectious agents. Among them, human papillomaviruses (HPVs) are very common and are now recognized as the etiological agent of cervical cancer, the second most common cancer in women worldwide, and they are increasingly linked with other forms of dysplasia. Carcinogenesis is a complex and multistep process requiring the acquisition of several genetic and/or epigenetic alterations. HPV-induced neoplasia, however, is in part mediated by the intrinsic functions of the viral proteins. In order to replicate its genome, HPV modulates the cell cycle, while deploying mechanisms to escape the host immune response, cellular senescence and apoptosis. As such, HPV infection leads directly and indirectly to genomic instability, further favouring transforming genetic events and progression to malignancy. This review aims to summarize our current understanding of the molecular mechanisms exploited by HPV to induce neoplasia, with an emphasis on the role of the 2 viral oncoproteins E6 and E7. Greater understanding of the role of HPV proteins in these processes will ultimately aid in the development of antiviral therapies, as well as unravel general mechanisms of oncogenesis.