HPV-transgenic mouse models: Tools for studying the cancer-associated immune response

Distribution and Clinical Significance of HPV16 Variants in Head and Neck Squamous Cell Carcinomas: Data from a Portuguese Cohort and Systematic Review

INTRODUCTION

Genomic variants of the human papillomavirus type 16 (HPV16) are thought to play differential roles in the susceptibility to head and neck squamous cell carcinomas (HNSCC) and its biological behaviour. This study aimed to establish the prevalence of HPV16 variants in an HNSCC cohort and associate them with clinical pathological characteristics and patient survival.

METHODS

We retrieved samples and clinical data from 68 HNSCC patients. DNA samples were available from tumour biopsy at the time of the primary diagnosis. Targeted next-generation sequencing was used to obtain whole-genome sequences, and variants were established based on phylogenetic classification.

RESULTS

74% of samples clustered in lineage A, 5.7% in lineage B, 2.9% in lineage C, and 17.1% in lineage D. Comparative genome analysis revealed 243 single nucleotide variations. Of these, one hundred were previously reported, according to our systematic review. No significant associations with clinical pathological variables or patient survival were observed. The E6 amino acid variations E31G, L83V, and D25E and E7 N29S, associated with cervical cancer, were not observed, except for N29S in a single patient.

CONCLUSION

These results provide a comprehensive genomic map of HPV16 in HSNCC, highlighting tissue-specific characteristics which will help design tailored therapies for cancer patients.

Single immunizations of self-amplifying or non-replicating mRNA-LNP vaccines control HPV-associated tumors in mice

As mRNA vaccines have proved to be very successful in battling the coronavirus disease 2019 (COVID-19) pandemic, this new modality has attracted widespread interest for the development of potent vaccines against other infectious diseases and cancer. Cervical cancer caused by persistent human papillomavirus (HPV) infection is a major cause of cancer-related deaths in women, and the development of safe and effective therapeutic strategies is urgently needed. In the present study, we compared the performance of three different mRNA vaccine modalities to target tumors associated with HPV-16 infection in mice. We generated lipid nanoparticle (LNP)-encapsulated self-amplifying mRNA as well as unmodified and nucleoside-modified non-replicating mRNA vaccines encoding a chimeric protein derived from the fusion of the HPV-16 E7 oncoprotein and the herpes simplex virus type 1 glycoprotein D (gDE7). We demonstrated that single low-dose immunizations with any of the three gDE7 mRNA vaccines induced activation of E7-specific CD8⁺ T cells, generated memory T cell responses capable of preventing tumor relapses, and eradicated subcutaneous tumors at different growth stages. In addition, the gDE7 mRNA-LNP vaccines induced potent tumor protection in two different orthotopic mouse tumor models after administration of a single vaccine dose. Last, comparative studies demonstrated that all three gDE7 mRNA-LNP vaccines proved to be superior to gDE7 DNA and gDE7 recombinant protein vaccines. Collectively, we demonstrated the immunogenicity and therapeutic efficacy of three different mRNA vaccines in extensive comparative experiments. Our data support further evaluation of these mRNA vaccines in clinical trials.

Characterization of the Human Papillomavirus 16 Oncogenes in K14HPV16 Mice: Sublineage A1 Drives Multi-Organ Carcinogenesis

The study of human papillomavirus (HPV)-induced carcinogenesis uses multiple in vivo mouse models, one of which relies on the cytokeratin 14 gene promoter to drive the expression of all HPV early oncogenes. This study aimed to determine the HPV16 variant and sublineage present in the K14HPV16 mouse model. This information can be considered of great importance to further enhance this K14HPV16 model as an essential research tool and optimize its use for basic and translational studies. Our study evaluated HPV DNA from 17 samples isolated from 4 animals, both wild-type (n = 2) and HPV16-transgenic mice (n = 2). Total DNA was extracted from tissues and the detection of HPV16 was performed using a qPCR multiplex. HPV16-positive samples were subsequently whole-genome sequenced by next-generation sequencing techniques. The phylogenetic positioning clearly shows K14HPV16 samples clustering together in the sub-lineage A1 (NC001526.4). A comparative genome analysis of K14HPV16 samples revealed three mutations to the human papillomaviruses type 16 sublineage A1 representative strain. Knowledge of the HPV 16 variant is fundamental, and these findings will allow the rational use of this animal model to explore the role of the A1 sublineage in HPV-driven cancer.

Bacterial-Viral Interactions in Human Orodigestive and Female Genital Tract Cancers: A Summary of Epidemiologic and Laboratory Evidence

Infectious agents, including viruses, bacteria, fungi, and parasites, have been linked to pathogenesis of human cancers, whereas viruses and bacteria account for more than 99% of infection associated cancers. The human microbiome consists of not only bacteria, but also viruses and fungi. The microbiome co-residing in specific anatomic niches may modulate oncologic potentials of infectious agents in carcinogenesis. In this review, we focused on interactions between viruses and bacteria for cancers arising from the orodigestive tract and the female genital tract. We examined the interactions of these two different biological entities in the context of human carcinogenesis in the following three fashions: (1) direct interactions, (2) indirect interactions, and (3) no interaction between the two groups, but both acting on the same host carcinogenic pathways, yielding synergistic or additive effects in human cancers, e.g., head and neck cancer, liver cancer, colon cancer, gastric cancer, and cervical cancer. We discuss the progress in the current literature and summarize the mechanisms of host-viral-bacterial interactions in various human cancers. Our goal was to evaluate existing evidence and identify gaps in the knowledge for future directions in infection and cancer.

The Red Seaweed Grateloupia turuturu Prevents Epidermal Dysplasia in HPV16-Transgenic Mice

The role of dietary profiles in promoting or reducing the risk of multiple types of cancer is increasingly clear, driving the search for balanced foods and nutraceuticals. The red seaweed Grateloupia turuturu has been used as human food showing a balanced nutritional profile. This study aims to test in vivo chemopreventive effects of G. turuturu against cutaneous pre-malignant lesions in transgenic mice for the human papillomavirus type 16 (HPV16). Forty-four female HPV^+/− or HPV^−/− mice received a standard diet or were supplemented with 10% G. turuturu for 22 consecutive days. Cutaneous lesions (ear and chest skin) were identified histologically. Complementarily, the weights and histology of internal organs as well as blood biochemical and DNA integrity parameters were also assessed. G. turuturu consistently reduced the incidence of epidermal dysplasia induced by HPV16 on both cutaneous sites. Moreover, biochemical, DNA integrity and histological analyses confirmed G. turuturu edibility as no signs of toxicity were found. Dietary supplementation with G. turuturu is an effective and safe chemopreventive strategy in this model.

Pteridium spp. and Bovine Papillomavirus: Partners in Cancer

Bovine papillomavirus (BPV) are a cause for global concern due to their wide distribution and the wide range of benign and malignant diseases they are able to induce. Those lesions include cutaneous and upper digestive papillomas, multiple histological types of urinary bladder cancers—most often associated with BPV1 and BPV2—and squamous cell carcinomas of the upper digestive system, associated with BPV4. Clinical, epidemiological and experimental evidence shows that exposure to bracken fern (Pteridium spp.) and other related ferns plays an important role in allowing viral persistence and promoting the malignant transformation of early viral lesions. This carcinogenic potential has been attributed to bracken illudane glycoside compounds with immune suppressive and mutagenic properties, such as ptaquiloside. This review addresses the role of BPV in tumorigenesis and its interactions with bracken illudane glycosides. Current data indicates that inactivation of cytotoxic T lymphocytes and natural killer cells by bracken fern illudanes plays a significant role in allowing viral persistence and lesion progression, while BPV drives unchecked cell proliferation and allows the accumulation of genetic damage caused by chemical mutagens. Despite limited progress in controlling bracken infestation in pasturelands, bracken toxins remain a threat to animal health. The number of recognized BPV types has steadily increased over the years and now reaches 24 genotypes with different pathogenic properties. It remains essential to widen the available knowledge concerning BPV and its synergistic interactions with bracken chemical carcinogens, in order to achieve satisfactory control of the livestock losses they induce worldwide.

Differential Incidence of Tongue Base Cancer in Male and Female HPV16-Transgenic Mice: Role of Female Sex Hormone Receptors

A growing proportion of oropharyngeal squamous cell carcinomas (OPSCC) are associated with infection by high-risk human papillomavirus (HPV). For reasons that remain largely unknown, HPV+OPSCC is significantly more common in men than in women. This study aims to determine the incidence of OPSCC in male and female HPV16-transgenic mice and to explore the role of female sex hormone receptors in the sexual predisposition for HPV+ OPSCC. The tongues of 30-weeks-old HPV16-transgenic male (n = 80) and female (n = 90) and matched wild-type male (n = 10) and female (n = 10) FVB/n mice were screened histologically for intraepithelial and invasive lesions in 2017 at the Centre for the Research and Technology of Agro-Environmental and Biological Sciences (CITAB), Portugal. Expression of estrogen receptors alpha (ERα) and beta (ERβ), progesterone receptors (PR) and matrix metalloproteinase 2 (MMP2) was studied immunohistochemically. Collagen remodeling was studied using picrosirius red. Female mice showed robust ERα and ERβ expression in intraepithelial and invasive lesions, which was accompanied by strong MMP2 expression and marked collagen remodeling. Male mice showed minimal ERα, ERβ and MMP2 expression and unaltered collagen patterns. These results confirm the association of HPV16 with tongue base cancer in both sexes. The higher cancer incidence in female versus male mice contrasts with data from OPSCC patients and is associated with enhanced ER expression via MMP2 upregulation.

HPV16 induces penile intraepithelial neoplasia and squamous cell carcinoma in transgenic mice: first mouse model for HPV-related penile cancer

Penile cancer is an under-studied disease that occurs more commonly in developing countries and 30-50% of cases show high-risk human papillomavirus (HPV) infection. Therapeutic advances are slow, largely due to the absence of animal models for translational research. Here, we report the first mouse model for HPV-related penile cancer. Ten-week-old mice expressing all the HPV16 early genes under control of the cytokeratin 14 (Krt14) gene promoter and matched wild-type controls were exposed topically to dimethylbenz(a)anthracene (DMBA) or vehicle for 16 weeks. At 30 weeks of age, mice were sacrificed for histological analysis. Expression of Ki67, cytokeratin 14, and of the HPV16 oncogenes E6 and E7 was confirmed using immunohistochemistry and quantitative PCR, respectively. HPV16-transgenic mice developed intraepithelial lesions including condylomas and penile intraepithelial neoplasia (PeIN). Lesions expressed cytokeratin 14 and the HPV16 oncogenes E6 and E7 and showed deregulated cell proliferation, demonstrated by Ki67-positive supra-basal cells. HPV16-transgenic mice exposed to DMBA showed increased PeIN incidence and squamous cell carcinoma. Malignant lesions showed varied histological features closely resembling those of HPV-associated human penile cancers. Wild-type mice showed no malignant or pre-malignant lesions even when exposed to DMBA. These observations provide the first experimental evidence to support the etiological role of HPV16 in penile carcinogenesis. Importantly, this is the first mouse model to recapitulate key steps of HPV-related penile carcinogenesis and to reproduce morphological and molecular features of human penile cancer, providing a unique in vivo tool for studying its biology and advancing basic and translational research. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Inducing Immunity Where It Matters: Orthotopic HPV Tumor Models and Therapeutic Vaccinations

Anogenital and oropharyngeal cancers caused by human papillomavirus (HPV) infections account for 4.5% of all cancer cases worldwide. So far, only the initial infection with selected high-risk types can be prevented by prophylactic vaccination. Already existing persistent HPV infections, however, can currently only be treated by surgical removal of resulting lesions. Therapeutic HPV vaccination, promoting cell-based anti-HPV immunity, would be ideal to eliminate and protect against HPV-induced lesions and tumors. A multitude of vaccination approaches has been tested to date, many of which led to high amounts of HPV-specific T cells in vivo. However, growing evidence suggests that not the induction of systemic but of local immunity is paramount for tackling mucosal infections and tumors. Therefore, recent therapeutic vaccination studies have focused on how to induce tissue-resident T cells in the anogenital and oropharyngeal mucosa. These approaches include direct mucosal vaccinations and influencing the migration of systemic T cells toward the mucosa. The efficacy of these new vaccination approaches is best tested in vivo by utilizing orthotopic tumor models, i.e. HPV-positive tumors being located in the animal's mucosa. In line with this, we here review existing HPV tumor models and describe two novel tumorigenic cell lines for the MHC-humanized mouse model A2.DR1. These were used for the establishment of an HPV16 E6/E7-positive vaginal tumor model, suitable for testing therapeutic vaccines containing HLA-A2-restricted HPV16-derived epitopes. The newly developed MHC-humanized orthotopic HPV16-positive tumor model is likely to improve the translatability of in vivo findings to the clinical setting.

HPV infection as a risk factor for atherosclerosis: A connecting hypothesis

Atheromatous plaques occurring in large arteries are common and life-threatening lesions. Multiple factors are involved in the pathogenesis of atheromatous plaques, such as hyperlipidaemia and hypercholesterolaemia, high blood pressure and chronic systemic inflammation. Recent findings have suggested that infection with high-risk human papillomavirus (HPV) may increase the risk of developing atheromatous plaques. However, HPV is considered a tissue-specific virus with a strong tropism towards squamous epithelial cells, and the mechanisms whereby it may promote the development of atheromas remain unclear. Here, we propose a connecting hypothesis to explain the possible causative role of HPV on atheroma development. We hypothesize that HPV infection may promote atheroma formation in infected patients by enhancing systemic inflammation or by directly targeting blood vessels via nucleic acids carried by extracellular vesicles such as exosomes. The pro-inflammatory effects of HPV and the release of extracellular vesicles by HPV-transformed cells are well documented in scientific literature. Possible experimental approaches to test this hypothesis are also discussed, especially experiments employing transgenic mice bearing HPV16 transgenes. If correct, this hypothesis would have major implications for the prevention of cardiovascular diseases, especially due to the preventable nature of HPV infection through vaccination.

HPV16 is sufficient to induce squamous cell carcinoma specifically in the tongue base in transgenic mice

Head and neck squamous cell carcinomas (HNSCCs) associated with human papillomavirus (HPV) occur specifically in the tonsils and the tongue base, but the reasons for this specificity remain unknown. We studied the distribution of oral and pharyngeal lesions in HPV16-transgenic mice where the expression of all the HPV16 early genes is targeted to keratinising squamous epithelia by the cytokeratin 14 (Krt14) gene promoter. At 30 weeks of age, 100% of mice developed low- and high-grade intraepithelial dysplasia at multiple sites. Twenty per cent of animals developed invasive cancers that remarkably were restricted to the tongue base, in association with the circumvallate papilla. The lesions maintained expression of CK14 (KRT14) and the HPV16 E6 and E7 oncogenes, and displayed deregulated cell proliferation and up-regulation of p16^INK4A . Malignant lesions were poorly differentiated and destroyed the tongue musculature. We hypothesised that the tongue base area might contain a transformation zone similar to those observed in the cervix and anus, explaining why HPV-positive cancers target that area specifically. Immunohistochemistry for two transformation zone markers, CK7 (KRT7) and p63 (TP63), revealed a squamocolumnar junction in the terminal duct of von Ebner's gland, composed of CK7⁺ luminal cells and p63⁺ basal cells. Dysplastic and invasive lesions retained diffuse p63 expression but only scattered positivity for CK7. Site-specific HPV-induced carcinogenesis in the tongue base may be explained by the presence of a transformation zone in the circumvallate papilla. This mouse model reproduces key morphological and molecular features of HPV-positive HNSCC, providing a unique in vivo tool for basic and translational research. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Manipulation of Epithelial Differentiation by HPV Oncoproteins

Papillomaviruses replicate and cause disease in stratified squamous epithelia. Epithelial differentiation is essential for the progression of papillomavirus replication, but differentiation is also impaired by papillomavirus-encoded proteins. The papillomavirus E6 and E7 oncoproteins partially inhibit and/or delay epithelial differentiation and some of the mechanisms by which they do so are beginning to be defined. This review will outline the key features of the relationship between HPV infection and differentiation and will summarize the data indicating that papillomaviruses alter epithelial differentiation. It will describe what is known so far and will highlight open questions about the differentiation-inhibitory mechanisms employed by the papillomaviruses.

CRISPR-Cas9 therapies in experimental mouse models of cancer

The CRISPR-Cas9, a part of the defence mechanism from bacteria, has rapidly become the simplest, fastest and the most precise genome-editing tool available. The therapeutic applications of CRISPR are boundless: correction of mutations in several disorders, inactivation of oncogenes and viral oncoproteins, and activation of tumor suppressor genes. In this review, we expose recent advances concerning animal models of cancer that use CRISPR-Cas9, addressing also the current efforts to develop CRISPR-Cas9-based therapies, focusing on proof-of-concept studies. Finally, the review exposes some of the main challenges that this genome-editing tool faces. The key issue remains: does CRISPR-Cas9 have real potential for therapeutic application or will it just remain a wonderful research tool?

Ozone therapy prevents the onset of dysplasia in HPV16-transgenic mice-A pre-clinical efficacy and safety analysis

Infection with high-risk human papillomavirus (HPV), most often HPV16, is associated with the development of anogenital and oropharyngeal cancers. Recently, ozone therapy was reported to have considerable efficacy against rabbit VX2 tumors, induced by the cottontail rabbit papillomavirus. The present study aims to determine whether similar results can be obtained in HPV16-transgenic mice, possibly paving the way for new therapeutic options against HPV-induced cancers. HPV16-transgenic and wild-type, female, 20 weeks-old mice were injected intraperitoneally with medical O₃/O₂ (80░mL/kg, at O₃ 50░μg/mL), once a day, for 5 consecutive days. The animals were sacrificed at 25 weeks-old, and skin samples were analyzed histologically to study tumour progression. Blood and internal organ samples were used to study toxicological parameters. 85.7% of untreated transgenic mice showed dysplastic skin lesions, compared with 28.6% of O₃-treated mice. This was associated with a marked reduction of dermal inflammation associated with those lesions. No significant changes were observed in any toxicological parameters. These preliminary results support the hypothesis that O₃ therapy is effective against papillomavirus-induced lesions, particularly against those induced by the most common high-risk virus, HPV16. Further studies are needed to confirm the mechanisms underlying these effects.

Cutaneous Papillomaviruses and Non-melanoma Skin Cancer: Causal Agents or Innocent Bystanders?

There is still controversy in the scientific field about whether certain types of cutaneous human papillomaviruses (HPVs) are causally involved in the development of non-melanoma skin cancer (NMSC). Deciphering the etiological role of cutaneous HPVs requires - besides tissue culture systems - appropriate preclinical models to match the obtained results with clinical data from affected patients. Clear scientific evidence about the etiology and underlying mechanisms involved in NMSC development is fundamental to provide reasonable arguments for public health institutions to classify at least certain cutaneous HPVs as group 1 carcinogens. This in turn would have implications on fundraising institutions and health care decision makers to force - similarly as for anogenital cancer - the implementation of a broad vaccination program against "high-risk" cutaneous HPVs to prevent NMSC as the most frequent cancer worldwide. Precise knowledge of the multi-step progression from normal cells to cancer is a prerequisite to understand the functional and clinical impact of cofactors that affect the individual outcome and the personalized treatment of a disease. This overview summarizes not only recent arguments that favor the acceptance of a viral etiology in NMSC development but also reflects aspects of causality in medicine, the use of empirically meaningful model systems and strategies for prevention.