Genetic analyses, protein expression, type and function with clinical and immunological correlates in human papillomavirus associated head and neck neoplasia
In head and neck squamous cell carcinoma (HNSCC), the evidence that human papillomavirus (HPV) is associated with a subgroup of tumours has increased over the last thirty years. Prospective randomised controlled clinical trials have now established that detection of HPV in oropharyngeal tumours (~60-70% of cases in North America and Europe) may confer a survival advantage to the patient. Within the oropharynx, HPV16 constitutes ~90-95% of HPV subtypes associated with malignancy. This contrasts with uterine cervix mucosa, where approximately 15 high-risk subtypes cause >99% of disease. Other factors such as differences in genetic background, host immune response, hormonal and environmental influences (e.g. tobacco smoke, alcohol) all play a part in the pathway and susceptibility to oncogenesis. Analogous to uterine cervix disease, HPV-associated cancers involve wild-type TP53 whilst HPV negative tumours often have mutations in this gene. As most patients with HPV associated OPSCC present at an advanced stage, the detection and genetic analysis of a pre-malignant state would be important as it infers the potential for a screening test (similar to the uterine cervix model). To investigate this, whole transcriptome analysis with verification of results by reverse transcription–quantitative polymerase chain reaction (PCR), was performed on OPSCC fresh tissue biopsy samples. Predictable fold changes of RNA expression in HPV-associated disease included multiple transcripts within the p53 oncogenic pathway (e.g. CDKN2A / CCND1). In addition to this, a testis-specific gene not normally expressed in somatic cells, SYCP2, showed a consistently elevated fold change from baseline in pre-malignant and malignant tissue. A subtle immune defect has long been thought to trigger the susceptibility of some individuals to persistent HPV infection with either low or high risk HPV types. Following on from this, we investigated if clinical outcomes in HPV-related head and neck cancer may be affected by host immune response. Peripheral blood from patients with OPSCC treated by chemoradiotherapy underwent IFN-γ enzyme-linked immunosorbent spot assay (ELISPOT) to examine cell-mediated immune responses to HPV16 E2, E6 and E7. T cell responses against E6 or E7 peptides correlated with HPV DNA/RNA status. Within the HPV16+ OPSCC cohort, enhanced immunoreactivity to antigen E7 was linked to improved survival. In addition, an observed increase in regulatory T cell frequencies after treatment would suggest that immunosuppression may contribute to a reduced HPV specific cell mediated response. A further aspect of this study was to determine the role of HPV and Epstein Barr Virus (EBV) in the pathogenesis of squamous cell carcinoma within the temporal bone region. This is an uncommon tumour which is normally preceded by a history of inflammation within the external auditory canal (EAC) or middle ear / mastoid cavity. Although HPV has been implicated in many head and neck malignancies, its role in SCC of the temporal bone has not been established. Treatment strategies could change if a viral aetiology can be found. HPV16 DNA was detected in ~20% of the cases studied, however, no significant difference in disease specific survival was noted for the papillomavirus positive group. Epstein-Barr virus was not detected. The data presented highlight the functional and biological influence of high risk HPV infection on HNSCC. Further studies are likely to focus on developing non-invasive screening tools, therapeutic strategies based on vaccination or immune modulation or indeed de-escalation of current treatment protocols.
Human papillomavirus, Head and Neck oncology, Immunology, Oropharyngeal carcinoma, Squamous Cell Carcinoma, Genome analysis, RNAseq, enzyme-linked immunospot (ELISpot) assay, Immunohistochemistry, Gel electrophoresis, RNA, DNA
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