Understanding oncogenic human papillomavirus persistence and immune modulation in tonsil epithelia

Viruses are obligate intracellular parasites that have evolved to manipulate the target cell and local tissue environment to facilitate replication. Some viruses can establish persistent, sub-clinical infection of target cells and these infections can evade host immune detection and exist for decades. Human papillomaviruses (HPV) are a family of viruses that infect the moist and dry surfaces of human skin.

The target cell of infection is a specific type of skin cell called a keratinocyte. Infection with many different types of HPV results in the formation of warts but persistent infection with a subset of HPV types, so called high-risk HPV, is the cause of cancers of anal and genital regions of the body (including the uterine cervix), and cancers of the head and neck, specifically in the tonsils and base of tongue, collectively known as the oropharynx.

Although robust strategies exist to prevent high-risk HPV infection and to detect pre-cancerous lesions through vaccination and national cervical screening programmes, these measures are not available in all countries. Indeed, the number of HPV-associated cancers has remained at around 600,000 cases per year worldwide despite screening and vaccination. Furthermore, the incidence of HPV-driven oropharyngeal cancer is increasing in patients that are younger, predominantly male and non-smokers.

The primary site of oropharyngeal HPV infection is the tonsil, a organ rich in immune cells that serve to detect invading pathogens and prevent respiratory and gastrointestinal infection. Establishment of persistent high-risk HPV infection in the tonsil must therefore require strong suppression of local immune cell activation. The majority (greater than 90%) of HPV-positive oropharyngeal cancers are caused by HPV type 16 (HPV16).

While HPV16 is also the most common HPV found in cervical cancers (~60%) the burden is much less than for oropharyngeal cancers. Another high-risk type, HPV18 accounts for ~15% of cervical cancers but is rarely found in oropharyngeal cancers. The reasons for this disparity in disease association at different body sites are not known.

Our preliminary data suggest that HPV16, but not HPV18, is able to suppress the production of immune activating molecules by reprogramming gene expression of the host tonsil keratinocyte.

Using state-of-the-art primary cell-based models of HPV infection and cutting-edge DNA and gene sequencing methods, we will investigate the similarities and differences in HPV16 and HPV18 life cycles in tonsil keratinocytes. We will determine how HPV16 suppresses host immune detection through repression of key pathways that activate and attract local immune cells to the site of infection.

We will then use our expertise in primary cell culture to combine primary keratinocytes with donor-matched lymphoidal tissue, which contains to tonsillar immune cells, to establish in vitro tonsil organ-like cultures that will be used to study immune cell activation and migration in response to HPV infection.

The results of this project will uncover novel mechanisms of HPV persistence in the tonsil. We will also determine the key differences in immune suppression by cancer-causing HPV16 and HPV18 and how these differences contribute to local immune cell activation and viral clearance. This is important as there is a critical need to understand how HPV16 can persist and induce cancer within the immune-rich oropharynx to enable the development of novel (immuno-) therapies to combat HPV-driven cancers.