Lung Immune Challenge Study: Controlled Exposure to Inhaled Resiquimod (R848)

Background The initial immune response to respiratory viral infections is key to determining what kind of clinical outcome is experienced. The COVID-19 pandemic highlights the key importance of gaining a thorough understanding of these immune mechanisms.

People with chronic lung conditions such as asthma often experience more severe and prolonged symptoms in response to external triggers. This can be due to ongoing inflammation in their airways and lungs. Animal and cell models fail to accurately recapitulate the disease, which limit its usefulness in developing new treatments.

Observational human studies of asthma attacks can be useful but have several confounding factors, which significantly influence the outcomes being assessed. For example, one issue may be the significant variability in time between exposure to a pathogen to the point at which they present to hospital.

One important method for understanding mechanisms of inflammation in humans, is to perform controlled and careful exposure to an inflammatory stimulus to assess why and how differences occur between individuals. This is already established using live viral infection studies - however these studies are technically difficult, resource intensive, may make participants feel unwell for several days, and can be inconvenient for them due to the need for prolonged quarantine.

An alternative approach for studying the first line of immune defence (or "innate immunity"), is to use a mimic of a virus that binds to the same receptors as respiratory viruses such as influenza and SARS-CoV-2. The study team have already established and published this research using a nasal spray with a synthetic compound called Resiquimod (R848). It generates an inflammatory response with the release of molecules such as interferons and cytokines in the nose in a very similar manner to what we see with live viral infections. This approach has been used to demonstrate differences in immune responses between healthy individuals and people with asthma.

However, there are important differences between how the nose and lungs may respond to an inflammatory stimulus. This is due to many reasons including differences in the types of cells present between the upper and lower airways, which is especially the case in people who have airway diseases such as asthma.

Lung Challenge Model A lung immune challenge model using Resiquimod would therefore represent an important approach for studying differences in innate immune responses between individuals, enable an understanding of which cells are responsible for driving inflammation, and have the potential to be a platform for testing new anti-inflammatory therapies.

The first step of this approach and the focus of the current study is to define what dose is the most suitable for generating an appropriate innate immune response, whilst also being clinically tolerable for volunteers. The dose has already been established in the respiratory tract using nasal challenge, so this is a very good starting point when designing the current study. The initial dose for lung challenge will be 100-fold lower than with nasal challenge and therefore it is not anticipated to generate an immune response. The subsequent doses will then be escalated and reach a maximum dose that has already been administered via the intranasal route in clinical trials.

Identifying whether an appropriate immune response has been generated will be done by measuring the inflammatory molecule CXCL10. It is known that CXCL10 is an excellent biomarker for immune activation as it is increased after nasal challenge with Resiquimod, as well as after natural viral infections. CXCL10 will be measured in the blood and in the lungs by analysing sputum samples.

The dose cohort design with 6 participants in each dose cohort, and 4 participants being randomised to Resiquimod, whilst 2 participants being randomised to saline is based on an already published AstraZeneca trial of a similar compound used for inhaled challenge. This will enable an accurate comparison of responses between saline and active groups.

An important aspect of this study is to ensure it is clinically tolerable for volunteers. They will have been informed in the PIS that they may experience flu-like symptoms as the purpose of the study is to mimic flu and therefore, they may have transient inflammation and cold symptoms. To ensure their safety - their symptoms, physiological observations, and airway function will be closely monitored for the first 24 hours of the study directly within the research facility with access to full healthcare resources and staff. Individuals with asthma will only undergo inhaled challenge once an appropriate dose has been established in healthy participants.