Case study: Creating a lung in the lab to study fungal infection in cystic fibrosis
Dr Sara Gago uses lung cells grown in the lab to understand how Aspergillus fungus colonise the lungs of people with cystic fibrosis and find ways to stop this from happening.
Every day, we breathe in up to ten billion fungal spores from the air around us. One of the most common fungi groups is Aspergillus, and for most people, these spores cause no problems in the lungs. However, this mould can sometimes grow and cause breathing difficulties, allergic reactions, and in rare cases can become invasive and life-threatening. Collectively, these conditions are known as aspergillosis.
Cystic fibrosis and aspergillosis
Understanding the difference in the host response to Aspergillus between people with cystic fibrosis and a person without will be critical to designing or repurposing drugs for patients in which treatment is failing.Dr Sara Gago / Division of Evolution, Infection and Genomics
One group that is particularly susceptible to aspergillosis is people living with cystic fibrosis. More than 10,800 people in the UK are living with the condition, caused by a mutation in the CFTR gene. This mutation leads to the production of thick sticky mucus which affects many parts of the body and causes people with cystic fibrosis to be particularly susceptible to aspergillosis. For example, about 10% of those with cystic fibrosis develop allergic reactions to Aspergillus, leading to further decline in lung function.
Dr Sara Gago is a Research Fellow in the Manchester Fungal Infection Group, who studies fungal diseases, including those caused by the species Aspergillus fumigatus. “With the new treatments for cystic fibrosis, the prevalence of aspergillosis has thankfully dropped quite significantly,” Dr Gago says, “but still, there are patients that, even though they are treated with the same treatments, are still getting an infection.”
The fact that not everyone gets aspergillosis suggests that the condition depends on a range of factors, some related to the fungus, and others dependent on the host (the person affected). This is a complication Dr Gago came up against in previous research. “When we tried to use cells from a healthy person and cells from a person with cystic fibrosis, we didn't know whether the differences that we observed were because of the genetic differences between people, or really due to the impact of the CFTR gene,” she says.
Research using lung cells
As part of a study by PhD student Kayleigh Earle funded by the NC3Rs, Co-Supervisor Dr Gago has adapted a lab-based model she previously used to study aspergillosis in asthma. Her model uses lung cells which have been genetically modified to carry a mutation in the CFTR gene, replicating a simple version of a lung with cystic fibrosis. As the lung cells are from a widely used cell line, all the cells have the same genetic background, getting around the problem of genetic variation between human donors.
To allow Dr Gago and Kayleigh to look in detail at the role of fungal factors, the team are testing a library of hundreds of Aspergillus fumigatus mutants that each lack one key gene. The growth of these fungi with the cystic fibrosis lung cells can be tracked and measured, as each fungal strain has a genetic ‘barcode’, allowing the team to identify the fungus genes most important in the development of aspergillosis in cystic fibrosis.
Screening hundreds of Aspergillus mutants in this way would be highly unethical in mouse models due to the sheer numbers that would be needed, not to mention time-consuming. By using the cell-based methods instead, Dr Gago’s team will whittle down the list of possible mutations to a short list that can then be confirmed in other experiments, first in human lung cells from people with cystic fibrosis; and then in mouse models of the disease.
Reducing animal experiments and improving fungal infection research
The next stage is to investigate the role of host factors in aspergillosis. Dr Gago expects that there are factors in both the Aspergillus and the human host which make each pairing ‘compatible’, leading to colonisation by the fungus and ultimately aspergillosis.
Dr Gago expects other research teams would be interested in using similar approaches for their work. “I think it's going to be very powerful to do high-throughput screening and to try to reduce the number of conditions that need to be tested further in other experiments”, she says. In this way, her model should reduce the number of mice needed in experiments and could replace some animal experiments entirely.
Ultimately, her aim is to better understand which people with cystic fibrosis are most at risk of developing aspergillosis and, therefore, identify who would benefit from preventative treatment with anti-fungal medication. “Identifying those patients will be critical to improve diagnosis and reduce mortality,” Dr Gago says.
Understanding the host and fungal factors involved in aspergillosis will also help develop treatments for the condition – either new medications or the repurposing of existing drugs. “I think that understanding the difference in the host response to Aspergillus between people with cystic fibrosis and person without cystic fibrosis will be critical to design or repurpose drugs for patients in which treatment is failing.”