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Why macrophages matter in the fight against cystic fibrosis

Lung macrophages play a significant role in the chronic inflammation associated with cystic fibrosis. ImmuONE, experts in lung immune systems, could help the pharmaceutical industry  assess how inhaled treatments for lung inflammatory diseases affect macrophages.

About one in every 2500 babies born in the UK will have cystic fibrosis, a life-threatening inherited disease caused by a defective gene that results in sticky mucus build-up in the lungs and digestive system, which leads to chronic infections and inflammation.

Although traditional treatment for cystic fibrosis has focused on the epithelial tissue, evidence shows that to develop effective long-term therapies for cystic fibrosis, we must consider the function of remarkably malleable white blood cells called macrophages.

The function of macrophages is to maintain the status quo within the lungs. In healthy cells, macrophages activate inflammatory responses to defend against invading microorganisms. Macrophages also perform a self-cleaning mechanism called “autophagy”, meaning that they engulf and recycle hostile, ageing or waste components within the cell. However, in people with cystic fibrosis, autophagy and inflammatory responses are altered, compromising the ability of macrophages to eliminate harmful bacteria.

Additionally, cystic fibrosis impairs the ability of macrophages to recognise disease-causing cells in the first place. Macrophages recognise foreign particles using receptors located on the surfaces of their cells. The cystic fibrosis lung environment contains an excess of elastases, enzymes that break down proteins. These elastases cleave the receptors of macrophages, preventing them from engulfing microorganisms.

Elastases also break down receptors that enable the recognition and removal of dying lung cells, leading to hyper-inflammation, and hyper-inflammation contributes to lung damage. Many products of the inflammatory response are highly potent, such as reactive oxygen radicals, cytokines and protein-modifying agents. These products can cause tissue damage, which is further enhanced by the inability of cystic fibrosis macrophages to effectively clear inhaled particles and inflammatory proteins.

No solution is perfect

A variety of models can be used to study the role of macrophages in cystic fibrosis, although no option is perfect. Mouse models have been widely used in previous research, but do not adequately reflect the increased susceptibility to bacterial lung infection observed in humans with cystic fibrosis. Macrophages extracted from mouse blood also differ from human macrophages in their responses to invasion and other environmental changes.

Alternatively, macrophage samples can be collected from human lungs to provide more human-relevant results. However, lung macrophages are laborious to isolate and batches of cells can be highly variable. As a result, performing reproducible studies using these models can be difficult. Additionally, only some types of macrophage can be obtained through non-invasive procedures. Interstitial macrophages, which are found between the air sacs of the lungs, cannot be isolated without surgery.

A promising alternative is cell-line based models, i.e. lung cells that are cultured outside the body, like ImmuONE’s models, ImmuLUNGTM and ImmuPHAGETM. These models offer stability, reproducibility and ease of manipulation. Cell-line based models also open up opportunities for genetic modification, which could be useful since cystic fibrosis is a gene-controlled disease. Macrophage models can be used to better understand the inflammation in the alveolar region associated with cystic fibrosis and other lung diseases.

Inhaled treatments for cystic fibrosis

Treatment for cystic fibrosis comes in a wide variety of forms, but inhaled treatments have a serious advantage – they quickly deposit large volumes of a drug within the target area – the airways.

Cystic fibrosis is caused by mutations in the CFTR gene, which encodes a protein that controls the transport of salt and water. Macrophages use the CFTR protein to restrict the growth of ingested bacteria and to maintain the acidity of lysosomes, spherical sacs involved in waste disposal and immune defence. An amazing treatment known as mRNA replacement therapy can help replace a faulty CFTR gene with a working one.

mRNA can also be used to target macrophages specifically. By adding different types of synthetic mRNA, researchers have been able to reprogram macrophages to either increase killing of harmful bacteria or enhance tissue repair.

Inhalation delivery is the ideal way to transport mRNA to the lung tissue. Vertex Pharmaceuticals and Arcturus Therapeutics are currently carrying out clinical trials of inhaled mRNA therapies.

One promising avenue of drug development is reducing agents, which break the bonds that hold mucus together. Right now, the only approved inhaled reducing agent is acetylcysteine, which is not particularly effective and can cause irritation. However, recent efforts to find alternatives have been encouraging. P-3001, a novel agent developed by Parion Sciences, has been proven to thin mucus more effectively than Dornase Alfa.

An alternative method of thinning mucus is to target sodium channels (ENaCs) on the surfaces of airway epithelial cells. By blocking ENaCs, we may be able to prevent the salt overabsorption that causes thick, sticky mucus. No ENaC blocker has yet progressed through clinical trials to licensing, but pharmaceutical companies are still fighting to find the perfect drug. Sodium channel blockers could also be useful for other conditions, such as chronic obstructive pulmonary disease (COPD).

For better or for worse, macrophages are remarkably adaptable to their surroundings – exposing a normal macrophage to mucus from a cystic fibrosis lung makes it behave like a cystic fibrosis macrophage. If we use drugs like mucus thinners to promote a healthy lung environment, macrophages should follow suit and improve their function.

Drug testing

Animal studies are currently mandatory for the testing of new drugs, but as previously mentioned, human lungs differ from those of laboratory animals like mice. To better predict how treatments affect humans, we can complement animal testing with cell-line based models.

A variety of epithelial cell models for cystic fibrosis exist, including cells from the nose, airways and intestines. These models were integral to the development of many of the best cystic fibrosis treatments we have today, like CFTR modulators. But to fully understand the effects of new therapies, we also need to consider macrophages and the role they play in this complex disease.

In recent years, ImmuONE and other companies have made strides in the development of in vitro macrophage models, like ImmuLUNGTM and ImmuPHAGETM, These models enable us to assess how macrophages in the deep lung respond to inhaled medicines. This is important not just to assess the efficacy of new drugs, but to check for side effects or toxicity.

Inflammation is a key factor in the progression and pathology of cystic fibrosis and other lung diseases. ImmuONE can provide models and methods that help pharmaceutical companies to better characterise lung inflammation, enabling the development of safe, effective drugs.

If you are developing inhaled medicines for the treatment of lung inflammatory diseases, and you’d like to find out how ImmuONE’s cell-line based human-relevant lung immune system models could help, please reach out and get in touch with us.

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