State of the art:

Up to 10% of patients with cystic fibrosis (CF) have signs of allergic bronchopulmonary aspergillosis (ABPA), an inflammatory syndrome caused by Aspergillus colonization of the airways and subsequent overzealous reaction of the immune system leading to immunoglobulin E (IgE) sensitization, eosinophilic type 2 inflammation, formation of sticky allergic mucin, a form of airway mucus that has a rubbery aspect, and causes mucus plugging and further deterioration of lung function. Because of pre-existing inflammation and lung function impairment, ABPA is very hard to diagnose in CF, yet adequate diagnosis and treatment are crucial, since ABPA has a major impact on CF disease burden and quality of life (QoL).

Research in our team has shown that Charcot-Leyden crystals (CLCs), that are abundantly found in ABPA and are produced from eosinophil-derived Galectin-10 (Gal-10) proteins that assemble into bipyramidal sharp crystals, play an important role in causing airway inflammation, epithelial damage, extracellular DNA release into mucus and mucus plugging. Our team developed anti-Gal-10 monoclonal antibodies (mAb), capable of rapidly dissolving CLCs in allergic mucin, thereby identifying Charcot-Leyden crystallopathy as a drugable trait in patients with airway disease.

Objectives:

1. To determine the burden of disease of ABPA in adolescents and adults living with CF and identify patients with ABPA (CFwABPA) within the participating CF centers.
2. To examine sputum rheology (the “stickiness” or viscosity and elasticity, G’ and G’’) in CFwABPA or patients without ABPA (CFsABPA) and link rheological findings to clinical features, lung function measurement, specialized CT imaging of the airways to calculate mucus plugging score, and inflammatory parameters in sputum (eosinophils, neutrophils, extracellular DNA, ECP, EPO, fibrin, cytokines).
3. To elucidate the role of the Gal-10 protein and CLCs as a diagnostic tool to improve ABPA diagnosis in CF and elucidate whether dissolution of CLCs with a monoclonal antibody has any effects on mucus rheology in CF.

Study design:

We will perform a case-control study of at least 15 CF patients presenting with ABPA (CFwABPA, incident cases) according to the consensus criteria, will be included over 3 years’ time, as well as 15 CF patients with negative sputum cultures for Aspergillus and absence of Aspergillus sensitization (CFsABPA, total IgE below 200 IU/L). To optimize assays, we will also include 15 CF patients with Aspergillus sensitization and/or prior but not current ABPA (CFpABPA). Sputum samples will be collected, as well as bronchoalveolar lavage (BAL) samples obtained by ultrafine bronchoscopy in a subgroup, and mucus plugging scores will be calculated on low dose HRCT. Subsequently, the sputum eosinophilia and rheology will be assessed by plate and cone rheometry, the role of Gal-10 and CLCs in the pathogenesis of ABPA, and the capacity of anti-Gal-10 antibodies to dissolve CLCs and mucus plugs in CFwABPA will be measured ex vivo.

Research hypotheses:

We hypothesize that (1) CFwABPA patients have a higher burden of disease than CFsABPA patients, with higher mucus plugging scores on CT, accompanied by worse lung function; (2) that sputum of CFwABPA patients has distinct rheologic characteristics as compared with sputum of CFsABPA patients; (3) that Gal-10 contributes to the increased elasticity / tenacity of sputum of CFwABPA patients by crosslinking mucins and other glycoproteins into lattice-like structures and formation of CLCs that additionally cause DNA release from neutrophils; (4) that the presence of CLCs and increased levels of sputum Gal10 could be used as a diagnostic tool for ABPA; and (5) that anti-Gal-10 mAbs are able to resolve CLCs and consequently improve the characteristics of mucus, identifying CLCs as a potential therapeutic target in CFwABPA patients.