A specialized method of sputum collection and processing for therapeutic interventions in cystic fibrosis

Cystic fibrosis (CF) lung disease is characterized by aggressive neutrophil-dominated inflammation mediated in large part by neutrophil elastase (NE), an omnivorous protease released by activated or disintegrating neutrophils and a key therapeutic target. To date, several short-term studies have shown that anti-NE compounds can inhibit NE and have anti-inflammatory effects. However, progression to large-scale or multicenter clinical trials has been hampered by the fact that the current gold standard methodology of evaluating airway NE inhibition, bronchoalveolar lavage (BAL), is invasive, difficult to standardize across sites and excludes those with severe lung disease. Attempts to utilize sputum that is either spontaneously expectorated (SS) or induced (IS) have been hindered by poor reproducibility, often due to the various processing methods employed. In this study, we evaluate TEmperature-controlled Two-step Rapid Isolation of Sputum (TETRIS), a specialized method for the acquisition and processing of SS and IS. Using TETRIS, we show for the first time that NE activity and cytokine levels are comparable in BAL, SS and IS samples taken from the same people with CF (PWCF) on the same day once this protocol is used. We correlate biomarkers in TETRIS-processed IS and clinical outcome measures including FEV₁, and show stability and reproducible inhibition of NE over time in IS processed by TETRIS. The data offer a tremendous opportunity to evaluate prognosis and therapeutic interventions in CF and to study the full spectrum of people with PWCF, many of whom have been excluded from previous studies due to being unfit for BAL or unable to expectorate sputum.