Effects of Anti-TSLP in Patients With Asthma

The mannitol test is increasingly used by clinicians to diagnose asthma. It has clinical advantages in terms of being feasible in a wide range of settings with the need of a minimum of equipment. Airway hyper responsiveness (AHR) to mannitol correlates with eosinophilic airway inflammation and the degree of asthma control, predicts the risk of exacerbation and response to inhaled steroids. Subjects with asthma and indirect AHR have increased levels of intraepithelial carboxypeptidase A3 (CPA3), a metalloexopeptidase specifically expressed by mast cells, compared to asthmatics without AHR. CPA3 is known to be selectively present in the MCTC phenotype (mast cells containing both tryptase and chymase), and recent studies suggest that increased CPA3 levels also constitutes a marker of a Th2-high/eosinophilic and steroid-responsive asthma. Interestingly, treating mast cell precursors with TSLP increases CPA3 immunostaining, suggesting that TSLP released by e.g. airway epithelium up-regulate a mast cell phenotype that is potentially important in AHR and also promotes eosinophilic airway inflammation. Previous published data by the investigators confirm that increased MCTC in submucosa of subjects with asthma is associated with an increased CPA3 and TSLP expression. The investigators speculate that the effect of MEDI9929 on AHR to mannitol is likely to be primarily a consequence of functional differences in mast cells. Treating subjects with asthma with MEDI9929 will potentially block downstream effects on mast cell activation as well as eosinophilic inflammation, which may reduce AHR to inhaled mannitol. The purpose of this study is to investigate whether AHR to mannitol is a suitable marker of response to MEDI9929, but also to better understand the anti-inflammatory effects of MEDI9929 in the lungs, including whether a reduced AHR to mannitol following treatment with MEDI9929 is related to a reduction in chymase/CPA-3 positive mast cells. The investigators hypothesize that MEDI9929 will decrease the response to mannitol (measured as an increase in PD15) after 12 weeks of treatment as compared to placebo. It is further hypothesized that the number of chymase/CPA-3 positive mast cells in airway epithelium and submucosa will be reduced after 12 weeks of treatment with MEDI9929 in subjects with AHR to mannitol. This trial offers the opportunity to study potential biomarkers and surrogate endpoints, but also to identify the anti-inflammatory effects of MEDI9929 on a mechanistic level. This study is a randomized, double-blind, placebo-controlled trial. It includes a enrolment period of maximum 2 weeks, 12 weeks of treatment (three IV doses of either 700mg MEDI9929 or placebo) and 8 weeks follow-up after the second bronchoscopy.