Rationale: IL-13 is a potential therapeutic target for idiopathic pulmonary fibrosis (IPF); preclinical data suggest a role in tissue fibrosis, and expression is increased in subjects with rapidly progressing disease.

Objectives: Investigate efficacy and safety of tralokinumab, a human anti–IL-13 monoclonal antibody, in subjects with mild to moderate IPF.

Methods: Subjects received tralokinumab (400 or 800 mg), or placebo, intravenously every 4 weeks for 68 weeks. The primary endpoint was change from baseline to Week 52 in percent predicted FVC in the intention-to-treat population. Exploratory analyses included assessment of clinical response in subgroups with baseline serum periostin concentration above/below median.

Measurements and Main Results: The study was stopped due to lack of efficacy after interim analysis. Neither tralokinumab 400 mg nor tralokinumab 800 mg met the primary endpoint; least-squares mean difference (95% confidence interval) percent predicted FVC from baseline to Week 52: −1.77 (−4.13 to 0.59) (P = 0.140) and −1.41 (−3.73 to 0.91) (P = 0.234), respectively. The primary endpoint was also not met in either treatment group in subgroups defined by periostin baseline concentration. The percentage of subjects with decline in percent predicted FVC greater than or equal to 10% at Week 52 was numerically greater for tralokinumab-treated subjects compared with placebo. The most common treatment-emergent adverse events for tralokinumab 400 mg, tralokinumab 800 mg, and placebo were cough (17.5, 30.5, 22.8%), IPF progression and exacerbation (21.1, 16.9, 22.8%), and upper respiratory tract infection (17.5, 20.3, 12.3%), respectively.

Conclusions: Tralokinumab demonstrated an acceptable safety and tolerability profile but did not achieve key efficacy endpoints.

Clinical trial registered with www.clinicaltrials.gov (NCT01629667).