Background: Asthma is a heterogeneous and complex disease in both its clinical course and response to treatment. IL-13 is central to Type 2 inflammation and contributes to many features of asthma. In a previous Phase 2 study, lebrikizumab, an anti-IL-13 monoclonal antibody, did not significantly improve FEV1 in mild-to-moderate asthma patients not receiving ICS therapy. This Phase 3 study was designed to further assess the efficacy and safety of lebrikizumab in adult patients with mild-to-moderate asthma treated with daily short-acting β2-agonist therapy alone. Methods: Adult patients with mild-to-moderate asthma were randomised to receive lebrikizumab 125 mg subcutaneously (SC), placebo SC, or montelukast 10 mg orally for 12 weeks, with an 8-week follow-up period. The primary efficacy endpoint was absolute change in pre-bronchodilator FEV1 from baseline at Week 12. Findings: A total of 310 patients were randomised and dosed in the study. The mean absolute change in FEV1 from baseline at Week 12 was higher in the lebrikizumab-treated arm compared with placebo (150 mL versus 67 mL); however, this improvement did not achieve statistical significance (overall adjusted difference of 83 mL [95% CI:-3, 170]; p = .06). Montelukast did not improve FEV1 as compared with placebo. Lebrikizumab was generally safe and well tolerated during the study. Interpretation: Lebrikizumab did not significantly improve FEV1 in mild-to-moderate asthma patients at a dose expected to inhibit the IL-13 pathway. Inhibiting IL-13 in this patient population was not sufficient to improve lung function. These data support the findings of a previous trial of lebrikizumab in patients not receiving ICS
