In some patients with moderate-to-severe asthma, particularly those with noneosinophilic inflammation, the disease remains uncontrolled. This trial evaluated the efficacy and safety of tezepelumab (AMG 157/MEDI9929), a human monoclonal antibody specific for the epithelial-cell-derived cytokine thymic stromal lymphopoietin (TSLP), in patients whose asthma remained uncontrolled despite treatment with long-acting beta-agonists and medium-to-high doses of inhaled glucocorticoids.In this phase 2, randomized, double-blind, placebo-controlled trial, we compared subcutaneous tezepelumab at three dose levels with placebo over a 52-week treatment period. The primary end point was the annualized rate of asthma exacerbations (events per patient-year) at week 52.The use of tezepelumab at a dose of 70 mg every 4 weeks (low dose; 145 patients), 210 mg every 4 weeks (medium dose; 145 patients), or 280 mg every 2 weeks (high dose; 146 patients) resulted in annualized asthma exacerbation rates at week 52 of 0.26, 0.19, and 0.22, respectively, as compared with 0.67 in the placebo group (148 patients). Thus, exacerbation rates in the respective tezepelumab groups were lower by 61%, 71%, and 66% than the rate in the placebo group (P<0.001 for all comparisons). Similar results were observed in patients regardless of blood eosinophil counts at enrollment. The prebronchodilator forced expiratory volume in 1 second at week 52 was higher in all tezepelumab groups than in the placebo group (difference, 0.12 liters with the low dose [P=0.01], 0.11 liters with the medium dose [P=0.02], and 0.15 liters with the high dose [P=0.002]). A total of 2 patients in the medium-dose group, 3 in the high-dose group, and 1 in the placebo group discontinued the trial regimen because of adverse events.Among patients treated with long-acting beta-agonists and medium-to-high doses of inhaled glucocorticoids, those who received tezepelumab had lower rates of clinically significant asthma exacerbations than those who received placebo, independent of baseline blood eosinophil counts. (Funded by MedImmune [a member of the AstraZeneca Group] and Amgen; PATHWAY ClinicalTrials.gov number, NCT02054130 .).