The primary objective is to determine if AMG 853 is effective compared with placebo as measured by change in Asthma Control Questionnaire (ACQ) composite symptoms scores from baseline to week 12.

Inclusion Criteria:

• Males or females 18 to 65 years of age
• Percent of predicted FEV1 ≥ 50% and ≤ 80%
• At least 12% reversibility over pre-bronchodilator FEV1
• Inhaled corticosteroid (ICS) ≥ 200 and ≤ 1000 µg/day fluticasone or equivalent.
• Ongoing asthma symptoms with ACQ score ≥ 1.5 points

Exclusion Criteria:

• History of chronic obstructive pulmonary disease or other chronic pulmonary condition other than asthma
• Any uncontrolled, clinically significant systemic disease
• Respiratory infection within 4 weeks of the screening visit