This randomized, double-blind, placebo-controlled study will evaluate the efficacy and safety of 3 dosing regimens of MEMP1972A in patients with allergic asthma who remain inadequately controlled on chronic therapy with high dose inhaled corticosteroids and a second controller medication.Patients will be randomized to 4 Arms to receive subcutaneous repeating dose of either MEMP1972A 150 mg, 300 mg, or 450 mg, or placebo. Patients will continue their usual asthma medication throughout the study. Anticipated time on study treatment is 36 weeks, with a 48-week follow-up.

Inclusion Criteria:

• Adult patients, 18 to 75 years of age inclusive
• Body weight >/= 40 kg
• Physician's diagnosis of asthma for at least 12 months
• Evidence of documented bronchodilator reversibility as defined by protocol
• Prebronchodilator FEV1 >/= 40% and </= 80% predicted at Visit 1
• Required daily use of ICS and a second controller for a minimum of 3 consecutive months prior to Visit 1
• History of at least one protocol-defined asthma exacerbation in the 18 months prior to Visit 1
• Inadequately controlled asthma despite compliance with asthma controller therapy

Exclusion Criteria:

• Asthma exacerbation requiring systemic steroids in the 30 days prior to Visit 1
• Pre-existing active lung disease other than asthma
• Any infection
• Clinically significant medical disease that is uncontrolled despite treatment or is likely to require a change in therapy during study or is of unknown etiology
• Known immunodeficiency, including but not limited to HIV infection, regardless of treatment status
• Current substance abuse
• Former smoker with >10 pack-year history or current smoker; former smokers must have stopped smoking more than 12 months prior to Visit 1
• History of anaphylaxis
• Pregnant and lactating women