This Phase II, double-blind, placebo-controlled, randomized, parallel-group study is designed to evaluate the efficacy, safety, and tolerability of huMAb OX40L administered to patients by IV infusion for the treatment of allergen-induced asthma.

Inclusion Criteria:

• Weight between 50 and 125 kg
• Mild, stable allergic asthma
• History of episodic wheeze and shortness of breath
• FEV1 at baseline ≥ 70% of the predicted value
• For women of childbearing potential, agreement to use an effective means of contraception while enrolled in the study
• For men with partners of childbearing potential, willingness to use condoms with spermicide during treatment
• Ability to comprehend and follow all required study procedures
• Positive skin prick test to common aeroallergens (e.g., cat, dust, mite, grass, and pollen)
• Positive allergen-induced early and late airway bronchoconstriction

Exclusion Criteria:

• A worsening of asthma or a respiratory tract infection within 6 weeks preceding study entry
• Acute infection (including viral infection) within the 6 weeks preceding dosing (8 weeks for respiratory infections) or any ongoing chronic infection
• History of recurrent bacterial infection as an adult or history or presence of any chronic infectious condition, including (but not limited to), tuberculosis, parasitic infection, etc.
• Lung disease other than mild allergic asthma
• History of heart, lung, kidney, liver, neurologic or chronic infectious disease
• Concomitant disease or condition, which could interfere with the conduct of the study, including, but not limited to, cancer, alcoholism, drug dependency or abuse, or psychiatric disease
• History of serious adverse reaction or hypersensitivity to any drug
• Pregnancy or lactation or positive serum pregnancy test at screening
• Chronic use of any other medication for treatment of allergic lung disease other than short-acting β2-agonists or ipratropium bromide
• Current (or history of) treatment with a monoclonal antibody or chimeric biomolecule within the past 5 months (5 half-lives of the drug), including omalizumab
• Regular use of tobacco products of any kind or within the previous 6 months, or smoking history > 10 pack-years