This Phase 1, randomized, double-blind, placebo-controlled study will evaluate the safety, tolerability and pharmacokinetics of two, single intravenous (IV) high doses of MHAA4549A as compared to placebo when administered to healthy volunteers.

Inclusion Criteria:

• Age 18 years and older
• Body mass index (BMI) between 18 and 32 kg/m2, inclusive
• Weight 40 - 100 kg
• In good health, determined by no clinically significant findings from medical history, 12-lead ECG, vital signs, and clinical laboratory evaluations
• Willing to use acceptable contraceptive measures as defined by the protocol
• Agreeable to, and deemed able to by the investigator, to comply with the requirements of the study, including the follow-up period
• Willing to abstain from the use of drugs of abuse while enrolled in the study

Exclusion Criteria:

• History or clinically significant manifestations of disorders
• History of acute allergic reaction or drug allergies
• History or presence of an abnormal ECG
• History of significant alcohol abuse within 1 year prior to screening or regular use of alcohol within 6 months prior to the screening visit
• History of significant drug abuse within 1 year prior to screening
• Current tobacco smokers
• Positive drug screen at screening or at check-in
• Positive pregnancy test result at screening or Day -1 or breast feeding during the study
• Males who have a pregnant female partner
• Donation of plasma within 7 days prior to study drug administration
• Donation or loss of whole blood
• Receipt of blood products within 2 months before initiation of dosing on Day 1
• History of malignancy within 10 years of screening except completely excised basal cell carcinoma or squamous cell carcinoma of the skin
• History of severe systemic bacterial, fungal, or parasitic infections associated with more than two hospitalizations per year or more than two courses of intravenous (IV) antibiotics within 1 year
• Received oral antibiotics within 4 weeks before initiation of dosing on Day 1, or IV antibiotics within 8 weeks before initiation of dosing
• Hospitalization within 4 weeks before initiation of dosing on Day 1
• Use of any over the counter or prescription medications/products within 7 days prior to Day 1 and unwilling to abstain from the use of such drugs up until at least the Day 29 study visit, unless deemed acceptable by the investigator and Sponsor
• Participation in a clinical trial within 4 weeks
• Received any vaccine within 14 days prior to screening
• Positive blood test for chronic viral infections