Single Ascending Dose Study of MEDI1341 in Healthy Volunteers

This is a single-center, randomized, double-blind, placebo-controlled study of single
ascending intravenous doses of MEDI1341 in male and nonfertile female healthy volunteers,
aged 18 to 80 years.

The study will include up to 5 planned cohorts; each cohort will comprise 8 subjects. Within
each cohort, 6 subjects will be randomized to receive MEDI1341 and 2 will be randomized to
receive placebo. A Safety Review Committee will review data from each cohort before
progression to the next higher dose cohort occurs. An optional sixth cohort of 8 subjects may
be studied, based on an interim review of safety, tolerability, and pharmacokinetic/
pharmacodynamic data, with a dose level that may be lower than, the same as, or higher than
for any preceding cohort.

On Day 1, each randomized subject will receive a single 60 minute intravenous infusion of
MEDI1341 or placebo and will undergo scheduled safety, pharmacokinetic, pharmacodynamic, and
immunogenicity assessments. Additional study assessments will occur on Days 2, 4, 8, 15, 22,
29, 43, 57, and 92.

Inclusion Criteria:

- Subjects must be healthy, with no clinically significant abnormality identified on the
medical or laboratory evaluation at screening

- Subjects must weigh ≥50 kg and must have a body mass index between 18 and 32 kg/m2,
inclusive

- Subjects must have a 12-lead ECG recorded at screening that is normal for the
appropriate age group and shows no abnormalities that will compromise safety in this
study

- Subjects must have clinical neurological examinations with normal findings at
screening and at baseline

Exclusion Criteria:

- Nicotine use within 6 months before screening

- Considered to be at a high risk of developing a stroke

- Significant medical history of dizziness, blackouts, fainting, or vaso-vagal attacks

- History of any significant neurological illness

- History of severe allergy or history of hypersensitivity to immunizations or
immunoglobulins

- History of any significant psychiatric disorder

- History of alcohol abuse

- History of cancer within 5 years of screening

- History of drug abuse

- Any contraindication to Lumbar Puncture

- Any clinically significant abnormality in ECG rhythm, conduction or morphology

- Positive serologic findings at screening for human immunodeficiency virus (HIV)
antibodies, hepatitis B surface antigen, or hepatitis C virus antibodies

- Use of prescription or non-prescription drugs

- For female subjects, a positive serum or urine pregnancy test result at screening