A Study to Evaluate CDX-301 (rhuFlt3L) in Healthy Volunteers

A total of seven cohorts of healthy volunteers are planned with doses of CDX-301 (rhuFlt3L)
ranging between 1 and 75 μg/kg and dosing durations between 5 and 10 days.

Volunteers will be admitted to an inpatient unit during the Treatment Period. Blood samples
will be collected periodically to assess the effect of CDX-301. Volunteers will be followed
for safety for 28 days following the last dose. Any volunteer who develops anti-CDX-301
antibodies will be followed monthly until the antibody response is below the limit of
detection. In general, the total duration of the study will be between approximately 33-38
days.

Inclusion Criteria:

Among other criteria, volunteers must meet the following conditions to be eligible for the
study:

1. Ages 18 - 55

2. Body Weight ≤ 120 kg

3. Generally good health and without significant medical conditions

4. Willing to use effective method of contraception

5. Abstinence from alcohol for 72 hours prior to study drug administration and
throughout the study

6. Negative screening test for HIV, hepatitis B, and hepatitis C

7. Provide written informed consent

Exclusion Criteria:

Among other criteria, volunteers who meet the following conditions are NOT eligible for
the study:

1. Drug or alcohol abuse within 12 months

2. Positive drug screen

3. Receipt of certain types of experimental drugs or other treatments, or certain
medications

4. Use of systemic immunosuppressive agents (excluding topical steroids) within 12
months

5. History of certain diseases including syphilis, herpes zoster, primary or secondary
immunodeficiency

6. Diagnosis with or family history of significant autoimmunity (ex: type I diabetes,
multiple sclerosis, rheumatoid arthritis, scleroderma)

7. Any history of cancer, excluding adequately treated and cured basal or squamous cell
carcinoma of the skin, or cervical carcinoma in situ within 2 years

8. History of asthma requiring any use of inhaled or oral medication within 5 years

9. Herpes zoster within 3 months

10. Donation of blood within 8 weeks, and donation of plasma within 2 weeks