The purpose of the study is to determine the safety and tolerability of PRO 140, an investigational anti-HIV drug, administered via intravenous infusion.

Study hypothesis: Single intravenous doses of PRO 140 can be safely administered to humans and will result in measurable concentrations of the product in serum.

PRO 140 is a man-made monoclonal antibody to the chemokine receptor CCR5, which serves as a co-receptor for HIV. In numerous preclinical models of HIV infection, PRO 140 broadly and potently blocks CCR5-mediated HIV entry without blocking the natural activity of CCR5. PRO 140 is being developed for therapy of HIV infected individuals. The purpose of this study is to evaluate the safety and tolerability of PRO 140 in HIV uninfected male volunteers. The pharmacokinetics and pharmacodynamics of PRO 140 will also be assessed in this study.

Participants in this study will be randomly assigned to receive a single dose of one of several possible doses of PRO 140 or placebo. Participants will remain in the clinic for observation and evaluation for 24 hours after the single-dose administration. Follow-up visits will occur at 2, 3, 5, 7, 10, 14, 28, 42, and 60 days post-treatment. Physical exams, electrocardiograms (ECGs), vital signs measurement, adverse event reporting, and blood and urine collection will occur at most visits.

Inclusion Criteria:

• Not more than 20% below or 20% above ideal weight for height and estimated frame size
• Good health, with no clinically significant abnormal findings on the physical examination, medical history, or laboratory tests

Exclusion Criteria:

• History of clinically significant disease
• History of clinically significant allergies, including drug allergy
• Participated in another clinical trial within the 3 months prior to study entry
• HIV infected
• Hepatitis B or C virus infected
• Active significant infection
• Prior exposure, allergy, or known hypersensitivity to PRO 140

Adverse event data was collected over an 18-month period.

Adverse events were systematically assessed through documented physical examinations, vital sign evaluation, ECGs as well as hematology, uranalysis and chemistry labs. All information is collected on case report forms.