This study will test the safety and tolerability (how the body reacts to the drug) of REGN727 compared with placebo (an inactive substance that contains no medicine) in healthy subjects. The study drug and placebo will be administered by an injection under the skin at one clinic visit. There will be 14 clinic visits, which will include 4 overnight stays. Subjects will be monitored by the study staff for side effects and the body's response to the study drug. Vital signs (blood pressure, temperature, breathing and heart rate) will be checked, and blood and urine samples will be collected at some or all visits.

Inclusion Criteria:

• Male or female 18 to 65 years of age.
• Weight> 50 kg and <95 kg inclusive
• For women of childbearing potential, a negative serum pregnancy test at the screening visit and a negative urine pregnancy test on day 1.
• For men and women of childbearing potential, willingness to utilize adequate contraception and not become pregnant (or have their partner[s] become pregnant during the full duration of the study.
• Willing, committed, and able to return for all clinic visits and complete all study-related procedures.
• Able to read, understand and willing to sign the informed consent form.

Exclusion Criteria:

• Initiation of a new exercise routine or major change to a previous exercise routine within 4 weeks prior to screening visit.
• Pregnant or breast-feeding females.
• Significant concomitant illness or history of significant illness such as cardiac, renal, neurological, endocrinological, metabolic or lymphatic disease, or any other illness or condition that would adversely affect the subject's participation in this study.
• Hospitalization for any reason within 60 days of screening.
• Known history of Human Immunodeficiency Virus (HIV) antibody; and/or positive Hepatitis B surface antigen, and/or positive Hepatitis C antibody at the screening visit.
• Previous exposure to any therapeutic or investigational biological agent.
• History of alcohol or substance abuse within previous 5 years.