This is a phase 1, randomized, double-blind, placebo-controlled first-in-human (FIH) study to assess the safety and tolerability of ascending single doses of REGN2009 administered to healthy volunteers.

Inclusion Criteria:

1. Healthy men and women ages 18 to 65 years inclusive
2. Body mass index between 18.0 kg/m^2 and 30.0 kg/m^2, inclusive

Exclusion Criteria:

1. Pregnant or breast-feeding women
2. Any clinically significant abnormalities observed during screening (day -21 to day -2)
3. 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
4. History of drug or alcohol abuse within a year prior to the screening visit (day -21 to day -2)
5. Hospitalization for any reason within 60 days of the screening visit (day -21 to day -2)
6. Participation in any clinical research study within 30 days of the screening visit (day -21 to day -2) or within 5 half-lives of the investigational drug or therapy being studied (whichever is longer)
7. History of a hypersensitivity reaction to doxycycline or similar compound
8. Any medical or psychiatric condition which, in the opinion of the investigator, would place the subject at risk, interfere with participation in the study or interfere with the interpretation of the study results
9. Previous adverse experience to any biological investigational or therapeutic agent
10. Sexually active men or women of childbearing potential who are unwilling to practice adequate contraception during the study

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial and not all inclusion/ exclusion criteria are listed.