This is a study of the Safety, Tolerability, Pharmacokinetics, and Immunogenicity of REGN668 Administered Subcutaneously to Healthy Volunteers.

Inclusion Criteria:

1. Male or female subjects 18 to 55 years of age.
2. Body weight between 60 kg and 80 kg, body mass index between 20 and 30 kg/m2 inclusive.
3. NHV as evidenced by comprehensive clinical assessment (detailed medical history and complete physical examination).
4. Normal resting blood pressure and heart rate
5. Willingness to refrain from the consumption of alcohol for 24 hours prior to each study visit.

Exclusion Criteria:

1. History or presence of currently relevant medical conditions, including any cardiovascular, pulmonary, gastrointestinal, hepatic, renal, metabolic, hematological, neurological, musculoskeletal, psychiatric, systemic, ocular, infectious or parasitic disease, or signs of acute illness.
2. Administration of any medications within 1 week before randomization, other than vitamins, nutritional supplements, or low doses of aspirin taken prophylactically.
3. Onset of a new exercise routine or major change to a previous exercise routine within 2 weeks prior to randomization. Subjects must be willing to maintain a relatively constant level of exercise during the study and refrain from unusually strenuous physical activities
4. Known history of human immunodeficiency virus (HIV) antibody; and/or positive hepatitis B surface antigen (HBsAg), and/or positive hepatitis C antibody (HCV) at the screening visit.
5. History of substance (eg. drug or alcohol) abuse or regular (daily) smoking within a year prior to randomization or positive results on urine drug screen.
6. Excessive consumption of beverages with xanthine derivates (caffeine, theophylline, theobromine), such as coffee, tea, cola, or yerba mate (more than 4 cups or glasses per day).
7. Hospitalization for any reason within 60 days of randomization.
8. Participation in any clinical research study evaluating another investigational drug or therapy within 30 days of the investigational drug, whichever is longer, prior to the randomization visit.
9. Live/attenuated vaccinations within 12 weeks of randomization or during the study.
10. Tuberculosis vaccination within the last year.
11. Previous exposure to any other biological agent within 12 months of randomization.
12. History of a hypersensitivity reaction to doxycycline or other tetracyclines.
13. Recent travel (within 12 months of randomization) to areas endemic for parasitic helminthes, such as developing countries, particularly in Africa and the tropical and subtropical regions of Asia.
14. Pregnant or breast-feeding women.
15. Unwilling to use adequate birth control if of reproductive potential and sexually active