This is a single-dose, double-blind, placebo-controlled, parallel group safety, tolerability and pharmacodynamic study of subcutaneously (SC) administered REGN88 in rheumatoid arthritis patients who are receiving concomitant methotrexate. Four (4) parallel groups of 8 subjects each with active rheumatoid arthritis will be dosed SC.

Inclusion Criteria:

1. Male or female ≥18 years of age
2. Subjects must weigh >50 and <100 kg
3. Diagnosis of Rheumatoid Arthritis (RA) as defined by the 1987 revised American College of Rheumatology (ACR) criteria with disease duration of no less than 6 months and ACR class I-III

Exclusion Criteria:

1. A history of Listeriosis or active tuberculosis (TB)
2. Persistent chronic or active recurring infection requiring treatment with antibiotics, antivirals, or antifungals within 4 weeks prior to the Screening Visit
3. History of prior articular or prosthetic joint infection
4. History of a hypersensitivity reaction, other than localized injection site reaction (ISR), to any biological molecule
5. Significant concomitant illness such as, but not limited to cardiac, renal, neurological, endocrinological, metabolic or lymphatic disease that would adversely affect the subject's participation in this study