Safety and Pharmacokinetics Study of XOMA 052 in Subjects With Active, Stable, Moderate to Severe Rheumatoid Arthritis

Inclusion Criteria: * American College of Rheumatology (ACR) diagnostic criteria for RA * Moderate to severe disease, defined as follows - At least six tender and six swollen joints (28 joint count) AND ESR \> 28 mm/hr or CRP \> 1.0 mg/dL * Current duration of RA at Screening ≥ 6 months and ≤ 20 years * RA and other medical conditions must be stable. * Age ≥ 18 and ≤ 75 at Screening * Weight ≥ 80 lbs (36.3 kg) and ≤ 275 lbs (125.0 kg) * For females with child-bearing potential, a negative serum pregnancy test Exclusion Criteria: * Major surgery within 28 days prior to Day 0 * Joint replacement surgery within 60 days prior to Day 0 or joint replacement surgery planned within 9 months following Day 0 * Known HIV antibody, or hepatitis B surface antigen * History of malignancy within 5 years prior to Screening other than carcinoma in situ of the cervix, or adequately treated, non-metastatic squamous or basal cell carcinoma of the skin * Immunodeficiency * History or symptoms of a demyelinating disease * History of severe allergic or anaphylactic reactions to humanized or murine monoclonal antibodies. Respiratory distress (dyspnea, oxygen desaturation with pO2 \< 90% or onset of acute respiratory distress syndrome), flank or back pain, and/or hypotension may be signs of anaphylaxis. * History of tuberculosis, positive PPD test, active atopic disease requiring medication, or asthma. A subject who has had a positive PPD test but has completed a course of treatment for tuberculosis, had a documented vaccination against tuberculosis, or had a negative QuantiFERON -TB test result is eligible. * Chronic obstructive pulmonary disease (COPD), asthma, or other pulmonary disease requiring more therapy than using one inhaler 4× daily * Significant systemic involvement secondary to RA (e.g. vasculitis, pulmonary fibrosis) * Liver disease (e.g., hepatitis, cirrhosis) or abnormal hepatic function. If the diagnosis of liver disease was based on positive Hep C serology due to prior vaccination, the subject is eligible. * Pregnant or planning to become pregnant during the course of the study, or breast-feeding