The purpose of this study is to assess the efficacy, pharmacokinetics, safety, and immunogenicity of KN019 after intravenous administration on background methotrexate in patients with active rheumatoid arthritis and inadequate response to methotrexate.

This study is designed to provide efficacy data in support of the proposed claims of reducing signs and symptoms, improvement in physical function, and 1 year safety data for KN019 dosed at 5 and 10 mg/kg in patients with inadequate response to stable weekly doses of background methotrexate.

Key Inclusion Criteria:

• The patient must meet the American College of Rheumatology (ACR) classification criteria for the diagnosis of rheumatoid arthritis (RA) by satisfying at least four of the seven criteria;

• Patients must have been taking methotrexate for at least 3 months with at least a weekly dose of 7.5-25 mg, and a stable dose for 28 days prior to treatment (Day 1)

• The patient must have active disease at both screening and baseline, as defined by having both:

  6 tender/painful joints on motion (out of 68 joints assessed); and; 6 swollen joints (out of 66 joints assessed); CRP ≥ 7 mg/L, or ESR ≥28 mm/h

Key Exclusion Criteria:

• Pregnant or lactating females.
• History of any other autoimmune rheumatic disease.
• Patients who have previously received CTLA4-Ig therapy for any reason.