Efficacy and Safety Study of TAS5315 Compared With Placebo in Participants With Rheumatoid Arthritis.

An Early Phase-II, Randomized, Double-blind, Study of TAS5315 in Rheumatoid Arthritis Patients With an Inadequate Response to Methotrexate

The purpose of this study is to assess the efficacy and safety of TAS5315 in combination with methotrexate in a 12 week or 36 week in participants with rheumatoid arthritis with inadequate response to methotrexate.

Inclusion Criteria:

• Have a diagnosis of RA according to 2010 ACR/ EULAR rheumatoid arthritis (RA) classification criteria
• Have been treated with methotrexate (MTX) for at least 90 days prior to screening, and must be on a stable dose between 8 and 16 mg/week for at least 56 days prior to screening.
• Have an inadequate response to MTX
• Have a minimum of 6 swollen and 6 tender joints from 66/68 joint count
• Have hsCRP of ≥ 0.6 mg/dL

Exclusion Criteria:

• Have been treated with conventional synthetic disease-modifying anti-rheumatic drug, except for MTX, within 28 days prior to randomization
• Have an inadequate response to biologic disease-modifying anti-rheumatic drug or Have been treated with 2 biologic treatment
• Have been treated with Janus Kinase inhibitors or other Bruton's Tyrosine Kinase inhibitors
• Have a positive result for hepatitis B surface antigen/antibody, hepatitis B core antibody, hepatitis C virus antibody or human immunodeficiency virus antigen/antibody at screening
• Have been treated with Oral steroids at dose above 10 mg/day of prednisone or prednisone equivalents
• Have a diagnosis of Felty's syndrome
• Have a positive result of the QuantiFERON®-tuberculosis (TB) Gold test or a T-spot ®-TB test at screening
• Have a positive result of β-D-glucan at screening