Safety and Efficacy Study of M2951 in Participants With Rheumatoid Arthritis

Exclusion Criteria

• •Use of oral corticosteroids \> 10 mg daily prednisone equivalent, use of injectable corticosteroids, or change in dose of corticosteroids within 2 weeks prior to Screening or during Screening
• •Initiation or change in dose for nonsteroidal anti-inflammatory drugs (NSAIDs) within 2 weeks prior to Screening
• •Treatment with tofacitinib, other Bruton's Tyrosine Kinase (BTK) inhibitors, or a biologic disease-modifying antirheumatic drug (DMARD; eg, anti-tumor necrosis factor alpha \[anti-TNF-α\], tocilizumab \[anti-interleukin-6 receptor\], abatacept \[CTLA4-Fc\]), or other immunosuppressive drugs(sulfasalazine would be acceptable at a stable dose) other than methotrexate within 3 months prior to Screening or during Screening
• •Treatment with anti-CD20 therapy (eg, rituximab) within 12 months prior to Screening or during Screening
• •Immunologic disorder other than Rheumatoid Arthritis (RA), with the exception of secondary Sjogren's syndrome associated with RA, and well-controlled diabetes or thyroid disorder, or any other condition requiring oral, intravenous, intramuscular, or intra-articular corticosteroid therapy
• •Vaccination with live or live-attenuated virus vaccine within 1 month prior to Screening
• •Active, clinically significant, viral, bacterial, or fungal infection, or any major episode of infection requiring hospitalization or treatment with parenteral anti-infectives within 4 weeks of Screening or during Screening, or completion of oral anti-infectives within 2 weeks before or during Screening, or a history of recurrent infections (ie, 3 or more of the same type of infection in a 12-month rolling period). Vaginal candidiasis, onychomycosis, and genital or oral herpes simplex virus considered by the Investigator to be sufficiently controlled would not be exclusionary
• •History of or positive testing for human immunodeficiency virus (HIV), hepatitis C antibody and/or polymerase chain reaction, hepatitis B surface antigen (HBsAg) (+) and/or hepatitis B core total, and/or IgM antibody (+) at Screening
• •History of or current diagnosis of active tuberculosis (TB); undergoing treatment for latent TB infection (LTBI); untreated LTBI (as determined by documented results within 3 months of the Screening Visit of a positive TB skin test with purified protein derivative with induration \>= 5 millimeter (mm), a positive QuantiFERON-TB test or positive or borderline T-SPOT \[Elispot\] test); or positive QuantiFERON-TB test at Screening. Participants with documented completed appropriate LTBI treatment would not be excluded and are not required to be tested
• •Participants with current household contacts with active TB will also be excluded
• •Indeterminate QuantiFERON-TB or T-SPOT tests may be repeated once, and will be considered positive if retest results are positive or indeterminate
• •History of cancer, except adequately treated basal cell or squamous cell carcinomas of the skin (no more than 3 lesions requiring treatment in lifetime) or carcinoma in situ/cervical intraepithelial neoplasia of the uterine cervix, unless considered cured \> 5 years
• •Clinically significant abnormality on electrocardiogram (ECG), or an active infective process or any other clinically significant abnormality on Screening chest X-ray (CXR) taken within 4 weeks of the first dose, per Investigator opinion. If a CXR has been taken within the previous 3 months and results are available and normal, the CXR does not need to be carried out
• •B cell (CD19) count less than (\<) 50% of the lower limit of normal at Screening
• •Significant cytopenia including absolute neutrophil count \< 1,500/ mm\^3, platelet count \< 100,000/mm\^3, or absolute lymphocyte count \< 1,000/mm\^3