A Study of LY3541860 in Adult Participants With Moderately to Severely Active Rheumatoid Arthritis

Inclusion Criteria:

• Have a diagnosis of adult-onset Rheumatoid Arthritis (RA) for at least 3 monthsprior to screening, as defined by the 2010 ACR/EULAR classification criteria.

• Have moderately to severely active RA, at screening (Visit 1) and baseline (Visit 2), defined by the presence of

• ≥6 swollen joints based on 66 joint count (and ≥4 swollen joints on 28 jointcount), and

• ≥6 tender joints based on 68 joint count (and ≥4 tender joints on 28 jointcount).

• Have active synovitis in ≥1 joint, in hands or wrists, of the investigator choosingat screening, having an MRI synovitis RAMRIS score of ≥2 as determined from thecentral reading of the images.

Exclusion Criteria:

• Have a diagnosis or history of malignant disease within 5 years prior to baseline,with the exceptions of

• basal cell or squamous epithelial carcinomas of the skin that have beenresected with no evidence of metastatic disease for 3 years, or

• cervical carcinoma in situ, with no evidence of recurrence within the 5 yearsprior to baseline.

• Have estimated glomerular filtration rate (eGFR) of <45 milliliter per minute (mL/minute) from serum creatinine using the Chronic Kidney Disease EpidemiologyCollaboration (CKD-EPI) creatinine equation.

• Have a current or recent active infection.

• Have presence of 1 or more significant concurrent medical conditions perinvestigator judgment, including but not limited to

• poorly controlled diabetes or hypertension

• chronic kidney disease Stage 3a or b, 4, or 5

• symptomatic heart failure according to New York Heart Association Class 2, 3,or 4

• myocardial infarction, unstable angina pectoris, stroke, or transient ischemicattack within the past 12 months before baseline

• severe chronic pulmonary disease, for example, requiring oxygen therapy majorchronic inflammatory disease or connective tissue disease other than RA,including but not limited to

• systemic lupus erythematosus

• psoriatic arthritis

• axial spondyloarthritis, including ankylosing spondylitis and non-radiographicaxial spondyloarthritis

• reactive arthritis

• gout

• scleroderma

• polymyositis

• dermatomyositis

• active fibromyalgia, or

• multiple sclerosis

• Have received any prior B-cell targeted therapy (for example, anti-CD19 antibodiesor anti-CD20 antibodies, such as rituximab).

• Received corticosteroids, opioids, conventional disease-modifying antirheumatic drug (cDMARD), with changes in dose or have received Janus kinase (JAK) inhibitors within 28 days prior to the screening MRI or plan on receiving these drugs during thestudy.