A Study of LY3337641 in Rheumatoid Arthritis

Inclusion Criteria:

- Female subjects of childbearing potential test negative for pregnancy at screening and
agree not to breastfeed

- Female subjects: agree to use a reliable method of birth control from the start of
screening until 28 days after the last dose of study drug or be of nonchildbearing
potential

- Male subjects: agree to use a reliable method of birth control from the start of
screening until 2 weeks after the last dose of study drug or have undergone vasectomy

- Have a diagnosis of RA based on the 2010 ACR/European League against Rheumatism
criteria

- Have at least 1 of the following:

- rheumatoid factor or anti-citrullinated peptide antibodies (ACPA) at screening OR

- radiographs documenting bony erosions

- Have active RA, defined as:

- Part A: ≥3 swollen joints (based on 66-joint counts)

- Part B:

- ≥6 swollen joints (based on 66-joint counts)

- ≥6 tender joints (based on 68-joint counts)

- hsCRP levels greater than the upper limit of normal (ULN) OR positive for ACPA

- Part B only: Have had inadequate response, loss of response, or intolerance to at
least 1 synthetic OR biologic disease-modifying antirheumatic drug (DMARD)

Exclusion Criteria:

- Have received any of the following:

- Part B only: any prior treatment with a product directly targeting Bruton's
tyrosine kinase (BTK) (marketed or investigational)

- belimumab, natalizumab, or vedolizumab within 6 months prior to baseline

- B-cell-depleting agents (such as rituximab) or other cell-depleting biologics
(eg, anti-CD3 antibody) within 12 months prior to screening for Part A or at any
time prior to screening for Part B

- Have known hypogammaglobulinemia

- Have hepatitis C virus, hepatitis B virus or human immunodeficiency virus

- Have active tuberculosis (TB)

- Are at high risk of infection or have recent evidence of clinically significant
infection

- Have had lymphoma, leukemia, or any malignancy within the previous 5 years except for
treated basal cell or squamous epithelial carcinomas of the skin

- Have received a live (attenuated) vaccine within 28 days prior to baseline or plan to
receive one during the study