Inclusion Criteria:  Are male or female not of childbearing potential Have a body weight between 18 and 32 kilograms per square meter (kg/m²) and a body weight ≥ 50 kilograms (kg) Have veins suitable for blood sampling  Exclusion Criteria:  Have or used to have health problems or laboratory test results or ECG readings that, in the opinion of the doctor, could make it unsafe to participate, or could interfere with understanding the results of the study Have active or latent TB Have had breast cancer within the past 10 years or had lymphoma, leukemia, or any malignancy within the past 5 years Show clinical evidence of syphilis, HIV, hepatitis C, or hepatitis B, and/or test positive Have received treatment with biologic agents (such as monoclonal antibodies, including marketed drugs) within 3 months or 5 half-lives (whichever is longer) prior to dosing. Have previously completed a clinical trial investigating any other molecule targeting CD19, CD20 or have previously discontinued from this study after receiving LY3541860 Are currently participating in or completed a clinical trial within the last 30 days Have received a vaccine containing a live (attenuated) virus within 28 days of screening or intend to receive during the course of the study.