A IMMA Master Protocol: A Study of LY3361237 in Participants With at Least Moderately Active Systemic Lupus Erythematosus

Inclusion Criteria: * Are diagnosed with SLE at least 24 weeks before Day 1 of study * Have documentation of having a score of 10 or more points on the European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) 2019 classification criteria for SLE * Have a SLEDAI-2K score ≥6 at screening (Day 1) and clinical Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) score ≥4 (not including any items related to laboratory values) at randomization (Day 2) * Must be receiving at least 1 background standard-of-care medication for SLE Exclusion Criteria: * Participants are excluded if they have received any of the following medications or therapies within the indicated timeframe prior to the randomization visit (Day 2). * Are currently receiving oral corticosteroids at doses \>20 mg per day of prednisone (or equivalent) or have adjusted the dosage of corticosteroids within 2 weeks before starting study treatment * Have received parenteral corticosteroids within 12 weeks before starting study treatment or are expected to require parenteral corticosteroids during the study * Have a current or recent acute, active infection * Have had a serious, chronic, recurring conditions of herpes simplex, herpes zoster, recurring cellulitis, chronic osteomyelitis) * Have human immunodeficiency virus (HIV) infection, hepatitis B virus (HBV), hepatitis C infection (HCV), active tuberculosis (TB) * Have active fibromyalgia or active occurrence of an inflammatory condition that, in the investigator's opinion, would make it difficult to appropriately assess SLE activity for the purposes of this study * Have experienced a cardiac event within 24 weeks to 12 months prior to screening * Have a history of clinically significant or uncontrolled illness that in the opinion of the investigator could put the participant at risk to participate in the study * Are, in the judgment of the investigator, actively suicidal and therefore deemed to be at significant risk for suicide * Are pregnant or are intending to become pregnant or to breastfeed at any time in the study