A Single Ascending Dose Study in Healthy Participants and Multiple Dose Study of JNJ-55920839 in Participants With Mild to Moderate Systemic Lupus Erythematosus

This is a Phase 1, randomized, placebo-controlled, multicenter study of JNJ-55920839. The study consists of Screening Period of 28 days. The healthy participants will have a 6-day/5-night inpatient period. All Participants will receive study agent on Day 1 and SLE Participants will receive additional doses on Days 15, 29, 43, 57, and 71. The total duration of participation for each participant will be approximately 13 weeks for healthy participants, 22 weeks for participants with SLE. All eligible participants will be randomly assigned to receive active agent or placebo. The study will be conducted in 2 parts. In Part 1, single ascending doses of JNJ55920839 or placebo will be administered to sequential cohorts of healthy participants as an IV infusion or as a subcutaneous injection. In Part 2, multiple doses of JNJ-55920839 or placebo will be administered as IV infusions to participants with SLE. Blood samples will be collected for assessment of pharmacokinetic and pharmacodynamics parameters in both part 1 and 2, along with assessment of safety and clinical outcomes. Participants' safety will be monitored throughout the study.