A Study to Assess Adverse Events, How the Drug Moves Through the Body and Effectiveness of Intravenous Infusions of ABBV-319 in Adult Participants With Systemic Lupus Erythematosus (SLE), Sjogren's Disease (SjD) and Rheumatoid Arthritis (RA)

Systemic lupus erythematosus (SLE) is a chronic, systemic autoimmune disease characterized by B cell hyperactivity. Sjorgren's disease (SjD) is a chronic, multisystem autoimmune disease characterized by lacrimal and salivary gland inflammation, with resultant dryness of the eyes and mouth and occasional glandular enlargement and Rheumatoid arthritis (RA) is a long-lasting autoimmune disease that causes the body's immune system to attack itself. RA targets the body's joints, causing inflammation (swelling, pain, and redness). ABBV-319 exhibits potential B cell depletion in SLE, SjD and RA which are characterized by B cell hyperactivity. The purpose of this study is to assess the pharmacokinetics, safety, and efficacy of ABBV-319 in adult participants with SLE, SjD and RA. ABBV-319 is an investigational drug being developed for the treatment of SLE , SjD and RA. Participants are placed in 1 of 8 groups called treatment arms. Each group receives a different dose of ABBV-319 depending on whether they have SLE, SjD or RA. Around 48 adult participants with SLE, SjD or RA will be enrolled at approximately up to 17 sites worldwide. Participants will receive 2 doses of IV ABBV-319 21 days apart and will be followed for up to 343 days. There may be higher treatment burden for participants in this trial compared to their standard of care (due to study procedures). Participants will attend regular visits during the study at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires.