Study to Assess Safety and Effectiveness of Branebrutinib Treatment in Participants With Active Systemic Lupus Erythematosus or Primary Sjögren's Syndrome, or Branebrutinib Treatment Followed by Open-label Abatacept Treatment in Study Participants With Active Rheumatoid Arthritis

Inclusion Criteria: Sub-study for Systemic Lupus Erythematosus (SLE)

• Active SLE as defined by the Systemic Lupus Erythematosus International CollaboratingClinics (SLICC) classification
• Diagnosed with SLE more than 24 weeks before screening visit Sub-study for primary Sjögren's Syndrome (pSS)
• Moderate to severe pSS, meeting ACR-EULAR classification criteria Sub-study for active Rheumatoid Arthritis (RA)
• Moderate to severe adult-onset RA
• ACR global functional status class I to III Women and men must agree to follow instructions for methods of contraception.

Exclusion Criteria: Sub-study for SLE

• Certain other autoimmune diseases and overlap syndromes Sub-study for pSS
• Certain other immune-mediated diseases, active fibromyalgia, or other medicalconditions Sub-study for RA
• Diagnosis with juvenile arthritis or idiopathic arthritis before age 16 For all sub-studies:
• History of any significant drug allergy
• Active infection, significant concurrent medical condition, or clinically significantabnormalities Other protocol defined inclusion/exclusion criteria could apply