• 17 years of age and older.

• Participants must have adequate organ function as defined in the protocol.

⁃ SLE/LN-specific Inclusion Criteria:

• Participants must have a diagnosis of SLE according to the 2019 European League Against Rheumatism/American College of Rheumatology classification criteria for systemic lupus erythematosus for at least 6 months.

• Participants must have current or history of elevated anti-double stranded deoxyribonucleic acid (anti-dsDNA), anti-Smith, anti-histone, and/or anti-nucleosome antibodies.

⁃ SLE-specific Inclusion Criteria:

⁃ 1\. Participants who have:

• A Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) score of ≥8 (including at least 4 points from non-laboratory assessments; excluding alopecia, mucosal ulcers, and fever) and at least 2 British Isles Lupus Assessment Group B (BILAG B) organ system scores and/or

• At least one British Isles Lupus Assessment Group A (BILAG A) organ system score, including cardiac (peri- or myocarditis), respiratory (pleuritis or lung involvement), vascular and renal.

⁃ LN-specific Inclusion Criteria:

⁃ 1\. Participants with active, biopsy-proven, proliferative LN Class III or IV, either with or without the presence of class V, according to the 2018 revised International Society of Nephrology/Renal Pathology Society (ISN/RPS) criteria. Biopsy must be within 12 months prior to Screening or during Screening.

⁃ IIM-specific Inclusion Criteria:

⁃ 1\. Classification of IIM (juvenile-onset IIM may be included):

• For Dermatomyositis (DM), meet 2017 American College of Rheumatology/European Alliance of Associations of Rheumatology (ACR/EULAR) diagnostic criteria for definite or probable DM.

• For participants with anti-synthetase syndrome (ASyS), meet Classification Criteria for anti-synthetase syndrome per the Classification Criteria for Anti-Synthetase Syndrome (CLASS) Project with a positive tRNA synthetase autoantibody at Screening or per medical history.

• For Polymyositis (PM)/ necrotizing myopathy (NM), meet 2017 ACR/ EULAR classification criteria for definite or probable PM/NM and meet one of the following criteria:

⁃ i. Positive myositis specific antibody (MSA) at Screening or per medical history or ii. Muscle biopsy at Screening or per medical history available for review

⁃ DcSSc-specific Inclusion Criteria:

• Meets the 2013 ACR/EULAR criteria for SSc with a total score of ≥9.

• Meets criteria for DcSSc, including skin involvement proximal to the elbow and/or knee.

• mRSS units ≥15 at Screening; for participants agreeing to biopsy, skin thickening from SSc in the forearm suitable for biopsy.