• Age ≥18 and ≤70

• For participants taking corticosteroids, the prednisone (or equivalent) dose must be ≤40 mg/day at 6 weeks prior to Screening and stable for ≥ 14 days before start of Screening

• For subjects on immunosuppressives or immunomodulators (other than corticosteroids), all doses must be stable for ≥ 4 weeks prior to Screening

⁃ SSc:

• Meets the 2013 American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) classification criteria for SSc

• Meet criteria a and/or b:

‣ Severe skin involvement defined as mRSS ≥ 30 or active skin disease defined as mRSS ≥ 15 at screening and one or more of the following within the prior 6 months of screening:

• An increase in mRSS of ≥ 3 units

∙ Involvement of 1 new body area with ≥ 2 mRSS units

∙ 2 new body areas with ≥ 1 mRSS unit

⁃ Moderate to severe Interstitial Lung Disease (ILD) defined by evidence of ILD on High-resolution computed tomography (HRCT) and FVC \< 70% of predicted or DLCO (hemoglobin or alveolar volume corrected) \< 70% of predicted or ILD on HRCT and progressive ILD meeting at least 2 of the following 3 criteria within the prior 6 months of screening:

• Worsening respiratory symptoms

∙ Evidence of progression on HRCT, or

∙ Evidence of absolute decline in FVC ≥ 5% (Raghu et al 2022)

• Presence of anti-nuclear antibody ≥ 2 x upper limit of normal (ULN)

• 10 years or less since the first non-Raynaud's sign or symptom

• Inadequate response or intolerance to at least one treatment, including cyclophosphamide, methotrexate, MMF/mycophenolic acid, nintedanib, rituximab, or tocilizumab

⁃ IIM:

• Diagnosis for IIM as per 2017 ACR/EULAR Classification Criteria

• One positive myositis antibody

• Activity defined as manual muscle testing (MMT-8) score \<136/150

• Creatinine kinase or aldolase ≥ 1.5 x ULN and Clinician Global Assessment ≥ 2 cm with at least one of the following:

‣ Evidence on magnetic resonance imaging (MRI) of active myositis within the last 6 months

⁃ Electromyography (EMG) with active myositis within the last 6 months

⁃ Muscle Biopsy of active myositis within last 6 months

• Refractory disease defined as ≥ 6 months failure (or intolerance) to at least 2 immunosuppressive therapies (including glucocorticoids)

⁃ AAV:

• Meets the 2022 ACR/EULAR classification criteria for Granulomatosis with Polyangiitis (GPA) (Robson 2022) or Microscopic Polyangiitis (MPA) (Suppiah 2022)

• Relapsed or refractory AAV despite repeated treatment with immunosuppressive agents or requiring prolonged and/or repeated courses of unacceptable doses of glucocorticoids to maintain disease control

• Positive test for anti-proteinase-3 (PR3-ANCA) or anti-myeloperoxidase (MPO-ANCA) at screening

• Have at least one major item, or at least 3 other items, or at least 2 renal items on the BVAS version 3