⁃ For Cohort 1: Subjects with LN:

• Clinical diagnosis of systemic lupus erythematosus (SLE) per 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria (Aringer 2019)

• Active kidney disease with biopsy-proven active LN Class III or IV (coexistent class V permitted) (per 2018 International Society of Nephrology \[ISN\]/Renal Pathology Society \[RPS\] criteria); biopsy should be performed within 6 months before enrolling in the study

• ECOG performance ≤ 2

• Proteinuria (or urine protein creatinine ratio \[UPCR\]) \> 1g / 24 hours

⁃ For Cohort 1: Subjects with SLE with Extrarenal Involvement

• Clinical diagnosis of systemic lupus erythematosus (SLE) per 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria (Aringer 2019).

• Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) score ≥ 8 with a clinical SLEDAI-2K score (SLEDAI-2K not including points for anti-dsDNA and/or low complement) ≥ 6 and/or ≥ 1 British Isles Lupus Assessment Group (BILAG)-2004 Category A

• Positive anti-nuclear antibody (ANA) test results and/or a positive anti-dsDNA and/or anti-Smith antibodies above the ULN

• Estimated creatinine clearance ≥ 60 mL/min

• Inadequate response in terms of active disease despite treatment with current standard of care for SLE including corticosteroids and at least 2 SLE therapy

⁃ For Cohort 2: Subjects with SSc

• Disease duration ≤ 6 years (from onset of first non-Raynaud manifestation)

• Participants with diffuse cutaneous SSc with worsening skin disease, must meet both of the following criteria: mRSS ≥ 15 at screening AND one of the following within 6 months prior to screening: (i) mRSS increase of ≥ 3 units in the total mRSS, OR (ii) Involvement of 1 new body area, OR (iii) Increase in mRSS ≥ 2 units in 1 body area

• Participants with diffuse or limited cutaneous SSc and ILD must meet both of the following criteria: ILD, i.e. fibrosis on HRCT within 4 months of screening AND Progression of ILD by FVC or HRCT in previous 24 months

• FVC ≥ 45% predicted, DLCO ≥ 40%

• Exclude PAH defined as RVSP ≥ 45 mmHg or right atrial or ventricular enlargement or dilatation, or renal crisis within 1 year of enrollment

⁃ For Cohort 3: Subjects with AAV

• Diagnosis of AAV defined as either GPA or MPA according to the 2012 Chapel Hill Consensus Conference

• Positive for PR3-ANCA or MPO-ANCA

• Relapsed or refractory AAV after at least 1 standard-of-care immunosuppressive regimen in addition to steroids.

• Severe disease (i.e., presence of one or more major AAV sign or symptom per the BVAS or ≥ 3 minor items, or at least the 2 renal items of proteinuria and hematuria due to vasculitis)

• Adequate renal function: CrCl ≥ 30 mL/min

• Proteinuria ≤ 8 g/24 hour

⁃ For Cohort 4: Subjects with Idiopathic Inflammatory Myopathies

• Meets the 2017 ACR/EULAR classification criteria (Lundberg 2017) for probable/definite IIM

• Muscle weakness defined as Manual Muscle Testing (MMT)-8 score \< 142/150, and ≥ 2 of the following abnormal core set measures: (i) Patient global assessment VAS ≥ 2 cm (on 10-cm VAS), (ii) Physician global assessment VAS ≥ 2 cm (10-cm VAS), (iii) HAQ-DI \> 0.25 , (iv) Extra-muscular global activity VAS ≥ 2 cm (10-cm VAS)

• Active disease defined as ≥ 1 of the following signs in the past 4 months: a) Elevated serum CK or aldolase levels ≥ 3 times ULN; b) Active myositis by muscle biopsy, muscle MRI, or EMG; c) Active DM rash and CDASI \>14; d) Active interstitial lung disease

• Positivity for ≥ 1 myositis-specific antibody or myositis-associated antibody at screening

• Inadequate response or intolerance/contraindication to glucocorticoids and to ≥ 2 immunosuppressants for 3 months/drug

⁃ For Cohort 4: Subjects with Stiff Person Syndrome

• Meets the 2009 criteria for diagnosis of stiff person syndrome (SPS) (Dalakas 2009): (a) Stiffness of the axial muscles, particularly the abdominal and thoraco-lumbar paraspinals, leading to hyperlordosis; (b) Superimposed painful spasms triggered by unexpected tactile or auditory stimuli; (c) Severe anxiety with task-specific phobias especially in anticipation of physically challenging tasks; (d) Electromyographic evidence of continuous motor unit activity of agonist and antagonist muscles; (e) Absence of other neurological findings that may suggest an alternative diagnosis; (f) Highly positive anti-GAD titer (\> 10,000 IU/mL in serum by ELISA or detectable in CSF)

• Inadequate response or intolerance or contraindication to ≥ 1 treatment including chronic IVIG or other biologic