Study Evaluating SC291 in Subjects With Severe r/r B-cell Mediated Autoimmune Diseases (GLEAM)

Inclusion Criteria: 1. Age ≥18 and ≤75 2. For LN cohort: * Diagnosis of SLE based on the 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) * Biopsy-proven LN class III or IV, according to 2018 Revised International Society of Nephrology/Renal Pathology Society (ISN/RPS) criteria * Refractory disease to ≥ 2 prior treatment regimens 3. For ERL cohort: * Diagnosis of SLE based on the 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria for adult SLE * Severe or relapsing disease not responding to at least 2 prior recent disease-modifying therapies 4. For AAV Cohort, diagnosed with Granulomatous Polyangiitis (GPA) or Microscopic Polyangiitis (MPA) based on the 2022 ACR/EULAR classification criteria Exclusion Criteria: 1. Prior CD19-directed cell therapy including CAR T treatment or other genetically modified cell therapy (e.g., Natural Killer (NK) cell) 2. For LN and ERL Cohorts, central nervous system (CNS) lupus manifestations or history or presence of CNS disorder 3. For LN and ERL Cohorts, diagnosis of anti-phospholipid antibody syndrome 4. For AAV Cohort only, Diagnosis of Eosinophilic Granulomatosis with Polyangiitis (EGPA) as defined by the 2022 ACR/EULAR classification criteria for EGPA -