IMPT-514 in Systemic Lupus Erythematosus, Anca-associated Vasculitis, and Idiopathic Inflammatory Myopathy

General Inclusion Criteria: 1. Willing and able to provide written informed consent. 2. Age 18 years of age or older and ≤75 years. 3. Weight \> 35 kg at enrollment. 4. On stable background therapy (such as mycophenolate, cyclophosphamide, etc.) for autoimmune disease (SLE, AAV, IIM) with stable dose of immunosuppressants for at least 4 weeks prior to screening. For SLE participants: 1\. Diagnosis of SLE according to the 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria or 2012 Systemic Lupus Collaborating Clinics (SLICC) criteria, including positive ANA \>1:80 or positive anti-dsDNA. For AAV participants: 1\. Meets the diagnostic criteria for ANCA vasculitis in 2022 ACR/EULAR, including microscopic polyangiitis (MPA), granulomatous polyangiitis (GPA), and eosinophilic granulomatous polyangiitis (EGPA). For IIM (Dermatomyositis, Anti-Synthetase Syndrome, and Immune-Mediated Necrotizing Myopathy) participants: 1\. Diagnosis of probable or definite IIM with subgroup classification of dermatomyositis, or immune-mediated necrotizing myopathy (IMNM) subgroup of polymyositis. Exclusion Criteria: 1. Any clinically significant underlying illness, other than systemic autoimmune disease (SLE, AAV, IIM), which would pose a safety risk or concern, as determined by the Investigator. 2. Rapidly progressive glomerulonephritis. 3. For SLE participants: Active central nervous system (CNS) lupus. 4. History of, or current significant neurologic disease. 5. History of allogeneic bone marrow or stem cell transplantation or solid organ transplantation (such as kidney, lung, heart transplant) or plans for such transplantation in future. 6. History of prior CAR T treatment, autologous or allogeneic. 7. Drug induced SLE, drug induced vasculitis or drug induced myopathy or myositis. 8. Any primary immunodeficiency. 9. History of, or current significant cardiovascular dysfunction.