A Clinical Study to Evaluate the Safety and Efficacy of GT801 Injection in the Treatment of Moderate-to-Severe Refractory Autoimmune Diseases

Inclusion Criteria: * 1\. The participant or their legal representative voluntarily signs a written informed consent form and is willing and able to comply with the study procedures. * 2\. Aged 18 to 65 years old (inclusive) at the time of signing the informed consent, regardless of gender. * 3\. Participants with Systemic Lupus Erythematosus (SLE) must meet the following criteria: * a) Fulfill the 2019 European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria for SLE. * b) Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2000) score ≥ 6, with at least one British Isles Lupus Assessment Group Index (BILAG-2004) Grade A (severe manifestation) or two Grade B (moderate manifestation) organ scores, or both; or SLEDAI-2000 score ≥ 8. * c) Meet the definition of refractory or relapsing disease: No response to conventional treatment for more than 6 months, or disease reactivation after achieving remission. Conventional treatment is defined as the use of glucocorticoids and cyclophosphamide plus at least one of the following immunomodulatory agents: antimalarials, azathioprine, mycophenolate mofetil, methotrexate, leflunomide, tacrolimus, cyclosporine, and biological agents including rituximab, belimumab, and tabalumab. * 4\. Participants with Idiopathic Inflammatory Myopathy (IIM) must meet the following criteria: * a) Fulfill the 2017 EULAR/ACR classification criteria for inflammatory myopathy (including Dermatomyositis \[DM\], Polymyositis \[PM\], Antisynthetase Syndrome \[ASS\], and Necrotizing Myopathy \[NM\]). * b) Positive for myositis-specific antibodies or myositis-associated antibodies. * c) Must have moderate to severe IIM at screening, defined as Manual Muscle Testing-8 (MMT-8) score ≥ 142, or MMT-8 score \< 142 plus meeting 2 of the following criteria: * 1\) Physician Global Assessment (PGA) (Visual Analog Scale \[VAS\]) ≥ 2 cm (on a 10-cm VAS). * 2\) Patient Global Assessment (PtGA) (VAS) ≥ 2 cm (on a 10-cm VAS). * 3\) Health Assessment Questionnaire (HAQ) score \> 0.25. * 4\) Elevation of one or more muscle enzymes (creatine kinase \[CK\], lactate dehydrogenase \[LDH\], aspartate aminotransferase \[AST\], alanine aminotransferase \[ALT\]) ≥ 1.5 × Upper Limit of Normal (ULN). * d) Meet the definition of refractory/relapsing or progressive disease: * 1\) Refractory/relapsing: No response to conventional treatment for more than 6 months, or disease reactivation after achieving remission. Conventional treatment is defined as the use of glucocorticoids and cyclophosphamide plus at least one of the following immunomodulatory agents: antimalarials, azathioprine, mycophenolate mofetil, methotrexate, leflunomide, tacrolimus, cyclosporine, and biological agents including rituximab, belimumab, and tabalumab. * 2\) Progressive: Development of worsening myositis or rapidly progressive interstitial lung disease. * 5\. Participants with Systemic Sclerosis (SSc) must meet the following criteria: * a). Fulfill the 2013 American College of Rheumatology (ACR) classification criteria for SSc. * b). Positive for SSc-related autoantibodies. * c). Meet the definition of refractory/relapsing or progressive disease: * 1\) Refractory/relapsing: No response to conventional treatment for more than 6 months, or disease reactivation after achieving remission. Conventional treatment is defined as the use of glucocorticoids and cyclophosphamide plus at least one of the following immunomodulatory agents: antimalarials, azathioprine, mycophenolate mofetil, methotrexate, leflunomide, tacrolimus, cyclosporine, and biological agents including rituximab, belimumab, and tabalumab. * 2\) Refractory/relapsing: No response to conventional treatment for more than 6 months, or disease reactivation after achieving remission. Conventional treatment is defined as the use of glucocorticoids and cyclophosphamide plus at least one of the following immunomodulatory agents: antimalarials, azathioprine, mycophenolate mofetil, methotrexate, leflunomide, tacrolimus, cyclosporine, and biological agents including rituximab, belimumab, and tabalumab. * 6\. Participants with ANCA-Associated Vasculitis (AAV) must meet the following criteria: * a). Fulfill the 2022 ACR/EULAR classification criteria for ANCA-associated vasculitis, including Microscopic Polyangiitis (MPA), Granulomatosis with Polyangiitis (GPA), and Eosinophilic Granulomatosis with Polyangiitis (EGPA). * b). Positive for ANCA-related antibodies (myeloperoxidase-ANCA \[MPO-ANCA\] or proteinase 3-ANCA \[PR3-ANCA\]). * c). Birmingham Vasculitis Activity Score (BVAS) ≥ 15 points (total score: 63 points), indicating active vasculitis. * d). Meet the definition of refractory/relapsing disease: No response to conventional treatment for more than 6 months, or disease reactivation after achieving remission. Conventional treatment is defined as the use of glucocorticoids and cyclophosphamide plus at least one of the following immunomodulatory agents: antimalarials, azathioprine, methotrexate, leflunomide, tacrolimus, cyclosporine, and biological agents including rituximab, belimumab, and tabalumab. * 7\. Participants with Sjogren's Syndrome must meet the following criteria: * a). Fulfill the 2002 American-European Consensus Group (AECG) criteria for primary Sjogren's Syndrome or the 2016 ACR/EULAR classification criteria. * b). EULAR Sjogren's Syndrome Disease Activity Index (ESSDAI) score ≥ 6. * c). Positive for anti-SSA/Ro antibodies. * d). Meet the definition of refractory/relapsing disease: No response to conventional treatment for more than 6 months, or disease reactivation after achieving remission. Conventional treatment is defined as the use of glucocorticoids and cyclophosphamide plus at least one of the following immunomodulatory agents: antimalarials, azathioprine, methotrexate, leflunomide, tacrolimus, cyclosporine, and biological agents including rituximab, belimumab, and tabalumab. * 8\. Laboratory test result