A Study of KITE-363 in Participants With Refractory Autoimmune Diseases

This study will have two Phases: Phase 1a and Phase 1b. The goal of this clinical study is to learn more about the study drug KITE-363, to establish dosing, tolerability, safety, and preliminary efficacy of KITE-363 in participants with refractory autoimmune diseases. The primary objectives of this study are: Phase 1a: To evaluate the safety and tolerability of KITE-363 in participants with autoimmune disease. To determine the recommended dose for Phase 1b. Phase 1b: To evaluate the safety and efficacy of KITE-363 in participants with autoimmune disease.

Key Inclusion Criteria: Inclusion Criteria for systemic lupus erythematosus (SLE) and lupus nephritis (LN): * Age ≥ 18 years * Meet the European Alliance of Associations for Rheumatology (EULAR)- American College of Rheumatology (ACR) 2019 classification criteria for SLE * Presence of either double-stranded deoxyribonucleic acid (DNA) anti- double-stranded DNA (anti-dsDNA) and/or anti-Smith antibodies at screening per local laboratory. * Moderate to severe, active disease defined as at least one British Isles Lupus Assessment Group (BILAG-A) score or 2 BILAG B (excluding constitutional and/or neuropsychiatric organ system). * Refractory to steroids and inadequate response or intolerance to at least 2 of the following treatments, used for at least 3 months each: cyclophosphamide, mycophenolate mofetil or its derivatives, belimumab, anifrolumab, rituximab, obinutuzumab, methotrexate, azathioprine, cyclosporin, tacrolimus, or voclosporin. * For LN: Refractory to steroids and inadequate response or intolerance to at least 2 of the following treatments, used for at least 3 months each: cyclophosphamide, mycophenolate mofetil or its derivatives, belimumab, rituximab, obinutuzumab, azathioprine, cyclosporin, tacrolimus, or voclosporin Inclusion Criteria for LN: * Renal biopsy-proven Class III or intravenous (IV) ± V LN according to the revised International Society of Nephrology and Renal Pathology Society (ISN/RPS) criteria within 6 months prior to or during screening * Evidence of active LN at screening Inclusion Criteria for systemic sclerosis (SSc): * Age ≥ 18 years * Diffuse Systemic Sclerosis (SSc) according to ACR/EULAR 2013 classification criteria with active skin disease and/or progressive SSc-interstitial lung disease (ILD) OR limited SSc with progressive ILD. * Refractory or intolerance to 1 of the following for a minimum of 3 months and/or contraindication: mycophenolate mofetil or its derivatives, methotrexate, tocilizumab (or other IL-6 inhibitor), rituximab (or other B-cell depleting agent), nintedanib (or other antifibrotic agents), cyclophosphamide. * High-resolution computer tomography (HRCT) scan and pulmonary function test (PFT) within 3 months prior to screening. Inclusion Criteria for idiopathic inflammatory myopathy (IIM): * Age ≥ 18 years * Probable or definite IIM based on EULAR/ACR 2017 classification (excluding inclusion body myositis). * Active disease demonstrated by electromyography (EMG), magnetic resonance imaging (MRI) or muscle enzymes * Moderate to severe disease activity * Positive for myositis specific antibodies for patients with non-dermatomyostitis IIM * HRCT scan and PFT within 3 months prior to screening. * Refractory or intolerance to at least 1 month of glucocorticoids and standardized use of at least 2 immunosuppressant/modulator (eg, intravenous gamma globulins, methotrexate, mycophenolate mofetil and its derivatives, azathioprine, cyclophosphamide, calcineurin inhibitors, Janus kinase (JAK) inhibitors, rituximab or other B-cell depleting agent). Inclusion Criteria for all Cohorts: * Adequate hepatic, renal, pulmonary, and cardiac function. Key Exclusion Criteria: Exclusion Criteria for all Cohorts: * Females of childbearing potential who are pregnant or breast feeding. * Dialysis within the past year. * History of malignancy, within the last 5 years. * Hypogammaglobulinemia requiring immunoglobulin replacement. * History of autologous or allogeneic stem cell transplant and/or organ transplant. * Prior treatment with cellular therapy, gene therapy and/or T-cell engager therapy. * Known history of HIV infection, or hepatitis B or C virus infections. * Active or untreated latent tuberculosis (TB). * Active or uncontrolled infections. * Nonspecific, overlap, mixed autoimmune diseases not clearly identified into any of the studied cohorts. Exclusion Criteria for LN: * Significant pre-existing damage or rapidly progressive glomerulonephritis (GN). Exclusion Criteria for SLE: * Drug-induced SLE. * Catastrophic antiphospholipid syndrome. * Thrombotic thrombocytopenic purpura. * Active or unstable lupus neuropsychiatric manifestations within last 6 months. Exclusion Criteria for SSc: * Infected digital ulceration or necrosis with signs of infection. * Severe pulmonary hypertension. * History of systemic sclerosis renal crisis within 12 months prior to enrollment. * History of active bleeding related to gastric antral vascular ectasia. Exclusion Criteria for IIM: * Other inflammatory and noninflammatory myopathies. * Severe, irreversible muscle damage. Note: Other protocol defined Inclusion/Exclusion criteria may apply.