BACKGROUND: Systemic lupus erythematosus (SLE) is a classic systemic autoimmune disease mediated by autoantibodies. Chimeric antigen receptor T (CAR-T) cell therapy, known for its success in cancer, has shown promise in achieving durable B cell depletion and long-term remission in SLE. Relmacabtagene autoleucel (relma-cel) is the second anti-CD19 CAR-T product approved for marketing by the National Medical Products Administration (NMPA) in China and demonstrates its long-term efficacy in relapsed/refractory (r/r) large B cell lymphoma (LBCL). We report the results from a phase I open-label clinical trial of relma-cel in treating patients with moderately to severely active SLE. METHODS: Eligible patients were aged 18-70 years, a ≥6-month history of SLE, and the disease had to remain active after at least 2 months of stable SLE standard treatment prior to screening. We evaluated four dose levels (DL) of relma-cel in a dose-escalation scheme: total dose of 25 × 10 FINDINGS: Between March 28, 2023 and April 8, 2024, a total of 12 patients were screened for study inclusion, of whom 8 patients were enrolled and assigned to different dose levels: 25 × 10 INTERPRETATION: This study preliminarily demonstrated that relma-cel is an effective and safe CAR-T product for the treatment of patients with moderately to severely active SLE, providing valuable clinical insights into the management of rare complications. Further studies with larger sample sizes are warranted. FUNDING: National Natural Science Foundation of China.