A Study to Evaluate the Safety, Tolerability, Cellular Kinetics, Pharmacodynamics, and Efficacy of P-CD19CD20-ALLO1 in Participants With Severe, Treatment-refractory Systemic Lupus Erythematosus (SLE)

Key Inclusion criteria: 18-75 years old SLE diagnosis per 2019 EULAR/ACR classification criteria ≥ 24 weeks Autoantibody positive and low complement at screening Treatment refractory: Failed ≥ 2 treatments for at least 3 months Highly active disease: SLEDAI-2K ≥ 8 (excluding alopecia, headache, and fever; additional protocol-specified requirements to enhance specificity of findings) BILAG-2004 cat A in ≥ 1 organ system and/or cat B in ≥ 2 organ systems (excluding constitutional, musculoskeletal, and/or mucocutaneous organ systems for category B) PGA score ≥ 1.0 on a 0 to 3 VAS For patients with lupus nephritis: Biopsy-proven Class III or IV (± Class V) active LN per 2018 ISN/RPS criteria within 12 months of screening Modified NIH activity index ≥ 1/24 UPCR ≥ 1g/g Key Exclusion criteria: Participants who are pregnant, breastfeeding, or intend to become pregnant within the timeframe in which contraception is required Prior treatment with CAR T-cell therapy, B-cell-targeting T-cell-dependent bispecific antibody, gene therapy product, total body irradiation, allograft organ transplant, or hematopoietic stem cell transplant Significant organ impairment (renal, hepatic, cardiac, or pulmonary) or uncontrolled medical disease which, in the investigator's opinion would preclude patient participation or that may require treatment with systemic corticosteroids or immunosuppressants during the study Active severe or unstable neuropsychiatric disease Protocol-specified active or chronic infections, recent major episode of infection High-risk medical conditions (e.g. high bleeding risk, history of cancer, recent major surgery, history of HLH/MAS, substance abuse within the previous year) Other protocol-defined inclusion/exclusion criteria apply