Male or female adults ≥18 years and ≤45 years of age at the time of signing the informed consent form (ICF).

Diagnosed with SLE by the 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria.

Positivity for antinuclear antibody, anti-ds-DNA antibody, and/or anti-Smith antibody at screening.

Active SLE at screening, as defined by SLEDAI-2K ≥8 points (with a clinical SLEDAI-2K ≥4 points, excluding alopecia, mucosal ulcers, and fever); AND one or more major organ systems with British Isles Lupus Assessment Group (BILAG) A score, excluding musculoskeletal, mucocutaneous, and/or constitutional organ systems.

Failure to respond to glucocorticoids and ≥2 of the following treatments for at least 3 months: cyclophosphamide (CY), mycophenolic acid or its derivatives, belimumab, methotrexate, azathioprine, anifrolumab, rituximab, obinutuzumab, cyclosporin, tacrolimus, or voclosporin.

Body weight <50 kg.

Active neurological symptoms of SLE at screening.

Potentially irreversible organ damage related to SLE, where in the opinion of the investigator, CD19 CAR T-cell therapy would be unlikely to benefit the participant.

Non-malignant CNS disease such as stroke, epilepsy, or neurodegenerative disease or receipt of medications for these conditions within 2 years prior to study enrollment.

Prior treatment with CAR T-cell therapy within the last 6 months, allograft organ transplant, or hematopoietic stem cell transplant.