FT819 for Lupus Nephritis

INCLUSION CRITERIA: * Age ≥12 to ≤70 years * Diagnosis of SLE per EULAR/ACR 2019 classification criteria * Biopsy-proven proliferative Class III or IV LN, with or without concomitant Class V involvement, based on the 2003/2018 ISN/RPS classification * Positivity for at least one of the following autoantibodies at screening: 1. Antinuclear antibody (ANA) 2. Anti-double-stranded DNA (anti-dsDNA) or 3. Anti-Smith antibody * Active disease, defined as: a. Evidence of SLE activity, defined as either: i. SLEDAI-2K ≥6 or ii. At least 1 BILAG A or 2 BILAG B scores for SLE-related organ involvement; and b. Evidence of renal involvement, defined as UPCr ≥1 g/g; and c. Moderate-to-severe renal disease with investigator's impression that improvement is possible * Refractory to ≥2 systemic immunosuppressive therapies for the treatment of LN EXCLUSION CRITERIA: * Evidence of inadequate organ function during the screening period * Active central nervous system (CNS) symptoms attributable to autoimmune disease within 12 months prior to trial intervention * History of or current renal diseases (other than LN) that, in the opinion of the investigator, could interfere with assessment of LN or confound evaluation of disease activity * Receipt of dialysis (hemodialysis or peritoneal dialysis) within 12 weeks of trial intervention * Irreversible organ damage related to underlying disease (e.g., ESRD) where, in the opinion of the investigator, CD19 CAR T-cell therapy would be unlikely to benefit the participant * History of malignancy in the prior 5 years * Known allergy to the following FT819 components: albumin (human) or DMSO * History of intolerance or contraindication to bendamustine * Body weight \<30 kg * Any medical condition, clinical laboratory abnormality, or nonmedical/social issue that, per investigator or medical monitor judgement, precludes safe participation in and completion of the trial or that could affect compliance with protocol conduct or interpretation of results