For a study, researchers sought to assess the outcomes of 18 patients with the isolated extramedullary disease (iEMD) relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL) treated with CD19-directed CAR T cells ARI-0001 in 2 centers (adult and pediatric), including patients treated in the CART19-BE-01 trial and the consecutive compassionate use program. PET-CT and cerebrospinal fluid analysis detected iEMD in patients 78% (14/18) and 28% (5/18). Patients were administered cyclophosphamide and fludarabine, followed by  1 × 106 ARI-0001 cells/kg, initially as a single dose (first patient) and then in three fractions (10%, 30%, and 60%). About 50% (9/18) of individuals experienced cytokine release syndrome (CRS), with no cases of a grade more than or equal to 3 CRS and 1 incidence (6%) of grade 1 neurotoxicity. Tocilizumab was administered to 6% of patients (1/18). At 2 years, the procedure-related death rate was 0%. About 94% (95% CI: 73% to 99%) of patients exhibited objective responses, with 78% (95% CI: 52% to 94%) demonstrating complete responses (CR). At 2 years, progression-free survival was 49% (95% CI: 30% to 79%), and overall survival was 61% (95% CI: 40% to 92%). The use of ARI-0001 cells in patients with R/R ALL and iEMD was linked with a safety and effectiveness profile comparable to that found in patients with bone marrow involvement and consistent with previous CART19 products.