Comparison of Obecabtagene Autoleucel Versus an External Control Arm in Adult Patients With Relapsed/Refractory B-Cell Acute Lymphoblastic Leukemia

Adults with relapsed or refractory B-cell acute lymphoblastic leukemia (B-ALL) treated with obecabtagene autoleucel (obe-cel) achieved higher remission rates and longer survival than matched patients given standard non-CAR T-cell therapies, according to an analysis published in Leukemia. As the pivotal FELIX trial was single-arm, investigators led from University Hospital of Würzburg constructed external control arms from historical trial data using propensity score matching. The comparison offers contextualized efficacy and safety estimates in a setting where randomized data are unavailable.

Approximately 5% to 10% of patients with B-ALL are refractory to primary chemotherapy and 30% to 60% relapse, and no randomized trials compare CD19 CAR T-cell therapy with standard options after relapse. Ten historical trials of blinatumomab, inotuzumab ozogamicin, or conventional chemotherapy were selected from 201 candidates, yielding 415 eligible control patients. Patients from FELIX cohort IIA were matched 1:1 on age, sex, performance status, bone marrow blast percentage, prior lines of therapy, extramedullary disease, prior allogeneic transplant, and refractoriness to the last line, producing 107 intent-to-treat and 84 modified intent-to-treat pairs. The primary endpoint was overall remission rate.

Overall remission rate was 67.3% with obe-cel versus 51.4% with standard of care in the intent-to-treat comparison (odds ratio, 1.9; 95% CI, 1.1-3.4; p = 0.0257) and 79.8% versus 54.8% in the modified intent-to-treat comparison (odds ratio, 3.3; p = 0.0009). Median overall survival censored for transplant was 15.1 versus 7.0 months (hazard ratio, 0.53; p = 0.0015) and 13.9 versus 7.8 months without censoring (hazard ratio, 0.70; p = 0.0430). Event-free survival favored obe-cel across analyses, with a median of 9.8 versus 2.5 months when censored for transplant (hazard ratio, 0.47; p < 0.0001). Grade 3 or higher treatment-emergent adverse events occurred in 81.0% versus 86.9% of patients, with identical rates of grade 3 or higher cytokine release syndrome (3.6%). The authors note that blinatumomab accounted for more than 80% of control-arm treatment and that transplant rates were roughly twice as high among controls, and conclude that obe-cel may improve outcomes over historical standard of care in adult relapsed/refractory B-ALL.

Reference:

Topp MS, Shah BD, Jabbour E, et al. Comparison of obecabtagene autoleucel versus an external control arm in adult patients with relapsed/refractory B-cell acute lymphoblastic leukemia. Leukemia. Published online July 17, 2026. http:doi.org/10.1038/s41375-026-03045-7