Phase II Trial of the Anti-CD19 Bispecific T Cell–Engager Blinatumomab Shows Hematologic and Molecular Remissions in Patients With Relapsed or Refractory B-Precursor Acute Lymphoblastic Leukemia

Patients with relapsed or refractory acute lymphoblastic leukemia (ALL) have a dismal prognosis. CD19 is homogenously expressed in B-precursor ALL and can be targeted by the investigational bispecific T cell-engager antibody blinatumomab. A phase II trial was performed to determine clinical activity in this patient cohort.Thirty-six patients with relapsed or refractory B-precursor ALL were treated with blinatumomab in cycles of 4-week continuous infusion followed by a 2-week treatment-free interval in a single-arm study with a dose-finding stage and an extension stage. The primary end point was complete remission (CR) or CR with partial hematologic recovery (CRh). Major secondary end points included minimal residual disease (MRD) response, rate of allogeneic hematopoietic stem-cell transplantation (HSCT) realization, relapse-free survival (RFS), overall survival (OS), and incidence of adverse events (AEs).Median age was 32 years (range, 18 to 77 years). Twenty-five patients (69%) achieved a CR or CRh, with 88% of the responders achieving an MRD response. Median OS was 9.8 months (95% CI, 8.5 to 14.9), and median RFS was 7.6 months (95% CI, 4.5 to 9.5). Thirteen responders (52%) underwent HSCT after achieving a CR or CRh. The most frequent AE during treatment was pyrexia (grade 1 or 2, 75%; grade 3, 6%). In six patients with nervous system or psychiatric disorder AEs and in two patients with cytokine release syndrome, treatment had to be interrupted or discontinued. These medical events were resolved clinically.The data support further investigation of blinatumomab for the treatment of adult patients with relapsed or refractory ALL in a larger confirmatory study.