A phase 1b study of blinatumomab in Japanese children with relapsed/refractory B-cell precursor acute lymphoblastic leukemia.

Novel therapies are needed for children with relapsed/refractory (R/R) B-cell precursor acute lymphoblastic leukemia (ALL). Blinatumomab is a bispecific T-cell engager immunotherapy that simultaneously binds to CD3-positive cytotoxic T cells and CD19-positive B cells and redirects the patient's T cells to lyse malignant and normal B cells. We conducted an open-label phase 1b study to determine the safety, pharmacokinetics, efficacy, and recommended dose of blinatumomab in Japanese children with R/R B-cell precursor ALL. Patients received induction blinatumomab for 4 weeks (5 μg/m2/day week 1; 15 μg/m2/day weeks 2-4), followed by a 2-week treatment-free interval (6-week cycle). In subsequent cycles, patients received blinatumomab 15 μg/m2/day. The primary end point was the incidence of dose-limiting toxicities. Nine patients received blinatumomab. Since no dose-limiting toxicities were reported, the maximum tolerated dose was 5 μg/m2/day for week 1, followed by 15 μg/m2/day weeks 2-4 (5-15 μg/m2/day, the global recommended dose of blinatumomab). All patients had ≥ 1 grade ≥ 3 adverse events; 89% had grade ≥ 3 treatment-related adverse events. M1 remission rate within the first two cycles of treatment was 56%; one patient had a minimal residual disease response. Consistent with global studies, blinatumomab appeared to be safe with preliminary evidence of efficacy in Japanese children with R/R B-cell precursor ALL.