A phase I/II study of blinatumomab in combination with pembrolizumab for adults with relapsed refractory B-lineage acute lymphoblastic leukemia: University of California Hematologic Malignancies Consortium Study 1504.

Abstract

TPS7064 Background: Outcomes for adults with relapsed/refractory B-cell ALL (R/R B-ALL) remain poor despite new targeted therapies. Blinatumomab is an anti-CD19/CD3 bifunctional T-cell engaging antibody that was superior to conventional salvage therapy for remission and overall survival in a Phase III study of patients with R/R B-ALL. The CR/CRh rate for blinatumomab was 65.5% with < 50% marrow lymphoblasts but dropped to 34.4% with ≥ 50% marrow lymphoblasts. Clinical and pre-clinical findings suggest that PD-L1 overexpression on lymphoblasts and in the bone marrow may mediate resistance to blinatumomab by inhibiting T-cell activation. We hypothesize that addition of pembrolizumab will improve CR/CRh rates to blinatumomab in R/R B-cell ALL. Methods: We are conducting a phase I/II multicenter trial to evaluate the safety and efficacy of blinatumomab with pembrolizumab in adults with R/R B-ALL and a high bone marrow lymphoblast percentage (NCT 03160079). The primary endpoint is ORR (CR+CRh) after 1-2 cycles with secondary endpoints of AEs, MRD-negative CR/CRh rate, 2-year DFS, 2-year OS, and allogeneic HCT rate. Exploratory studies are evaluating cytokine expression, PD-1 expression on T-cells, PD-L1 and PD-L2 protein expression on lymphoblasts, and T-cell populations at diagnosis and in response to therapy. Eligibility includes: adults with R/R CD19+ B-ALL after ≥ 1 prior line of therapy, R/R Ph+ B-ALL must fail a 2nd- or 3rd-generation TKI or be TKI intolerant, > 50% lymphoblasts on screening bone marrow sample. Blinatumomab is given by continuous IV at 9 mcg/day days 1-7 of cycle 1, 28 mcg/day days 8-28 of cycle 1, then at 28 mcg/day days 1-28 in subsequent cycles. Pembrolizumab 200 mg IV is given on days 15 and 36 of each 42-day cycle. Patients in CR/CRh after 1-2 cycles will complete 5 cycles. Patients not in CR/CRh after 2 cycles of therapy or progressing after Day 15 of cycle 1 go off study. CNS prophylaxis with IT methotrexate is given at screening and once per cycle. A phase I run-in of 3-6 patients precedes accrual of 18-21 patients for a target of 24. The study opened in July 2017 and 4 patients have been treated. No DLTs have occurred to date. Clinical trial information: NCT03160079.