Long-term survival in adult patients with relapsed/refractory B-precursor acute lymphoblastic leukemia (ALL) who achieved minimal residual disease (MRD) response following anti-CD19 BiTE® blinatumomab

Introduction: Relapsed/refractory (r/r) B-precursor ALL in adults has an unfavorable prognosis with a median overall survival of 4-8 months and a 5-year survival of <10%. Long-term follow-up data are presented from an exploratory phase 2 study with blinatumomab, an investigational bispecific T-cell engager (BiTE®) antibody construct that directs cytotoxic T-cells to CD19-expressing target cells (Topp MS et al. Blood 2012;120(21):670). Methods: The primary endpoint was hematologic complete remission (CR) or CR with partial hematologic recovery (CRh∗) within 2 cycles of blinatumomab. Secondary endpoints included rate of minimal residual disease (MRD) response (defined as < 10-4), overall survival (OS), and relapse-free survival (RFS). Blinatumomab was administered by continuous intravenous infusion for 28 days followed by a 14-day treatment-free interval. Responding patients had the option to receive 3 additional cycles of treatment or to proceed to allogeneic hematopoietic stem cell transplantation (aHSCT). Results: 36 patients were treated; 25 (69%) responded, with 15 (42%) achieving CR and 10 (28%) CRh∗. MRD response was achieved in 22 (88%) of these 25 patients with CR or CRh∗. Thirteen patients with CR or CRh∗ proceeded to aHSCT after blinatumomab treatment. In addition, one patient with hypocellular bone marrow and MRD response after the first cycle underwent aHSCT. Follow-up for RFS is 22.4 months; median RFS is 8.8 months. Median follow-up for OS is 30.2 months; median OS is 12.9 months. Ten patients (28%) are alive at 29.7 months (Figure). We analyzed the characteristics of the 10 living long-term survivors, defined as OS of 2 years or longer, seven of whom were relapse-free. The age of these 10 patients at the time of first infusion ranged from 21 to 72 years; the blast count at screening ranged from 8% to 97% (median, 56%). Four of the 10 patients alive had received aHSCT prior to blinatumomab treatment. Of the six patients without a prior aHSCT, two were primary refractory; two had the first relapse within 12 months and two after 12 months post first diagnosis. In the 10 surviving patients blinatumomab treatment induced CR in seven patients, CRh∗ in two patients, and blast-free hypo-cellular bone marrow in one patient. All 10 surviving patients had an MRD response following blinatumomab treatment. The patient with hypocellular bone marrow received a transplant after the first cycle before potential recovery of blood counts qualifying for CR/CRh∗ could occur. Seven of the surviving patients underwent aHSCT after blinatumomab, including four patients who received a second aHSCT after they had already received an aHSCT prior to blinatumomab. One of the three patients who did not undergo aHSCT after CRh∗ had grade 4 cytokine release syndrome requiring resuscitation after 1 day of blinatumomab treatment and has remained in ongoing remission for 22 months without any further treatment aside from 5 cycles of blinatumomab. Another one of these three patients, who had a grade 3 neurologic event on day 2 of cycle 2, has remained in ongoing remission for 34 months without any further treatment aside from 5 cycles of blinatumomab. The third of these three patients had two CD19-positive relapses after CR following blinatumomab treatment. The patient was retreated with 3 cycles of blinatumomab, resulting twice in CR and MRD response. Two of the 10 surviving patients relapsed after blinatumomab and aHSCT; one patient with a CD 19-negative relapse achieved another hematologic remission by chemotherapy. Summary: These data show that patients with r/r ALL, who achieved MRD response and received subsequent aHSCT following blinatumomab immunotherapy may achieve long-term survival longer than 2 years. Studies with a larger sample size are warranted to confirm these data. Two patients with grade 3 or 4 toxicities showed long-term survival without aHSCT after blinatumomab. (Figure Presented).