CD19-negative relapse of pediatric B-cell precursor acute lymphoblastic leukemia following blinatumomab treatment

CD19-negative relapse in B-cell precursor acute lymphoblastic leukemia (ALL) is observed as an infrequent event after chemotherapy and in up to 20% of patients after CD19-directed chimeric antigen receptor (CAR) T-cell immunotherapy. Patients with CD19-negative relapse usually have a poor prognosis . The mechanisms underlying CD19-negative relapse are not fully understood but are important to elucidate to further optimize CD19-directed immunotherapies . Monitoring blasts in patients with CD19-negative relapse by flow cytometry is challenging due to the lack of cell surface markers other than CD19 that are consistently expressed. Furthermore, CD19 is often used as a parameter to quantify minimal residual disease (MRD) and diagnose relapse. Potential markers to monitor persistent or recurrent leukemic blasts in an emergent CD19-negative blast population include B-cell lineage antigens (CD20, CD22, CD24, and intracellular iCD79a) and the common ALL antigen CD10. Blinatumomab is an anti-CD3/CD19 bispecific T-cell engager (BiTE) antibody construct indicated to treat patients with relapsed/refractory B-precursor ALL. In a phase 1/2 multicenter trial, blinatumomab monotherapy showed 39% (n= 27) complete remission in 70 pediatric patients with relapsed/refractory ALL, with 14 patients achieving complete MRD response. Seventy-one percent of patients had experienced relapse within 6 months after last treatment, demonstrating an unfavorable prognosis. At the end of a 2-year follow-up, 19 total patients relapsed (2 were still alive at the last assessment, 15 died, and 2 withdrew consent). Here, we present four pediatric patients (two each from phase 1 and 2) who experienced CD19-negative relapse and one patient with CD19negative progression during treatment. Detailed descriptions of study design, patient eligibility, dose modifications, interruptions, and discontinuations were previously reported and flow cytometry and MRD analyses (flow cytometry and polymerase chain reaction (PCR)) are summarized in the Supplementary Methods. Briefly, a panel of 29 (patients #1–4) or 20 (patient #5) markers were used for flow cytometry analysis, as detailed in the Supplementary Methods. Samples were measured on cytometers (BD LSR II (BD Biosciences, San Jose, CA, USA) or Dako CyAn (DakoCytomation, Glostrup, Denmark)), and analyses were performed using the FlowJo software, version 8.5.3 or 7 (FlowJo, LLC, Ashland, CA, USA). The study completion date was 24 May 2016. Baseline characteristics of patients with either CD19-positive or CD19-negative relapse (Table 1) were consistent with those of the entire patient population. Flow cytometric profiles at study entry and relapse are summarized in Supplementary Table 1. Patient #1 achieved hematologic remission during cycle 1 of blinatumomab and complete MRD response by PCR (Supplementary Table 2), with MRD reappearance on day 29 by flow cytometry at a level of 0.01%. In cycle 3, day 29 of blinatumomab, approximately 3 months after achieving hematologic remission, patient experienced a hematologic relapse. Blasts at relapse were CD19− CD10+ CD22− CD34− CD38+ CD45dim CD58+ iCD79a+ (Fig. 1a, Supplementary Table 1). Patient received antileukemic medication after relapse and was alive at time of withdrawn consent.