The maximum tolerated dose (MTD) was defined as one or fewer out of 6 participants experiencing a dose limiting toxicity (DLT) or the maximum administered dose (MAD).

A dose limiting toxicity is any Grade ≥ 3 adverse event related to study drug, Grade 3 fatigue, headache, insomnia, fever, hypotension or infection were not considered dose limiting toxicities. Laboratory parameters of Grade ≥ 3 but not considered as clinically relevant and/or responding to routine medical management, thrombocytopenia, leukopenia (including neutropenia and lymphopenia), and anemia were not considered dose limiting toxicities.

Participants in the Phase 1 dose evaluation/escalation part of the study

Hematological assessments were performed from bone marrow biopsy samples. All hematological assessments of bone marrow were reviewed in a central laboratory. Complete remission (CR) was defined as

• M1 bone marrow (bone marrow blasts < 5%)
• No evidence of circulating blasts or extra-medullary disease

Complete remission includes participants with incomplete recovery of peripheral blood counts.

The full analysis set includes all participants who received any infusion of blinatumomab.

The severity (or intensity) of adverse events (AEs) was assessed according to the National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE), v4.03 and according to the following:

Grade 1 - Mild adverse event; Grade 2 - Moderate adverse event; Grade 3 - Severe and undesirable adverse event; Grade 4 - Life-threatening or disabling adverse event; Grade 5 - Death. The investigator used medical judgment to determine if there was a causal relationship (ie, related, unrelated) between an adverse event and blinatumomab.

Full analysis set

Blinatumomab serum concentrations were quantified in all patients during the first 2 treatment cycles in the phase 1 part of the study only. Blinatumomab concentrations were quantified using a validated bioassay, the lower limit of quantification was 50 pg/mL. Steady state serum concentration (Css) was presumed on day 1, approximately 5 half-lives after the start of the IV infusion.

The steady state serum concentration reported is the mean of the observed concentrations collected after during cycles 1 and 2.

Phase 1 participants with available blinatumomab concentration data

Time to hematological relapse was measured only for participants in remission and was measured from the time the participant first achieved remission until first documented relapse or death due to disease progression. Participants without a documented relapse (hematological or extramedullary) and who did not die were censored at the time of their last bone marrow assessment or their last survival follow-up visit confirming remission. Participants who died without having reported hematological relapse or without showing any clinical sign of disease progression were censored on their date of death.

Hematological relapse is defined as the proportion of blasts in bone marrow > 25% following documented remission, or extramedullary relapse.

Time to hematological relapse was analyzed by Kaplan-Meier methods and the median observation time was calculated by the reverse Kaplan Meier method.

Full analysis set with complete remission

Overall survival (OS) was measured for all participants from the first treatment of blinatumomab until death due to any cause or the date of the last follow-up. Participants who did not die were censored on the last documented visit date or the date of the last contact when the patient was last known to have been alive. For patients who withdrew their informed consent only information until the date of withdrawal was analyzed.

Overall survival was estimated using Kaplan-Meier methods. The median follow-up time with respect to overall survival was calculated by the reverse Kaplan-Meier method.

Full analysis set

Relapse-free survival (RFS) was assessed for participants who achieved a complete remission during the core study and was measured from the time the participant first achieved remission until first documented relapse or death due to any cause. Participants without a documented relapse (hematological or extramedullary) or who did not die were censored at the time of their last bone marrow assessment or their last survival follow-up visit confirming remission.

Relapse free survival was estimated using Kaplan-Meier methods and the median observation time was calculated by the reverse Kaplan-Meier method.

Full analysis set with complete remission

The percentage of participants who received allogeneic hematopoietic stem cell transplantation (HSCT) while in remission due to treatment with blinatumomab during the first two cycles, and received no further anti-leukemic medication before HSCT.

Full analysis set

Antibodies to blinatumomab were detected using an electrochemiluminescence (ECL)-based assay.

Full analysis set

The activation of immune effector cells was monitored by the measurement of peripheral blood cytokine levels including interleukin (IL)-2, IL-4, IL-6, IL-10, tumor necrosis factor-alpha (TNF-α) and interferon gamma (IFN-ɣ) using cytometric bead assays. The limit of detection of the assay (LOD) was 20 pg/mL and the lower limit of quantification (LLOQ) was 125 pg/mL. Data below LOD were set to 10 pg/mL while data < LOQ and > LOD were reported as measured.

Phase 1 full analysis set participants with available data