PURPOSE:Blinatumomab is a CD19/CD3 BiTE (bispecific T-cell engager) antibody construct for the treatment of Philadelphia chromosome-negative acute B-lymphoblastic leukemia. We evaluated blinatumomab in relapsed/refractory B-cell non-Hodgkin lymphoma (NHL).PATIENTS AND METHODS:This 3 + 3 design, phase I dose-escalation study determined adverse events and the maximum tolerated dose (MTD) of continuous intravenous infusion blinatumomab in patients with relapsed/refractory NHL. Blinatumomab was administered over 4 or 8 weeks at seven different dose levels (0.5 to 90 μg/m(2)/day). End points were incidence of adverse events, pharmacokinetics, pharmacodynamics, and overall response rate.RESULTS:Between 2004 and 2011, 76 heavily pretreated patients with relapsed/refractory NHL, who included 14 with diffuse large B-cell lymphoma, were enrolled; 42 received treatment in the formal dose-escalation phase. Neurologic events were dose limiting, and 60 μg/m(2)/day was established as the MTD. Thirty-four additional patients were recruited to evaluate antilymphoma activity and strategies for mitigating neurologic events at a prespecified MTD. Stepwise dosing (5 to 60 μg/m(2)/day) plus pentosan polysulfate SP54 (n = 3) resulted in no treatment discontinuations; single-step (n = 5) and double-step (n = 24) dosing entailed two and seven treatment discontinuations due to neurologic events, respectively. Grade 3 neurologic events occurred in 22% of patients (no grade 4/5). Among patients treated at 60 μg/m(2)/day (target dose; n = 35), the overall response rate was 69% across NHL subtypes and 55% for diffuse large B-cell lymphoma (n = 11); median response duration was 404 days (95% CI, 207 to 1,129 days).CONCLUSION:In this phase I study of relapsed/refractory NHL, continuous infusion with CD19-targeted immunotherapy blinatumomab at various doses and schedules was feasible, with an MTD of 60 μg/m(2)/day. Single-agent blinatumomab showed antilymphoma activity.

This long-term follow-up analysis evaluated overall survival (OS) and relapse-free survival (RFS) in a phase 2 study of the bispecific T-cell engager antibody construct blinatumomab in 36 adults with relapsed/refractory B-precursor acute lymphoblastic leukemia (ALL). In the primary analysis, 25 (69%) patients with relapsed/refractory ALL achieved complete remission with full (CR) or partial (CRh) hematologic recovery of peripheral blood counts within the first 2 cycles. Twenty-five patients (69%) had a minimal residual disease (MRD) response (<10(-4) blasts), including 22 CR/CRh responders, 2 patients with hypocellular bone marrow, and 1 patient with normocellular bone marrow but low peripheral counts. Ten of the 36 patients (28%) were long-term survivors (OS ≥30 months). Median OS was 13.0 months (median follow-up, 32.6 months). MRD response was associated with significantly longer OS (Mantel-Byar P = .009). All 10 long-term survivors had an MRD response. Median RFS was 8.8 months (median follow-up, 28.9 months). A plateau for RFS was reached after ∼18 months. Six of the 10 long-term survivors remained relapse-free, including 4 who received allogeneic stem cell transplantation (allo-SCT) as consolidation for blinatumomab and 2 who received 3 additional cycles of blinatumomab instead of allo-SCT. Three long-term survivors had neurologic events or cytokine release syndrome, resulting in temporary blinatumomab discontinuation; all restarted blinatumomab successfully. Long-term survivors had more pronounced T-cell expansion than patients with OS <30 months.

Blinatumomab, a bispecific antibody construct targeting CD19, is the most advanced member of bispecific T-cell engager (BiTE®) molecules. The clinical development program includes B-precursor acute lymphoblastic leukemia (ALL) and B-cell non-Hodgkin lymphoma (NHL). Minimal residual disease (MRD) response in patients with MRD-positive B-precursor ALL has translated into long-term clinical benefits as demonstrated by an estimated relapse-free survival (RFS) of 60% with sustained MRD negativity at a follow-up of 31 months. Remissions induced in pediatric and adult patients with relapsed/refractory B-precursor ALL have allowed for successful allogeneic hematopoietic stem cell transplantation (HSCT) in this setting. Blinatumomab has also induced durable responses in low-grade B-cell NHL. Blinatumomab recently gained approval in the United States by the U.S. Food and Drug Administration for treatment of Philadelphia chromosome-negative B-precursor relapsed/refractory acute lymphoblastic leukemia. AMG 330 is an investigational anti-CD33 BiTE® antibody construct. Targeting CD33 ex vivo in primary samples from patients with acute myeloid leukemia (AML) has shown AMG 330-mediated T-cell expansion and T-cell cytotoxicity against AML cells.

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).

Synaptopodin 2 is a natively unfolded actin binding protein that stimulates actin polymerization in a Ca2+-calmodulin dependent manner, has multiple binding partners and is rich in smooth muscle dense bodies. Various synaptopodin 2 isoforms have cytoplasmic and nuclear localizations in non-muscle cells and the distribution changes in certain cancers. We prepared an antibody against the C-terminus that recognizes isoform B and myopodin, the truncated form. Immunological staining showed a nuclear location in several cell lines. In further studies with the colon cancer cell line, HT-29 and African green monkey kidney cells, CV1, we observed intense staining in irregular areas within the nucleus. Staining was also observed at the nuclear periphery of HT-29 cells. The strong synaptopodin 2 staining pattern was 90% correlated with markers of nucleoli including a commercial antibody against nucleolin and a counter stain with DAPI. Furthermore, when Actinomycin D was used to inhibit transcription the nuclear stain disappeared. When HT-29 cells were forced to differentiate with sodium butyrate, the synaptopodin 2 antibody revealed a re-localization of the protein into the cytoplasm. RT-PCR and Western blot analysis showed that HT-29 cells lacked Synaptopodin2B, but contained the smaller isoform, myopodin. These studies were performed using cytoplasmic and nuclear fractions. Further analysis showed that the nuclear fraction contained a smaller cross-reactive protein with an apparent mass of 55-60 kDa. Both myopodin and the 60 kDa protein were immunoprecipitated along with proteins tentatively identified as actin and α-actinin. These results show that myopodin and a smaller synaptopodin-like protein are present in nucleoli along with actin and other actin binding proteins.

Sol i 2 is a potent allergen from the venom of red imported fire ant, which contains allergens Sol i 1, Sol i 2, Sol i 3, and Sol i 4 that are known to be powerful triggers of anaphylaxis. Sol i 2 causes IgE antibody production in about one-third of individuals stung by fire ants. Baculovirus recombinant dimeric Sol i 2 was crystallized as a native and selenomethionyl-derivatized protein, and its structure has been determined by single-wavelength anomalous dispersion at 2.6 Å resolution. The overall fold of each subunit consists of five helices that enclose a central hydrophobic cavity. The structure is stabilized by three intramolecular disulfide bridges and one intermolecular disulfide bridge. The nearest structural homologue is the sequence-unrelated odorant binding protein and pheromone binding protein LUSH of the fruit fly Drosophila, which may suggest a similar biological function. To test this hypothesis, we measured the reversible binding of various pheromones, plant odorants, and other ligands to Sol i 2 by the changes in N-phenyl-1-naphthylamine fluorescence emission upon binding of ligands that compete with N-phenyl-1-naphthylamine. The highest binding affinity was observed for hydrophobic ligands such as aphid alarm pheromone (E)-β-farnesene, analogs of ant alarm pheromones, and plant volatiles decane, undecane, and β-caryophyllene. Conceivably, Sol i 2 may play a role in capturing and/or transporting small hydrophobic ligands such as pheromones, odors, fatty acids, or short-living hydrophobic primers. Molecular surface analysis, in combination with sequence alignment, can explain the serological cross-reactivity observed between some ant species.

Persistence or recurrence of minimal residual disease (MRD) after chemotherapy results in clinical relapse in patients with acute lymphoblastic leukemia (ALL). In a phase 2 trial of B-lineage ALL patients with persistent or relapsed MRD, a T cell-engaging bispecific Ab construct induced an 80% MRD response rate. In the present study, we show that after a median follow-up of 33 months, the hematologic relapse-free survival of the entire evaluable study cohort of 20 patients was 61% (Kaplan-Meier estimate). The hema-tologic relapse-free survival rate of a subgroup of 9 patients who received allogeneic hematopoietic stem cell transplantation after blinatumomab treatment was 65% (Kaplan-Meier estimate). Of the subgroup of 6 Philadelphia chromosome-negative MRD responders with no further therapy after blinatumomab, 4 are in ongoing hematologic and molecular remission. We conclude that blinatumomab can induce long-lasting complete remission in B-lineage ALL patients with persistent or recurrent MRD. The original study and this follow-up study are registered at www.clinicaltrials.gov as NCT00198991 and NCT00198978, respectively.

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Abstract Abstract 1637 Blinatumomab (MT103) is a single-chain bispecific antibody construct with specificity for CD19 and CD3 belonging to the class of bispecific T cell engager (BiTE®). A phase I trial with indolent and mantle cell lymphoma patients established a maximal tolerable dose (MTD) at 60 μg/m2/d. The trial was subsequently amended to evaluate blinatumomab in patients with diffuse large B cell lymphoma (DLBCL). Patients were treated by 4–8-week continuous i.v. administration with the following dosing regimen: first week at 5 μg/m2/d, second week at 15 μg/m2/d and for the remaining treatment period at 60 μg/m2/d. Two cohorts each with 6 DLBCL patients were enrolled. The two cohorts solely differed by the dose and schedule of corticosteroid medication administered at the beginning of blinatumomab infusion for mitigation of adverse events. In the first cohort 100 mg prednisolone was applied 1 hour prior to start; and in the second cohort patients received dexamethasone on days 1, 2, and 3. Three sequential patients received dexamethasone also 6–12 hours prior to start of infusion. Out of the twelve patients, 5 were male and 7 female. The median age was 57 years (range from 26 to 78 years). Patients had received a median of 4 prior regimens (range from 2–6). All patients had been exposed to rituximab. Eight of the 12 patients had undergone autologous stem cell transplantation (ASCT). International prognostic index (IPI) at screening ranged from 1 to 3 with a median of 2. The most common clinical adverse events (AEs) regardless of causality (>30%) were pyrexia (81.8%), fatigue (54.5%), constipation (36.4%), headache (36.4%), tremor (36.4%) and weight increase (36.4%). The most frequent laboratory AEs regardless of causality (>30%) were hyperglycemia (63.6%), lymphopenia (54.5%), C-reactive protein increase (45.5%), gamma-glutamyltransferase increase (45.5%) and thrombocytopenia (36.4%). Most AEs occurred early and were reversible. Four of 12 patients discontinued infusion due to fully reversible CNS events, 2 of which qualified as dose limiting toxicities (DLTs). Although just one DLT (reversible CNS event grade 3) occurred in the prednisolone cohort, a further cohort applying prophylactic dexamethasone was opened to optimize management of CNS events. A further refinement of the dexamethasone schedule, starting longer time prior to start of blinatumomab, was introduced after one early patient in the cohort receiving dexamethasone had experienced a reversible CNS event leading to discontinuation. All three patients treated in this manner completed the first blinatumomab cycle without discontinuations. Only one showed a grade 1 tremor, and no other CNS AEs were reported in these three patients. Two of 12 patients were not exposed to 60 μg/m2/d due to early discontinuations and 1 patient is too early in treatment for response evaluation. Five out of the remaining 9 evaluable patients (56%) showed objective clinical responses (4 CR/CRu; 1 PR). Three out of the 5 patients with CR/CRu or PR had prior ASCT. Two patients achieved objective responses (1 CR, 1 PR) despite of discontinuation at 60 μg/m2/d. The median response duration is +182 days (longest current duration +428 days), with 4 out of 5 responses still ongoing. Further evaluation of the last cohort will refine the recommended phase II dose, and the intensity and timing of dexamethasone comedication. The observation of lasting CRs after blinatumomab monotherapy in DLBCL patients is promising and warrants further exploration in a phase II study. Disclosures: Krause: Micromet: Research Funding. Mackensen:Micromet Inc.: Research Funding. Topp:Micromet: Consultancy, Honoraria. Scheele:Micromet Inc.: Employment, Equity Ownership, Patents & Royalties. Nagorsen:Micromet Inc.: Employment, Equity Ownership, Patents & Royalties. Zugmaier:Micromet: Employment. Degenhard:Micromet Inc: Employment. Schmidt:Micromet AG: Employment. Kufer:Micromet Inc: Employment, Equity Ownership. Libicher:Micromet Inc.: Consultancy, Honoraria. Bargou:Micromet: Consultancy, Honoraria.

PURPOSE Blinatumomab, a bispecific single-chain antibody targeting the CD19 antigen, is a member of a novel class of antibodies that redirect T cells for selective lysis of tumor cells. In acute lymphoblastic leukemia (ALL), persistence or relapse of minimal residual disease (MRD) after chemotherapy indicates resistance to chemotherapy and results in hematologic relapse. A phase II clinical study was conducted to determine the efficacy of blinatumomab in MRD-positive B-lineage ALL. PATIENTS AND METHODS Patients with MRD persistence or relapse after induction and consolidation therapy were included. MRD was assessed by quantitative reverse transcriptase polymerase chain reaction for either rearrangements of immunoglobulin or T-cell receptor genes, or specific genetic aberrations. Blinatumomab was administered as a 4-week continuous intravenous infusion at a dose of 15 μg/m2/24 hours. RESULTS Twenty-one patients were treated, of whom 16 patients became MRD negative. One patient was not evaluable due to a grade 3 adverse event leading to treatment discontinuation. Among the 16 responders, 12 patients had been molecularly refractory to previous chemotherapy. Probability for relapse-free survival is 78% at a median follow-up of 405 days. The most frequent grade 3 and 4 adverse event was lymphopenia, which was completely reversible like most other adverse events. CONCLUSION Blinatumomab is an efficacious and well-tolerated treatment in patients with MRD-positive B-lineage ALL after intensive chemotherapy. T cells engaged by blinatumomab seem capable of eradicating chemotherapy-resistant tumor cells that otherwise cause clinical relapse.

Background: Rising serum levels of prostate-specific antigen (PSA) after radical prostatectomy are indicative of recurrent prostate cancer. This double-blind, placebo-controlled phase II study evaluated the anti-tumour activity of the anti-epithelial cell adhesion molecule (EpCAM) antibody adecatumumab in delaying biochemical disease progression. Patients and Methods: Prostate cancer patients with increasing serum PSA levels following radical prostatectomy were randomized to low- (2 mg/kg) or high-dose adecatumumab (6 mg/kg) or placebo. The primary efficacy endpoint was the mean change from baseline in total serum PSA at week 24. Secondary endpoints included PSA response rate, prolongation of serum PSA doubling time and time to biochemical disease progression. Results: The primary and secondary endpoints of the study were not met in the predefined analyses. In a retrospective analysis of patients with baseline PSA ≤1 ng/ml and a high EpCAM expression, both the mean increase in PSA from baseline to week 24 and the PSA doubling time at week 15 were significantly improved in the high-dose adecatumumab group compared with the placebo group. Most frequent treatment-related clinical adverse events were gastrointestinal (diarrhoea and nausea) or general events (chills), showing a dose dependency but no grade 3/4 intensity in any patient. Conclusion: In men with rising PSA levels after radical prostatectomy and no evidence of clinical relapse, adecatumumab delayed disease progression in a subgroup of patients with baseline PSA levels ≤1 ng/ml and high EpCAM-expressing tumours.

Abstract Abstract 2880 Blinatumomab (MT103) is a single-chain bispecific antibody construct with specificity for CD19 and CD3 belonging to the class of bispecific T cell engager (BiTE®). We have previously reported that blinatumomab delivered as single agent to patients with relapsed NHL and B-precursor acute lymphoblastic leukemia by continuous intravenous (CIV) infusion over 4–8 weeks depleted peripheral B cells, expanded T effector cells, and resulted in clinical responses. In this phase I study 52 patients (41 males, 11 females) have been treated, 21 with FL, 21 with MCL and 10 with other subtypes of lymphoma (MZL, SLL, LPL, CLL). Patients have received a median of 3 prior regimens (range 1 to 12). Ninety percent of the patients had prior exposure to rituximab and 45% to fludarabine. Patients were treated at a dose range from 0.5 to 90 μg/m2/d. The most common adverse events (AEs) occurred early, were transient, reversible and did not require discontinuation of treatment. The most common clinical AEs regardless of causality were pyrexia (75%), headache (45%) and fatigue (37%). The most common laboratory abnormality AEs regardless of causality were lymphopenia (75%), leukopenia (57%), thrombocytopenia (39%), C-reactive protein increase (53%) and fibrin D dimer increase (37%). The medically most important AEs that resulted in permanent discontinuation were CNS events. Signs and symptoms observed included kinetic tremor, speech impairment, disorientation, apraxia and seizure. All CNS events were fully reversible without sequelae and no pathological findings by MRI imaging were reported. Out of the 52 patients treated, 9 had to discontinue treatment permanently in the first cycle due to these CNS events. At a dose of 90 μg/m2/d two DLTs were observed which were CNS events during the DLT period of the first 2 weeks of treatment. Therefore 60μg/m2/d is the currently recommended dose. A low B to T cell ratio (<1:8) determined by FACS analysis in peripheral blood was found to be a risk factor for CNS events. No CNS events requiring treatment discontinuation occurred in 32 out of 34 patients with a high B:T cell ratio (≥1:8) up to 60μg/m2/d. In the 18 patients with low B:T cell ratio, 7 had CNS events requiring treatment discontinuation. Patients with low B:T cell ratio were subsequently treated with an alternative dosing schedule in which reduced doses of either 5 and 15 μg/m2/d were sequentially administered for 1 week respectively followed by an increase to 60 μg/m2/d. First single-step dosing was applied. However, CNS events leading to treatment discontinuation were still observed. Therefore a double-step regimen was implemented; in the initial cohort of 3 patients with low B:T cell ratio there were no treatment discontinuations due to CNS events. Overall 18 patients with FL or MCL were treated with constant or step dosing regimens at or reaching 60 μg/m2/d dose level. Eight out of the 9 patients with constant dosing showed an objective response by Cheson criteria. All responders had a high B:T cell ratio. One patient with a low B:T cell ratio was discontinued due to a CNS AE. Six out of 9 patients with low B:T cell ratio enrolled for step dosing showed an objective response. One patient (single step dosing) discontinued treatment because of a CNS AE and 2 patients discontinued because of tumor progression. As of June 15th 2010, response duration ranged from 1 to 30+ months. Median for response duration was 26 months with 5 out of 14 responses ongoing. Table 1: Response evaluation in patients enrolled in 60 μg/m2/d cohorts. Dose Level Cohort Patients Complete Response Partial Response Overall Response FL MCL Total FL MCL Total FL MCL Total FL MCL Total 60 μg/m2/d Constant 6 3 9 2 1 3 4 1 5 6 2 8 5 or 15 then 60 μg/m2/d Single step 3 3 6 2 0 2 1 1 2 3 1 4 5/15/60 μg/m2/d Double Step 2 1 3 0 0 0 2 0 2 2 0 2 Total 11 7 18 4 1 5 7 2 9 11 3 14 These data confirm high single-agent activity of blinatumomab with long lasting remissions. Initial data with double step dosing demonstrate that this approach maintains clinical activity without discontinuations due to CNS AEs. Evaluation of safety and clinical efficacy of this uniform double step schedule including other subtypes of NHL is ongoing. Disclosure: Scheele: Micromet Inc.: Employment. Zugmaier:Micromet Inc.: Employment. Nagorsen:Micromet Inc.: Employment. Klinger:Micromet Inc.: Employment. Schmidt:Micromet Inc.: Employment. Klappers:Micromet. Inc: Employment. Kufer:Micromet Inc.: Employment. Bargou:Micromet Inc.: Consultancy.

Abstract Abstract 174 Blinatumomab, a bispecific, T cell-engaging (BiTE®) antibody, can effectively redirect T cells for highly selective lysis of CD19+ target cells. The B-cell differentiation antigen CD19 is a marker for B-ALL cells. In B-lineage acute lymphoblastic leukemia (ALL), persistence or relapse of minimal residual disease (MRD) is an independent poor prognostic factor, and new treatments are urgently needed. MRD relapse during or after maintenance treatment in adult standard risk patients generally heralds a hematological relapse in 90% of patients. A phase 2 study was conducted to determine the efficacy of blinatumomab in ALL patients with MRD persistence or relapse (MRD level <310-4) after induction and consolidation therapy. MRD was assessed by qRT-PCR for rearrangements of immunoglobulin (Ig) or T-cell receptor (TCR) genes, or for specific fusion genes. Blinatumomab was administered as a 4-week continuous i.v. infusion at a dose of 15 μ g/m2/d followed by a 2-week treatment free period (1 cycle). Primary endpoint was the proportion of patients with MRD response defined by individual rearrarrangement of Ig or TCR below 10-4. Patients who showed neither MRD progression nor response were permitted to receive up to 7 cycles of treatment. Patients who had achieved MRD response received 3 additional consolidation cycles. Between May 2008 and November 2009, 21 patients (16 Ph-negative; 2 patients with MLL-AF4; 5 patients with Ph+ ALL) were enrolled. The cut-off date for data analysis was May 15, 2010. Patients received between 1 and 7 cycles of blinatumomab (total of 66 cycles). Transient pyrexia (100%) and chills (43%) were the most common clinical AEs. There were no blinatumomab related deaths. Sixteen patients became MRD-negative. One patient was not evaluable due to a grade 3 adverse event (AE) leading to treatment discontinuation. Of the responding patients, 13 had never before achieved a negative MRD status on chemotherapy. Regardless of their MRD level prior to study treatment, all 16 (13/15 patients with Ph− and 3/5 patients with Ph+ ALL) became MRD-negative after the first cycle of blinatumomab. Nine patients were enrolled with a MRD load >10-2 prior to study treatment and all reached complete MRD response. Thirteen out of 16 patients with persisting MRD prior to study treatment and 3 out of 4 patients with MRD relapse showed complete MRD response. Overall relapse-free survival (RFS) currently is 78% at a median follow up of 405 days. RFS is 100% for the 8 patients who received subsequent allogeneic stem cell transplantation (median follow up 434 days). Blinatumomab is a highly active treatment for patients with MRD-positive B-lineage ALL after intensive chemotherapy and has an acceptable safety profile. T cells engaged by blinatumomab seem capable of eradicating chemotherapy-resistant tumor cells in bone marrow that otherwise might cause clinical relapse. A long RFS suggests that blinatumomab may improve outcome in patients with B-precursor ALL. A multicenter international study of blinatumomab in patients with MRD-positive B-lineage ALL has been initiated. Disclosures: Zugmaier: Micromet Inc.: Employment. Degenhard:Micromet Inc.: Employment. Schmidt:Micromet Inc.: Employment. Scheele:Micromet Inc.: Employment. Kufer:Micromet Inc.: Employment. Klinger:Micromet Inc.: Employment. Nagorsen:Micromet Inc.: Employment. Bargou:Micromet Inc.: Consultancy.

Abstract Abstract 2723 Poster Board II-699 Indolent and mantle cell lymphoma (MCL) are predominantly treated with chemotherapy or a combination of chemotherapy with monoclonal antibodies. Despite high initial response rates, eventually almost all patients however relapse, leaving the disease incurable. Moreover, with increasing numbers of regimens administered, the responsiveness of patients is reduced. Blinatumomab is a single-chain bispecific antibody construct with specificity for CD19 and CD3, belonging to the class of bispecific T cell engager (BiTE®). Here, we report on patients in an ongoing phase 1 trial treated at a dose of 60 μg/m2/d for 4–8-week by continuous i.v. infusion with single-agent blinatumomab. In total, 12 patients with indolent mainly follicular lymphoma or MCL were treated at 60 μg/m2/d during the first treatment cycle. 11/12 patients showed an objective response (7 PR and 4 CR). As of July 2009, median response duration was 12 months with 6 out of 11 responses still ongoing. The single non-responding patient experienced a reversible, neurological adverse event leading to early discontinuation of treatment. Of the 11 responders, one patient developed a port infection and 4 patients showed neurological symptoms, which were all fully reversible. In order to mitigate neurological adverse events during first dosing, which can occur in a defined subset of patients, patients were treated for 1–2 weeks with a lower initial dose (5 and/or 15 μg/m2/d) followed by a maintenance dose of 60 μg/m2/d. A lower starting dose appeared to ameliorate initial adverse events to an extent that treatment could be continued without interruption. Taken together, our data confirm a high single-agent activity of 60 μg/m2/d blinatumomab infused for 4–8 week with long lasting remissions and a favorable risk/benefit profile. The confirmed dose will be considered for further clinical development of blinatumomab in follicular lymphoma and MCL. New data on patients treated with a dose of 90 μg/m2/d will be presented. Disclosures: Nagorsen: Micromet: Employment, Equity Ownership. Zugmaier:Micromet: Employment, Equity Ownership. Schmidt:Micromet: Employment, Equity Ownership. Klappers:Micromet: Employment, Equity Ownership. Baeuerle:Micromet: Employment, Equity Ownership. Kufer:Micromet: Employment, Equity Ownership, Patents & Royalties. Bargou:Micromet: Consultancy, Patents & Royalties.

Abstract 840 Introduction: In patients with B-precursor ALL, presence of MRD after induction therapy or at any time point later predicts a hematological relapse, despite continued intensive chemotherapy or/and an allogeneic hematological stem cell transplantation (HSCT). Blinatumomab (MT103) targets the CD19 antigen, and is a member of a novel class of bispecific BiTE ® antibodies that redirect T cells for lysis of target cells. A phase II study was conducted in collaboration with the German Multicenter Study Group on Adult Lymphoblastic Leukemia (GMALL) in patients with MRD-positive B precursor ALL. Methods: B–precursor ALL patients in complete hematological remission with either persistent or reappeared MRD at any time after consolidation I of front-line therapy were included. One treatment cycle of blinatumomab is a 4-week continuous i.v. infusion, which can be followed by allogeneic HSCT or in case of response by repeated consolidation cycles of blinatumomab with 2-week treatment-free intervals. The dose level at enrollment is 15 μg/m 2 /day. In patients, who do not respond within four cycles of treatment, the dose can be increased to 30 μg/m 2 /day. Molecular response is assessed by quantitative PCR of either individual rearrangements of immunoglobulin/TCR-genes or specific genetic aberrations such as bcr/abl or MLL-AF4. Results: Nineteen patients have been treated to date and 16 patients are already evaluable for response. Thirteen of 16 evaluable patients went into molecular complete remission (CR) already after one cycle of blinatumomab. Three patients had a stable MRD level. Of note, 10 of the responding 13 patients had never achieved a molecular CR before blinatumomab treatment despite multiple treatment cycles including tyrosine kinase inhibitors in case of Ph-positive ALL. Two patients in molecular CR had an extra-medullary relapse one in testis and one in cerebro-spinal fluid, both representing immunological niches with limited accessibility for T cells. One patient with stable MRD level had a medullary relapse. All other patients are still relapse-free. None of the patients with molecular CR has shown a medullary relapse to date. The maximum follow-up of molecular CR has been 12 months. Most common adverse events (AEs) included lymphopenia, pyrexia, leucopenia and hypoimmunoglobulinemia. Only one patient had to be discontinued because of a fully reversible epileptical seizure. All other AEs resolved during treatment. Overall, treatment with blinatumomab was well tolerated. Response data of all 21 patients will be presented at ASH. Conclusions: Treatment with blinatumomab converted MRD-positive B–precursor ALL into molecular CR in 13 of 16 evaluable patients with refractory disease as indicated by persistent MRD after intensive chemotherapy. This amounts to a response rate of 81% providing thus the rationale for introducing blinatumomab as a novel agent in the treatment of B–precursor ALL. Disclosures: Zugmaier: Micromet: Employment, Equity Ownership. Goekbuget: Micromet: Consultancy, Research Funding. Kufer: Micromet: Employment, Equity Ownership, Patents & Royalties. Klinger: Micromet: Employment, Equity Ownership. Degenhard: Micromet: Employment, Equity Ownership. Baeuerle: Micromet: Employment, Equity Ownership. Schmidt: Micromet: Employment, Equity Ownership. Nagorsen: Micromet: Employment, Equity Ownership. Riethmueller: Micromet: Consultancy, Equity Ownership. Bargou: Micromet: Consultancy, Equity Ownership, Patents & Royalties.