Background: Blinatumomab is a bispecific T-cell engager (BiTE (R)) antibody construct targeting CD3 epsilon on T cells and CD19 on B cells. We describe the relationship between pharmacokinetics (PK) of blinatumomab and pharmacodynamic (PD) changes in peripheral lymphocytes, serum cytokines, and tumor size in patients with non-Hodgkin lymphoma (NHL). Methods: In a phase 1 study, 76 patients with relapsed/refractory NHL received blinatumomab by continuous intravenous infusion at various doses (0.5 to 90 mu g/m(2) /day). PD changes were analyzed with respect to dose, blinatumomab concentration at steady state (C-ss), and cumulative area under the concentration-versus-time curve (AUC(cum)). Results: B-cell depletion occurred within 48 hours at doses >= 5 mu g/m(2) /day, followed first-order kinetics, and was blinatumomab exposure-dependent. Change in tumor size depended on systemic blinatumomab exposure and treatment duration and could be fitted to an Emax model, which predicted a 50% reduction in tumor size at AUC(cum) of >= 1,340 hx mu g/L and Css of >= 1,830 pg/mL, corresponding to a blinatumomab dose of 47 mu g/m(2) /day for 28 days. The magnitude of transient cytokine elevation, observed within 1-2 days of infusion start, was dose-dependent, with less pronounced elevation at low starting doses. Conclusion: B-lymphocyte depletion following blinatumomab infusion was exposure-dependent. Transient cytokine elevation increased with dose; it was less pronounced at low starting doses. Tumor response was a function of exposure, suggesting utility for the PK/PD relationship in dose selection for future studies, including NHL and other malignant settings.

T cell engaging bispecific antibody constructs (BiTE®), such as blinatumomab which targets CD19-positive cells, have shown great promise for treating certain CD19-positive hematological malignancies. Blinatumomab comprises a single chain Fv (scFv) that binds CD19 and a scFv that targets the T cell CD3 protein. The molecular weight of this “canonical” BiTE® is ~ 55 kDa, making it susceptible to kidney-mediated clearance and resulting in a short serum half-life (~ 4 hours). To maintain effective serum concentrations, canonical BiTE® antibody constructs must be administered by continuous IV (cIV) infusion. While there are many advantages associated with cIV administration (e.g., safety and uniform PK profile), patient convenience could be enhanced if the BiTE® antibody construct were compatible with once-weekly administration. To achieve this, the serum half-life of the BiTE® antibody construct would need to be extended. A canonical BiTE® targeting CD33 (AMG 330) is currently being evaluated in a phase I clinical trial. Like blinatumomab, AMG 330 is dosed cIV. To extend the serum half-life of AMG 330 and enable once-weekly dosing, several approaches were evaluated including fusion of AMG 330 to human albumin and Fc-containing moieties. Each of these half-life extended (HLE) constructs was evaluated in vitro, in mouse xenograft models and in non-human primates. In vitro assays evaluated 1) binding to both human and cynomolgus CD33 and CD3 proteins, and 2) cytotoxicity using human and cynomolgus target and effector cells. In each of these assays the canonical and HLE BiTE® antibody constructs demonstrated similar activity: single-digit nM binding and single digit pM cytotoxicity. Canonical and HLE BiTE® antibody constructs were subsequently evaluated in an orthotopic mouse model in which MOLM13 cells were administered IV and activated human T cells were administered IP two days later. The Fc-based HLE BiTE® antibody constructs provided a similar survival advantage when administered Q4D or Q5D as the canonical BiTE® when administered QD. However, the albumin fusion–based HLE BiTE® was less efficacious when administered Q4D than the QD- administered canonical BiTE®. Lastly, the PK/PD relationship was evaluated for each of the constructs in non-human primates. The serum half-lives varied from 6 hours for the canonical BiTE® to 44-167 hours for the HLE BiTE® antibody constructs. Each of the HLE BiTE® antibody constructs showed on-target depletion of CD33-positive monocytes and neutrophils in the blood and depletion of CD33-positive cells in the bone marrow. These data demonstrate that half-life extended BiTE® antibody constructs can be generated that retain comparable in vitro and in vivo activity as a canonical BiTE® and achieve a serum half-life compatible with once weekly dosing. Citation Format: Tara L. Arvedson, Mercedesz Balazs, Pamela Bogner, Kurt Black, Kevin Graham, Anja Henn, Matthias Friedrich, Patrick Hoffmann, Roman Kischel, Peter Kufer, Ralf Lutterbuese, Markus Muenz, Tobias Raum, Benno Rattel, Karen Rex, Dan Rock, Oliver Thomas, Joachim Wahl, Andreas Wolf, Angela Coxon. Generation of half-life extended anti-CD33 BiTE® antibody constructs compatible with once-weekly dosing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 55. doi:10.1158/1538-7445.AM2017-55

We evaluated blinatumomab pharmacokinetics, pharmacodynamics (CD3+ T‐cell, CD19+ B‐cell, and cytokine levels), and their associations with efficacy or safety in relapsed/refractory acute lymphoblastic leukemia. Blinatumomab pharmacokinetics (continuous intravenous infusion) from a phase 2 study (n = 189; NCT01466179) were assessed noncompartmentally. Associations between steady‐state concentration (Css) and efficacy (complete remission [CR] or CR with partial hematologic recovery [CRh]) or safety (cytokine release syndrome [CRS] and neurologic events [NEs]) were evaluated with statistical models. Blinatumomab mean ± SD Css was 621 ± 502 pg/mL (28 μg/day dose). Cytokines were transiently elevated in >50% of patients; B‐cell levels decreased in most patients. Lower B‐cell and bone marrow (BM) blast percentages and higher T‐cell percentages were associated with higher CR/CRh (P < .001) in univariate analysis. Higher Css (OR, 1.90; 95%CI, 1.12‒3.21), higher peak IL‐10 level (1.59; 1.13‒2.22), and lower BM blast percentage (0.78; 0.69‒0.89) were associated with higher CR/CRh in multivariate analysis. Higher Css (HR, 1.40; 1.01–1.94) and lower B‐cell level (0.90; 0.84‒0.97) were associated with shorter time to NEs. Cytokine peaks were not associated with NEs or CRS. In conclusion, blinatumomab led to T cell‐mediated depletion of target B cells in blood and blasts in the bone marrow. Immune system effectiveness was important for treatment responses.

Background Blinatumomab has shown a remission rate of 69% in an exploratory single-arm, phase II dose-escalation study in adult patients with relapsed/refractory B-precursor acute lymphoblastic leukemia (ALL). We evaluated changes in laboratory parameters and immunopharmacodynamic markers in patients who received blinatumomab in the exploratory phase II study. Methods Data from 36 adults with relapsed/refractory ALL receiving blinatumomab as 4-week continuous IV infusions in various dose cohorts were analyzed for changes in liver enzymes, first-dose parameters, peripheral blood cell subpopulations, and cytokine/granzyme B release. Associations with clinical response were evaluated. Results Liver enzymes and inflammatory parameters transiently increased primarily during the first treatment week without clinical symptoms and reversed to baseline levels thereafter. B and T cells showed expected depletion and redistribution kinetics, respectively. Similarly, thrombocytes and T cells displayed an initial decline in cell counts, whereas neutrophils peaked during the first days after infusion start. T-cell redistribution coincided with upregulation of LFA-1 and CD69. Patients who responded to blinatumomab had more pronounced T-cell expansion, which was associated with proliferation of CD4 + and CD8 + T cells and memory subsets. Release of cytokines and granzyme B primarily occurred during the first week of cycle 1, except for IL-10, which was released in subsequent cycles. Blinatumomab step-dosing was associated with lower cytokine release and lower body temperature. Conclusions In this study of relapsed/refractory ALL, blinatumomab-induced changes in laboratory parameters were transient and reversible. The evaluated PD markers demonstrated blinatumomab activity, and the analysis of cytokines supported the rationale for stepwise dosing. ( ClinicalTrials.gov Identifier NCT01209286.)

Blinatumomab is a bispecific T-cell engager (BiTE®) antibody construct that transiently links CD19-positive B cells to CD3-positive T cells, resulting in induction of T-cell-mediated serial lysis of B cells and concomitant T-cell proliferation. Blinatumomab showed anti-leukemia activity in clinical trials and was approved by the US Food and Drug Administration for the treatment of Philadelphia chromosome-negative relapsed/refractory B-cell precursor acute lymphoblastic leukemia (r/r ALL). The objectives of this work were to characterize blinatumomab pharmacokinetics and pharmacodynamics and to evaluate dosing regimens.

2561 Background: Blinatumomab is a CD19-directed bispecific T-cell engager antibody construct indicated for treatment of Ph-negative r/r ALL. We evaluated blinatumomab PK/PD and explored their associations with efficacy/safety in 189 r/r ALL patients in a phase 2 study (Topp et al. Lancet Oncol 2015;16:57). Methods: Blinatumomab was given by continuous IV infusion (4 wk on/2 wk off) for ≤ 5 cycles (Cycle 1: 9 µg/d days 1–7; then 28 µg/d; thereafter: 28 µg/d). Association between exposure and measures of efficacy (complete response [CR]/CR with partial hematologic recovery [CRh] within the first 2 cycles) and safety (cytokine release syndrome [CRS]; neurologic events [NE]) was evaluated by logistic regression. Impact of covariates on exposure-response was assessed in multivariate analyses. Results: Blinatumomab PK was linear; mean (SD) serum steady state concentration (Css) at 28 µg/d was 621 (502) pg/mL in Cycle 1. IL-6, IL-10 and IFNγ were transiently elevated in > 50% of pts on days 1–2 of Cycle 1, much less in later cycles; interpatient variability was high. In Cycle 1, mean peripheral B cells fell from 4660 to ≤ 10 cells/µL. Responders had lower percentages of CD19+ B cells and bone marrow (BM) blasts and higher percentages of CD3+ T cells and granulocytes at screening than nonresponders (P< .001); absolute counts were not associated with response. In multivariate analyses, higher Css (OR, 1.90 [95% CI, 1.12–3.21]; P= .017), higher peak IL-10 levels (1.59 [1.13–2.22]; P= .007) and lower percentage of BM blasts at screening (0.78 [0.69–0.89]; P< .001) were associated with CR/CRh. No association between Css and time to CR/CRh was found after adjusting for percentage of blasts and B/T cell ratio. Higher platelet counts (0.996 [95% CI, 0.992–1.0]; P= .03), CD19+ B cell counts at screening (0.90 [0.84–0.97]; P= .004) and Css (1.40 [1.01–1.94]; P= .046) were associated with time to NE. Cytokine peaks were not associated with NE or CRS. Css was not associated with CRS. Conclusions: We found empirical associations of blinatumomab PK, PD and disease-related prognostic factors with CR/CRh and NE. Confounding factors and confirmation of the associations deserve further evaluation. Clinical trial information: NCT01466179.

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Abstract Prostate-specific membrane antigen (PSMA) has been frequently selected as target antigen for antibody-based therapy of prostate cancer. Here, we recombinantly constructed a PSMA/CD3-bispecific BiTE antibody, called MT112/BAY 2010112. The BiTE antibody was produced in Chinese hamster ovary cells as a secreted protein of 55 kDa, showing high serum and thermal stability. MT112/BAY 2010112, purified as homogenous monomeric protein, bound at low nanomolar concentrations to defined epitopes on PSMA and CD3 antigens of human and macaque origin, respectively. In cell culture studies bispecific binding of MT112/BAY 2010112 selectively redirected human T cells against several PSMA-positive human prostate cancer cell lines as well as PSMA cDNA-transfected cell lines and potently induced specific target cell lysis with EC50 values ranging from 1 to 50 pM using non-stimulated human peripheral blood mononuclear cells as effector cells. EC50 values correlated with the number of PSMA molecules on the cell surface ranging from 37,000-500,000 molecules per cell among the cell lines analyzed. The anti-tumor activity of MT112/BAY 2010112 was assessed in several SCID mouse models bearing subcutaneous xenografts derived from the human prostate cancer cell lines LNCaP, PC3 and 22Rv1. The BiTE antibody completely inhibited growth of tumors at doses as low as 0.005 mg/kg administered daily intravenously when human T cells and tumor cells were co-inoculated. Transient regression of tumors were observed in a model where human T cells were adoptively transferred into the peritoneal space of mice with subcutaneously established tumors. These data suggest that the PSMA/CD3-bispecific antibody MT112/BAY 2010112 has high therapeutic potential for treatment of prostate cancer. Its cross-reactivity with human and macaque PSMA and CD3 antigens will greatly facilitate assessment of pharmacology, pharmacokinetics and safety during further pre-clinical development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4561. doi:10.1158/1538-7445.AM2011-4561

Ectodomains of target antigens for antibody-based therapies can be shed from the target cell surface and found in sera of patients. Shed ectodomains of therapeutic targets not only pose the risk of sequestering therapeutic antibodies but, in a multimeric form, of triggering T cell activation by bispecific antibodies binding to CD3 on T cells. Recently, epithelial cell adhesion molecule (EpCAM) has been shown to be activated by release of its ectodomain, called EpEX. Here, we show that only very low amounts of EpEX are detectable in sera of cancer patients. Among 100 cancer patient samples tested, only 17 (17%) showed serum levels of EpEX in excess of 0.05 ng/ml with highest EpEX concentrations of 5.29, 1.37 and 0.52 ng/ml. A recombinant form of human EpEX (recEpEX) was produced to assess its possible effect on redirected lysis and T cell activation by EpCAM/CD3-bispecific BiTE antibody MT110, currently being tested in patients with solid tumor malignancies. RecEpEX had a very minor effect on redirected lysis by MT110 with an approximate IC 50 value of 3,000 ng/ml, which is a concentration close to three orders of magnitude higher than the highest EpEX concentration found in cancer patients. Concentrations of 30 ng/ml EpEX in combination with 250 ng/ml MT110 were minimally required to induce a detectable activation of CD4 (+) and CD8 (+) T cells. We conclude that soluble EpEX in sera of cancer patients is unlikely to pose an issue for the efficacy or safety of MT110, and perhaps other antibodies binding to N-terminal epitopes of EpCAM.

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 Treatment with chimeric monoclonal antibody cetuximab has become the standard of care for patients with advanced colorectal cancer (CRC). Cetuximab and other EGFR-specific monoclonal antibodies predominantly inhibit cancer growth by interfering with receptor signalling. Recent analyses have shown that CRC patients with mutated KRAS and BRAF oncogenes do not profit from treatment with such antibodies. Here we have used the binding domains of cetuximab to construct a BiTE antibody that can directly engage and activate T cells by transiently connecting T cells via the CD3 subunit with EGFR-expressing target cells. The cetuximab-based BiTE antibody (C-BiTE) showed potent redirected lysis of KRAS- and BRAF-mutated human CRC lines HCT116 and HT-29, respectively, by unstimulated peripheral human T cells at half maximal concentrations of 10-40 pg/ml (ca. 0.2-0.8 picomolar). The BiTE antibody also completely prevented the outgrowth of tumors from HCT116 and HT-29 xenografts in mice at doses as low as 0.005 mg/kg when given daily i.v. for 10 days. The monoclonal antibody cetuximab was not effective in these models even at 50 mg/kg given twice weekly for 4 weeks. As a prerequisite for nonclinical safety assessment of C-BiTE in non-human primates, crossreactive binding of C-BiTE to CD3 and EGFR antigens of human and Cynomolgus monkey (Macaca fascicularis) origin was demonstrated. This binding translated into a comparable potency of redirected lysis of human EGFR-expressing cancer cells by stimulated Cynomolgus and human PBMC. Continuous i.v. infusion of 6.2 or 12.4 µg/kg C-BiTE to Cynomolgus monkeys for 3 weeks was well tolerated and led to relatively constant serum concentrations of C-BiTE between 1 and 10 ng/ml. In vitro, these serum levels would support a >90% lysis of EGFR-overexpressing CRC cells within 24 h by both Cynomolgus and human effector cells. Of note, no skin toxicity was observed during the 3-week exposure to C-BiTE. The highest doses of 31 and 154 µg/kg caused lethal damage to EGFR-expressing cells in vital organs. Inflammatory cell infiltration into the EGFR-positive tissues was observed at all dose levels but its incidence and severity showed no correlation with clinical signs. Our data suggest that C-BiTE can be safely administered to a relevant non-human primate species at dose levels similar to those of CD19-specific BiTE antibody blinatumumab, which has shown partial and complete responses in lymphoma patients. We anticipate that C-BiTE has a therapeutic window in humans. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2429.

Epidermal growth factor receptor (EGFR)-specific monoclonal antibodies predominantly inhibit colorectal cancer (CRC) growth by interfering with receptor signaling. Recent analyses have shown that patients with CRC with mutated KRAS and BRAF oncogenes do not profit from treatment with such antibodies. Here we have used the binding domains of cetuximab and pantitumumab for constructing T cell-engaging BiTE antibodies. Both EGFR-specific BiTE antibodies mediated potent redirected lysis of KRAS- and BRAF-mutated CRC lines by human T cells at subpicomolar concentrations. The cetuximab-based BiTE antibody also prevented at very low doses growth of tumors from KRAS- and BRAF-mutated human CRC xenografts, whereas cetuximab was not effective. In nonhuman primates, no significant adverse events were observed during treatment for 3 wk at BiTE serum concentrations inducing, within 1 d, complete lysis of EGFR-overexpressing cancer cells. EGFR-specific BiTE antibodies may have potential to treat CRC that does not respond to conventional antibodies.

Abstract MEDI-565 (MT111) is a novel bispecific single-chain antibody of the BiTE (Bispecific T cell engager) class that transiently links carcinoembryonic antigen (CEA) on cancer cells with human CD3 on T cells. MEDI-565 specifically binds to human CEA with an affinity of 8.5 nM but not to any other member of the CEACAM family. In targeted expression studies on cryopreserved and formalin-fixed paraffin-embedded sections, MEDI-565 demonstrated membrane-localized binding specifically to epithelial cells in human cancerous tissues. The highest prevalence of MEDI-565 binding (∼90%) was in adenocarcinomas of gastrointestinal origin. In in vitro killing assays, MEDI-565 recruited T cells via the CD3 antigen (affinity of 310 nM) in a process that required concomitant binding to CEA positive tumor cells for T cell activation. As a consequence, T cells expanded, increased cell surface expression of the activation markers CD69 and CD25, and released perforin and granzymes. The release of cytotoxic granule content led to a Ca2+-dependent activation of pro-caspases and subsequent apoptosis of CEA-expressing tumor cells. Efficient target cell lysis by MEDI-565 was predominantly mediated by CD8+ T cells and occurred within a wide range of effector-to-target ratios (80:1 to 5:1) for T cells derived from various human donors. BiTE mediated killing was not affected by the presence of soluble CEA (≤5 µg/mL). The in vivo activity of MEDI-565 was investigated in subcutaneous xenograft models using immunocompromised SCID mice inoculated with mixtures of human T cells and human cancer cell lines. The antibody was eliminated from the serum with a half-life of a few hours following a single intravenous (IV) or subcutaneous (SC) injection. Despite a relatively short serum half-life, daily IV or SC bolus treatments over 5 days provided sufficient levels of exposure to inhibit the growth of CEA-positive tumors in a dose-dependent manner. Inhibition of growth was observed for tumors of different tissue origins and was dependent on the presence of human T cells and CEA expression by tumor cells. There were no MEDI-565-related in-life observations following treatment. These studies demonstrated that MEDI-565 has potent and selective anti-cancer activity in vitro and in vivo and provides evidence that MEDI-565 may be an effective monotherapy to treat CEA-expressing malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5625.

Abstract Nonclinical safety assessment of biopharmaceuticals for human use relies on their cross-reactivity with the respective target in other species, the absence of which precludes testing in commonly used animal models. This is the case for a first-generation of T cell-engaging BiTE antibodies, which solely cross-react with T cells of chimpanzee. BiTE antibodies are designed to transiently connect the CD3 subunit of T cell receptors on T cells with an antigen on target cells. This can very effectively activate T cells, leading to a potent redirected lysis of target cells. Here, we have generated a series of novel human anti-CD3 antibodies that cross-react with non-human primate species, including Cynomolgus monkeys (Macaca fascicularis) and marmoset (Callithrix jacchus). The variable domains of a selected anti-CD3 antibody were used to generate next-generation BiTE antibodies specific for (1) CD33, a target antigen for treatment of acute myelogenous leukemia, (2) melanoma-associated chondroitin sulfate proteoglycan (MCSP), a potential target for treatment of melanoma, and (3) epidermal growth factor receptor 1 (EGFR), a validated target for treatment of colorectal cancer. In vitro, CD33-, MCSP- and EGFR-specific BiTE antibodies showed comparable binding to CD3 on human and macaque T cells, and to CHO cells expressing CD33, MCSP and EGFR of human or macaque origin. In human and macaque cell-based assays, bispecific binding triggered redirected target cell lysis as well as conditional T cell activation, as previously described for first-generation BiTE antibodies. When continuously infused for one week to Cynomolgus monkeys, the CD33-specific BiTE antibody caused depletion of CD33-expressing peripheral blood cells at tolerated doses, and reached a maximum tolerated dose (MTD) at 120 µg/m2/day. The EGFR-specific BiTE antibody reached an MTD at 150 µg/m2/kg. In contrast, the MCSP-specific BiTE antibody was well-tolerated up to a dose of 5,000 µg/m2/day. Our primate data suggest that the tolerability and toxicity of CD33-, MCSP- and EGFR-specific BiTE antibodies were apparently determined by target cell-dependent bispecific binding, and not by monovalent binding to CD3 on macaque T cells. Our data validate the Cynomolgus monkey as a relevant species for assessing the safety and tolerability of next-generation BiTE antibodies that use a more broadly cross-reactive anti-CD3 human single-chain antibody. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2435.

Previous attempts have shown the potential of T cells in immunotherapy of cancer. Here, we report on the clinical activity of a bispecific antibody construct called blinatumomab, which has the potential to engage all cytotoxic T cells in patients for lysis of cancer cells. Doses as low as 0.005 milligrams per square meter per day in non–Hodgkin's lymphoma patients led to an elimination of target cells in blood. Partial and complete tumor regressions were first observed at a dose level of 0.015 milligrams, and all seven patients treated at a dose level of 0.06 milligrams experienced a tumor regression. Blinatumomab also led to clearance of tumor cells from bone marrow and liver. T cell–engaging antibodies appear to have therapeutic potential for the treatment of malignant diseases.