A recombinant bispecific single-chain antibody, CD19 × CD3, induces rapid and high lymphoma-directed cytotoxicity by unstimulated T lymphocytes

Redirection of CD4+ and CD8+ T lymphocytes via an anti-CD3 × anti-CD19 bi-specific antibody combined with cytosine arabinoside and the efficient lysis of patient-derived B-ALL cells

Background

B-acute lymphoblastic leukemia (B-ALL) is derived from B cell progenitors. Recently, the development of appropriate combinations of chemotherapy and immunotherapy represents a promising approach for eliminating cancer. We previously constructed an anti-CD3 × anti-CD19 bi-specific antibody in a diabody configuration and its disulfide-stabilized format (ds-diabody). The combination of the diabody or ds-diabody and Ara-C was highly effective in enhancing the cytotoxicity of T cells against the CD19+ human leukemia cell-line, Nalm-6, both in vitro and in vivo. This study verified whether B-ALL patient-derived cells were sensitive to the diabody or ds-diabody and low-dosage Ara-C combination.

Methods

This study aimed to detect the B7 family members B7.1 (CD80) and B7.2 (CD86) that were expressed in B-ALL patient-derived cells pre-treated by Ara-C (0.25 μM) and to determine the targeted killing ability of T cell subtypes induced by the diabody or ds-diabody combination with Ara-C both in vitro and in vivo. We also determined the levels of the cytokines that were released by activated CD4+ or CD8+ T cells during therapy.

Result

Low-dose Ara-C enhanced CD80 and CD86 expression in nearly 50 % of specimens of B-ALL patient-derived cells. A combination of diabody or ds-diabody and Ara-C enhanced T cell against B-ALL cells in vitro and in vivo. Both CD8+ and CD4+ T cells were potently activated. Expression of CD25 and CD69 was augmented equally by CD4+ or CD8+ T cells. However, CD8+ T cells made the major contribution by redirecting target cell lysis in a granzyme B and perforin-dependent mechanism. CD4+ T cells played an important immunomodulatory role by secreting IL2. Consequently, IL3, IL6, TNFα, and IFNγ were also released by CD4+ or CD8+ T cells following diabody-mediated T cell activation.

Conclusion

T cell therapy induced by diabody or ds-diabody combined with low dose of Ara-C was effective against cancer cell-lines and in clinical trials. In vivo, the ds-diabody was more efficient than its parent diabody due to its enhanced stability.

Mechanisms of action of therapeutic antibodies for cancer

The therapeutic utility of antibodies and their derivatives is achieved by various means. The FDA has approved several targeted antibodies that disrupt signaling of various growth factor receptors for the treatment of a number of cancers. Rituximab, and other anti-CD20 monoclonal antibodies are active in B cell malignancies. As more experience has been gained with anti-CD20 monoclonal antibodies, the multifactorial nature of their anti-tumor mechanisms has emerged. Other targeted antibodies function to dampen inhibitory checkpoints. These checkpoint inhibitors have recently achieved dramatic results in several cancers, including melanoma. These and related antibodies continue to be investigated in the clinical and pre-clinical settings. Novel antibody structures that target two or more antigens have also made their way into clinical use. Tumor targeted antibodies can also be conjugated to chemo- or radiotherapeutic agents, or catalytic toxins, as a means to deliver toxic payloads to cancer cells. Here we provide a review of these mechanisms and a discussion of their relevance to current and future clinical applications.

Novel Targeted Agents in Hodgkin and Non-Hodgkin Lymphoma Therapy

There has been a recent emergence of novel targeted agents for treatment of Hodgkin and non-Hodgkin lymphoma. In particular, antibodies and antibody-drug conjugates directed against surface antigens, agents that block immune checkpoint pathways, and small molecule inhibitors directed against cell signaling pathways have shown significant promise in patients with relapsed and refractory disease and in the frontline setting. With the development of these new therapies, cytotoxic chemotherapy may be avoided entirely in some clinical settings. This review will present the latest information on these novel treatments in Hodgkin and non-Hodgkin lymphoma and will discuss both recently approved agents as well as drugs currently being studied in clinical trials.

Activation of acid-sensing ion channels by localized proton transient reveals their role in proton signaling

Extracellular transients of pH alterations likely mediate signal transduction in the nervous system. Neuronal acid-sensing ion channels (ASICs) act as sensors for extracellular protons, but the mechanism underlying ASIC activation remains largely unknown. Here, we show that, following activation of a light-activated proton pump, Archaerhodopsin-3 (Arch), proton transients induced ASIC currents in both neurons and HEK293T cells co-expressing ASIC1a channels. Using chimera proteins that bridge Arch and ASIC1a by a glycine/serine linker, we found that successful coupling occurred within 15 nm distance. Furthermore, two-cell sniffer patch recording revealed that regulated release of protons through either Arch or voltage-gated proton channel Hv1 activated neighbouring cells expressing ASIC1a channels. Finally, computational modelling predicted the peak proton concentration at the intercellular interface to be at pH 6.7, which is acidic enough to activate ASICs in vivo. Our results highlight the pathophysiological role of proton signalling in the nervous system.

Blinatumomab: a bispecific T cell engager (BiTE) antibody against CD19/CD3 for refractory acute lymphoid leukemia

Targeted therapy has been the forefront of cancer treatment. Cancer immunotherapy is the most recent focus. In addition, novel immunotherapeutics targeting B cell receptor signaling (e.g., ibrutinib), T cell receptor ( e.g., CART19), and NK cells (e.g., AFM13) are being developed. This review summarized the new development in blinatumomab (MT103/MEDI-538), a first-in-class bispecific T engager (BiTE) antibody against CD19/CD3 in patients with relapsed/refractory precursor B cell acute lymphoid leukemia.

Treatment of chronic lymphocytic leukemia with monoclonal antibodies, where are we heading?

Chronic lymphocytic leukemia (CLL) is the most prevalent leukemia in the western world and monoclonal antibodies (mAbs) are important part of CLL treatment. The goal of this article was to summarize current literature on the position of mAbs in CLL treatment and to mention factors influencing effectiveness of mAbs in CLL. Several new mAbs have been developed and investigated in CLL over the past few years. Mainly anti-CD20 monoclonal antibodies are still used routinely in CLL therapy. Unfortunately, the clinical application of mAbs needs to be further improved. Novel combinations and sequences of mAbs with other compounds need to be studied in clinical trials in order to increase overall response rate and prolong remission duration. Mechanisms of action of mAbs or mechanisms of resistance to mAbs have to be also investigated to predict effectiveness of mAb in particular patient.

Novel immunotherapies for hematologic malignancies

The immune system is designed to discriminate between self and tumor tissue. Through genetic recombination, there is fundamentally no limit to the number of tumor antigens that immune cells can recognize. Yet, tumors use a variety of immunosuppressive mechanisms to evade immunity. Insight into how the immune system interacts with tumors is expanding rapidly and has accelerated the translation of immunotherapies into medical breakthroughs. Herein, we appraise novel strategies that exploit the patient's immune system to kill cancer. We review various forms of immune-based therapies, which have shown significant promise in patients with hematologic malignancies, including (i) conventional monoclonal therapies like rituximab; (ii) engineered monoclonal antibodies called bispecific T-cell engagers; (iii) monoclonal antibodies and pharmaceutical drugs that block inhibitory T-cell pathways (i.e. PD-1, CTLA-4, and IDO); and (iv) adoptive cell transfer therapy with T cells engineered to express chimeric antigen receptors or T-cell receptors. We also assess the idea of using these therapies in combination and conclude by suggesting multi-prong approaches to improve treatment outcomes and curative responses in patients.

Blinatumomab for the Treatment of Philadelphia Chromosome-Negative, Precursor B-cell Acute Lymphoblastic Leukemia

Blinatumomab is a CD19/CD3 bispescific antibody designed to redirect T cells toward malignant B cells and induce their lysis. It recently gained accelerated approval by the FDA for the treatment of relapsed or refractory Philadelphia chromosome-negative B-cell acute lymphoblastic leukemia (RR-ALL). In the phase II trial that served as the basis for approval, blinatumomab demonstrated significant single-agent activity and induced remission [complete remission (CR) and CR with incomplete recovery of peripheral blood counts (CRh)] in 43% of 189 adult patients with RR-ALL; the majority of responders (82%) also attained negative minimal residual disease (MRD(-)) status that did not generally translate into long-term remissions in most cases. Additional studies show that blinatumomab can induce high response rates associated with lasting remissions in patients in first remission treated for MRD positivity, suggesting a role for blinatumomab in the upfront, MRD-positive setting. Blinatumomab infusion follows a predictable immunopharmacologic profile, including early cytokine release that can be associated with a clinical syndrome, T-cell expansion, and B-cell depletion. Neurologic toxicities represent a unique toxicity that shares similarities with adverse effects of other T-cell engaging therapies. Further studies are needed to clarify the optimal disease setting and timing for blinatumomab therapy. Additional insights into the pathogenesis, risk factors, and prevention of neurologic toxicities as well as a better understanding of the clinical consequences and biologic pathways that are associated with drug resistance are needed.

Blockade of the PD-1/PD-L1 axis augments lysis of AML cells by the CD33/CD3 BiTE antibody construct AMG 330: reversing a T-cell-induced immune escape mechanism

Bispecific T-cell engagers (BiTEs) are very effective in recruiting and activating T cells. We tested the cytotoxicity of the CD33/CD3 BiTE antibody construct AMG 330 on primary acute myeloid leukemia (AML) cells ex vivo and characterized parameters contributing to antileukemic cytolytic activity. The E:T ratio and the CD33 expression level significantly influenced lysis kinetics in long-term cultures of primary AML cells (n=38). AMG 330 induced T-cell-mediated proinflammatory conditions, favoring the upregulation of immune checkpoints on target and effector cells. Although not constitutively expressed at the time of primary diagnosis (n=123), PD-L1 was strongly upregulated on primary AML cells upon AMG 330 addition to ex vivo cultures (n=27, P<0.0001). This phenomenon was cytokine-driven as the sole addition of interferon (IFN)-γ and tumor necrosis factor-α also induced expression. Through blockade of the PD-1/PD-L1 interaction, AMG 330-mediated lysis (n=9, P=0.03), T-cell proliferation (n=9, P=0.01) and IFN-γ secretion (n=8, P=0.008) were significantly enhanced. The combinatorial approach was most beneficial in settings of protracted AML cell lysis. Taken together, we have characterized a critical resistance mechanism employed by primary AML cells under AMG 330-mediated proinflammatory conditions. Our results support the evaluation of checkpoint molecules in upcoming clinical trials with AMG 330 to enhance BiTE antibody construct-mediated cytotoxicity.

Structure, development, preclinical and clinical efficacy of blinatumomab in acute lymphoblastic leukemia

ABSTRACT 

The treatment of acute lymphoblastic leukemia (ALL) in adults remains challenging and novel therapies are needed. The antigen, CD19, is expressed by >90% of pre-B ALLs and represents an attractive therapeutic target. The bispecific T-cell-engaging antibody, blinatumomab, targets CD19 and has demonstrated encouraging results in minimal residual disease positive and relapsed/refractory pre-B ALL. In this review, we discuss in detail the mechanism of action and key pharmacologic aspects of blinatumomab. In addition, the preclinical studies, clinical studies and toxicities are summarized.

B7H6-Specific Bispecific T Cell Engagers Lead to Tumor Elimination and Host Antitumor Immunity

Substantial evidence showed that T cells are the key effectors in immune-mediated tumor eradication; however, most T cells do not exhibit antitumor specificity. In this study, a bispecific T cell engager (BiTE) approach was used to direct T cells to recognize B7H6(+) tumor cells. B7H6 is a specific ligand for the NK cell-activating receptor NKp30. B7H6 is expressed on various types of primary human tumors, including leukemia, lymphoma, and gastrointestinal stromal tumors, but it is not constitutively expressed on normal tissues. Data from this study showed that B7H6-specific BiTEs direct T cells to mediate cellular cytotoxicity and IFN-γ secretion upon coculturing with B7H6(+) tumors. Furthermore, B7H6-specific BiTE exhibited no self-reactivity to proinflammatory monocytes. In vivo, B7H6-specific BiTE greatly enhanced the survival benefit of RMA/B7H6 lymphoma-bearing mice through perforin and IFN-γ effector mechanisms. In addition, long-term survivor mice were protected against an RMA lymphoma tumor rechallenge. The B7H6-specific BiTE therapy also decreased tumor burden in murine melanoma and ovarian cancer models. In conclusion, B7H6-specific BiTE activates host T cells and has the potential to treat various B7H6(+) hematological and solid tumors.

Clinical overview of anti-CD19 BiTE(®) and ex vivo data from anti-CD33 BiTE(®) as examples for retargeting T cells in hematologic malignancies

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.

Novel agents for the treatment of childhood acute leukemia

Together, acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) make up approximately one-third of all pediatric cancer diagnoses. Despite remarkable improvement in the treatment outcomes of these diseases over the past several decades, the prognosis for certain high-risk groups of leukemia and for relapsed disease remains poor. However, recent insights into different types of 'driver' lesions of leukemogenesis, such as the aberrant activation of signaling pathways and various epigenetic modifications, have led to the discovery of novel agents that specifically target the mechanism of transformation. In parallel, emerging approaches in cancer immunotherapy have led to newer therapies that can exploit and harness cytotoxic immunity directed against malignant cells. This review details the rationale and implementation of recent and specifically targeted therapies in acute pediatric leukemia. Topics covered include the inhibition of critical cell signaling pathways [BCR-ABL, FMS-like tyrosine kinase 3 (FLT3), mammalian target of rapamycin (mTOR), and Janus-associated kinase (JAK)], proteasome inhibition, inhibition of epigenetic regulators of gene expression [DNA methyltransferase (DNMT) inhibitors, histone deacetylase (HDAC) inhibitors, and disruptor of telomeric signaling-1 (DOT1L) inhibitors], monoclonal antibodies and immunoconjugated toxins, bispecific T-cell engaging (BiTE) antibodies, and chimeric antigen receptor-modified (CAR) T cells.

Immunotherapy for Acute Myeloid Leukemia

Despite longstanding efforts in basic research and clinical studies, the prognosis for patients with acute myeloid leukemia (AML) remains poor. About half of the patients are not medically fit for intensive induction therapy to induce a complete remission and are treated with palliative treatment concepts. The patients medically fit for intensive induction therapy have a high complete remission rate but the majority suffers from relapse due to chemo-refractory leukemic cells. Allogeneic stem cell transplantation as post-remission therapy can significantly reduce the likelihood of relapse, but it is associated with a high rate of morbidity and mortality. Novel therapeutic concepts are therefore urgently sought after. During recent years, the focus has shifted towards the development of novel immunotherapeutic strategies. Some of the most promising are drug-conjugated monoclonal antibodies, T-cell engaging antibody constructs, adoptive transfer with chimeric antigen receptor (CAR) T cells, and dendritic cell vaccination. Here, we review recent progress in these four fields and speculate about the optimal time points during the course of AML treatment for their application.

Blinatumomab for the treatment of B-cell lymphoma

INTRODUCTION

Blinatumomab is a bispecific T-cell engager (BiTE) molecule that recruits cytotoxic T cells to target tumor B cells by linking the CD3 and CD19 antigens. Among the various formats of bispecific antibodies developed in the past 50 years, the BiTE class is remarkable for its low effector-to-target ratio, high tissue penetration and singular ability to activate T cells independent of MHC class I presentation or costimulation. Blinatumomab has been studied in patients with relapsed or refractory non-Hodgkin's lymphoma (NHL) and B-precursor acute lymphoblastic leukemia (B-ALL).

AREAS COVERED

This article reviews the current literature on blinatumomab including its pharmacology, preclinical findings, clinical trials in B-cell NHL and, to a lesser extent, Phase II studies in B-ALL. The authors discuss the potential future directions in light of other new competing therapies for NHL and unmet clinical needs in the market.

EXPERT OPINION

The recent approval of blinatumomab for B-ALL symbolizes a breakthrough for BiTE technology with prospective application in the targeted therapy of other cancers. Although blinatumomab seems an unlikely option for treating indolent lymphoma due to toxicity, the need for long-term continuous infusion therapy and multiple promising well-tolerated oral agents, it holds promise for aggressive NHL patients whose diseases are refractory to current standard approaches. Larger trials are needed to demonstrate blinatumomab's curative potential in aggressive histologies.

How to train your T cell: genetically engineered chimeric antigen receptor T cells versus bispecific T-cell engagers to target CD19 in B acute lymphoblastic leukemia

Antigen-specific T cell-based immunotherapy is getting its day in the sun. The contemporaneous development of two potent CD19-specific immunotherapeutic modalities for the treatment of B-cell malignancies provides exciting opportunities for patients, physicians and scientists alike. Patients with relapsed, refractory or poor-risk B-cell acute lymphoblastic leukemia (ALL) previously had few therapeutic options and now have two potential new lifelines. Physicians will have the choice between two powerful modalities and indeed could potentially enroll some patients on trials exploring both modalities if needed. For scientists interested in tumor immunology, the advent of chimeric antigen receptor T-cell therapy and of bispecific T-cell engagers (BiTEs) provides unprecedented opportunities to explore the promise and limitations of antigen-specific T-cell therapy in the context of human leukemia. In this article, we compare chimeric antigen receptor T cells and BiTEs targeting CD19 in B-cell ALL in the setting of the available clinical literature.

Generation and characterization of a bispecific diabody targeting both EPH receptor A10 and CD3

The EPH receptor A10 (EphA10) is up-regulated in breast cancer but is not normally expressed in healthy tissue, thus it has been suggested that EphA10 may be a useful target for cancer therapy. This study reports a diabody, an antibody derivative binding two different target molecules, EphA10 expressed in tumor cells and CD3 expressed in T cells, which showed T cell dependent-cytotoxicity. The diabody, which has His-tagged and FLAG-tagged chains, was expressed in Escherichia coli and purified in both heterodimer (Db-1) and homodimer (Db-2) formulations by liquid chromatography. Flow cytometry analysis using EphA10-expressing cells showed that binding activity of heterodimers was stronger than that of homodimers. Addition of diabodies to PBMC cultures resulted in T-cell mediated redirected lysis, and the bioactivity was consistent with the stronger binding activity of heterodimeric diabody formulations. Our results indicate that diabodies recognizing both EphA10 and CD3 could have a range of potential applications in cancer therapy, such as breast cancers that express the EPH receptor A10, especially triple negative breast cancer.

Bispecific antibody platforms for cancer immunotherapy

Over the past decades advances in bioengineering and expanded insight in tumor immunology have resulted in the emergence of novel bispecific antibody (bsAb) constructs that are capable of redirecting immune effector cells to the tumor microenvironment. (Pre-) clinical studies of various bsAb constructs have shown impressive results in terms of immune effector cell retargeting, target dependent activation and the induction of anti-tumor responses. This review summarizes recent advances in the field of bsAb-therapy and limitations that were encountered. Furthermore, we will discuss potential future developments that can be expected to take the bsAb approach successfully forward.

Bispecific T-cell engagers for cancer immunotherapy

Bispecific T-cell engagers (BiTEs) are a new class of immunotherapeutic molecules intended for the treatment of cancer. These molecules enhance the patient's immune response to tumors by retargeting T cells to tumor cells. BiTEs are constructed of two single-chain variable fragments (scFv) connected in tandem by a flexible linker. One scFv binds to a T-cell-specific molecule, usually CD3, whereas the second scFv binds to a tumor-associated antigen. This structure and specificity allows a BiTE to physically link a T cell to a tumor cell, ultimately stimulating T-cell activation, tumor killing and cytokine production. BiTEs have been developed, which target several tumor-associated antigens, for a variety of both hematological and solid tumors. Several BiTEs are currently in clinical trials for their therapeutic efficacy and safety. This review examines the salient structural and functional features of BiTEs, as well as the current state of their clinical and preclinical development.

A novel method using blinatumomab for efficient, clinical-grade expansion of polyclonal T cells for adoptive immunotherapy

Current treatment of chronic lymphocytic leukemia (CLL) patients often results in life-threatening immunosuppression. Furthermore, CLL is still an incurable disease due to the persistence of residual leukemic cells. These patients may therefore benefit from immunotherapy approaches aimed at immunoreconstitution and/or the elimination of residual disease following chemotherapy. For these purposes, we designed a simple GMP-compliant protocol for ex vivo expansion of normal T cells from CLL patients' peripheral blood for adoptive therapy, using bispecific Ab blinatumomab (CD3 × CD19), acting both as T cell stimulator and CLL depletion agent, and human rIL-2. Starting from only 10 ml CLL peripheral blood, a mean 515 × 10(6) CD3(+) T cells were expanded in 3 wk. The resulting blinatumomab-expanded T cells (BET) were polyclonal CD4(+) and CD8(+) and mostly effector and central memory cells. The Th1 subset was slightly prevalent over Th2, whereas Th17 and T regulatory cells were <1%. CMV-specific clones were detected in equivalent proportion before and after expansion. Interestingly, BET cells had normalized expression of the synapse inhibitors CD272 and CD279 compared with starting T cells and were cytotoxic against CD19(+) targets in presence of blinatumomab in vitro. In support of their functional capacity, we observed that BET, in combination with blinatumomab, had significant therapeutic activity in a systemic human diffuse large B lymphoma model in NOD-SCID mice. We propose BET as a therapeutic tool for immunoreconstitution of heavily immunosuppressed CLL patients and, in combination with bispecific Ab, as antitumor immunotherapy.

Management of relapsed acute lymphoblastic leukemia in childhood with conventional and innovative approaches

PURPOSE OF REVIEW

To review and summarize the available evidence on factors predicting prognosis of children with relapsed acute lymphoblastic leukemia (ALL) and on the currently used treatment strategies, as well as on the most promising and innovative molecular or cellular therapies.

RECENT FINDINGS

Relapse still represents the most common cause of treatment failure, occurring in approximately 15-20% of childhood ALL. Risk-oriented standard salvage regimens are mostly based on combinations of the same agents incorporated in frontline therapies. Allogeneic hematopoietic stem cell transplantation (HSCT) is largely employed as postremission therapy, being superior to chemotherapy in high-risk patients. With conventional therapies including HSCT, 40-50% of children with relapsed ALL can be rescued. Thus, innovative approaches are needed to further improve the outcome of patients, especially when carrying poor prognostic factors. The last decade has witnessed the development of novel agents, including nucleoside analogues, anti-CD22 monoclonal antibodies and bi-specific, anti-CD3/CD19 antibodies, together with new formulations of existing chemotherapeutic agents and targeted molecules, such as tyrosine kinase inhibitors and FLT3 inhibitors.

SUMMARY

A significant proportion of children with relapsed ALL are salvaged by risk-oriented therapies. Novel agents should be integrated into combination regimens with the aim of further improving outcome of patients.

Cloning, expression, purification and characterization of a bispecific single-chain diabody against fluoroquinolones and sulfonamides in Escherichia coli

A recombinant bispecific single-chain diabody (scDb), recognizing fluoroquinolones (FQs) and sulfonamides (SAs), was successfully constructed with two single-chain variable fragment antibodies (scFvs). The scDb gene was cloned into the expression vector pJB33, and 6×His-tagged scDb was expressed as soluble bodies in Escherichia coli RV308 host, then purified by one step affinity chromatography of immobilized metal ion affinity chromatography (IMAC). SDS-PAGE and Western blotting analysis of the purified scDb indicated that the prepared scDb was successfully expressed as a ∼60 kDa and the final purity of the scDb protein was up to 95% with yields of approximately 6 mg/L of bacterial culture. The scDb was further characterized by indirect competitive enzyme linked immunosorbent assay (icELISA), showing that the affinity and specificity of scDb were fully retained from the two parental scFvs, capable of simultaneously binding FQs and SAs. The 50% inhibition concentration (IC50) values of the optimized immunoassay were 0.45 ng mL(-1) for FQs and 0.75 ng mL(-1) for SAs, respectively. The scDb exhibited high affinity to 20 FQs and 14 SAs. Taken together, these findings suggested that the prepared scDb could be used to develop future novel immunoassay for simultaneous determination of 20 FQs and 14 SAs.

Antibody therapy for pediatric leukemia

Despite increasing cure rates for pediatric leukemia, relapsed disease still carries a poor prognosis with significant morbidity and mortality. Novel targeted therapies are currently being investigated in an attempt to reduce adverse events and improve survival outcomes. Antibody therapies represent a form of targeted therapy that offers a new treatment paradigm. Monoclonal antibodies are active in pediatric acute lymphoblastic leukemia (ALL) and are currently in Phase III trials. Antibody-drug conjugates (ADCs) are the next generation of antibodies where a highly potent cytotoxic agent is bound to an antibody by a linker, resulting in selective targeting of leukemia cells. ADCs are currently being tested in clinical trials for pediatric acute myeloid leukemia and ALL. Bispecific T cell engager (BiTE) antibodies are a construct whereby each antibody contains two binding sites, with one designed to engage the patient's own immune system and the other to target malignant cells. BiTE antibodies show great promise as a novel and effective therapy for childhood leukemia. This review will outline recent developments in targeted agents for pediatric leukemia including monoclonal antibodies, ADCs, and BiTE antibodies.

Treatment of Philadelphia-positive acute lymphoid leukemia

SUMMARY Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL) represents approximately 15–30% of ALL in adults and is characterized by the expression of the fusion protein BCR–ABL with oncogenic activity. Remission and survival rates were lower whereas relapse risk was increased in Ph+ compared with Philadelphia-negative ALL, until remarkable improvements in the management of Ph+ ALL were achieved through the introduction of tyrosine kinase inhibitors that reduce the activity of the BCR–ABL protein. However, in patients achieving complete remission, allogeneic hematopoietic stem cell transplantation is in most cases a mandatory therapeutic step because rate of relapses are still high. This review will illustrate the current therapeutic options for the management of Ph+ ALL and indicate how better curative options may stem from appropriate implementation of tyrosine kinase inhibitors and novel antitumoral agents.

T-cell engager-armed oncolytic vaccinia virus significantly enhances antitumor therapy

Oncolytic vaccinia virus (VV) therapy has shown promise in preclinical models and in clinical studies. However, complete responses have rarely been observed. This lack of efficacy is most likely due to suboptimal virus spread through the tumor resulting in limited tumor cell destruction. We reasoned that redirecting T cells to the tumor has the potential to improve the antitumor activity of oncolytic VVs. We, therefore, constructed a VV encoding a secretory bispecific T-cell engager consisting of two single- chain variable fragments specific for CD3 and the tumor cell surface antigen EphA2 (EphA2-T-cell engager-armed VV (EphA2-TEA-VV)). In vitro, EphA2-TEA-VV's ability to replicate and induce oncolysis was similar to that of unmodified virus. However, only tumor cells infected with EphA2-TEA-VV induced T-cell activation as judged by the secretion of interferon-γ and interleukin-2. In coculture assays, EphA2-TEA-VV not only killed infected tumor cells, but in the presence of T cells, it also induced bystander killing of noninfected tumor cells. In vivo, EphA2-TEA-VV plus T cells had potent antitumor activity in comparison with control VV plus T cells in a lung cancer xenograft model. Thus, arming oncolytic VVs with T-cell engagers may represent a promising approach to improve oncolytic virus therapy.

CD33 target validation and sustained depletion of AML blasts in long-term cultures by the bispecific T-cell-engaging antibody AMG 330

Antibody-based immunotherapy represents a promising strategy to target and eliminate chemoresistant leukemic cells. Here, we evaluated the CD33/CD3-bispecific T cell engaging (BiTE) antibody (AMG 330) for its suitability as a therapeutic agent in acute myeloid leukemia (AML). We first assessed CD33 expression levels by flow cytometry and found expression in >99% of patient samples (n = 621). CD33 was highest expressed in AMLs with NPM1 mutations (P < .001) and lower in AMLs with complex karyotypes and t(8;21) translocations (P < .001). Furthermore, leukemic stem cells within the CD34(+)/CD38(-) compartment displayed CD33 at higher levels than healthy donor stem cells (P = .047). In MS-5 feeder cell-based long-term cultures that supported the growth of primary AML blasts for up to 36 days, AMG 330 efficiently recruited and expanded residual CD3(+)/CD45RA(-)/CCR7(+) memory T cells within the patient sample. Even at low effector to target ratios, the recruited T cells lysed autologous blasts completely in the majority of samples and substantially in the remaining samples in a time-dependent manner. This study provides the first correlation of CD33 expression levels with AML genotype in a comprehensive analysis of adult patients. Targeting CD33 ex vivo using AMG 330 in primary AML samples led to T cell recruitment and expansion and remarkable antibody-mediated cytotoxicity, suggesting efficient therapeutic potential in vivo.

Optically induced cell fusion using bispecific nanoparticles

Redirecting the immune system to eliminate tumor cells is a promising alternative to traditional cancer therapies, most often requiring direct interaction between an immune system effector cell and its target. Herein, a novel approach for selective attachment of malignant cells to antigen-presenting cells by using bispecific nanoparticles is presented. The engaged cell pairs are then irradiated by a sequence of resonant femtosecond pulses, which results in widespread cell fusion and the consequent formation of hybrid cells. The dual role of gold nanoparticles as conjugating agents and fusion promoters offers a simple yet effective means for specific fusion between different cells. This technology could be useful for a variety of in vitro and in vivo applications that call for selective fusion between cells within a large heterogenic cell population.

A tale of two specificities: bispecific antibodies for therapeutic and diagnostic applications

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Recombinant DNA technologies are leading the rapid expansion of bispecific antibody formats.

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The therapeutic potential of bispecific antibodies is being realized through creative design.

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Bispecific antibodies are potentially underutilized reagents for diagnostics.

Artificial manipulation of antibody genes has facilitated the production of several unique recombinant antibody formats, which have highly important therapeutic and biotechnological applications. Although bispecific antibodies (bsAbs) are not new, they are coming to the forefront as our knowledge of the potential efficacy of antibody-based therapeutics expands. The next generation of bsAbs is developing due to significant improvements in recombinant antibody technologies. This review focuses on recent advances with a particular focus on improvements in format and design that are contributing to the resurgence of bsAbs, and in particular, on innovative structures applicable to next generation point-of-care (POC) devices with applicability to low resource environments.

Novel targeted therapies in acute lymphoblastic leukemia

Chemotherapy alone cures only 25-45% of adult patients with acute lymphoblastic leukemia (ALL), making novel treatment agents and strategies desperately needed. The addition of monoclonal antibodies (rituximab, alemtuzumab, epratzumab) to chemotherapy has demonstrated encouraging results in patients with newly diagnosed and relapsed ALL. The anti-CD22 immunoconjugate, inotuzumab ozogamicin, and the anti-CD19 BiTE(®) antibody, blinatumomab, have demonstrated impressive single agent activity in patients with relapsed or refractory B-ALL. Early reports of chimeric antigen receptor therapies have been promising in patients with relapsed ALL. Other agents targeting NOTCH1, FLT3, the proteasome and DNA methylation are early in development. These new agents hope to improve the outcome of ALL therapy with less toxicity. The challenge going forward will be to find safe and effective combinations and determine where in the treatment schema these agents will be most effective in ALL therapy.

Cytokine release syndrome after blinatumomab treatment related to abnormal macrophage activation and ameliorated with cytokine-directed therapy

Blinatumomab is a CD19/CD3-bispecific T-cell receptor-engaging (BiTE) antibody with efficacy in refractory B-precursor acute lymphoblastic leukemia. Some patients treated with blinatumomab and other T cell-activating therapies develop cytokine release syndrome (CRS). We hypothesized that patients with more severe toxicity may experience abnormal macrophage activation triggered by the release of cytokines by T-cell receptor-activated cytotoxic T cells engaged by BiTE antibodies and leading to hemophagocytic lymphohistiocytosis (HLH). We prospectively monitored a patient during blinatumomab treatment and observed that he developed HLH. He became ill 36 hours into the infusion with fever, respiratory failure, and circulatory collapse. He developed hyperferritinemia, cytopenias, hypofibrinogenemia, and a cytokine profile diagnostic for HLH. The HLH continued to progress after discontinuation of blinatumomab; however, he had rapid improvement after IL-6 receptor-directed therapy with tocilizumab. Patients treated with T cell-activating therapies, including blinatumomab, should be monitored for HLH, and cytokine-directed therapy may be considered in cases of life-threatening CRS. This trial was registered at www.clinicaltrials.gov as #NCT00103285.

Outcomes of second allogeneic hematopoietic stem cell transplantation for patients with acute lymphoblastic leukemia

For patients with ALL who relapse following allo-SCT, only a second SCT provides a realistic chance for long-term disease remission. We retrospectively analyzed the outcomes of 31 patients with relapsed ALL after a prior allo-SCT, who received a second SCT (SCT2) at our center. With a median follow-up of 3 years, 1- and 3-year PFS was 23 and 11% and 1- and 3 year OS rates were 23 and 11%. Twelve patients (39%) were transplanted with active disease, of whom 75% attained a CR. We found a significant relationship between the time to treatment failure following first allograft (SCT1) and PFS following SCT2 (P=0.02, hazard ratio=0.93/month). In summary, a second transplant remains a potential treatment option for achieving response in a highly refractory patient population. While long-term survival is limited, a significant proportion of patients remains disease-free for up to 1 year following SCT2, providing a window of time to administer preventive interventions. Notably, our four long-term survivors received novel therapies with their second transplant underscoring the need for a fundamental change in the methods for SCT2 to improve outcome.

Application of a new wall-less plate technology to complex multistep cell-based investigations using suspension cells

The DropArray technology is compatible with the retention of suspension cells in multistep procedures thus enabling novel assay methods. This technology enabled visualization and quantification of specific killing events triggered by bispecific antibodies engaging T cells.

Disulfide-stabilized diabody antiCD19/antiCD3 exceeds its parental antibody in tumor-targeting activity

BACKGROUND

A diabody is a bispecific antibody that is capable of recruiting a polyclonal T cell to antibody target-expressing tumor cells. However, the two chains of diabodies tend to dissociate because they are integrated non-covalently. Therefore, it is necessary to remodel the diabody to increase its stability in order to enhance the antitumor activity.

METHODS

We constructed an antiCD3×antiCD19 diabody with one binding site for the T cell antigen receptor (TCRCD3) and the other for the B cell-specific antigen (CD19) by recombinant gene engineering technology. Cysteine residues were introduced into the V domains of the anti-CD3 segment. The stability and cytotoxicity of the two diabodies were compared in vitro and vivo.

RESULTS

The disulfide-stabilized (ds) diabodies produced by Escherichia coli were secreted with high yields in a fully active form without a decrease in affinity. Compared with the parental diabody, the disulfide-stabilized (ds) diabody proved more stable in vitro and in vivo without reducing binding affinity. Both were able to effectively eliminate human lymphoma Raji cells by redirecting T lymphocytes in vitro and in vivo, but the ds diabody was more effective in inhibiting the growth of xenografts transplanted in BALB/C nude mice.

CONCLUSION

The antiCD3×antiCD19 ds diabody is more suitable for a controlled polyclonal T cell therapy of human CD19-positive B cell malignancies than its parental diabody.

Cytotoxic T lymphocyte-dependent tumor growth inhibition by a vascular endothelial growth factor-superantigen conjugate

T cells are major lymphocytes in the blood and passengers across the tumor vasculature. If these T cells are retained in the tumor site, a therapeutic potential will be gained by turning them into tumor-reactive cytotoxic T lymphocytes (CTLs). A fusion protein composed of human vascular endothelial growth factor (VEGF) and staphylococcal enterotoxin A (SEA) with a D227A mutation strongly repressed the growth of murine solid sarcoma 180 (S180) tumors (control versus VEGF-SEA treated with 15μg, mean tumor weight: 1.128g versus 0.252g, difference=0.876g). CD4(+) and CD8(+) T cells driven by VEGF-SEA were accumulated around VEGFR expressing tumor cells and the induced CTLs could release the tumoricidal cytokines, such as interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). Meanwhile, intratumoral CTLs secreted cytolytic pore-forming perforin and granzyme B proteins around tumor cells, leading to the death of tumor cells. The labeled fusion proteins were gradually targeted to the tumor site in an imaging mice model. These results show that VEGF-SEA can serve as a tumor targeting agent and sequester active infiltrating CTLs into the tumor site to kill tumor cells, and could therefore be a potential therapeutical drug for a variety of cancers.

T and NK cells of B cell NHL patients exert cytotoxicity against lymphoma cells following binding of bispecific tetravalent antibody CD19 × CD3 or CD19 × CD16

Bispecific tetravalent antibodies (TandAb) directed against the B cell surface marker CD19 and activating receptors on T or NK cells (CD19 × CD3 or CD19 × CD16) have shown promising effects in vitro and in preclinical studies. Here, we examine the cytotoxic efficacy of T and NK cells from patients with B cell Non-Hodgkin's Lymphoma (NHL) against B-lymphoma cells following the binding of the matching TandAb. The addition of CD19 × CD16 TandAb led to a threefold increase in NK cell activation in the presence of B-lymphoma cells. Similarly, T cells displayed a sevenfold increase in cytotoxic activity after the addition of CD19 × CD3 TandAb. Comparison of T and NK cell effector function of patients and healthy controls showed comparable levels of cytotoxic activity in response to lymphoma cells and no reduction in functional activity due to age, disease stage or the type and amount of previous therapy. Thus, T and NK cells of patients with B cell NHL are fully capable of being activated by therapeutic crosslinking antibodies. These results provide a rationale for the use of TandAbs for patients with B cell NHL, particularly in cases where remission with minimal residual disease could be achieved by cytotoxic chemotherapy.

Long-term follow-up of hematologic relapse-free survival in a phase 2 study of blinatumomab in patients with MRD in B-lineage ALL

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.

WITHDRAWN: Tetravalent Bispecific Single-Chain Fv Antibodies for Lysis of Leukemia Cells by Autologous T Cells

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Blinatumomab: a historical perspective

For decades, chemotherapy has been the backbone for the treatment of patients with B cell malignancies. Depending on the individual disease, monoclonal antibodies, irradiation and/or hematopoietic stem cell transplantation are added. However, the current standard of care--particularly for patients with relapsed disease--is often not sufficient to achieve durable remissions. A highly promising new drug candidate in late-stage clinical development for treatment of B cell malignancies is blinatumomab (MT103 or AMG 103). This bispecific antibody construct has dual specificity for CD19 and CD3 and belongs to the class of bispecific T cell engager (BiTE®) antibodies, which can potentially engage all cytotoxic T cells of a patient for redirected lysis of tumor cells. Here, we review how blinatumomab has so far been pre-clinically and clinically developed for the treatment of patients with non-Hodgkin's lymphoma and acute lymphoblastic leukemia.

Phage display--a powerful technique for immunotherapy: 1. Introduction and potential of therapeutic applications

One of the most effective molecular diversity techniques is phage display. This technology is based on a direct linkage between phage phenotype and its encapsulated genotype, which leads to presentation of molecule libraries on the phage surface. Phage display is utilized in studying protein-ligand interactions, receptor binding sites and in improving or modifying the affinity of proteins for their binding partners. Generating monoclonal antibodies and improving their affinity, cloning antibodies from unstable hybridoma cells and identifying epitopes, mimotopes and functional or accessible sites from antigens are also important advantages of this technology. Techniques originating from phage display have been applied to transfusion medicine, neurological disorders, mapping vascular addresses and tissue homing of peptides. Phages have been applicable to immunization therapies, which may lead to development of new tools used for treating autoimmune and cancer diseases. This review describes the phage display technology and presents the recent advancements in therapeutic applications of phage display.

How I treat relapsed childhood acute lymphoblastic leukemia

The most common cause of treatment failure in childhood acute lymphoblastic leukemia (ALL) remains relapse, occurring in ~ 15%-20% of patients. Survival of relapsed patients can be predicted by site of relapse, length of first complete remission, and immunophenotype of relapsed ALL. BM and early relapse (< 30 months from diagnosis), as well as T-ALL, are associated with worse prognosis than isolated extramedullary or late relapse (> 30 months from diagnosis). In addition, persistence of minimal residual disease (MRD) at the end of induction or consolidation therapy predicts poor outcome because children with detectable MRD are more likely to relapse than those in molecular remission, even after allogeneic hematopoietic stem cell transplantation. We offer hematopoietic stem cell transplantation to any child with high-risk features because these patients are virtually incurable with chemotherapy alone. By contrast, we treat children with first late BM relapse of B-cell precursor ALL and good clearance of MRD with a chemotherapy approach. We use both systemic and local treatment for extramedullary relapse, mainly represented by radiotherapy and, in case of testicular involvement, by orchiectomy. Innovative approaches, including new agents or strategies of immunotherapy, are under investigation in trials enrolling patients with resistant or more advanced disease.

Novel humanized and highly efficient bispecific antibodies mediate killing of prostate stem cell antigen-expressing tumor cells by CD8+ and CD4+ T cells

Prostate cancer is the most common noncutaneous malignancy in men. The prostate stem cell Ag (PSCA) is a promising target for immunotherapy of advanced disease. Based on a novel mAb directed to PSCA, we established and compared a series of murine and humanized anti-CD3-anti-PSCA single-chain bispecific Abs. Their capability to redirect T cells for killing of tumor cells was analyzed. During these studies, we identified a novel bispecific humanized Ab that efficiently retargets T cells to tumor cells in a strictly Ag-dependent manner and at femtomolar concentrations. T cell activation, cytokine release, and lysis of target cells depend on a cross-linkage of redirected T cells with tumor cells, whereas binding of the anti-CD3 domain alone does not lead to an activation or cytokine release. Interestingly, both CD8+ and CD4+ T cells are activated in parallel and can efficiently mediate the lysis of tumor cells. However, the onset of killing via CD4+ T cells is delayed. Furthermore, redirecting T cells via the novel humanized bispecific Abs results in a delay of tumor growth in xenografted nude mice.

Targeting T cells with bispecific antibodies for cancer therapy

Bispecific antibodies (BiAbs) offer a unique opportunity to redirect immune effector cells to kill cancer cells. BiAbs combine the benefits of different binding specificities of two monoclonal antibodies (mAbs) into a single construct. This unique feature of BiAbs enables approaches that are not possible with single mAbs. Advances in antibody engineering and antigen profiling of malignant cells have led to the development of a number of BiAb formats and their combinations for redirecting effector cells to tumor targets. There have been significant advances in the design and application of BiAbs for intravenous and local injection.The initial barrier of cytokine storm has been partially overcome by more recent constructs that have improved clinical effectiveness without dose-limiting toxicities. Since the recent revival of BiAbs, there has been multiple, ongoing, phase I/II and III trials, and some promising clinical outcomes have been reported in completed clinical studies. This review focuses on arming T cells with BiAbs to create the 'poor man's cytotoxic lymphocyte'.