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

Immunopharmacologic response of patients with B-lineage acute lymphoblastic leukemia to continuous infusion of T cell-engaging CD19/CD3-bispecific BiTE antibody blinatumomab

T cell-engaging CD19/CD3-bispecific BiTE Ab blinatumomab has shown an 80% complete molecular response rate and prolonged leukemia-free survival in patients with minimal residual B-lineage acute lymphoblastic leukemia (MRD(+) B-ALL). Here, we report that lymphocytes in all patients of a phase 2 study responded to continuous infusion of blinatumomab in a strikingly similar fashion. After start of infusion, B-cell counts dropped to < 1 B cell/μL within an average of 2 days and remained essentially undetectable for the entire treatment period. By contrast, T-cell counts in all patients declined to a nadir within < 1 day and recovered to baseline within a few days. T cells then expanded and on average more than doubled over baseline within 2-3 weeks under continued infusion of blinatumomab. A significant percentage of reappearing CD8(+) and CD4(+) T cells newly expressed activation marker CD69. Shortly after start of infusion, a transient release of cytokines dominated by IL-10, IL-6, and IFN-γ was observed, which no longer occurred on start of a second treatment cycle. The response of lymphocytes in leukemic patients to continuous infusion of blinatumomab helps to better understand the mode of action of this and other globally T cell-engaging Abs. The trial is registered with www.clinicaltrials.gov identifier NCT00560794.

The CEA/CD3-bispecific antibody MEDI-565 (MT111) binds a nonlinear epitope in the full-length but not a short splice variant of CEA

MEDI-565 (also known as MT111) is a bispecific T-cell engager (BiTE®) antibody in development for the treatment of patients with cancers expressing carcinoembryonic antigen (CEA). MEDI-565 binds CEA on cancer cells and CD3 on T cells to induce T-cell mediated killing of cancer cells. To understand the molecular basis of human CEA recognition by MEDI-565 and how polymorphisms and spliced forms of CEA may affect MEDI-565 activity, we mapped the epitope of MEDI-565 on CEA using mutagenesis and homology modeling approaches. We found that MEDI-565 recognized a conformational epitope in the A2 domain comprised of amino acids 326–349 and 388–410, with critical residues F³²⁶, T³²⁸, N³³³, V³⁸⁸, G³⁸⁹, P³⁹⁰, E³⁹², I⁴⁰⁸, and N⁴¹⁰. Two non-synonymous single-nucleotide polymorphisms (SNPs) (rs10407503, rs7249230) were identified in the epitope region, but they are found at low homozygosity rates. Searching the National Center for Biotechnology Information GenBank® database, we further identified a single, previously uncharacterized mRNA splice variant of CEA that lacks a portion of the N-terminal domain, the A1 and B1 domains, and a large portion of the A2 domain. Real-time quantitative polymerase chain reaction analysis of multiple cancers showed widespread expression of full-length CEA in these tumors, with less frequent but concordant expression of the CEA splice variant. Because the epitope was largely absent from the CEA splice variant, MEDI-565 did not bind or mediate T-cell killing of cells solely expressing this form of CEA. In addition, the splice variant did not interfere with MEDI-565 binding or activity when co-expressed with full-length CEA. Thus MEDI-565 may broadly target CEA-positive tumors without regard for expression of the short splice variant of CEA. Together our data suggest that MEDI-565 activity will neither be impacted by SNPs nor by a splice variant of CEA.

Production of bispecific antibodies: diabodies and tandem scFv

Recombinant bispecific antibodies have many different applications; especially promising is their therapeutic potential due to their ability to retarget an effector molecule or a cell to a disease-related target structure. In the last years, many formats have been developed: two commonly used are the bispecific diabody and the tandem scFv. In this chapter, the cloning, bacterial production, purification, and characterization of the two antibody formats are described in detail.

From tumor immunosuppression to eradication: targeting homing and activity of immune effector cells to tumors

Unraveling the mechanisms used by the immune system to fight cancer development is one of the most ambitious undertakings in immunology. Detailed knowledge regarding the mechanisms of induction of tolerance and immunosuppression within the tumor microenvironment will contribute to the development of highly effective tumor eradication strategies. Research within the last few decades has shed more light on the matter. This paper aims to give an overview on the current knowledge of the main tolerance and immunosuppression mechanisms elicited within the tumor microenvironment, with the focus on development of effective immunotherapeutic strategies to improve homing and activity of immune effector cells to tumors.

Construction and humanization of a functional bispecific EGFR × CD16 diabody using a refolding system

We previously reported the construction and activity of a humanized, bispecific diabody (hEx3) that recruited T cells towards an epidermal growth factor receptor (EGFR) positive tumor. Herein, we describe the construction of a second functional, fully humanized, anti-EGFR bispecific diabody that recruits another subset of lymphocyte effectors, the natural killer cells, to EGFR-expressing tumor cells. After we confirmed that an anti-EGFR × anti-CD16 bispecific diabody (Ex16) consisting of a previously humanized anti-EGFR variable fragment (Fv) and a mouse anti-CD16 Fv had growth inhibitory activity, we designed a humanized anti-CD16 Fv to construct the fully humanized Ex16 (hEx16). However, the humanized form had lower activity for inhibition of cancer growth. To restore its growth inhibitory activity, we introduced mutations into the Vernier zone, which is located near the complementarity-determining regions and is involved in their binding activity. We efficiently prepared 15 different hEx16 mutants by expressing each chimeric single-chain component for hEx16 separately. We then used our in vitro refolding system to select the most functional mutant, which had a growth inhibitory effect comparable with that of the commercially available chimeric anti-EGFR antibody, cetuximab. Our refolding system could aid in the efficient optimization of other proteins with heterodimeric structure.

Targeted cell-cell interactions by DNA nanoscaffold-templated multivalent bispecific aptamers

Cell-cell interactions are essential for multicellular organisms, playing important roles in their development, function, and immunity. Herein a bottom-up strategy to construct self-assembled DNA nanostructures is reported, consisting of multivalent, bispecific, cell-targeting aptamers to specifically induce cell-cell interactions. Various DNA nanoscaffolds are rationally designed to assemble aptamers with different valencies and flexibilities, and their cellular binding capabilities are tested. Multivalent aptamers, assembled on more rigid scaffolds, display higher binding activities. Further, multivalent bispecific aptamer fusion molecules are constructed based on this configuration, and successfully link two types of cells. Using cell-targeting aptamers, the presented strategy eliminates the need to chemically modify cell surfaces and offers excellent cell specificity, binding efficiency, and stability. This proof-of-concept study establishes that multivalent bispecific aptamers linked on DNA-nanoscaffolds can mediate cellular engagement, which could lead to their use in directing or guiding cell-cell interactions in many biological events.

Targeted therapy with the T-cell-engaging antibody blinatumomab of chemotherapy-refractory minimal residual disease in B-lineage acute lymphoblastic leukemia patients results in high response rate and prolonged leukemia-free survival

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.

Novel antibodies against follicular non-Hodgkin's lymphoma

The anti-CD20 monoclonal antibody rituximab has revolutionized the treatment of patients with follicular B-cell lymphoma. With the combination of chemotherapy and rituximab the overall survival rate has increased with approximately 30%. Unfortunately, there is resistance to rituximab with relapse of the disease in about 60% of the patients during the first five years of treatment and eventually in all patients. To this end, there is a need to develop improved anti-CD20 monoclonal antibodies and antibodies that target other attractive molecules expressed on the follicular lymphoma cell. This review describes the development and clinical achievements so far of next generation anti-CD20 and other antibodies in the treatment of follicular B-cell lymphoma.

Effective targeting of prostate cancer by lymphocytes redirected by a PSMA × CD3 bispecific single-chain diabody

BACKGROUND

For redirecting T-lymphocytes to induce prostate cancer cell lysis, we constructed a novel bispecific single-chain (bsc) diabody directed to the prostate specific membrane antigen (PSMA) and the T-cell receptor (TCR)-associated CD3 molecule on T-cells.

METHODS

The PSMA × CD3 bsc diabody was generated from an anti-CD3 single chain Fv fragment (scFv) and the anti-PSMA scFv D7. It was expressed in E. coli and purified from the periplasmic extract and culture supernatant by immobilized metal affinity chromatography (IMAC). The binding properties were tested on PSMA-expressing prostate cancer cells and PSMA-negative cell lines as well as on Jurkat cells by flow cytometry. For in vitro functional analysis, a cell viability test (WST-1) was used and activation of T-cells was determined by measuring the surface marker expression of CD25 and CD69. For in vivo evaluation, the diabody was administered in combination with human peripheral blood lymphocytes (Ly) in a C4-2 xenograft-SCID mouse model.

RESULTS

Specific binding of the PSMA × CD3 bsc diabody both to CD3-positive Jurkat cells and PSMA-expressing C4-2 cells was shown by flow cytometry. In vitro, the PSMA × CD3 bsc diabody proved to be a potent agent for retargeting CD4+ and CD8+ human lymphocytes to lyse C4-2 prostate cancer cells. Treatment of SCID mice bearing C4-2 tumor xenografts with the diabody and human lymphocytes efficiently inhibited tumor growth.

CONCLUSIONS

The PSMA × CD3 bsc diabody bears a high potential for the immunotherapy of prostate cancer.

Bispecific antibodies engage T cells for antitumor immunotherapy

INTRODUCTION

Although considerable evidence supports the hypothesis that T cells play a critical role in the immune response against cancer, the ability to mount and sustain tumor-specific cellular responses in vivo remains a challenge. A strategy that harnesses the cytotoxic advantage of T cell therapy is the use of bispecific antibodies designed to engage and activate endogenous polyclonal T cell populations via the CD3 complex, but only in the presence of a tumor antigen. While antibody constructs with dual specificity were first described as anticancer therapeutics over 25 years ago, it was not until recently that one subclass of bispecific single-chain antibody, the bispecific T cell engager (BiTE), emerged as superior to previous iterations in achieving efficacy in animal models and early clinical trials.

AREAS COVERED

The evolution of bispecific antibodies in antitumor immunotherapy is reviewed and the greatest hurdles impeding their clinical translation are discussed, specifically in the context of immunoprivileged sites as is the case for intracerebral malignancy.

EXPERT OPINION

The BiTE platform has great potential in the treatment of malignant disease. Despite burgeoning interest in bispecific antibodies and permutations thereof, the issues of stability and cost-effective production persist as obstacles.

The Bs20x22 anti-CD20-CD22 bispecific antibody has more lymphomacidal activity than do the parent antibodies alone

Previous studies have shown that bispecific antibodies that target both CD20 and CD22 have in vivo lymphomacidal properties. We developed a CD20-CD22 bispecific antibody (Bs20x22) from anti-CD20 and the anti-CD22 monoclonal antibodies (mAb), rituximab and HB22.7, respectively. Bs20x22 was constructed using standard methods and was shown to specifically bind CD20 and CD22. In vitro cytotoxicity assays showed that Bs20x22 was three times more effective than either parent mAb alone and twice as effective as a combination of both parent mAb used at equimolar concentrations. Bs20x22 was also nearly four times more effective at inducing apoptosis than either mAb alone. Examination of the MAPK and SAPK signaling cascades revealed that Bs20x22 induced significantly more p38 phosphorylation than either mAb alone. In an in vivo human NHL xenograft model, treatment with Bs20x22 resulted in significantly greater tumor shrinkage and improved overall survival when compared to either mAb alone or treatment with a combination of HB22.7 and rituximab. The effect of the initial tumor volume was assessed by comparing the efficacy of Bs20x22 administered before xenografts grew versus treatment of established tumors; significantly, greater efficacy was found when treatment was initiated before tumors could become established.

Application of dual affinity retargeting molecules to achieve optimal redirected T-cell killing of B-cell lymphoma

We describe the application of a novel, bispecific antibody platform termed dual affinity retargeting (DART) to eradicate B-cell lymphoma through coengagement of the B cell-specific antigen CD19 and the TCR/CD3 complex on effector T cells. Comparison with a single-chain, bispecific antibody bearing identical CD19 and CD3 antibody Fv sequences revealed DART molecules to be more potent in directing B-cell lysis. The enhanced activity with the CD19xCD3 DART molecules was observed on all CD19-expressing target B cells evaluated using resting and prestimulated human PBMCs or purified effector T-cell populations. Characterization of a CD19xTCR bispecific DART molecule revealed equivalent potency with the CD19xCD3 DART molecule, demonstrating flexibility of the DART structure to support T-cell/B-cell associations for redirected T cell-killing applications. The enhanced level of killing mediated by DART molecules was not accompanied by any increase in nonspecific T-cell activation or lysis of CD19(-) cells. Cell-association studies indicated that the DART architecture is well suited for maintaining cell-to-cell contact, apparently contributing to the high level of target cell killing. Finally, the ability of the CD19xTCR DART to inhibit B-cell lymphoma in NOD/SCID mice when coadministered with human PBMCs supports further evaluation of DART molecules for the treatment of B-cell malignancies.

Solid tumor-targeted infiltrating cytotoxic T lymphocytes retained by a superantigen fusion protein

Successful immune-mediated regression of solid tumors is difficult because of the small number of cytotoxic T lymphocytes (CTLs) that were traffic to the tumor site. Here, the targeting of tumor-specific infiltrating CTLs was dependent on a fusion protein consisting of human epidermal growth factor (EGF) and staphylococcal enterotoxin A (SEA) with the D227A mutation. EGF-SEA strongly restrained the growth of murine solid sarcoma 180 (S180) tumors (control versus EGF-SEA, mean tumor weight: 1.013 versus 0.197 g, difference  = 0.816 g). In mice treated with EGF-SEA, CD4+, CD8+ and SEA-reactive T lymphocytes were enriched around the EGFR expressing tumor cells. The EGF receptors were potentially phosphorylated by EGF-SEA stimulation and the fusion protein promoted T cells to release the tumoricidal cytokines interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). Intratumoral CTLs secreted cytolytic pore-forming perforins and granzyme B proteins near the surface of carcinomas, causing the death of many tumor cells. We additionally show that labeled EGF-SEA was directly targeted to the tumor tissue after intravenous (i.v.) injection. The findings demonstrate that antibody-like EGF-SEA plays an important role in arresting CTLs in the solid tumor site and has therapeutic potential as a tumor-targeting agent.

Monoclonal antibody-induced cytokine-release syndrome

Monoclonal antibodies (mAbs) are widely used in anti-inflammatory and tumor therapy. Although effective, mAbs can cause a variety of adverse effects. An important toxicity seen with a few mAbs is cytokine-release syndrome (CRS). These mAbs include: alemtuzumab, muromonab-CD3, rituximab, tosituzumab, CP-870,893, LO-CD2a/BTI-322 and TGN1412. By contrast, over 30 mAbs used clinically are not associated with CRS. In this review, the clinical aspects of CRS, the mAbs associated with CRS, the cytokines involved and putative mechanisms mediating cytokine release will be discussed. This will be followed by a discussion of the poor predictive value of studies in animals and the prospects for creating in vitro screens. Finally, approaches to decreasing the probability of CRS, decreasing the severity or treating CRS, should it occur, will be described.

Bispecific antibodies for cancer therapy: the light at the end of the tunnel?

With 23 approvals in the US and other countries and four approvals outside US, antibodies are now widely recognized as therapeutic molecules. The therapeutic and commercial successes met by rituximab, trastuzumab, cetuximab and other mAbs have inspired antibody engineers to improve the efficacy of these molecules. Consequently, a new wave of antibodies with engineered Fc leading to much higher effector functions such as antibody-dependent cell-mediated cytotoxicity or complement-dependent cytotoxicity is being evaluated in the clinic, and several approvals are expected soon. In addition, research on a different class of antibody therapeutics, bispecific antibodies, has recently led to outstanding clinical results, and the first approval of the bispecific antibody catumaxomab, a T cell retargeting agent that was approved in the European Union in April 2009. This review describes the most recent advances and clinical study results in the field of bispecific antibodies, a new class of molecules that might outshine conventional mAbs as cancer immunotherapeutics in a near future.

Eradication-resolution dynamics with stochastic flare-ups

In infectious disease as well as in cancer, the ultimate outcome of the curative response, mediated by the body itself or through drug treatment, is either successful eradication or a resurgence of the disease ("flare-up" or "relapse"), depending on random fluctuations that dominate the dynamics of the system when the number of diseased cells has become very low. The presence of a low-numbers bottle-neck in the dynamics, which is unavoidable if eradication is to take place at all, renders at least one phase of the dynamics essentially stochastic. However, the eradicating agents (e.g. immune cells, drug molecules) generally remain at high numbers during the critical bottle-neck phase, sufficiently so to warrant a deterministic treatment. This leads us to consider a hybrid stochastic-deterministic approach where the infected cells are treated stochastically whereas the eradicating agents are treated deterministically. Exploiting the fact that the number of eradicating agents typically decreases monotonically during the resolution phase of the response, we derive a set of coupled first-order differential equations that describe the probability of ultimate eradication as a function of the system's state, and we consider a number of biomedical applications.

A novel antibody-4-1BBL fusion protein for targeted costimulation in cancer immunotherapy

Costimulation is an essential step in T-cell activation and hence, represents an important aspect in cancer immunotherapy. 4-1BB, a member of the tumor necrosis factor receptor family, has gained particular interest as a costimulatory molecule. Here, we investigated the potential of a targeted activation of 4-1BB-mediated costimulation at the tumor site by generating a recombinant antibody-cytokine fusion protein composed of a single-chain antibody fragment (scFv36) specific for the tumor stromal antigen fibroblast activation protein (FAP) and the extracellular domain of the 4-1BB ligand (4-1BBL). The scFv36-4-1BBL fusion protein is a homotrimeric molecule that binds specifically to FAP and the receptor 4-1BB. T-cell costimulation was demonstrated by interferon-gamma release of peripheral blood mononuclear cells cocultured with FAP-expressing HT1080 cells upon T-cell receptor triggering by monoclonal anti-CD3 antibody. Costimulatory activity of the scFv36-4-1BBL fusion protein was concentration dependent, ligand-specific, and substantially constrained to FAP-expressing target cell binding. Furthermore, scFv36-4-1BBL enhanced T-cell activation when the bispecific antibody scDb33CD3 (specific for FAP and CD3) was used as primary stimulus. Thus, target cell-dependent costimulation with scFv36-4-1BBL constitutes a new option to enhance T-cell activation by bispecific antibodies or antigen-dependent T-cell receptor triggering and should be useful to improve T cell-mediated antitumor responses.

Redirecting NK cells mediated tumor cell lysis by a new recombinant bifunctional protein

Natural killer (NK) cells are at the crossroad between innate and adaptive immunity and play a major role in cancer immunosurveillance. NK cell stimulation depends on a balance between inhibitory and activating receptors, such as the stimulatory lectin-like receptor NKG2D. To redirect NK cells against tumor cells, we designed bifunctional proteins able to specifically bind tumor cells and to induce their lysis by NK cells, after NKG2D engagement. To this aim, we used the 'knob into hole' heterodimerization strategy, in which 'knob' and 'hole' variants were generated by directed mutagenesis within the CH3 domain of human IgG1 Fc fragments fused to an anti-CEA or anti-HER2 scFv or to the H60 murine ligand of NKG2D, respectively. We demonstrated the capacity of the bifunctional proteins produced to specifically coat tumor cells surface with H60 ligand. Most importantly, we demonstrated that these bifunctional proteins were able to induce an NKG2D-dependent and antibody-specific tumor cell lysis by murine NK cells. Overall, the results show the possibility to redirect NK cytotoxicity to tumor cells by a new format of recombinant bispecific antibody, opening the way of potential NK cell-based cancer immunotherapies by specific activation of the NKG2D receptor at the tumor site.

Tumor regression in cancer patients by very low doses of a T cell-engaging antibody

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.

Therapeutic window of MuS110, a single-chain antibody construct bispecific for murine EpCAM and murine CD3

EpCAM (CD326) is one of the most frequently and highly expressed tumor-associated antigens known and recently has also been found on cancer stem cells derived from human breast, colon, prostate, and pancreas tumors. However, like many other tumor-associated antigens used for antibody-based immunotherapeutic approaches, EpCAM is expressed on normal tissues including epithelia of pancreas, colon, lung, bile ducts, and breast. To assess the therapeutic window of an EpCAM/CD3-bispecific single-chain antibody construct of the bispecific T-cell engager (BiTE) class, we constructed murine surrogate of MT110 (muS110) from single-chain antibodies specific for murine EpCAM and CD3 antigens. Immunhistochemical analysis showed that, with minor differences, the expression of EpCAM protein on a large variety of tissues from man and mouse was similar with respect to distribution and level. MuS110 exhibited significant antitumor activity at as low as 5 microg/kg in both syngeneic 4T1 orthotopic breast cancer and CT-26 lung cancer mouse models. Dosing of muS110 for several weeks up to 400 microg/kg by intraanimal dose escalation was still tolerated, indicating existence of a significant therapeutic window for an EpCAM-specific BiTE antibody in mice. MuS110 was found to have similar in vitro characteristics and in vivo antitumor activity as MT110, a human EpCAM/human CD3-bispecific BiTE antibody that currently is in formal preclinical development.

The effect of dexamethasone on polyclonal T cell activation and redirected target cell lysis as induced by a CD19/CD3-bispecific single-chain antibody construct

BiTE molecules comprise a new class of bispecific single-chain antibodies redirecting previously unstimulated CD8+ and CD4+ T cells for the elimination of target cells. One example is MT103 (MEDI-538; bscCD19xCD3), a CD19-specific BiTE that can induce lysis of normal and malignant B cells at low picomolar concentrations, which is accompanied by T cell activation. Here, we explored in cell culture the impact of the glucocorticoid derivative dexamethasone on various activation parameters of human T cells in response to MT103. In case cytokine-related side effects should occur with BiTE molecules and other T cell-based approaches during cancer therapy it is important to understand whether glucocorticoids do interfere with the cytotoxic potential of T cells. We found that MT103 induced in the presence of target cells secretion by peripheral T cells of interleukin (IL)-2, tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), IL-6, IL-10 and IL-4 into the cell culture medium. Production of all studied cytokines was effectively reduced by dexamethasone at a concentration between 1 and 3x10(-7) M. In contrast, upregulation of activation markers CD69, CD25, CD2 and LFA-1 on both CD4+ and CD8+ T cells, and T cell proliferation were barely affected by the steroid hormone analogue. Most importantly, dexamethasone did not detectably inhibit the cytotoxic activity of MT103-activated T cells against a human B lymphoma line as investigated with lymphocytes from 12 human donors. Glucocorticoids thus qualify as a potential co-medication for therapeutic BiTE molecules and other cytotoxic T cell therapies for treatment of cancer.

Novel antibodies as anticancer agents

In recent years antibodies, whether generated by traditional hybridoma technology or by recombinant DNA strategies, have evolved from Paul Ehrlich's 'magic bullets' to a modern age 'guided missile'. In the recent years of immunologic research, we are witnessing development in the fields of antigen screening and protein engineering in order to create specific anticancer remedies. The developments in the field of recombinant DNA, protein engineering and cancer biology have let us gain insight into many cancer-related mechanisms. Moreover, novel techniques have facilitated tools allowing unique distinction between malignantly transformed cells, and regular ones. This understanding has paved the way for the rational design of a new age of pharmaceuticals: monoclonal antibodies and their fragments. Antibodies can select antigens on both a specific and a high-affinity account, and further implementation of these qualities is used to target cancer cells by specifically identifying exogenous antigens of cancer cell populations. The structure of the antibody provides plasticity resonating from its functional sites. This review will screen some of the many novel antibodies and antibody-based approaches that are being currently developed for clinical applications as the new generation of anticancer agents.

A bispecific diabody directed against prostate-specific membrane antigen and CD3 induces T-cell mediated lysis of prostate cancer cells

Background

Although cancer of the prostate is one of the most commonly diagnosed cancers in men, no curative treatment currently exists after its progression beyond resectable boundaries. Therefore, new agents for targeted treatment strategies are needed. Cross-linking of tumor antigens with T-cell associated antigens by bispecific monoclonal antibodies have been shown to increase antigen-specific cytotoxicity in T-cells. Since the prostate-specific membrane antigen (PSMA) represents an excellent tumor target, immunotherapy with bispecific diabodies could be a promising novel treatment option for prostate cancer.

Methods

A heterodimeric diabody specific for human PSMA and the T-cell antigen CD3 was constructed from the DNA of anti-CD3 and anti-PSMA single chain Fv fragments (scFv). It was expressed in E. coli using a vector containing a bicistronic operon for co-secretion of the hybrid scFv V_HCD3-V_LPSMA and V_HPSMA-V_LCD3. The resulting PSMAxCD3 diabody was purified from the periplasmic extract by immobilized metal affinity chromatography (IMAC). The binding properties were tested on PSMA-expressing prostate cancer cells and PSMA-negative cell lines as well as on Jurkat cells by flow cytometry. For in vitro functional analysis, a cell viability test (WST) was used. For in vivo evaluation the diabody was applied together with human peripheral blood lymphocytes (PBL) in a C4-2 xenograft-SCID mouse model.

Results

By Blue Native gel electrophoresis, it could be shown that the PSMAxCD3 diabody is mainly a tetramer. Specific binding both to CD3-expressing Jurkat cells and PSMA-expressing C4-2 cells was shown by flow cytometry. In vitro, the diabody proved to be a potent agent for retargeting PBL to lyze C4-2 prostate cancer cells. Treatment of SCID mice inoculated with C4-2 tumor xenografts with the diabody and PBL efficiently inhibited tumor growth.

Conclusions

The PSMAxCD3 diabody bears the potential for facilitating immunotherapy of prostate cancer and for the elimination of minimal residual disease.

Selective targeting and potent control of tumor growth using an EphA2/CD3-Bispecific single-chain antibody construct

The EphA2 receptor tyrosine kinase is frequently overexpressed and functionally altered in malignant cells and thus provides opportunities for selective targeting of tumor cells. We describe here the development of a novel, bispecific single-chain antibody (bscAb) referred to as bscEphA2xCD3. This molecule simultaneously targets EphA2 on tumor cells and the T-cell receptor/CD3 complex on T cells and possesses structural and functional characteristics of the recently developed BiTE technology. An EphA2-specific single-chain antibody was selected for recognition of an epitope that is preferentially exposed on malignant cells based on the concept of epitope exclusion; this was fused to a CD3-specific single-chain antibody to generate bscEphA2xCD3. The resultant bscAb redirected unstimulated human T cells to lyse EphA2-expressing tumor cells both in vitro and in vivo. In separate experiments, efficient tumor cell lysis was achieved in vitro at drug concentrations <or=1 microg/mL, at a low T-cell effector-to-tumor target cell ratio (1:1), and with tumor cells that possess few available binding sites (2,400 per cell) for bscEphA2xCD3. Time-lapsed microscopy revealed potent cytotoxic activity of bscEphA2xCD3-activated T cells against monolayers of malignant cells but not against monolayers of nontransformed EphA2-positive cells except at the edges of the monolayer where the target epitope was exposed. BscEphA2xCD3 was also efficacious in human xenograft mouse models modified to show human T-cell killing of tumors. Together, our results reveal opportunities for redirecting the potent activity of cytotoxic T cells towards tumor cells that express selectively accessible epitopes and establish EphA2-specific bscAb molecules as novel and potent therapeutics with selectivity for tumor cells.

Bispecific Antibodies: Molecules That Enable Novel Therapeutic Strategies

Bispecific antibodies are unique in the sense that they can bind simultaneously two different antigens. This property enables the development of therapeutic strategies that are not possible with conventional monoclonal antibodies. The large panel of imaginative bispecific antibody formats that has been developed reflects the strong interest for these molecules. Although in many cases the manufacturing of clinical grade material remains challenging, several bispecific antibody formats are currently in clinical trials.

CD19-/CD3-bispecific antibody of the BiTE class is far superior to tandem diabody with respect to redirected tumor cell lysis

Many kinds of bispecific antibodies recruiting T cells for cancer therapy have been developed. Side-by-side comparison has shown that CD19-/CD3-bispecific antibodies of the diabody, tandem diabody (Tandab) and quadroma format had similar cytotoxic activity, with Tandab being the most active format. Tandab has also been claimed to be superior to single-chain (sc) Fv-based bispecific constructs although data from a side-by-side comparison are not available. In this study, we compared side-by-side MT103 (bscCD19xCD3), a single-chain bispecific antibody of the BiTE class, with a CD19-/CD3-bispecific representative of the Tandab class. Based on literature data, we have constructed, produced and characterized the LL linker version of Tandab, which was reported to be the most active version of Tandab proteins. A dimeric protein of 114kDa was obtained that showed proper bispecific binding to CD3- and CD19-positive cells and could redirect both pre-stimulated and unstimulated human T cells for lysis of human B lymphoma lines Raji, MEC-1 and Nalm-6. Raji cells were lysed at a half-maximal concentration (EC50) of 10 nM Tandab using pre-stimulated T cells, which closely matched the published activity of LL-Tandab with this particular cell line. MT103 had between 700- and 8000-fold higher efficacy than Tandab for redirected lysis of the three human B lymphoma lines. These data demonstrate that under identical experimental conditions, the BiTE format has far superior activity compared to the Tandab format and is also superior to conventional diabody and quadroma formats. The extraordinary potency of the BiTE class and its representative MT103 may translate into improved anti-tumor activity, lower dosing and lower costs of production compared to other bispecific antibody formats.

Fucose removal from complex-type oligosaccharide enhances the antibody-dependent cellular cytotoxicity of single-gene-encoded bispecific antibody comprising of two single-chain antibodies linked to the antibody constant region

Bispecific antibodies (bsAbs) have the potential to extend binding selectivity, increase avidity and exert potent cytotoxicity due to the combination of dual specificities. scFv2-Fc type of single-gene-encoded bispecific antibody, composed of two different single-chain Fvs and an Fc, has been reported to be capable of binding to different antigens. The aim of this study was to determine the effect of fucose removal on effector functions of scFv2-Fc since fucose depletion from oligosaccharide of human IgG1 and scFv-Fc results in significant enhancement of ADCC. We generated novel single-gene-encoded bsAb with dual specificity against tumor associated glycoprotein (TAG)-72 and MUC1 mucin as fucose-negative scFv2-Fc from alpha-1,6-fucosyltransferase knock-out CHO cells and a highly fucosylated scFv2-Fc comparator from parental CHO cells. Expression, assembly and the antigen-binding activity of the scFv2-Fc were not influenced by removal of fucose. The fucose negative scFv2-Fc bound with higher avidity to FcgammaRIIIa and enhanced ADCC compared to the highly fucosylated scFv2-Fc. These results demonstrate that ADCC-enhancement by removal of fucose is effective in not only whole IgG1 and scFv-Fc, but also scFv2-Fc targeting two different antigens, and thus increases the potential of fucose-negative scFv2-Fcs as novel therapeutic candidates.

Potent inhibition of local and disseminated tumor growth in immunocompetent mouse models by a bispecific antibody construct specific for Murine CD3

Bispecific single-chain antibody constructs specific for human CD3 have been extensively studied for antitumor activity in human xenograft models using severe combined immunodeficient mice supplemented with human T cells. High efficacy at low effector-to-target ratios, independence of T cell costimuli and a potent activation of previously unstimulated polyclonal T cells were identified as hallmarks of this class of bispecific antibodies. Here we studied a bispecific single-chain antibody construct (referred to as 'bispecific T cell engager', BiTE) in an immunocompetent mouse model. This was possible by the use of a murine CD3-specific BiTE, and a syngeneic melanoma cell line (B16F10) expressing the human Ep-CAM target. The murine CD3-specific BiTE, called 2C11x4-7 prevented in a dose-dependent fashion the outgrowth of subcutaneously growing B16/Ep-CAM tumors with daily i.v. injections of 5 or 50 microg BiTE which was most effective. Treatment with 2C11x4-7 was effective even when it was started 10 days after tumor cell inoculation but delayed treatments showed a reduction in the number of cured animals. 2C11x4-7 was also highly active in a lung tumor colony model. When treatment was started on the day of intravenous tumor cell injection, seven out of eight animals stayed free of lung tumors, and three out of eight animals when treatment was started on day 5. Our study shows that BiTEs also have a high antitumor activity in immunocompetent mice and that there is no obvious need for costimulation of T cells by secondary agents.

T-cell activation and B-cell depletion in chimpanzees treated with a bispecific anti-CD19/anti-CD3 single-chain antibody construct

BscCD19xCD3 is a bispecific single-chain antibody construct with exceptional cytotoxic potency in vitro and in vivo. Here, we have investigated the biological activity of bscCD19xCD3 in chimpanzee, the only animal species identified in which bscCD19xCD3 showed bispecific binding, redirected B-cell lysis and cytokine production comparable to human cells. Pharmacokinetic analysis following 2-h intravenous infusion of 0.06, 0.1 or 0.12 mug/kg of bscCD19xCD3 as part of a dose escalation study in a single female chimpanzee revealed a half-life of approximately 2 h and elimination of the bispecific antibody from circulation within approximately 8 h after the end of infusion. This short exposure to bscCD19xCD3 elicited a transient increase in serum levels of IFNgamma, IL-6, IL-2, soluble CD25, and transiently upregulated expression of CD69 and MHC class II on CD8-positive cells. Cytokine release and upregulation of T-cell activation markers were not observed with vehicle controls. A multiple-dose study using 5 weekly doses of 0.1 mug/kg in two animals also showed transient cytokine release and an activation of peripheral T cells with a first-dose effect, accompanied by a transient lymphopenia. While oscillations of T-cell counts were relatively even during repeated treatments, the amplitudes of peripheral B cells declined with every infusion, which was not observed in a vehicle control animal. Our data show that bscCD19xCD3 can be safely administered to chimpanzees at dose levels that cause fully reversible T-cell activation and, despite a very short exposure time, cumulative loss of peripheral B lymphocytes. A clinical trial testing prolonged administration of bscCD19xCD3 (MT103) for improving efficacy is currently ongoing.

MT110: A novel bispecific single-chain antibody construct with high efficacy in eradicating established tumors

We have developed a novel single-chain Ep-CAM-/CD3-bispecific single-chain antibody construct designated MT110. MT110 redirected unstimulated human peripheral T cells to induce the specific lysis of every Ep-CAM-expressing tumor cell line tested. MT110 induced a costimulation independent polyclonal activation of CD4- and CD8-positive T cells as seen by de novo expression of CD69 and CD25, and secretion of interferon gamma, tumor necrosis factor alpha, and interleukins 2, 4 and 10. CD8-positive T cells made the major contribution to redirected tumor cell lysis by MT110. With a delay, CD4-positive cells could also contribute presumably as consequence of a dramatic upregulation of granzyme B expression. MT110 was highly efficacious in a NOD/SCID mouse model with subcutaneously growing SW480 human colon cancer cells. Five daily doses of 1 microg MT110 on days 0-4 completely prevented tumor outgrowth in all mice treated. The bispecific antibody construct also led to a durable eradication of established tumors in all mice treated with 1 microg doses of MT110 on days 8-12 after tumor inoculation. Finally, MT110 could eradicate patient-derived metastatic ovarian cancer tissue growing under the skin of NOD/SCID mice. MT110 appears as an attractive bispecific antibody candidate for treatment of human Ep-CAM-overexpressing carcinomas.

The role of B cells and autoantibodies in rheumatoid arthritis

In this article, we will review B lymphocyte development and function, then discuss the role of B cells in RA, including immune complex formation; the K/BxN mouse model of RA; toll-like receptors; B cells as antigen presenting cells; germinal center-like structures in RA synovium; and influence on T cell activation, leukocyte infiltration, and angiogenesis. With regard to autoantibody production, we will focus on rheumatoid factor (RF) and anti-CCP antibodies, particularly mechanisms of their production; sensitivity and specificity in RA; and their roles as prognostic factors. Other autoantibodies will be discussed, as will treatment implications and future areas of investigation related to B cells and autoantibodies in RA.

Bispecific and human disease-related anti-keratin rabbit monoclonal antibodies

Rabbit antibodies may have favorable properties compared to mouse antibodies, including high affinities and better antigen recognition. We used a biochemical and reverse immunologic approach to generate and characterize rabbit anti-phospho-keratin and anti-keratin monoclonal antibodies (MAb). Human keratins 8 and 18 (K8/K18) were used as immunogens after isolation from cells pretreated with okadaic acid or pervanadate to promote Ser/Thr or Tyr hyperphosphorylation, respectively. Selected rabbit MAb were tested by immunofluorescence staining, immunoprecipitation, and 2-dimensional gels. Keratin phospho and non-phospho-mutants were used for detailed characterization of two unique antibodies. One antibody recognizes a K8 G61-containing epitope, an important epitope given that K8 G61C is a frequent mutation in human liver diseases. This antibody binds K8 that is not phosphorylated on S73, but its binding is ablated by G61 but not S73 mutation. The second antibody is bispecific in that it simultaneously recognizes two epitopes: one phospho (K8 pS431) conformation-independent and one non-phospho conformation-dependent, with both epitopes residing in the K8 tail domain. Therefore, a reverse immunologic and biochemical approach is a viable tool for generating versatile rabbit MAb for a variety of cell biologic applications including the potential identification of physiologic phosphorylation sites.

BiTEs: bispecific antibody constructs with unique anti-tumor activity

Bispecific T-cell engager molecules (BiTEs) constitute a class of bispecific single-chain antibodies for the polyclonal activation and redirection of cytotoxic T cells against pathogenic target cells. BiTEs combine a unique set of properties that have not yet been reported for any other kind of bispecific antibody construct, namely extraordinary potency and efficacy against target cells at low T-cell numbers without the need for T-cell co-stimulation. Here we review novel insights into the mechanism of BiTE action, which help to explain the unique features of BiTEs, as well as data from various animal models demonstrating the outstanding therapeutic potential of BiTEs for the treatment of malignant diseases.

Effective lysis of lymphoma cells with a stabilised bispecific single-chain Fv antibody against CD19 and FcgammaRIII (CD16)

A recombinant bispecific single-chain fragment variable antibody (bsscFv), directed against the B-cell antigen CD19 and the low affinity Fc-receptor FcgammaRIII (CD16), was designed for use in the treatment of patients with leukaemias and lymphomas. The Fc-portions of whole antibodies were deliberately eliminated in this construct to avoid undesired effector functions. A stabilised bsscFv, ds[CD19 x CD16], was generated, in which disulphide bonds bridging the respective variable light (VL) and variable heavy (VH) chains were introduced into both component single-chain (sc)Fvs. After production in 293T cells and chromatographic purification, ds[CD19 x CD16] specifically and simultaneously bound both antigens. The serum stability of ds[CD19 x CD16] was increased more than threefold when compared with the unstabilised counterpart, while other biological properties were not affected by these mutations. In antibody-dependent cellular cytotoxicity experiments, ds[CD19 x CD16] mediated specific lysis of both CD19-positive malignant human B-lymphoid cell lines and primary tumour cells from patients with B-cell chronic lymphocytic leukaemia or B-cell acute lymphoblastic leukaemia. Natural killer cells, mononuclear cells (MNCs) from healthy donors and, in some instances, MNCs isolated from patients after allogeneic stem cell transplantation, were used as effectors. Thus, ds[CD19 x CD16] holds promise for the treatment of CD19(+) B-lineage malignancies.

Serial killing of tumor cells by cytotoxic T cells redirected with a CD19-/CD3-bispecific single-chain antibody construct

Certain bispecific antibodies exhibit an extraordinary potency and efficacy for target cell lysis by eliciting a polyclonal T-cell response. One example is a CD19-/CD3-bispecific single-chain antibody construct (bscCD19xCD3), which at femtomolar concentrations can redirect cytotoxic T cells to eliminate human B lymphocytes, B lymphoma cell lines and patient-derived malignant B cells. Here we have further explored the basis for this high potency. Using video-assisted microscopy, bscCD19xCD3 was found to alter the motility and activity of T cells from a scanning to a killing mode. Individual T cells could eliminate multiple target cells within a 9 hr time period, resulting in nuclear fragmentation and membrane blebbing of target cells. Complete target cell elimination was observed within 24 hr at effector-to-target cell ratios as low as 1:5. Under optimal conditions, cell killing started within minutes after addition of bscCD19xCD3, suggesting that the rate of serial killing was mostly determined by T-cell movement and target cell scanning and lysis. At all times, T cells remained highly motile, and no clusters of T and target cells were induced by the bispecific antibody. Bystanding target-negative cells were not detectably affected. Repeated target cell lysis by bscCD19xCD3-activated T cells increased the proportion of CD19/CD3 double-positive T cells, which was most likely a consequence of transfer of CD19 from B to T cells during cytolytic synapse formation. To our knowledge, this is the first study showing that a bispecific antibody can sustain multiple rounds of target cell lysis by T cells.

Eradication of tumors from a human colon cancer cell line and from ovarian cancer metastases in immunodeficient mice by a single-chain Ep-CAM-/CD3-bispecific antibody construct

Bispecific T-cell engager (BiTE) are a class of bispecific single-chain antibodies that can very effectively redirect cytotoxic T cells for killing of tumor target cells. Here, we have assessed the in vivo efficacy of one representative, called bscEp-CAMxCD3, with specificity for tumors overexpressing epithelial cell adhesion molecule (Ep-CAM) in human xenograft models. Cells of the human colon carcinoma line SW480 were mixed at a 1:1 ratio with unstimulated human peripheral mononuclear cells, s.c. injected in nonobese diabetes/severe combined immunodeficiency (NOD/SCID) mice, and animals were treated with bscEp-CAMxCD3. Five daily i.v. injections of as little as 100 ng per mouse of bscEp-CAMxCD3 completely prevented tumor outgrowth when treatment was started at the day of tumor cell inoculation. BscEp-CAMxCD3 was also efficacious when administered up to 8 days after xenograft injection. Established tumors could be eradicated in all animals by five 10 microg doses given between days 8 and 12 after tumor cell inoculation. To test the efficacy of bscEp-CAMxCD3 in a more physiologic model, pieces of primary metastatic tumor tissue from ovarian cancer patients were implanted in NOD/SCID mice. Partial tumor engraftment and growth was observed with four of six patient samples. Treatment of established tumors with daily 5 microg doses led to a significant reduction and, in some cases, eradication of human tumor tissue. These effects obviously relied on the tumor-resident T cells reactivated by bscEp-CAMxCD3. Our data show that the class of single-chain bispecific antibodies has very high antitumor efficacy in vivo and can use previously unstimulated T cells at low effector-to-target ratios.

Induction of regular cytolytic T cell synapses by bispecific single-chain antibody constructs on MHC class I-negative tumor cells

Certain bispecific single-chain antibody constructs exhibit an extraordinary potency for polyclonal T cell engagement and target cell lysis. Here we studied the structural basis for this potency, using laser scanning confocal microscopy. Cytolytic human T cell synapses could be triggered either by addition of a specific peptide antigen or an Ep-CAM-/CD3-bispecific T cell engager (BiTE). Both kinds of synapses showed a comparable distribution of all protein markers investigated. Two other BiTEs constructed from different Ep-CAM-specific antibodies gave similar results. BiTEs could also induce lytic synapses between human T cells and a MHC class I-negative, Ep-CAM cDNA-transfected cell line resulting in potent target cell lysis. This shows that certain T cell recognition molecules on target cells are dispensable for synapse formation and BiTE activity, and suggests that BiTE-activated polyclonal T cells may ignore major immune evasion mechanisms of tumor cells in vivo, such as loss of MHC class I expression.

T-cell triggering by CD3- and CD28-binding molecules linked to a human virus-modified tumor cell vaccine

The aim was to develop T cell costimulatory molecules that are broadly applicable to augment anti-tumor immune responses upon application of a virus-modified tumor vaccine to cancer patients. We generated recombinant bispecific single-chain antibodies with one specificity directed against the CD3 or the CD28 antigen on human T cells and the other against the viral target molecule hemagglutinin-neuraminidase (HN) of Newcastle Disease Virus (NDV). By re-directing unstimulated primary human T cells against HN-expressing NDV-infected tumor cells, the bispecific molecule bsHN-CD3 cross-linked effector and target cells and rapidly induced cytotoxicity at nanomolar concentrations. The bsHN-CD28 molecule exerted T cell co-stimulatory function. Maximal T cell activation was achieved with tumor cells infected by NDV and modified with both new stimulatory molecules. This was revealed by T cell proliferation, upregulation of CD69 and CD25 and by release of cytokines, interferons and chemokines. The new molecules combine high-effectivity with specificity and safety.

Recombinant bispecific antibodies for cancer therapy

Bispecific antibodies can serve as mediators to retarget effector mechanisms to disease-associated sites. Studies over the past two decades have revealed the potentials but also the limitations of conventional bispecific antibodies. The development of recombinant antibody formats has opened up the possibility of generating bispecific molecules with improved properties. This review summarizes recent developments in the field of recombinant bispecific antibodies and discusses further requirements for clinical development.

Bispecific single-chain diabody-mediated killing of endoglin-positive endothelial cells by cytotoxic T lymphocytes

We present a novel vascular tumor therapy approach based on lysing endothelial cells by cytotoxic T lymphocytes (CTLs). Retargeting of CTLs is achieved by a recombinant bispecific antibody molecule (bispecific single-chain diabody) directed against human endoglin (CD105, EDG) and the T-cell coreceptor CD3 (scDb EDGCD3). Bacterially expressed scDb EDGCD3 was able to bind to endoglin-expressing endothelial cells as well as CD3-expressing T lymphocytes. The single-chain diabody mediated killing of endothelial cells (HUVEC, HMEC) by activated cytotoxic T lymphocytes at picomolar concentrations, and cells not expressing endoglin were not affected. Because endoglin is up-regulated in the vasculature of many solid tumors, this antibody molecule should be capable of lysing tumor endothelial cells and thus destroying the vascular bed of the tumor.