Bispecific antibodies in cancer therapy, from the laboratory to the clinic

A novel redox method for rapid production of functional bi-specific antibodies for use in early pilot studies

We demonstrate here a rapid alternative method for the production of functional bi-specific antibodies using the mild reducing agent 2-mercaptoethanesulfonic acid sodium salt (MESNA). Following reduction of a mixture of two monoclonal antibodies with MESNA to break inter heavy chain bonds, this solution is dialysed under oxidising conditions and antibodies are allowed to reform. During this reaction a mixture of antibodies is formed, including parental antibodies and bi-specific antibody. Bi-specific antibodies are purified over two sequential affinity columns. Following purification, bi-specificity of antibodies is determined in enzyme-linked immunosorbent assays and by flow cytometry. Using this redox method we have been successful in producing hybrid and same-species bi-specific antibodies in a time frame of 6-10 working days, making this production method a time saving alternative to the time-consuming traditional heterohybridoma technology for the production of bi-specific antibodies for use in early pilot studies. The use of both rat and mouse IgG antibodies forming a rat/mouse bi-specific antibody as well as producing a pure mouse bi-specific antibody and a pure rat bi-specific antibody demonstrates the flexibility of this production method.

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.

Application of the Fc fusion format to generate tag-free bi-specific diabodies

We previously reported the use of a humanized bi-specific diabody that targets epidermal growth factor receptor and CD3 (hEx3-Db) for cancer immunotherapy. Bacterial expression can be used to express small recombinant antibodies on a large scale; however, their overexpression often results in the formation of insoluble aggregates, and in most cases artificial affinity peptide tags need to be fused to the antibodies for purification by affinity chromatography. Here, we propose a novel method for preparing refined, functional, tag-free bi-specific diabodies from IgG-like bi-specific antibodies (BsAbs) in a mammalian expression system. We created an IgG-like BsAb in which bi-specific diabodies were fused to the human Fc region via a designed human rhinovirus 3C (HRV3C) protease recognition site. The BsAb was purified by protein A affinity chromatography, and the refined tag-free hEx3-Db was efficiently produced from the Fc fusion format by protease digestion. The tag-free hEx3-Db from the Fc fusion format showed a greater inhibition of cancer growth than affinity-tagged hEx3-Db prepared directly from Chinese hamster ovary cells. We also applied our novel method to another small recombinant antibody fragment, hEx3 single-chain diabody (hEx3-scDb), and demonstrated the versatility and advantages of our proposed method compared with papain digestion of hEx3-scDb. This approach may be used for industrial-scale production of functional tag-free small therapeutic antibodies.

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.

The apoptotic and proliferative fate of cytokine-induced killer cells after redirection to tumor cells with bispecific Ab

BACKGROUND

Cytokine-induced killer (CIK) cells are ex vivo expanded T cells with co-expression of CD3 and CD56 and NK activity. They have recently been evaluated in a phase I/II clinical trial against malignant lymphoma. Bispecific Ab (bsAb) redirect CIK cells to tumor targets, thus enhancing their cytotoxicity. While bsAb may improve T-cell mediated anti-tumor activity, little is known about the fate of effector cells upon redirection to tumor targets using a bsAb.

METHODS

Using ex vivo-activated CIK cells, Her2/neu expressing breast and ovarian cell lines and a F(ab')2 Her2/neu x CD3 bsAb, we investigated the anti-tumor activity and the proliferative and apoptotic outcome of CIK cells.

RESULTS

When redirected to tumor targets with bsAb, there was a significant increase in anti-tumor activity as well as an increase in both CIK cell proliferation and apoptosis. The addition of agonistic Ab against CD28 did not significantly increase proliferation or apoptosis of CIK cells redirected to CD80- and CD86- tumor targets. To attempt to reduce T-cell apoptosis, we incubated CIK cells in the presence of the pan-caspase inhibitor z-VAD-fmk, which led to a partial reduction in T-cell apoptosis without increasing cellular cytotoxicity.

DISCUSSION

bsAb are effective in redirecting activated T cells to tumor targets and such redirection leads to both T-cell proliferation and apoptosis that are not altered by co-stimulation through CD28. Effector cell apoptosis can be reduced by using a caspase inhibitor but this does not increase CIK cell cytotoxicity.

Antigen targeting to dendritic cells with bispecific antibodies

We have developed a universal DC targeting vehicle that could be a convenient method to deliver any type of antigen to DC. P125, a quadroma (hybrid-hybridoma) secreting bispecific monoclonal antibodies (bsmAb), with one paratope specific for mouse DC DEC-205 and another paratope specific for biotin, was developed by PEG-fusion of the two parental hybridomas and selected by a fluorescence activated cell sorter. The bsmAb were purified using a biotin-Agarose column and the bsmAb activity was demonstrated using ELISA method employing mouse bone marrow DC and biotinylated BSA. Both confocal microscopy and ELISA studies have shown enhanced binding and internalization of biotinylated and FITC-labelled M13 to DC cell in the presence of bsmAb. In vivo studies in mice with biotinylated OVA has shown that in the presence of bsmAb and anti-CD40 mAb, both humoral and cell-mediated responses can be augmented. In addition, only a low concentration of antigen (500 fold less) is required using bsmAb to achieve a similar immune response in mice that were immunized using complete Freund's adjuvant. In the absence of traditional adjuvants, bsmAb targeting of biotinylated antigens to DC could be an alternative, convenient method to deliver antigens to DC. Moreover, this method could be an alternative method to ex vivo stimulation of DC to overcome DC defects and for treatment of cancer.

A new format of bispecific antibody: highly efficient heterodimerization, expression and tumor cell lysis

Bispecific antibodies (BsAbs) have been considered as potential therapeutics for cancer. A major obstacle in the development of BsAb has been the difficulty in producing a heterodimer with two different arms and in sufficient quantity for clinical application by the traditional methods. We describe a new format of BsAb that consists of two single-chain variable fragment of antibodies (scFvs), one for human epidermal growth factor receptor 2 (HER2)/neu and the other for CD16, heterodimerized by a "knobs-into-holes" device from the CH3 domains of the human IgG1 Fc fragment. The two chains were functionally expressed in CHO cells and assembled into heterodimers with dual antigen-binding specificity. Compared with other types of engineered BsAbs expressed in mammalian cells, the yield of this BsAb was relatively high (12-14 mg/l). In vitro experiments demonstrated that the BsAb was able to recruit human peripheral blood mononuclear cells (PBMC) to kill SK-BR-3 cells more effectively than the commercial anti-HER2/neu antibody Herceptin (Roche, Shanghai). This new format of BsAb possesses properties that support its potential as a new antitumor agent.

Bispecific antibody conjugates in therapeutics

Bispecific monoclonal antibodies have drawn considerable attention from the research community due to their unique structure against two different antigens. The two-arm structure of bsMAb allows researchers to place a therapeutic agent on one arm while allowing the other to specifically target the disease site. The therapeutic agent can be a drug, toxin, enzyme, DNA, radionuclide, etc. Furthermore, bsMAb may redirect the cytotoxicity of immune effector cells towards the diseased cells or induce a systemic immune response against the target. BsMAb holds great promise for numerous therapeutic needs in the light of: (1) recent breakthroughs in recombinant DNA technology, (2) the increased number of identified disease targets as the result of the completion of human genomic map project, and (3) a better understanding of the mechanism of human immune system. This review focuses on therapeutic applications and production of bsMAb while providing the up-to-date clinical trial information.

European approach to antibody-based immunotherapy of melanoma

In the past two decades, the worldwide steadily rising incidence of melanoma, its dismal prognosis when locally advanced or metastatic, and the absence of clinically effective therapeutic options have prompted studies that generated extensive preclinical knowledge on the biology of melanoma cells and their interaction with the host's immune system. As a consequence, among solid tumors, melanoma represents a "model malignancy" to design and apply in the clinic new bioimmunotherapeutic approaches, that are eventually translated to solid tumors of different histotypes. Despite its waxing and waning appeal as a therapeutic strategy, antibody treatment still represents a promising clinical approach to melanoma. Europe is no exception in the clinical interest for antibodies as therapeutic tools in melanoma patients; European researchers have also focused on preclinical issues that may improve current antibody-based therapeutic approaches on the one hand, while providing novel clinical strategies on the other hand.

Improving the efficacy of antibody-based cancer therapies

A quarter of a century after their advent, monoclonal antibodies have become the most rapidly expanding class of pharmaceuticals for treating a wide variety of human diseases, including cancer. Although antibodies have yet to achieve the ultimate goal of curing cancer, many innovative approaches stand poised to improve the efficacy of antibody-based therapies.

A review of modifications to recombinant antibodies: attempt to increase efficacy in oncology applications

Although monoclonal antibodies have high specificity, their usefulness in the clinic, especially against solid tumors, has been limited. This arises in part from the inability of antibody molecules to penetrate into the tumor and kill the tumor cells. In addition, natural cytotoxic effects of antibodies, mediated through complement or Fc receptors, may not be sufficient to kill malignant cells. This review will present some of the antibody modifications used to increase efficacy. Modified recombinant antibodies have been designed to be more cytotoxic (immunotoxins), to increase natural effector functions (bivalent antibodies, antibody-fusion molecules, multimeric antibodies, directed mutations in Fc region), or to pretarget cells for concentration of cytotoxic drugs. This review will also focus on engineering of smaller versions of antibodies that retain specificity (single chain Fvs, Fabs, Fab(2)s, minibodies, domain deleted antibodies) and have increased penetrability of solid tumors. Many of these antibody modifications may result in antigenic compounds which can limit repeat administration. Clinical experiences will be highlighted if information is available.

The development of novel mouse monoclonal antibodies against the CC531 rat colon adenocarcinoma

In this paper we describe 4 new monoclonal antibodies to be applied in rat models for cancer. The monoclonal antibodies were obtained by immunizing Balb/c mice with CC531 rat colon adenocarcinoma cells. Hybridomas were produced and 4 were selected for their reactivity with CC531 in vitro (MG1, 2, 3 and 4). All 4 antibodies recognized other rat tumour cell lines and showed limited cross-reactivity with normal rat tissues. Intraperitoneally injected MG1, 2 and 4 homed to in vivo growing, artificially induced CC531 liver metastases. In these in vivo experiments, limited cross-reactivity with normal rat tissues, predominantly of the gastro-intestinal tract, was found. MG4 was found to enhance lysis of CC531 tumour cells mediated by IL-2 activated, cultured natural killer cells. These antibodies are potentially useful for antibody-based laboratory techniques and for investigation of antibody-based immunotherapy of cancer in a rat model.

The comparison of the ability of monoclonal antibodies directed to different proteins (human IgG, human myoglobin and HRP) and bispecific antibodies derived thereof to bind antigens immobilized on a surface of a solid phase

BACKGROUND

Bindings of mouse monoclonal antibodies (mAbs) and affinity purified bispecific antibodies (bAbs), derived thereof, to antigens adsorbed on immunoplates have been compared, using ELISA and RIA methods.

METHODS

The analysed panel of antibodies included mAbs specific to human myoglobin (Mb), human IgG (hIgG) and horseradish peroxidase (HRP) and biologically produced bAbs with double specificity to Mb and HRP, and to hIgG and HRP.

RESULTS

The degree of difference between different mAbs and corresponding bAbs varied markedly from antibody to antibody, depending on whether the parental mAbs could bind immobilized antigens bivalently. The observed equilibrium binding constant (K(obs)) for anti-HRP mAbs was 21-38 times higher that of anti-HRP site of bAbs (anti-hIgG/HRP or anti-Mb/HRP, respectively), due to bivalent binding of mAbs. Anti-Mb mAbs also bound bivalently with immobilized Mb. On the contrary, anti-hIgG mAbs bound monovalently with immobilized hIgG in the same conditions. The avidity of anti-Mb/HRP bAbs increased, if both antigens were simultaneously adsorbed on a solid phase.

CONCLUSIONS

The obtained data indicate that the use of bAbs in heterogeneous immunoassays instead of traditional mAb-enzyme conjugates hardly can provide the significant gain in assay performance if parental mAbs bind bivalently.

Administration of BiMAb-retargeted T cells in a rat hepatic metastases colon tumour model results in T-cell tumour infiltration independent of the route of administration

In this study, cultured T cells, pre-incubated with the bispecific monoclonal antibody (BiMAb) R73IgG1 x CC52IgG1 were adoptively transferred, via systemic and regional routes, to rats bearing day 10 hepatic metastases of the CC531 adenocarcinoma of the colon to investigate the role of the route of administration in tumour infiltration by these BiMAb-retargeted effector cells. The BiMAb, directed against the T-cell receptor and the tumour-associated antigen CC52, were used to crosslink CC531 tumour cells and T cells to induce tumour cell lysis. Retargeted T cells were administered via the jugular vein, hepatic artery or the portal vein. The number of BiMAb-retargeted T cells that reached the liver tumours was independent of the route of administration. There was also no difference between the number of T cells that reached the portal tracts, central veins of parenchyma of the liver, after loco-regional or systemic administration. These findings are in contrast to the interleukin (IL)-2 activated NK (A-NK) cells biodistribution studies earlier performed in the same animal model in our laboratory. Compared with A-NK cells, a lower number of BiMAb-retargeted T cells reached the tumours, irrespective of their route of administration while for A-NK cells, there was an advantage of administration via the hepatic artery.

Bispecific human IgG by design

A major obstacle facing the development of bispecific antibodies as therapeutics has been the formidable task of producing these complex molecules in sufficient quantity and purity for clinical trials. These production difficulties have been largely overcome with the advent of efficient methods for the secretion of designer bispecific antibody fragments such as diabodies and miniantibodies from Escherichia coli. In contrast, the creation of bispecific IgG by the coexpression of two different IgG is highly inefficient due to unwanted pairings of the component heavy and light chains. A robust technology for the creation of bispecific IgG has recently been developed that virtually precludes IgG contaminants, as reviewed here. This technology is anticipated to spur the clinical development of bispecific IgG and other bifunctional Fc-containing molecules such as antibody/immunoadhesin hybrids and bispecific immunoadhesins.

Immunotherapeutic perspective for bispecific antibodies

Bispecific antibodies (BsAb) can, by virtue of combining two binding specificities, improve the selectivity and efficacy of antibody-based treatment of human disease. Recent studies underline the importance of both the 'anti-trigger' and 'anti-target' modalities of BsAb for therapeutic efficacy. Several BsAb induce effective cytotoxicity as well as 'vaccine effects' in vivo. Here, Annemiek van Spriel and colleagues discuss how these results have catalysed renewed efforts to translate BsAb concepts into effective therapies.