Bispecific antibodies retarget murine T cell cytotoxicity against syngeneic breast cancer in vitro and in vivo

T-cell surface generation of dual bivalent, bispecific T-cell engaging, RNA duplex cross-linked antibodies (dbBiTERs) for re-directed tumor cell lysis

BACKGROUND

Genetic engineered Bispecific T-cell engagers (BiTEs) generate potent cytotoxic effects.

METHODS

Alternately, click chemistry engineered, dual specific bivalent Bispecific T-cell engaging antibodies (dbBiTEs) on T-cell surfaces can be generated from parent monoclonal antibodies.

RESULTS

We show the formation of dbBiTEs on the surface of T-cells along with the introduction of complementary 2'-OMe RNA 32-mer oligonucleotides allowing duplex formation between antibodies, designated as dbBiTERs. dbBiTERs generated in solution from anti-CEA and anti-CD3 OKT3 antibodies retained specific binding to CEA positive versus CEA negative cancer cells and to CD3 positive T-cells comparable to dbBiTEs. When T-cells were precoated with dbBiTEs or dbBiTERs and mixed with CEA positive versus CEA negative cancer cells, similar dose dependent and specific cytotoxicity were observed in redirected cell lysis assays. On-cell generated dbBiTERs exerted potent cytotoxic responses against CEA positive targets and were localized at the cell surface by immuno-gold EM. In addition, we demonstrate that target and T-cells, each coated separately with complementary 2'OMe-RNA-linked antibodies can be cross-linked by RNA duplex formation in vitro to generate redirected cell lysis.

CONCLUSION

The facile generation of dbBiTERs with specific cytolytic activity from intact antibodies and their generation on-cell offers a new avenue for antigen specific T-cell therapy.

Efficient Generation of Bispecific Murine Antibodies for Pre-Clinical Investigations in Syngeneic Rodent Models

Therapeutic concepts exploiting tumor-specific antibodies are often established in pre-clinical xenograft models using immuno-deficient mice. More complex therapeutic paradigms, however, warrant the use of immuno-competent mice, that more accurately capture the relevant biology that is being exploited. These models require the use of (surrogate) mouse or rat antibodies to enable optimal interactions with murine effector molecules. Immunogenicity is furthermore decreased, allowing longer-term treatment. We recently described controlled Fab-arm exchange (cFAE) as an easy-to-use method for the generation of therapeutic human IgG1 bispecific antibodies (bsAb). To facilitate the investigation of dual-targeting concepts in immuno-competent mice, we now applied and optimized our method for the generation of murine bsAbs. We show that the optimized combinations of matched point-mutations enabled efficient generation of murine bsAbs for all subclasses studied (mouse IgG1, IgG2a and IgG2b; rat IgG1, IgG2a, IgG2b, and IgG2c). The mutations did not adversely affect the inherent effector functions or pharmacokinetic properties of the corresponding subclasses. Thus, cFAE can be used to efficiently generate (surrogate) mouse or rat bsAbs for pre-clinical evaluation in immuno-competent rodents.

Tracking and treating activated T cells

Upon activation, T cells of various subsets are the most important mediators in cell-mediated immune responses. Activated T cells play an important role in immune system related diseases such as chronic inflammatory diseases, viral infections, autoimmune disease, transplant rejection, Crohn disease, diabetes, and many more. Therefore, efforts have been made to both visualize and treat activated T cells specifically. This review summarizes imaging approaches and selective therapeutics for activated T cells and gives an outlook on how tracking and treating can be combined into theragnositc agents for activated T cells.

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.

HSV-1 virions engineered for specific binding to cell surface receptors

Expression of specific peptide epitopes on the surface of virions has significant potential for studying viral biology and designing vectors for targeted gene therapy. In this study, an HSV-1 amplicon plasmid expressing a modified glycoprotein C (gC), in which the heparan sulfate binding domain was replaced with a His-tag, was used in generating HSV-1 virions. Western blot analysis demonstrated the presence of modified gC in the purified virions. The amplicon vectors were packaged using a gC-, lacZ+ helper virus to generate a mixture of high-titer helper virus (lacZ+) and amplicon vectors (GFP+), which expressed modified gC in the virion envelope. His-tagged virions bound to 293 6H cells expressing a cell surface pseudo-His-tag receptor four-fold more efficiently than to parental 293 cells and also proved more effective than wild-type virus in binding to both cell types. Binding resulted in productive infection by the modified virions with expression of reporter genes and cytopathic effect comparable to those of wild-type virions. Thus, not only can HSV-1 tropism be manipulated to recognize a non-herpes simplex binding receptor, but it is also possible to increase the infective capacity of the vectors beyond that of the wild-type virus via specific ligand receptor combinations.

Tumor-growth inhibition with bispecific antibody fragments in a syngeneic mouse melanoma model: the role of targeted T-cell co-stimulation via CD28

The ability of bispecific antibodies with anti-tumor x anti-CD3 specificity to mediate the killing of tumor cells by activated T cells has been demonstrated in many in vitro experiments. Moreover, long-term survival of lymphoma-bearing mice has been observed after treatment with such reagents. The therapeutic effect of bispecific antibodies in solid-tumor models has been less impressive, in particular if fragmented antibodies were used to avoid systemic T-cell activation by bispecific constructs binding to Fc-receptor-positive cells. Here we report that bispecific anti-tumor x anti-CD3-fragments markedly inhibit intraperitoneal as well as pulmonary tumor growth in mice inoculated with B16 melanoma cells, resulting in the long-term survival of animals. Therapeutic success critically depends on the number of recruitable effector cells at the site of tumor growth. A second bispecific construct triggering the co-stimulatory CD28-molecule on the T-cell surface increased tumor-cell killing in vitro and in vivo, despite rather low avidity of this reagent to mouse T cells. Finally, long-term-surviving animals showed improved survival after i.v. rechallenge with tumor cells, indicating that bispecific antibodies are capable of inducing long-lasting protective immunity.

Dissociation of intracellular signaling pathways in response to partial agonist ligands of the T cell receptor

The T cell receptor (TCR) is a versatile receptor able to generate different signals that result in distinct T cell responses. The pattern of early signals is determined by the TCR binding kinetics that control the ability of the ligand to coengage TCR and coreceptor. Coengagement of TCR and CD4 results in an agonist signaling pattern with complete tyrosine phosphorylation of TCR subunits, and recruitment and activation of ZAP-70. In contrast, TCR engagement without CD4 coengagement causes a partial agonist type of signaling, characterized by distinct phosphorylation of TCR subunits and recruitment but no activation of ZAP-70. The pathways triggered by partial agonist signaling are unknown. Here, we show that agonists cause association of active lck and active ZAP-70 with p120-GTPase-activating protein (p120-GAP). These associations follow engagement of CD4 or CD3, respectively. In contrast, partial agonists do not activate lck or ZAP-70, but induce association of p120-GAP with inactive ZAP-70. Despite these differences, both agonist and partial agonist signals activate the mitogen-activated protein kinase (MAPK) pathway. However, MAPK activation by partial agonists is transient, supporting a kinetic, CD4-dependent model for the mechanism of action of variant TCR ligands. Transient MAPK activation may explain some of the responses to TCR partial agonists and antagonists.

Affinity reagents against tumour-associated extracellular molecules and newforming vessels

Here we report some recent results of tumour targeting using extracellular matrix components of tumour stroma as targets. The possibility of using human recombinant antibodies in tumour targeting is also described. Preliminary results indicate that neovasculature markers can be targeted by recombinant antibodies and that they allow long residence time in tumours, thus exploiting the avidity properties of multivalent recombinant fragments.

Superantigen-Activated T Cells Redirected by a Bispecific Antibody Inhibit Vesicular Stomatitis Virus Replication In Vitro and In Vivo

A bispecific Ab (BsAb) that binds the TCR on T cells and the G protein of the vesicular stomatitis virus (VSV) can redirect staphylococcal enterotoxin B (SEB)-activated T cells to kill VSV-infected cells and to inhibit VSV replication in vitro. Inhibition of virus replication in our system is dependent upon the specificity of the Ab for the viral protein. IFN-γ does not play a very important role in this phenomenon, which is mainly mediated by the release of Pfp from CD8+ T cells. We have used a Stat1 knockout mouse model in which VSV infection is lethal. Infusion of staphylococcal enterotoxin-activated B T cells and bispecific Ab significantly slowed virus progression and prolonged the survival of VSV-infected Stat1 knockout mice in vivo.