Introduction: Bispecific T cell Engagers (BiTEs) represent an emerging class of bispecific antibodies that have been shown to effectively redirect T cells against cancer. However, these promising constructs have not previously targeted tumor-specific antigens, and have not been tested for their ability to mediate activity against solid tumors or tumors of the central nervous system (CNS). Here, we designed a BiTE (EGFRvIIIxCD3) against the EGFRvIII tumor-specific antigen and performed preclinical tests to determine its efficacy against EGFRvIII-expressing glioblastoma.
Methods: In vitro cytotoxicity against human malignant glioma cell lines U87MG and U87MG.EGFRvIII was measured by standard chromium release assay. To examine in vivo efficacy, tumors were implanted intracranially in NSG mice. Animals were immune-reconstituted with unstimulated human peripheral mononuclear cells and treated with five daily intravenous infusions of EGFRvIIIxCD3.
Results: Our results demonstrate that EGFRvIIIxCD3 is both potent and antigen-specific, mediating an eight-fold increase in specific lysis against EGFRvIII-expressing glioma cells over wild-type controls (p<.001) at exceedingly low concentrations (10 ng/mL) and effector-to-target ratios (2.5:1). Early intravenous infusion of EGFRvIIIxCD3 produced cures in 7/10 mice, and delayed treatment of late-stage tumors in even moribund animals (5 days before death) significantly extended survival at doses as low as 10 mcg/mouse/day (p<.01). Histological analyses of brain tissue confirmed that EGFRvIIIxCD3 mediates trafficking of peripheral T cells to EGFRvIII-expressing tumor residing behind the blood-brain-barrier. Further studies using intravital confocal microscopy revealed that CNS localization was strictly dependent on the exquisite tumor specificity of EGFRvIIIxCD3 and its lack of cross-reactivity with systemic tissues.
Conclusions: These results demonstrate for the first time that bispecific antibodies of the BiTE class can recruit immune effectors to intracerebral tumors and elicit functional antitumor responses there. Additionally, our work highlights the critical importance of antigen specificity when applying this therapeutic platform to tumors of the CNS.
Patient Care: This work has the potential to provide a novel therapeutic for patients with GBM.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe how bispecific antibodies localize to the CNS despite the blood-brain-barrier and activate T cells to mediate antitumor efficacy; 2) Discuss in small groups the importance of tumor-specificity in the elicitation of potent T cell responses; 3) Identify an alternative therapeutic approach that harnesses the bispecific antibody platform.
References: CHOI, B. D., CAI, M., BIGNER, D. D., MEHTA, A. I., KUAN, C. T. & SAMPSON, J. H. 2011. Bispecific antibodies engage T cells for antitumor immunotherapy. Expert Opin Biol Ther, 11, 843-53.
BARGOU, R., LEO, E., ZUGMAIER, G., KLINGER, M., GOEBELER, M., KNOP, S., NOPPENEY, R., VIARDOT, A., HESS, G., SCHULER, M., EINSELE, H., BRANDL, C., WOLF, A., KIRCHINGER, P., KLAPPERS, P., SCHMIDT, M., RIETHMULLER, G., REINHARDT, C., BAEUERLE, P. A. & KUFER, P. 2008. Tumor regression in cancer patients by very low doses of a T cell-engaging antibody. Science, 321, 974-7.