Abstract
CEA TCB (RG7802, RO6958688) is a novel T-cell bispecific antibody, engaging CD3ε upon binding to carcinoembryonic antigen (CEA) on tumor cells. Containing an engineered Fc region, conferring an extended blood half-life while preventing side effects due to activation of innate effector cells, CEA TCB potently induces tumor lysis in mouse tumors. Here we aimed to characterize the pharmacokinetic profile, the biodistribution, and the mode of action of CEA TCB by combining in vitro and in vivo fluorescence imaging readouts. CEA-expressing tumor cells (LS174T) and human peripheral blood mononuclear cells (PBMC) were cocultured in vitro or cografted into immunocompromised mice. Fluorescence reflectance imaging and intravital 2-photon (2P) microscopy were employed to analyze in vivo tumor targeting while in vitro confocal and intravital time-lapse imaging were used to assess the mode of action of CEA TCB. Fluorescence reflectance imaging revealed increased ratios of extravascular to vascular fluorescence signals in tumors after treatment with CEA TCB compared with control antibody, suggesting specific targeting, which was confirmed by intravital microscopy. Confocal and intravital 2P microscopy showed CEA TCB to accelerate T-cell-dependent tumor cell lysis by inducing a local increase of effector to tumor cell ratios and stable crosslinking of multiple T cells to individual tumor cells. Using optical imaging, we demonstrate specific tumor targeting and characterize the mode of CEA TCB-mediated target cell lysis in a mouse tumor model, which supports further clinical evaluation of CEA TCB. Clin Cancer Res; 22(17); 4417-27. ©2016 AACRSee related commentary by Teijeira et al., p. 4277.
Highlights
The notion that increased numbers of tumor infiltrated T cells correlate with survival in patients suffering from different types of cancer including colorectal and ovarian cancer, non-Hodgkin lymphoma, and glioblastoma has instigated the development ofNote: Supplementary data for this article are available at Clinical Cancer Research Online.C
To assess carcinoembryonic antigen (CEA) T-cell–engaging bispecific (TCB) binding to the human CEA–expressing colon cancer cell line LS174T, the model utilized throughout this study [13], fluorescently (Alexa 647) labeled CEA TCB and nonbinding control TCB (DP47 TCB) were added to LS174T cells at different antibody concentrations
CEA TCB increases the fraction of apoptotic tumor cells within 24 hours by accelerating tumor cell lysis and simultaneous engaging of multiple T cells by individual tumor cells
Summary
Aside from cancer vaccines, adoptive transfer of ex vivo–modified T cells expressing chimeric antigen receptors (CAR-T) targeting tumor antigens and T-cell–activating checkpoint inhibitors, recent research efforts have focused on the generation of T-cell–engaging bispecific (TCB) antibody constructs [3]. Binding to a tumor-specific cell surface antigen and a T-cell–stimulating molecule, typically the T-cell receptor (TCR)-associated protein CD3, TCBs cross-link T- and tumor cells, thereby triggering T-cell–mediated tumor cell lysis [1, 3]. By cross-linking polyclonal T cells independent of their antigen specificity, TCBs circumvent potential pitfalls associated with approaches requiring specific immune responses, frequently hampered by immune escape reactions [4]. BiTEs potently elicit T-cell–dependent target cell lysis and have proven single-agent efficacy in patients with relapsed or refractory B-ALL and non-Hodgkin lymphoma BiTEs potently elicit T-cell–dependent target cell lysis and have proven single-agent efficacy in patients with relapsed or refractory B-ALL and non-Hodgkin lymphoma (NHL; ref. 5), these molecules are composed of two single-chain variable fragments (scFv) www.aacrjournals.org
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