Abstract 4734: Impact of various immune escape mechanisms on redirected lysis by T cells engaged via EpCAM/CD3 bispecific BiTE® antibody AMG 110 .
Authors: Deisting Wibke , Raum Tobias , Kufer Peter , Baeuerle Patrick A. , Muenz Markus 
Published: August 2014

Abstract
BiTE antibodies are single-chain bispecific antibody constructs with dual specificity for CD3 on T cells and a surface antigen on target cells. They are capable of temporarily mounting a polyclonal T cell response that is not restricted by T cell receptor specificity, presence of MHC class I, generation and presentation of peptide antigen, or the addition of T cell co-stimuli. Examples are the CD19/CD3-bispecific BiTE antibody blinatumomab, which has been reported to show high response rates in leukemia and lymphoma patients, and EpCAM/CD3-bispecific BiTE antibody solitomab (AMG 110), which is in a dose-escalating phase 1 study in patients with solid tumors. Because specific T cell responses against cancer cells are frequently hampered by a variety of immune escape mechanisms, we have here assessed to what extent surface expression of PD-L1 (B7-H1) and CD73, cytoplasmic expression of IDO and serpin PI-9, and secretion of TGF-ß and IL-10 can protect target cells from redirected lysis by AMG 110-engaged T cells.
The six human proteins, which are all known to be associated with immune escape of cancer cells by inhibition of T cell function, were stably expressed in human EpCAM-expressing Chinese hamster ovary (CHO) cells. In all cases, expression levels of the six proteins in stable CHO cell lines exceeded those found in human cancer cell lines. Characterized CHO cell lines and the parental EpCAM+ CHO line were used in co-culture assays as target cells for analysis of EC50 values for redirected lysis, and induction of proliferation of resting human peripheral T cells in the presence of various AMG 110 concentrations.
High level cytosolic expression of the tryptophan metabolizing enzyme IDO had no effect on redirected lysis but reduced AMG 110-induced T cell proliferation, while expression of the granzyme inhibitor PI-9 increased the EC50 value for redirected lysis but had no effect on T cell proliferation. High level expression of the membrane-bound ligand for PD-1, PD-L1, and of secreted IL-10 and TGF-β all had no impact on AMG 110-induced T cell proliferation. The EC50 value for redirected lysis was however impacted by expression of TGF-ß and PD-L1 as determined by a FACS-based cytotoxicity assays. In no case, transfected CHO cell lines became completely resistant to BiTE-induced lysis despite expressing the immune escape proteins at higher levels than observed in tumor cell lines. Our data suggest that BiTE-engaged T cells are relatively insensitive to proteins expressed by cancer cells to fend off T cells, and that inhibitory effects can be compensated by higher concentrations of the BiTE antibody.
Citation Format: Wibke Deisting, Tobias Raum, Peter Kufer, Patrick A. Baeuerle, Markus Muenz. Impact of various immune escape mechanisms on redirected lysis by T cells engaged via EpCAM/CD3 bispecific BiTE® antibody AMG 110 . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4734. doi:10.1158/1538-7445.AM2013-4734