title: Mode of cytotoxic action of T cell-engaging BiTE antibody MT110.
abstract: MT110 is an EpCAM/CD3-bispecific antibody construct in clinical development for the treatment of patients with adenocarcinoma expressing EpCAM (CD326). Like other members of this antibody class, MT110 can engage resting, polyclonal CD8(+) and CD4(+) T cells for highly potent redirected lysis of target cells. Here we further explored the mechanism of this action. Complete lysis of EpCAM(+) Kato III gastric cancer cells by previously unstimulated T cells was achieved within 48 h. During this period, a high percentage of CD4(+) and CD8(+) T cells became activated and increased expression of granzyme B. This apparently boosted the capacity for serial target cell lysis as studied at very low effector-to-target ratios. Elimination of cancer cells by MT110-redirected T cells involved membrane damage as was evident from nuclear uptake of propidium iodide and release of the cytosolic enzyme adenylate kinase. Redirected T cells also potently triggered programmed cell death in cancer cells as was evident by membrane blebbing, activation of procaspases 3 and 7, fragmentation of nuclear DNA and cleavage of the caspase substrate poly (ADP ribose) polymerase. Chelation of extracellular calcium fully protected cancer cells from lysis by MT110-redirected T cells, while the pan-caspase inhibitor Z-VAD-FMK blocked activation of procaspases, cleavage of poly (ADP ribose) polymerase and fragmentation of nuclear DNA in cancer cells, but could not prevent nuclear uptake of propidium iodide. Soluble factors did not significantly contribute to cancer cell death. Our study shows that MT110 can efficiently gear up the potential of CD8(+) and CD4(+) T cells for serial lysis, and mediate kill of cancer cells predominantly through poreforming and pro-apoptotic components of cytotoxic T cell granules.
authors.affiliation: Micromet AG, Staffelseestr. 2, 81477 Munich, Germany.
authors.forename: Cornelia
authors.initials: C
authors.lastname: Haas
authors.forename: Eva
authors.initials: E
authors.lastname: Krinner
authors.forename: Klaus
authors.initials: K
authors.lastname: Brischwein
authors.forename: Patrick
authors.initials: P
authors.lastname: Hoffmann
authors.forename: Ralf
authors.initials: R
authors.lastname: Lutterbüse
authors.forename: Bernd
authors.initials: B
authors.lastname: Schlereth
authors.forename: Peter
authors.initials: P
authors.lastname: Kufer
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Baeuerle
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000951:Antigens, Neoplasm / Q000276:immunology / Q000378:metabolism; D017209:Apoptosis; D017252:CD3 Complex / Q000276:immunology / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D061945:Caspase Inhibitors; D015815:Cell Adhesion Molecules / Q000276:immunology / Q000378:metabolism; D045744:Cell Line, Tumor; D024161:Collagen Type XI / Q000037:antagonists & inhibitors; D003602:Cytotoxicity, Immunologic / Q000187:drug effects* / Q000276:immunology; D053938:DNA Fragmentation / Q000187:drug effects; D000071858:Epithelial Cell Adhesion Molecule; D053804:Granzymes / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects; D009369:Neoplasms / Q000276:immunology / Q000473:pathology / Q000628:therapy; D057127:Single-Chain Antibodies
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D017252:CD3 Complex; C499319:COL11A2 protein, human; D061945:Caspase Inhibitors; D015815:Cell Adhesion Molecules; D024161:Collagen Type XI; D000071858:Epithelial Cell Adhesion Molecule; C509173:MT110 monoclonal antibody; D057127:Single-Chain Antibodies; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D053804:Granzymes; D000262:Adenylyl Cyclases