title: The tumor targeted superantigen ABR-217620 selectively engages TRBV7-9 and exploits TCR-pMHC affinity mimicry in mediating T cell cytotoxicity.
abstract: The T lymphocytes are the most important effector cells in immunotherapy of cancer. The conceptual objective for developing the tumor targeted superantigen (TTS) ABR-217620 (naptumomab estafenatox, 5T4Fab-SEA/E-120), now in phase 3 studies for advanced renal cell cancer, was to selectively coat tumor cells with cytotoxic T lymphocytes (CTL) target structures functionally similar to natural CTL pMHC target molecules. Here we present data showing that the molecular basis for the anti-tumor activity by ABR-217620 resides in the distinct interaction between the T cell receptor β variable (TRBV) 7-9 and the engineered superantigen (Sag) SEA/E-120 in the fusion protein bound to the 5T4 antigen on tumor cells. Multimeric but not monomeric ABR-217620 selectively stains TRBV7-9 expressing T lymphocytes from human peripheral blood similar to antigen specific staining of T cells with pMHC tetramers. SEA/E-120 selectively activates TRBV7-9 expressing T lymphocytes resulting in expansion of the subset. ABR-217620 selectively triggers TRBV7-9 expressing cytotoxic T lymphocytes to kill 5T4 positive tumor cells. Furthermore, ABR-217620 activates TRBV7-9 expressing T cell line cells in the presence of cell- and bead-bound 5T4 tumor antigen. Surface plasmon resonance analysis revealed that ABR-217620 binds to 5T4 with high affinity, to TRBV7-9 with low affinity and to MHC class II with very low affinity. The T lymphocyte engagement by ABR-217620 is constituted by displaying high affinity binding to the tumor cells (KD approximately 1 nM) and with the mimicry of natural productive immune TCR-pMHC contact using affinities of around 1 µM. This difference in kinetics between the two components of the ABR-217620 fusion protein will bias the binding towards the 5T4 target antigen, efficiently activating T-cells via SEA/E-120 only when presented by the tumor cells.
authors.affiliation: Active Biotech AB, Lund, Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Hedlund
authors.forename: Helena
authors.initials: H
authors.lastname: Eriksson
authors.forename: Anette
authors.initials: A
authors.lastname: Sundstedt
authors.forename: Göran
authors.initials: G
authors.lastname: Forsberg
authors.forename: Bent K
authors.initials: BK
authors.lastname: Jakobsen
authors.forename: Nicholas
authors.initials: N
authors.lastname: Pumphrey
authors.forename: Karin
authors.initials: K
authors.lastname: Rödström
authors.forename: Karin
authors.initials: K
authors.lastname: Lindkvist-Petersson
authors.forename: Per
authors.initials: P
authors.lastname: Björk
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000378:metabolism; D000970:Antineoplastic Agents / Q000276:immunology*; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D003602:Cytotoxicity, Immunologic / Q000276:immunology*; D017931:DNA Primers / Q000235:genetics; D004768:Enterotoxins / Q000276:immunology* / Q000378:metabolism; D005434:Flow Cytometry; D019674:Genes, T-Cell Receptor beta / Q000235:genetics / Q000276:immunology; D006801:Humans; D018796:Immunoconjugates / Q000276:immunology* / Q000378:metabolism; D007700:Kinetics; D008156:Luciferases; D008562:Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism; D018716:Molecular Mimicry / Q000276:immunology*; D009369:Neoplasms / Q000276:immunology*; D018089:Superantigens / Q000276:immunology* / Q000378:metabolism; D020349:Surface Plasmon Resonance; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; D017931:DNA Primers; D004768:Enterotoxins; D018796:Immunoconjugates; D008562:Membrane Glycoproteins; D018089:Superantigens; C479099:enterotoxin A E-120, Staphylococcal; C063709:trophoblastic glycoprotein 5T4, human; C543500:naptumomab estafenatox; D008156:Luciferases