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: Gunnar Hedlund, Helena Eriksson, Anette Sundstedt, Göran Forsberg, Bent K Jakobsen, Nicholas Pumphrey, Karin Rödström, Karin Lindkvist-Petersson, Per Björk
• Journal: PloS one (PLoS One) Vol. 8 Issue 10 Pg. e79082 ( 2013) ISSN: 1932-6203 [Electronic] United States
• PMID: 24194959 (Publication Type: Journal Article)

Chemical References

• Antibodies, Monoclonal
• Antineoplastic Agents
• DNA Primers
• Enterotoxins
• Immunoconjugates
• Membrane Glycoproteins
• Superantigens
• enterotoxin A E-120, Staphylococcal
• trophoblastic glycoprotein 5T4, human
• naptumomab estafenatox
• Luciferases

Topics

• Antibodies, Monoclonal (immunology, metabolism)
• Antineoplastic Agents (immunology)
• Cell Line, Tumor
• Cloning, Molecular
• Cytotoxicity, Immunologic (immunology)
• DNA Primers (genetics)
• Enterotoxins (immunology, metabolism)
• Flow Cytometry
• Genes, T-Cell Receptor beta (genetics, immunology)
• Humans
• Immunoconjugates (immunology, metabolism)
• Kinetics
• Luciferases
• Membrane Glycoproteins (immunology, metabolism)
• Molecular Mimicry (immunology)
• Neoplasms (immunology)
• Superantigens (immunology, metabolism)
• Surface Plasmon Resonance
• T-Lymphocytes (immunology)