Anatumomab mafenatox (ABR-214936) is a fusion protein containing an engineered 5T4 Fab moiety fused via
the C terminus of the heavy chain to a mutated form of the Staphylococcal enterotoxin A (SEA) superantigen [1
]. SEA is secreted by the pathogen and it stimulates a massive MHC class II-T cell receptor-mediated polyclonal T cell activation, which results in the release of large amounts of cytotoxic and proinflammatory cytokines. Anatumomab mafenatox targets the destructive power of SEA to 5T4-expressing tumour cells. The Asp227Ala mutation is the SEA moiety is designed to reduce MHC class II binding affinity so as to reduce killing of MHC class II positive cells.