title: Man-made superantigens: Tumor-selective agents for T-cell-based therapy.
abstract: Superantigens (SAgs) are a collection of bacterial and viral proteins with potent immunostimulatory properties. SAgs bind to Major Histocompatibility Complex Class II (MHC II) molecules of antigen presenting cells (APCs) and activate a high frequency of T lymphocytes. To target a T-cell attack against tumor cells we genetically linked tumor-specific antibody Fab fragments to the SAg Staphylococcal enterotoxin A (SEA). Fab-SEA fusion protein efficiently targeted to solid tumors and induced a T-cell-mediated eradication of established metastases in animal models. Successful therapy was T-cell-dependent and required tumor specificity of the Fab moiety of the Fab-SEA fusion protein. Due to the high affinity of SAg for MHC II, a limitation of this approach was retention of Fab-SEA proteins in normal tissues expressing MHC II, which caused systemic immune activation and dose limiting toxicity. We recently solved the structure of SEA and applied structure-based drug design to develop a novel generation of 'man-made' SAg with improved pharmacological and pharmacokinetic properties. Mutation of the major MHC II binding site of SEA substantially reduced retention in MHC II(+) tissues and systemic toxicity, while local immune activation at targeted tumor sites was retained. The Fab-SEA mutants display a 10000-fold higher affinity for tumor tissue compared to normal tissue and the therapeutic window was improved >100-fold compared to native Fab-SEA protein. Thus protein engineering can be applied to convert harmful bacterial toxins into tolerable tumor-specific agents.
authors.affiliation: Pharmacia & Upjohn, Lund Research Center, Scheelevägen 22, S-223 63 Lund, Sweden
authors.initials: M
authors.lastname: Dohlsten
authors.initials: T
authors.lastname: Kalland
authors.initials: P
authors.lastname: Gunnarsson
authors.initials: P
authors.lastname: Antonsson
authors.initials: A
authors.lastname: Molander
authors.initials: J
authors.lastname: Olsson
authors.initials: R
authors.lastname: d'Argy
authors.initials: L
authors.lastname: Ohlsson
authors.initials: M
authors.lastname: Soegaard
authors.initials: R
authors.lastname: Persson
authors.initials: TN
authors.lastname: Brodin