title: Engineering a CD123xCD3 bispecific scFv immunofusion for the treatment of leukemia and elimination of leukemia stem cells.
abstract: Engineered bispecific antibodies that recruit cytotoxic lymphocytes to kill specific tumor cells have been showing promising clinical results. Here, we describe a bispecific single-chain Fv (scFv) immunofusion or BIf to target CD123(+) leukemia, that contains an anti-CD123 scFv fused at the N-terminus of human IgG1 hinge-C(H)2-C(H)3, and an anti-CD3 scFv fused at C-terminus. When expressed from transfected CHO-S cells, CD123xCD3 BIf forms a homodimer that provides a structure of N-terminal tumor-targeting domain that closely resembles natural antibody. The CD123xCD3 dimeric structure also provides binding affinity to CD123(+) tumor cells with a Kd of 10(-10) M, one to two orders of magnitude stronger than traditional bispecific antibody constructs. The location of the anti-CD3 scFv at C-terminus of BIf reduces the binding affinity to CD3(+) T cells by two orders, which could help to prevent non-specific T-cell activation. CD123xCD3 BIf is able to achieve T-cell-mediated target cell killing activities at low pM levels with E/T ratios as low as 2. Overall, the inclusion of human IgG1 constant region in BIf construct increases target cell-binding affinity; potentially increases serum half-life by its larger size and FcRn-mediated salvage system; and includes the abilities to activate the additional antibody-mediated cellular cytotoxicities.
authors: Cancer Research Institute, Scott & White Healthcare, Temple, TX 76502,  USA.
authors: Shu-Ru
authors: SR
authors: Kuo
authors: Lucas
authors: L
authors: Wong
authors: Jen-Sing
authors: JS
authors: Liu
mesh_terms: D000818:Animals; D018033:Antibodies, Bispecific / Q000235:genetics / Q000276:immunology* / Q000627:therapeutic use*; D017252:CD3 Complex / Q000276:immunology*; D002460:Cell Line; D045744:Cell Line, Tumor; D003602:Cytotoxicity, Immunologic; D006801:Humans; D007167:Immunotherapy; D053650:Interleukin-3 Receptor alpha Subunit / Q000276:immunology*; D007938:Leukemia / Q000276:immunology / Q000628:therapy*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology / Q000627:therapeutic use; D057127:Single-Chain Antibodies / Q000235:genetics / Q000276:immunology* / Q000627:therapeutic use*; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D018033:Antibodies, Bispecific; D017252:CD3 Complex; D053650:Interleukin-3 Receptor alpha Subunit; D011993:Recombinant Fusion Proteins; D057127:Single-Chain Antibodies