Immunosuppressive properties of anti-CD3 single-chain Fv and diabody

The mouse anti-human CD3 monoclonal antibody OKT3 is a potent immunosuppressive agent used in clinical transplantation. However, OKT3 therapy is associated with unpleasant and often serious side effects which appear to result from cytokine release, complement activation and a human anti-mouse antibody (HAMA) response. To decrease these adverse side effects, we constructed antibody fragments comprising OKT3 variable domains without any constant domains. Single-chain Fv (scFv) monomers, dimers and trimers were generated by changing the linker length between the V-H and V-L domains. The linkers used were the natural extensions of the V-H into the C(H)1 domain. The dimeric molecules (diabodies) demonstrated the best CD3-binding activity. The diabody with the six amino acid linker was produced in bacteria with a tenfold higher yield than other scFvs and possessed CD3-binding affinity approaching that of the parental mAb. In contrast to OKT3 mAb, the anti-CD3 diabody and scFv monomer did not cause any T-cell activation and cytokine release in vitro, while demonstrating CD3 modulation. In mixed lymphocyte cultures, both diabody and scFv, but not the monoclonal antibody OKT3, were able to suppress T-cell activation and secretion of IL-2 and IFN-gamma in a dose-dependent manner. The anti-CD3 diabody may provide a potent immunosuppressive drug with low toxicity and immunogenicity. (C) 2004 Elsevier B.V. All rights reserved.