Humanized anti-CD3 bispecific binding molecules having reducedimmunogenicity are provided. Humanized antibody constructs derived from OKT3inthe format of bispecific binding molecules can have reduced specificactivities andrelated antibody-derived compounds having reduced side-effects that are usefulinthe treatment of human diseases are derisible. Accordingly, there is providedabispecific binding molecule having a first domain which contains a humanizedantibody-derived light chain that specifically binds to/interacts with thehuman CD3complex. The bispecific binding molecule has a second domain which contains adifferent antigen-interaction-site or an effector domain. Specific amino acidsubstitutions in light chain of OKT3 ¨ specifically at Ser24, Val54 and Leu96according to the Kabat system ¨ in the first domain of the bispecific bindingmolecule result in the humanization, reduced immunogenicity, and enhancedcytotoxicity. Uses, methods, compositions, cells and vectors relating theretoare alsodescribed.
