The present invention provides a bispecific binding molecule, wherein said molecule comprises or consists of at least two domains whereby one of said at least two domains specifically binds to / interacts with the human CD3 complex and said domain comprises an
amino acid sequence of an
antibody derived light chain, wherein said
amino acid sequence is a particularly identified
amino acid sequence comprising specific amino acid substitutions, and a second domain is or contains at least one further
antigen-interaction-site and / or at least one further
effector domain. The invention further provides
nucleic acid molecules encoding the bispecific binding molecules of the invention, vectors comprising said
nucleic acid molecules and host cells transformed or transfected with said vectors. Moreover, the invention concerns a method for the production of bispecific binding molecules of the invention and compositions comprising the bispecific binding molecules of the invention, the
nucleic acid molecules of the invention or the host cells of the invention.