Abstract: The present invention relates to a nucleic acid molecule encoding a polypeptide, wherein the polypeptide comprises (a) a first immunoglobulin domain comprising a VL domain linked to a VH domain, wherein the immunoglobulin domain specifically binds to an antigen expressed on tumour cells; (b) a second immunoglobulin domain comprising a VL domain linked to a VH domain, wherein the immunoglobulin domain specifically binds to an antigen expressed on tumour cells; and (c) a third immunoglobulin domain comprising a VL domain linked to a VH domain, wherein the immunoglobulin domain specifically binds to an effector cell antigen, wherein the effector cell is selected from the group consisting of NK cells, T cells, neutrophilic granulocytes, monocytes and macrophages; wherein at least one of the antigens expressed on tumour cells and bound by the immunoglobulin domain of (a) or (b) is an antigen expressed on tumour stem cells and/or on tumour precursor or progenitor cells; and wherein the ratio of immunoglobulin domai

Abstract: Bispecific antibody derivatives are disclosed which are comprised of a first region which binds to a first antigen and a second region which binds to a second antigen different from the first antigen. The first and second regions of the bispecific antibody are each stabilized by an additional internal disulfide bridge, and connected by a flexible polypeptide linker. The bispecific antibody is devoid of an Fc portion and is encoded as a single chain-sequence.