The invention relates to novel binding domain-immunoglobulin fusion proteinsthat feature a binding domain for a cognate structure such as an antigen, acounterreceptor or the like, a hinge region polypeptide having either zero orone cysteine residue, and immunoglobulin CH2 and CH3 domains, and that arecapable of ADCC and/or CDC while occurring predominantly as monomericpolypeptides. The fusion proteins can be recombinantly produced at highexpression levels. Also provided are related compositions and methods,including immunotherapeutic applications.
