Complement recruitment using bispecific diabodies.

We describe the engineering of antibody fragments produced in bacteria for recruitment of complement effector functions. From a phage display repertoire we isolated human antibody fragments directed against complement C1q, and linked these to lysozyme-specific antibody fragments, creating bispecific antibodies (diabodies). One diabody was able to recruit C1q, resulting in efficient lysis of lysozyme-coated sheep erythrocytes, and also induced rosette-formation of erythrocytes with human monocytes and phagocytosis after phorbol ester stimulation. These diabodies may have therapeutic applications requiring the activation of complement.