Bispecific antibodies were initially developed as a way to physically target the immune system by bringing an effector cell and its target together. But early bispecfic products have required concomitant treatment with various other molecules to co-stimulate an immune response. Micromet AG has now developed bispecific antibodies that generate immune activity without co-stimulation, but it's not sure how the feat has been accomplished.

Bispecific antibodies consist of the epitope recognition region (Fab region) of two different antibodies linked together. They link an epitope that recognizes an immune effector cell, such as a T lymphocyte or a macrophage, to an epitope that recognizes a target cell, such as a tumor cell.