Although immunotherapy has achieved increasing prominence in the panoply of innovative cancer treatments, it remains an imperfect tool — too many tumors simply do not respond. To the rescue is an evolving class of engineered proteins that go by the unusual name of bispecific antibodies. As their name implies, these proteins have dual recognition capability: They are engineered to home in on a T cell surface receptor as well as bind to the surface antigen of a cancer cell itself. The aim is to bring the two types of cells together and to activate the tumor annihilating capability of T cells.