Alternative triggering molecules and single chain bispecific antibodies.

Although T cell receptors and Fc receptors are the best known cytotoxic triggering molecules, a number of adhesion molecules recently have been identified as alternative triggering molecules. We discuss how CD44, an adhesion molecule found on all leukocytes and many other cell types, becomes a triggering molecule on NK cells following stimulation with IL-2. We also describe a genetically engineered single chain bispecific antibody, produced in mammalian cells and in bacteria, that is capable of redirecting lysis in the nanogram per milliliter range.