is being tested as an anti-rejection medication for use in renal transplantation. A new co-stimulatory superagonistic drug, TGN1412, was the subject of a clinical trial at Northwick Park Hospital, London. The trial became surrounded in controversy as the six volunteers became seriously ill within minutes of being given the drug. In essence, the co-stimulatory molecules function as "flashing red lights" that interact with the T cell, communicating that the material being presented by the dendritic cell material indicates danger. Dendritic cells displaying co-stimulatory molecules while presenting antigen are able to activate T cells. In contrast, T cells that recognize antigen presented by a dendritic cell not displaying co-stimulatory molecules are generally driven to apoptosis, or may become unresponsive to future encounters with the antigen. References Immunology