TGN1412 drug molecule. Computer model showing the secondary structure of the drug TGN1412. This drug was shown to have serious side effects during a clinical trial in the UK in 2006 when it caused systemic failure in 6 volunteers. The drug is a monoclonal antibody that activates T cells by binding to CD28 receptors on the cell's surface. T cells are a type of white blood cell and a component of the body's immune system.