Drugs from new chemical or biological classes being tested in phase I trials—the earliest trials of a new drug in humans—should be tested in only one person at a time, a specialist said after a UK phase I trial resulted in six healthy volunteers becoming severely ill.

The young men were taking part in the first study in humans of TGN1412, a fully humanised monoclonal antibody designed to bind to CD28, a cell surface molecule on T cells which play a role in a variety of cell mediated immune reactions. The drug was being developed for the treatment of autoimmune and inflammatory diseases and leukaemia by a German company, TeGenero.

The six volunteers developed severe reactions within three hours of being given TGN1412 intravenously, while two other men who were given a placebo showed no sign of illness. One of those who was given the placebo told the BBC that the men who became ill reported feeling cold before developing severe headache and swelling of the head and neck. They later developed multiple organ failure and needed intensive care.

Ganesh Suntharalingam, clinical director of intensive care at Northwick Park …