Six men have been admitted to the intensive care unit of a North London hospital after suffering a severe reaction to an antibody administered in a Phase I clinical trial.

The men had volunteered for a study of a compound called TGN1412, in development by German biotechnology company TeGenero as a treatment for chronic inflammatory diseases and leukaemia. Shortly after being dosed with the drug, the men experienced multi-organ failure and two are said to be critically ill. Two other men who received placebo were unharmed.

The trial was being conducted by contract clinical research organisation (CRO) Parexel, which owns and operates the dedicated clinical research facility unit at the Northwick Park Hospital where the trial took place.

“It is assumed that the adverse affects were based on a drug reaction," said Prof Herman Scholtz, head of Parexel International clinical pharmacology, in a statement. "Such an adverse drug reaction occurs extremely rarely and this is an unfortunate and unusual situation."

The UK Medicine and Healthcare products Regulatory Agency (MHRA) has sent inspectors into the unit to investigate the trial, and other regulatory bodies in Europe have been warned about the dangers with TGN1412 to prevent any trials getting underway overseas.

“Our immediate priority has been to ensure that no further patients are harmed,” said Prof Kent Woods, chief executive of the MHRA. “We will now undertake an exhaustive investigation to determine the cause and ensure all appropriate actions are taken.”

TGN1412 is a humanised monoclonal antibody targeted at the CD28 receptor, and has already been granted orphan status by the European Medicines Agency for treating B cell chronic lymphomatous leukaemia (B-CLL).