The findings yesterday suggested that the drug TGN1412 caused an unprecedented and unexpected reaction that did not occur in tests on animals.

Uncertainty over the entire class of drugs similar to TGN1412— monoclonal antibodies — will remain until the chemical trigger that caused the adverse reactions is identified.

Most of these drugs alter the behaviour of the human immune system and are used to treat many diseases, including cancer and arthritis.

Kent Woods, chief executive of the Medicines and Healthcare products Regulatory Agency (MHRA), said yesterday that future trial applications for biological agents would be subject to new levels of scrutiny.

They will now be seen by the Commission on Human Medicines as well as the MHRA, with further external experts brought in ad hoc should any doubts remain.

About 10 per cent of the 360 phase 1 trials each year are likely to be affected. The MHRA said that the 40 monoclonal antibody trials accepted since May 2004 had been reviewed to assuage any other concerns.

Professor Woods said that the interim report raised questions about the potential risk involved in human trials, particularly the new “superagonistic” class of monoclonal antibodies, such as TGN1412, which work by stimulating action affecting cells in the immune system. Many monoclonal antibodies work by blocking immune actions, rather than encouraging them. “In this case the resulting activity seen in humans was not predicted from apparently adequate pre-clinical testing,” Professor Woods said. “This is a complex scientific issue which raises important scientific and medical questions about the potential risks associated with this type of drug and how to make the transition from pre-clinical testing to trials in humans.”

A working group is also being set up by the Government to examine the transition from animal tests to studies in humans involving biological agents with novel actions. It will look at how trials can be conducted using new drugs that have a “highly speciesspecific action”, drugs that are directed towards the immune system and the broader science surrounding monoclonal antibody treatment.

Gordon Duff, Professor of Molecular Medicine at Sheffield University, will head the group, which will also include international experts. Professor Duff is the chairman of the Commission on Human Medicines and the National Biological Standards Board and a former chairman of the Committee on Safety of Medicines.

His group is expected to give its initial findings to Patricia Hewitt, the Health Secretary, within three months, but no date is scheduled for its final conclusions. These would form the basis of a further refinement of drug trial protocols, Professor Woods said.

The MHRA said that it could not be firm about its findings and further tests were planned, but it appeared that the Northwick Park drug did not contain “anything other than the correct ingredients”.

Six men were taken into intensive care with multiple organ failure hours after being injected with the drug, which was designed to treat chronic inflammatory conditions and leukaemia. The trial was run by Parexel, a pharmaceutical research company, on behalf of TeGenero, a German company that designed the drug.The MHRA chief executive rejected suggestions that his agency should not have allowed the trial to go ahead with a protocol that involved the testing of six healthy volunteers in quick succession.

A paper from the Academy of Medical Sciences, published yesterday, questioned the practice and said that it would be usual “to administer a single dose in a single patient, who would then be observed for an appropriate period of time”.

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