Trials last year in America of a similar “monoclonal antibody” caused severe toxic reactions in patients. But the UK study went ahead after the regulatory authority failed to consult outside specialists who would have warned against proceeding.

Angus Dalgleish, a world expert on immunology, said yesterday that he was amazed the trial had been allowed to proceed. “The previous studies which caused similar severe side effects were in patients already suffering from cancer, but [the researchers] should have known they would get a meltdown because this drug was hitting exactly the same immune response pathways,” said Dalgleish, a professor of cancer at St George’s hospital medical school, south London.

Last week six healthy young male volunteers, who were to be paid £2,000 for the trial, suffered catastrophic side effects within minutes of receiving an experimental drug called TGN1412, which was being tested as a potential treatment for leukaemia, rheumatoid arthritis and multiple sclerosis.

Yesterday two of those given the drug remained in a coma at Northwick Park hospital, northwest London. The other four had regained consciousness.

Dalgleish said the Medicines and Healthcare Products Regulatory Agency (MHRA), which approves such trials, should have consulted a specialist before approving the study. “I can’t understand it. They are normally super-cautious. I would have told the people doing this trial not to do it because the dangers were so great,” he said.

Dalgleish also criticised the way the drug was administered at the start of the study. “I am amazed they gave it to six people at once instead of waiting to observe the effects in one of them.”

The data that should have raised the alarm were presented at a meeting of the American Society of Clinical Oncology last May. Dalgleish said an engineered antibody, developed by a team led by Steven Rosenberg at America’s National Cancer Institute, and using the same pathway as TGN1412 had produced severe side effects in about half of a group of patients dying of cancer.

The MHRA defended its decision, saying: “We have [since] given the trial protocol to a new set of assessors and they came to the same conclusions. There was nothing wrong with it.”

Parexel, the American firm contracted to run the human trials for the drug firm TeGenero, said: “We believe that best practices were followed and the appropriate policies and procedures were adhered to.”

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