Six men were in a London hospital's intensive care unit after participating in trials of a new drug that were immediately suspended as Britain's health watchdog launched an investigation. The men, who were all healthy, paid volunteers, were admitted to the Northwick Park hospital in northwest London on Tuesday night, a hospital spokeswoman said.
Two of the men were in a "critical condition" while the other four were "serious but stable" in intensive care, she said. The BBC reported that they had suffered multiple organ failure.
The health watchdog Medicines and Healthcare products Regulatory Agency (MHRA) said it halted the trial of the drug, intended to treat immunological diseases such as multiple sclerosis, rheumatoid arthritis and certain cancers.
The watchdog sent in inspectors and sounded an international alert, warning other European regulatory bodies of the problem.
One other European country is thought to be carrying out trials of the drug, the Press Association news agency said.
Britain's Health Secretary Patricia Hewitt branded the incident a "shocking event" and said her thoughts were with "those young people and with their families."
She added that the police had been involved.
The men had taken the drug at an independent medical research unit operated by Parexel, a US drug research company, on the Northwick Park campus.
German biopharmaceutical company TeGenero AG said the clinical trials were of their drug TGN1412.
Doctor Benedikte Hatz, TeGenero's Chief Executive Officer, said the adverse reactions were completely unexpected.
They "do not reflect the results we obtained from initial laboratory studies which enabled us to progress investigations into human volunteers," he said in a statement on the company's website.
They described TGN1412 as an immunomodulatory humanised agonistic anti-CD28 monoclonal antibody.
Such an adverse reaction to a drug being tested on humans for the first time -- called phase one -- is very rare.
Richard Ley, spokesman for the Association of the British Pharmaceutical Industry, said: "This is an absolutely exceptional occurrence. I cannot remember anything comparable."
New drugs are first tested on animals before being tried out on a small number of humans.
"Phase one trials use healthy volunteers and are designed to test the safety of the drug. These go on to further tests with people who have the condition to determine whether the drug works," Ley explained.
Professor Herman Scholtz, from Parexel, said: "When the adverse drug reaction occurred, the Parexel clinical pharmacology medical team responded swiftly to stop the study procedures immediately."
He insisted Parexel had acted within regulatory, medical and clinical research guidelines during the study.
"We use standardised procedures for testing a drug in humans for the first time, based on a well-defined protocol, designed by the sponsor company and approved by ethics committees and regulatory authorities," he said.
Each year, thousands of people in Britain sign up for medical trials and are generally well paid for volunteering.
The Sun newspaper named one victim as student Ryan Flanagan, 21, of Highbury, north London.
Family friend Sarah Brown, 27, told the daily: "Ryan was a healthy young man and he saw the trial advertised on the Internet.
"He is at college and was doing it to make a bit of extra money.
"He told us he would be paid 2,000 pounds (2,900 euros, 3,500 dollars) and did not think there would be any problems.
"His mother got a call to say his head and neck were swelling up and his legs were purple."
