The drug which has imperilled the lives of six men who took part in a trial to test its safety is one of a new class for which medics have very high hopes.
Scientists insist trials are tightly regulated
TGN 1412, which does not even have a generic name yet, is one of a wave of drugs called monoclonal antibodies.
It is hoped they could combat a wide range diseases, including cancer.
They are created in the lab by fusing or merging a cell that produces antibodies - the foot soldiers of the immune system - with a cancer cell.
The theory is that you end up with a cell that can produce antibodies to fight disease, and which also has the ability of the cancer cell to reproduce endlessly.
Thus, in theory, you get a huge supply of cells producing antibodies for the condition you are trying to target.
Other drugs in the same class include the controversial breast cancer drug Herceptin, and the rheumatoid arthritis treatment Humira.
Most monoclonal antibody treatments are designed to inhibit, or block the action of a specific molecule or process in the body.
However, TGN 1412 works to stimulate activity of T-cells, which regulate the production of the body's own antibodies. This makes it an agonistic monoclonal antibody.
The concern about this approach is that the drug might over-stimulate the immune system, with the result that it might turn in on itself, attacking the body's own tissues.
Some believe it might be inappropriate to test such drugs on healthy volunteers, whose immune systems are already working effectively, as a further boost might push their systems into over-drive.
At this stage, there is no hard evidence to suggest this is what happened in the study that left six men seriously ill. The problem might equally be due to a fault with the manufacturing process, or simply a unique reaction to the drug in humans that could not have been predicted.
Professor David Isenberg, a rheumatologist at University College London, is concerned that the current problem could undermine confidence in monoclonal antibodies.
"If it is seen out of context it could indeed give monoclonal antibodies a very bad name.
"But I want to emphasise that there have been wonderful successes in the fields of cancer, and the fields of inflammatory diseases, particularly arthritis.
"People's lives have been saved, and the quality of people's lives has improved dramatically over the last 25 years, thanks to monoclonal antibodies."
Professor Chris Higgins, director of the Medical Research Council's clinical sciences centre, said the current case was "really tragic".
"On the other hand, we should keep things in perspective. I have never heard of any case like this before, and all those people I have spoken to have also said they have never heard of a case like this before.
"We should not forget about the millions of lives which have been saved, and the enormous amount of pain and suffering that has been alleviated by testing drugs to make sure they are safe. We all use them."
Professor Higgins stressed that all drugs are tested on at least two species of animals before they can be tested on humans.
"Animals are the best models we have for humans, but we all know they aren't absolutely perfect.
"Very occasionally animals do not pick up potential problems.
"But, of course, there are thousands of potential drugs that were tested on animals, and never got to humans because their potential toxicity effects were recognised.
"I should emphasise to everybody who is thinking of volunteering for clinical studies that if we don't undertake such trials under very closely regulated conditions, we won't have new medicines."