London: Scientists claim to have developed "serial killer" cells that can wipe out leukaemia within three weeks, a breakthrough they say could lead to new and effective treatments for the fatal blood cancer.

Researchers at the University of Pennsylvania's Abramson Cancer Centre in the US engineered a technique that involved leukaemia patients being treated with their own T cells – a type of white blood cell -- that have been genetically modified to attack and destroy tumours within their bodies.

The treatment, according to the researchers, was so powerful that tumours were "blown away" in under a month with few side effects, a news paper reported.

After removing the patient's T cells, the researchers reprogrammed them to attack tumours by binding to a protein expressed by cancerous cells.

In most forms of cancer these crucial cells are unable to distinguish tumour cells from healthy tissue, which allows the cancer to spread unchecked.

But they managed to reprogramme them to attack tumour cells by inserting a "secret ingredient" -- a protein called a Chimeric Antigen Receptor (CAR).

When this protein is on the surface of the T cells, it will bind with another protein, called CD19, which is found in leukaemia tumour cells.

By doing this it not only kills the cancer cells, but causes other T cells to rapidly multiply so they can attack the tumour too.

Professor Carl June, senior author of the study, said: "The infused T cells are serial killers. On average each fused T cell led to the killing of thousands of tumour cells – and overall, destroyed at least two pounds [one kilo] of tumour in each patient.

"We saw at least a 1000-fold increase in the number of modified T cells, which is unprecedented, and it happened in each of the patients. Drugs don't do that.

"Within three weeks the tumours had been blown away, in a way that was much more violent than we ever expected." The study, published in the Journal of Medicine and Science Translational Medicine, showed that side effects of this process were not as bad as chemotherapy because the CAR only targeted tumour cells and B cells rather than all normal tissue.

The treatment was trialled on three patients suffering from chronic lymphocytic leukaemia, which affects the blood and bone marrow and is the most common form of leukaemia.

It can be managed with chemotherapy but only be cured by a bone marrow transplant, which carries a one in five risk of dying while only offering a 50/50 chance of success.

Gene transfer therapy using T cells has been a holy grail of treatment for various cancers over the past 25 years but has proved very difficult to achieve in human trials.

The researchers said their success in activating the T cells, making them multiply and then kill the cancer cells in this type of cancer, is "unprecedented".

The team now hopes to test the same treat in children with leukaemia and patients with non-Hodgkins lymphoma.

Dr David Porter, who co-authored the study, said: "Most of what I do is treat patients with no other options, with a very, very risky therapy with the intent to cure them.

"This approach has the potential to do the same thing, but in a safer manner. This massive killing of tumour is a direct proof of principle of the concept."