In one study, 94 per cent of participants with acute lymphoblastic leukaemia (ALL) saw their symptoms vanish completely.
Patients with other blood cancers saw response rates greater than 80 per cent, with more than half experiencing complete remission.
The technique involves removing immune cells called T-cells from patients, tagging them with “receptor” molecules that target cancer, and infusing them back in the body.
Scientists screened specially bred genetically engineered mice for the targeting molecules, known as chimeric antigen receptors or Cars.
Once attached to the T-cells, they reduce the chances of the cancer being able to shield itself from the immune system.
Lead scientist Professor Stanley Riddell, from the Fred Hutchinson Cancer Research Centre in Seattle, US, said: “These [results] are in patients that have failed everything. Most of the patients in our trial would be projected to have two to five months to live.
“This is extraordinary. This is unprecedented in medicine to be honest, to get response rates in this range in these very advanced patients.”
Prof Riddell, who was speaking at the American Association for the Advancement of Science annual meeting in Washington DC, described the results as a “potential paradigm shift” in cancer treatment. But he acknowledged that much more work had to be done, and it was not clear how long the symptom-free patients would remain in remission.
So far, the technique has only been tried on patients with “liquid” blood cancers. Prof Riddell hopes to progress to patients with solid tumours, but says that this will be challenging.
Although the immune system is geared to combat cancer, very often it fails in the task. Cancer cells are not recognised by the body’s defences, or find ingenious ways to mask their identity.
In the most promising study, around 35 patients with ALL were treated with Cars-modified T-cells. Almost all – 94 per cent – experienced complete remission, meaning their symptoms disappeared.
That is not the same as saying they were cured, because the symptoms could return.
More than 40 patients with lymphoma have also been treated. Remission rates of more than 50 per cent and response rates of more than 80 per cent were seen in one group with non-Hodgkinson’s lymphoma.
Patients with chronic lymphocyte leukaemia showed similar results.
“We have a long way to go,” said Prof Riddell. “The response is not always durable, some of these patients do relapse, we are cognisant of that. But the early data is unprecedented.”