In one trial, 94 percent of patients with acute lymphoblastic leukaemia (ALL) went into complete remission. Patients with other blood cancers had response rates greater than 80 percent, and more than half experienced complete remission.
'This is unprecedented in medicine, to be honest, to get response rates in this range in these very advanced patients,' said Dr Stanley Riddell of the Fred Hutchinson Cancer Research Center in Seattle, who presented the findings at the American Association for the Advancement of Science's annual meeting.
The therapy involves removing T cells – a type of white blood cell – from patients and genetically modifying them to express a type of synthetic receptor that allows them to target specific cancerous cells. Patients then undergo chemotherapy to deplete their existing T cells, after which the engineered cells are infused back into the body.
'Essentially what this process does is it genetically reprogrammes the T cell to seek out and recognise and destroy the patient's tumour cells,' Dr Riddell told BBC News.
In his team's research, 27 of 29 patients with ALL showed no trace of cancer in their bone marrow following the infusions, and 19 out of 30 non-Hodgkin's lymphoma patients experienced partial or complete responses.
He added: '[The patients] were really at the end of the line in terms of treatment options, and yet a single dose of this therapy put more than 90 percent of these patients in complete remission, where we can't detect any of these leukaemia cells.'
T cell therapy is considered as a last resort because reprogramming the immune system can cause serious side effects that can result in patients needing intensive care, and sometimes causes death.
In the ALL studies, the researchers selected specific subsets of T cells with the greatest potential for proliferation within the body. This allowed them to lower the doses given in an attempt to reduce side effects while maintaining efficacy.
Overall, 20 patients suffered symptoms of fever, hypotension and neurotoxicity, and two died, but the scientists noted that chemotherapy had previously failed in all of them.
T-cell therapy works best on tumours of the blood and bone marrow, which are known as 'liquid tumours'. Until now, the trials have only targeted certain blood cancers, and the scientists say in future research will need to explore if it could be used on solid tumours. They will also need to track how long patients remain in remission.
Dr Alan Worsley of Cancer Research UK was quite reserved in his assessment of the findings. Speaking to BBC News, he described the research as a 'baby step'.
'We've been working for a while using this type of technology, genetically engineering cells. So far it's really shown some promise in this type of blood cancer,' said Dr Worsley.
He added: 'The real challenge now is how do we get this to work for other cancers, how do we get it to work for what's known as solid cancers, cancers in the tissue.'
The findings have not yet appeared in a scientific journal, but an article on the ALL research is currently under review and pending publication.