Cancer researchers are claiming “extraordinary” success in a new breakthrough therapy that involves engineering immune cells to target a specific type of blood cancer.

In clinical trials involving several dozen patients given only had months to live, researchers we able to use the immune system’s T-cells to eliminate the cancer, The Guardian reports.

In one study, 94 percent of the patients with acute lymphoblastic leukaemia (ALL) had their symptoms disappear. About 80 percent of patients with other blood cancers benefitted from the new therapy, 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  researcher Stanley Riddell, speaking at the annual meeting for the American Association for the Advancement for Science (AAAS).

T-cell therapy involves removing immune cells from patients, engineering  them target a specific cancer, as other T-cells target the flu or infections, then infusing the cells back in the body.

“There are reasons to be optimistic, there are reasons to be pessimistic,” said Riddell, of the Fred Hutchinson Cancer Research Center in Washington state. “These 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.”