An astounding 93 percent of patients with advanced leukemia that was resistant to multiple other forms of therapy went into admission after their T-cells were genetically engineered to fight their cancers.

Researchers at Fred Hutchinson Cancer Research Center worked with the University of Washington Cancer Consortium to enroll patients with B-cell acute lymphoblastic leukemia. All of the patients had advanced disease that had relapsed and were immune to other therapies.

The patients received genetically engineered versions of their own T-cells — disease-fighting immune cells — with a synthetic receptor molecule called a CAR (chimeric antigen receptor) that allows T-cells to recognize and kill cancer cells that carry a specific marker called CD19.

T-cells were extracted from patients, and a specialized virus delivered the DNA instructions for making the CAR into the cells. Then, the cells were multiplied to the billions in the lab.

After chemotherapy, the reengineered cells were infused back into the patients they came from about two weeks after they were first extracted.

A few weeks after the infusion, highly sensitive tests could find no trace of cancer in the bone marrow of 27 of 29 patients.  CAR T-cells eliminated cancers anywhere in the body they appeared.

Of the two participants who did not go into complete remission, one eventually reenrolled in the trial and went into complete remission after receiving a higher dose of cells.

Not all patients stayed in complete remission: Some relapsed and were treated again with CAR T-cells, and two relapsed with leukemias that were immune to the CAR T-cells.

Researchers say it is too early to know the long-term outcomes of the cell therapy.

"Patients who come onto the trial have really limited options for treatment," said study leader Dr. Cameron Turtle. "They have refractory, acute leukemia. So the fact that we're getting so many into remission is giving these people a way forward."

"In early-phase trials, you're continually learning," said senior author Dr. David Maloney. "You don't expect results like these from early-phase trials. That's why these response rates are so extraordinary."

"This is just the beginning," said Turtle. "It sounds fantastic to say that we get over 90 percent remissions, but there's so much more work to do make sure they're durable remissions, to work out who's going to benefit the most, and extend this work to other diseases."