The U.S. Food & Drug Administration (FDA) on Wednesday endorsed a first-of-its-kind cancer treatment that makes use of patients’ revved-up immune cells to fight back the deadly disease.

Advisers to the FDA recommended approval of a new experimental cancer treatment called CAR-T therapy for kids with leukemia. The new treatment retrains the patient’s immune system to kill tumor cells.

Oncologic Drugs Advisory Committee member Timothy Cripe, an oncologist with Nationwide Children’s Hospital in Ohio, said the recommendation for the treatment was the most exciting thing she had seen in her lifetime.

However, Dr. Wilson Bryan, who directs the agency’s office that oversees these kinds of treatments, said it would be difficult to standardize.

Commenting on the treatment, Dr. Bryan said, “Particularly, we are concerned that the same safety and benefit seen in clinical trials may not translate into routine use. This is a complex product.”

The recommendation from the federal agency’s Oncologic Drugs Advisory Committee indicates that Novartis’ experimental treatment can be approved by the agency by the end of September this year.