University of Pennsylvania doctors say they cured two men of leukemia with a gene therapy that transforms a patient's own cells into cancer killers.

A decade after they were treated, doctors couldn't find any sign of cancer in their bodies.

Researchers described the two cases in a study published Wednesday in the journal Nature.

They say the two examples show the gene therapy treatment can attack cancer immediately, then stay inside the body for years and keep the disease at bay.

"We can now conclude that CAR-T cells can actually cure patients with leukemia," said Dr. Carl June, a cancer immunologist at the University of Pennsylvania and one of the study's authors.

According to Axios, the treatment involves collecting a person's T-cells from the blood and modifying them to include a receptor that targets and kills cancerous cells.

T-cells are a type of white blood cell that's essential to the body's immune response.

Thousands around the world now use the one-time treatment to treat certain blood cancers.

While the treatment has been shown to be effective, concerns still linger about the high costs — something health experts hope will come down as it becomes more accessible.