LA Times describes the procedure:
To build the cancer-attacking cells, the researchers modified a virus to carry instructions for making a molecule that binds with leukemia cells and directs T cells to kill them. Then they drew blood from three patients who suffered from chronic lymphocytic leukemia and infected their T cells with the virus.
When they infused the blood back into the patients, the engineered T cells successfully eradicated cancer cells, multiplied to more than 1,000 times in number and survived for months. They even produced dormant "memory" T cells that might spring back to life if the cancer was to return.
On average, the team calculated, each engineered T cell eradicated at least 1,000 cancer cells.
A year later, two out the three patients are cancer free! This could be the next big cancer breakthrough.