It wasn't long ago that Bob Levis was in pain whenever he moved. But a clinical trial to treat his cancer helped save his life. America Tonight

Less than a year ago, Bob Levis was dying. Chronic lymphocytic leukemia raged throughout his 61-year-old body, swelling his lymph nodes and infiltrating his organs. Most dangerous of all, cancerous cells packed his bone marrow, crippling his immune system and preventing the production of red blood cells and their life-sustaining oxygen.

Levis was pale, weak and living from blood transfusion to blood transfusion. Once an avid cyclist and golfer, he now barely had the energy to wheel his garbage to the end of the driveway. Fearful of a potentially lethal infection, he wore a mask anytime he left house. The businessman who had lived and worked throughout Asia stopped traveling altogether, and he avoided malls and children because they might expose him to germs that could kill him.

As 2012 came to a close, Levis hunkered down with his wife, Sue, at their hillside home outside Allentown, Pa., and devoted what little energy he had left to preparing his will. He summed up 2012 as a “pretty dismal year.”

But in January, Levis received a call that would save his life — an invitation to join a clinical trial at the University of Pennsylvania that offered a revolutionary new therapy using HIV to fight leukemia. The trial was reserved for the hopeless cases, people for whom no other treatment was available. Levis became patient 15.