Best known as the co-discoverer of HIV, French scientist Françoise Barré-Sinoussi, MD, PhD, told CNN that a cure for HIV “is almost an impossible mission.”

Why? “Because the reservoir of cells is not only in the blood,” the Nobel Prize winner explained. “How to eliminate all the cells which are reservoirs is why I say it’s an impossible mission. They are everywhere—in the gut, in the brain, in all the lymphoid tissue.

“Even if you have a very efficient strategy,” she continued, “how you can make sure that there’s not one or two cells still there and if one is there the virus will reappear again? That’s why I say it’s an impossible mission. But you never know.”

She was speaking about a sterilizing cure, which is when the virus is completely eradicated. This compares with a functional cure, in which the virus is under control without meds.

When asked about a functional cure, Barré-Sinoussi said, “I prefer to say remission (when the virus is brought down to low levels in the body) … That’s possible. I’m convinced one day—I don’t know when—we will have a strategy to induce durable remission. I don’t believe that we will have only one treatment. It will be a combination of treatments. (But) we need both—a cure and a vaccine.”

Barré-Sinoussi spoke with CNN during the 8th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention in Vancouver, British Columbia. She is a former president of the IAS, and she is also retiring next month because “in my country it’s mandatory to retire.”

For the complete POZ coverage of IAS 2015, click here.