December 1st is World AIDS Day. HIV AIDS affects 35 million people worldwide, and although the number of new infections is slowly decreasing, last year it still caused one million deaths. The virus, HIV, attacks the body's immune system by infecting white blood cells, also called "lymphocytes". Lewis Thomson has been finding out what the future holds for treatment, and what it's like to be diagnosed with the virus, and met with Professor Andrew Lever from the University of Cambridge, who researches the virus.