Results that scientists are describing as "unprecedented" in the treatment of cancer have been announced at a conference this week. A team led by Stanley Riddell, a researcher at the Fred Hutchinson Cancer Research Center in the US, have developed a method to reprogramme the immune system to selectively target cancer cells. This means that, unlike traditional chemotherapy, which can't tell healthy and tumour tissue apart - and this is what causes unpleasant side effects - the immune system acts with surgical precision, selectively weeding out rogue cancer cells while leaving healthy tissue untouched. But how does this work, what are the risks and is this the game changer we've all been waiting for? Chris Smith asked Chris Rudd, who's an immunologist at the University of Cambridge where he works on this same approach, for his opinion