With Professor Paul Klenerman Principal Investigator, Institute for Emerging Infections. Paul Klenerman demonstrates the way our immune systems work and discusses the best way to boost our natural defences in an effort to fight infection from Hep C and HIV. Dr Bennett Foddy, Deputy Director, Institute for Science and Ethics, addresses the ethical dilemmas which can arise from the process of clinical trials. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/