This study aims to define the early immune response to MVA85A and is the first to apply a safe, non-radioactive 'label' - deuterium - to measure T-cell turnover following vaccination. This labelling approach has been used successfully by the study collaborators to examine immune cell kinetics in human clinical studies in the UK over the last 8 years. The resulting data will provide insight into the immune response generated by MVA85A and aid in the future design and modification of other T-cell inducing vaccines.