Paul Lehner is a Wellcome Trust Senior Clinical Fellow in Cambridge. He has discovered novel features of the mechanisms by which cells display pathogens to the immune system and the way in which viruses evade these mechanisms. He showed a critical role for a molecule associated with so-called TAP transporters involved in the precise loading of peptides on class I molecules for presentation to cytotoxic T cells. He has extensively studied viral evasion of the MHC class I antigen presentation pathway and identifed two herpes viral gene products that evade MHC class I antigen presentation. He was the first to identify a lumenal inhibitor of an ABC transporter – this is a CMV encoded gene product - and the first to reveal a viral product that subverts trafficking of a human protein by ubiquitylation. His work has significant implications for immunisation strategies against viruses.