Professor Len Harrison was among the first to characterise the insulin receptor, including its clinical relevance. He inaugurated Australian research into the pathogenesis, pre-clinical diagnosis and prevention of type 1 diabetes (T1D). He discoveries include: mechanisms of pancreatic beta-cell destruction, the primacy of insulin as an autoantigen, protective immune tolerance induced by insulin, T-cell epitopes in pancreatic beta-cell autoantigens; insulin resistance as a risk factor for T1D and the CD52-Siglec system of immune regulation. Following ‘proof-of-concept’ studies in mice, he has conducted a series of trials, currently Phase 2b, of a nasal insulin vaccine to prevent T1D.