Contemporary science and technology policy is concerned with improving the diffusion of knowledge from basic science into the clinic. Nowhere is this more apparent than in the emerging field of Regenerative Medicine. In this paper we critically explore the changing relationships between the bench and the bedside through the development of haematopoietic stem cells (HSCs). In the history of HSCs over a 50-year period, the relationship between basic science and clinical research communities has been based on a two-way flow of knowledge; clinical innovation has played a key role in the translation process. Concepts from the sociology of expectations illuminate the 'communities of promise' which are formed around such emerging technologies. From this case study, we challenge assumptions underpinning many contemporary policy initiatives.