The defined combination of growth factors controls generation of long-term-replicating islet progenitor-like cells from cultures of adult mouse pancreas.

Application of pancreatic islet transplantation to treatment of diabetes is severely hampered by the inadequate islet supply. This problem could in principle be overcome by generating islet cells from adult pancreas in vitro. Although it is possible to obtain replicating cells from cultures of adult pancreas, these cells, when significantly expanded in vitro, progressively lose pancreatic-specific gene expression, including that of a "master" homeobox transcription factor Pdx1. Here we show for the first time that long-term proliferating islet progenitor-like cells (IPLCs) stably expressing high levels of Pdx1 and other genes that control early pancreatic development can be derived from cultures of adult mouse pancreas under serum-free defined culture conditions. Moreover, we show that cells derived thus can be maintained in continuous culture for at least 6 months without any substantial loss of early pancreatic phenotype. Upon growth factor withdrawal, the IPLCs organize into cell clusters and undergo endocrine differentiation of various degrees in a line-dependent manner. We propose that our experimental strategy will provide a framework for developing efficient approaches for ex vivo expansion of islet cell mass.