Mesenchymal cells appearing in pancreatic tissue culture are bone marrow-derived stem cells with the capacity to improve transplanted islet function.

Adherent fibroblast-like cells have been reported to appear in cultures of human endocrine or exocrine pancreatic tissue during attempts to differentiate human beta cells from pancreatic precursors. A thorough characterization of these mesenchymal cells has not yet been completed, and there are no conclusive data about their origin.We demonstrated that the human mesenchymal cells outgrowing from cultured human pancreatic endocrine or exocrine tissue are pancreatic mesenchymal stem cells (pMSC) that propagate from contaminating pMSC. The origin of pMSC is partly extrapancreatic both in humans and mice, and by using green fluorescent protein (GFP(+)) bone marrow transplantation in the mouse model, we were able to demonstrate that these cells derive from the CD45(+) component of bone marrow. The pMSC express negligible levels of islet-specific genes both in basal conditions and after serum deprivation or exogenous growth factor exposure, and might not represent optimal candidates for generation of physiologically competent beta-cells. On the other hand, when cotransplanted with a minimal pancreatic islet mass, pMSC facilitate the restoration of normoglycemia and the neovascularization of the graft. These results suggest that pMSCs could exert an indirect role of "helper" cells in tissue repair processes.