GCG and pancreatic insulinoma: PIs created with heterotypic co-cultures of insulinoma cell lines and accessory cells such as endothelial [7,16,22], stellate [49], neuroblastoma [50], glucagon- and somatostatin secreting [51] as well as GLP-1 releasing [18] or mesenchymal stem cells [52] have also been explored to provide the added benefit of restoring transformed insulinomas to resemble primary islets.