Current progress and emerging technologies for generating extrapancreatic functional insulin-producing cells

Table 1 Summary of target cells and the degree of β-cell similarity

Characteristics	Target cell
	Liver	Pituitary	Muscle	Kidney	Bone marrow
Endodermal origin	+	-	-	-	+
Possession of β-cell transcription factors	-	-	-	-	+
Glucose sensing system	+	-	-	+	-
Processing enzymes	-	+	-	+	-
Glucose-regulatable promoter	+	-	-	+	-
Exocytosis system	-	+	-	+	-
Autologous use	+	+	+	+	+
Allogenic use	-	-	-	-	+

Table 2 The pros and cons of different transplantation sites used for cell delivery in diabetic condition

Transplantation site	Pros	Cons	Ref.
Liver	Ease of transplant, Portal insulin delivery	Portal hypertension, bleeding, portal vein thrombosis, inflammation, portal circulation	Kim et al[77], 2010
Kidney subcapsule	Graft retrieval, immunological tolerance	Not ideal site, invasive procedure, graft tissue oxygen tension	Reece-Smith et al[78], 1981
Spleen	Good vascular supply, portal vein insulin delivery	Rich in lymphocytes, risk of bleeding	Gray[79], 1990; Alderson et al[80], 1984
Pancreas	Home of islets, ideal oxygen tension	Autoimmune destruction, invasive procedure	Stagner et al[81], 2008
Omental pouch	High vascular density, neoangiogenesis, good blood supply, impure islets can be implanted	Large graft unstable, islet cells estimation is empirical	Gustavson et al[82], 2005
Gastro intestinal wall	Ease of accessibility, portal vein delivery of insulin	Thickening of gastric walls after islet cells transplantation	Wszola et al[83], 2009
Bone marrow	Ease of accessibility, no graft rejection	Conserved differentiation into α and β cells	Salazar-Bañuelos et al[84], 2008; Cantarelli et al[85], 2009