Pigs to help us with diabetes

                                                                                         

Given the current practical limitations of glucose monitoring and insulin delivery systems, in addition to the current shortage of cadaveric organs, an alternative source of cells that can sense blood glucose levels and respond by releasing appropriate amounts of mature insulin must be identified to turn the promise of cellular therapy for diabetes into a reality for all those who would benefit.

Xenogeneic cells are a potential source of cells for transplantation therapy. Because pigs regulate glucose in a similar physiological range to that of humans, and because porcine insulin has been used as an exogenous source of insulin, pigs are generally considered the most promising donor animal. However, islets form xenogeneic pancreata are more immunogenic than allogeneic islets. Islets or islet precursors from porcine and bovine sources have been encapsulated in various biomaterials in order to reduce the immune rejection. Recently, pigs have been genetically engineered to lack a specific cell surface molecule that triggers hyperacute rejection due to preformed antibodies. However, there is experimental evidence that Gal is not the only epitope recognised by preformed xenoreactive antibodies. An additional concern with xenografted tissue is the transmission of infectious agents into humans.
Porcine endogenous retrovirus transmission has been a focus of several conflicting studies. Some studies report no transmission following transplantation of living porcine tissue into human patients and no evidence of transmission when porcine islets are co-incubated with permissive human stem cells in vitro. Contrary to these reports, porcine endogenous retrovirus transmission was frequently observed between cultured porcine endogenous retrovirus-producing porcine cells or specific pathogen-free porcine islets and human or mouse cells in vivo. Transmission of porcine cytomegalovirus and lymphotropic herpesvirus is also of concern.

Stem cells offer a potential solution to the opposed requirements of cell proliferation and function. In theory, these cells can proliferate in an undifferentiated state and then be converted to take on required metabolic functions through genetic and epigenetic manipulations. Stem cells have been isolated from embryonic tissues as well as a variety of fetal and adult sources, including umbilical cord blood, bone marrow, central nervous system, liver and pancreas. One potential advantage of adult stem cells is that they could be used for autologous transplantation.

About the author:
Wayne Channon, Director of Cells4Life Ltd, a stem cells and cord blood storage expert. They specialize in umbilical cord blood collection .

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