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Stem cell sources for clinical islet transplantation in type 1 diabetes: Embryonic and adult stem cells
Medical Hypotheses (2006) 67, 909–913
http://intl.elsevierhealth.com/journals/mehy
Stem cell sources for clinical islet transplantation in type 1 diabetes: Embryonic and adult stem cells Helena Miszta-Lane b,1, Mohammadreza Mirbolooki A.M. James Shapiro a,b, Jonathan R.T. Lakey a,b,*
a,b,1
,
a
Clinical Islet Transplantation Program, Department of Surgery, Faculty of Medicine and Dentistry, University of Alberta, 1074 Dentistry/Pharmacy Centre, Edmonton, Alta., Canada T6G 2N8 b Surgical-Medical Research Institute, Department of Surgery, Faculty of Medicine and Dentistry, University of Alberta, 1074 Dentistry/Pharmacy Centre, Edmonton, Alta., Canada T6G 2N8 Received 26 March 2006; accepted 29 March 2006
Summary Lifelong immunosuppressive therapy and inadequate sources of transplantable islets have led the islet transplantation benefits to less than 0.5% of type 1 diabetics. Whereas the potential risk of infection by animal endogenous viruses limits the uses of islet xeno-transplantation, deriving islets from stem cells seems to be able to overcome the current problems of islet shortages and immune compatibility. Both embryonic (derived from the inner cell mass of blastocysts) and adult stem cells (derived from adult tissues) have shown controversial results in secreting insulin in vitro and normalizing hyperglycemia in vivo. ESCs research is thought to have much greater developmental potential than adult stem cells; however it is still in the basic research phase. Existing ESC lines are not believed to be identical or ideal for generating islets or b-cells and additional ESC lines have to be established. Research with ESCs derived from humans is controversial because it requires the destruction of a human embryo and/or therapeutic cloning, which some believe is a slippery slope to reproductive cloning. On the other hand, adult stem cells are already in some degree specialized, recipients may receive their own stem cells. They are flexible but they have shown mixed degree of availability. Adult stem cells are not pluripotent. They may not exist for all organs. They are difficult to purify and they cannot be maintained well outside the body. In order to draw the future avenues in this field, existent discrepancies between the results need to be clarified. In this study, we will review the different aspects and challenges of using embryonic or adult stem cells in clinical islet transplantation for the treatment of type 1 diabetes. c 2006 Elsevier Ltd. All rights reserved.
Introduction * Corresponding author. Tel.: +1 780 492 4660; fax: +1 780 492 6335. E-mail addresses: [email protected], jlakey@ ualberta.ca (J.R.T. Lakey). 1 These authors contributed equally to this study.
Type 1 diabetes, insulin-dependent diabetes mellitus (IDDM), is an autoimmune disease caused by the progressive destruction of the insulin secreting bcells in the islets of Langerhans [1]. The discovery of insulin by Banting and Best in 1922 changed
0306-9877/$ - see front matter c 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mehy.2006.03.036
910 diabetes from a fatal disease to a chronic illness with intolerable co-morbidities and premature death. It is well known that even aggressive insulin therapy will never re-create the real-time variation of blood glucose. Furthermore, the effects of chronic hyperglycemia and peripheral hyperinsulinemia are believed to accelerate diabetic microangiopathy. That is why, b-cell replacement has been assumed to be the only treatment that reestablishes and maintains long-term glucose homeostasis with near-perfect feedback controls [2]. Transplanting extracts of pancreas in patients with diabetes was firstly performed over 100 years ago [3]; however, hastened progresses, and improved understanding of the issues that face clinical islet transplantation during the last 30 years have led this simple concept to a successful treatment for diabetes. Islet transplantation involves the isolation of islets of Langerhans from the pancreas of cadaver organ donors through complex digestion and purification processes and transplanting them into recipient’s liver. It results in near-perfect, moment-to-moment control of blood glucose, far more effectively than injected insulin. The hope is that, with tighter glucose control, the long-term complications of diabetes could be avoided. The ‘‘Edmonton Protocol’’ [4], a glucocorticoidfree immunosuppression regimen, combined with an optimal islet engraftment mass was an impressive departure from previous attempts. The Edmonton Protocol has been successfully replicated in more than 50 centers worldwide, with cumulative data from more than 500 patients. This represents a significant goal, as more patients with type 1 diabetes have now received islet implants in the past 6 years than in the entire former 30-year history of islet transplantation. However, lifelong immunosuppressive therapy and inadequate sources of transplantable islets have led the islet transplantation benefits to less than 0.5% of type 1 diabetics. It is required to find alternative sources of insulin-producing, glucose-responsive tissue to treat more than 175 million children and adult diabetics worldwide [5]. Whereas the potential risk of infection by animal endogenous viruses limits the uses of islet xeno-transplantation, deriving islets from stem cells seems to be able to overcome the current problems of islet shortages and immune compatibility. Stem cells are known as clonogenic. They have the ability to self-renew (produce identical daughter cells) and multilineage differentiation (produce daughters that are fated to differentiate) [6]. Both embryonic (derived from the inner cell mass of blastocysts) and adult stem cells (derived from
Miszta-Lane et al. Table 1 The definition of cell types as a potential source of b-cells Source of stem cells
Definition of terms
Embryonic stem cells (ESC)
Highly pluripotent stem cell with highest proliferation ability, initially derived from a blastocyst Highly pluripotent stem cells, with high proliferation ability, initially derived from the gonadal region of aborted human fetuses Derived from teratocarcinoma tissue, ESC and EGC are diploid, genetically normal, but ECC are commonly aneuploid Adult bone-marrow stem cells, giving rise to cells of the supportive marrow structure The islet stem/progenitor cells within pancreatic-ducts, from where they regenerate, differentiate and migrate to form new islets both during organogenesis and in regeneration Liver developed from endoderm during organogenesis
Embryonic germ cells (EGC)
Embryonic carcinoma cells (ECC) Mesenchymal stem cells Fetal, duct and adult pancreas stem cells
Liver stem cells
adult tissues) have shown controversial results in secreting insulin in vitro and normalizing hyperglycemia in vivo. Table 1 describes the different cell types as a potential source of b-cells. In order to draw the future avenues in this field, existent discrepancies between the results need to be clarified. In this study, we will review the different aspects and challenges of using embryonic and adult stem cells in clinical islet transplantation for the treatment of type 1 diabetes to make it clear if both resources of stem cells should be searched or one of them is prior to the other one.
Embryonic stem cells (ESCs) The most remarkable characteristic of ESCs is their potential ability to differentiate into every type of adult cell [7]. They are able to be differentiated into insulin-producing cells in culture conditions, as well. ESC-derived insulin-expressing islet-like structures were firstly reported by Lumelsky et al. They showed clusters with insulin positive cells located in the centre and surrounded by neurons. They found that majority of glucagon and somato-
Stem cell sources for clinical islet transplantation in type 1 diabetes statin positive cells surround the insulin positive cells. These cells showed intracellular insulin content of about 50-fold lower than that of normal pancreatic b-cells, and they were not able to reverse hyperglycemia in diabetic mice [8]. There is a report showing that insulin content in ESCs derived cultures may result from insulin uptake from the culture medium, rather than from endogenous synthesis [9], however transplantation of ESCs derived insulin-producing cells has reversed diabetes in animals [10], indicating that these cells do synthesis and release insulin. It has been also reported that genetically altered ESCs for insulin expression when injected into diabetic rats, improve glucose control [11]. It seems that regulated expression of transcription factors might be the reason for this discrepancy [12]. Schuldiner et al. [13] showed that both undifferentiated human embryonic stem cells and differentiated embryoid bodies expressed receptors for a number of different soluble growth factors with established effects on developmental pathways in vivo. The addition of phosphoinositide kinase inhibitors promoted differentiation of large number of ESCs towards functional b-cells [10]. According to Wells [14], embryonic development of the pancreas shares similarities with islet regeneration. In both processes, multipotent endocrine progenitor cells contained within a duct-like tube respond to signals by delaminating from the ducts, where they proliferate, differentiate, and form the islets. There are also similarities between islet regeneration and embryonic pancreas development at the gene expression level. A number of putative markers [15] transiently expressed in embryonic ducts have been suggested as indicator of islet progenitor cells. ESCs express high levels of telomerase, as well. The expression of telomerase, a ribonucleoprotein that adds telomere repeats to chromosome ends, thereby maintaining their length correlates strongly with immortality in human embryonic cell lines [16]. Therefore, problems in control of differentiation and tumorogenesity of ESC-derived insulin-producing cells remain to be overcome [17]. The number of undifferentiated ESCs exists in the graft, their ability to proliferate in an uncontrolled fashion, the number of transplanted cells, immunological rejection and the immunocompetence of the host are of important factors affecting the final outcome of ESC-derived establishments. The ability of the grafted cells to ‘‘integrate’’ with the host tissue is of the other important factors. This phenomenon may possibly rely on spontaneous fusion of the ESCs with host tissue-specific cells [18]. While undeniable evidence that true b-cells can be created in vitro from ESCs is still controver-
911
sial; ethical concerns about the use of ESCs need to be addressed and resolved.
Adult stem cells It was previously believed that stem cells are vanished soon after birth, but researches, have revealed that they exist in the adult tissues, as well. It was also believed that each of these cells could produce just one particular type of cell, however in the past few years; evidences have been issued of stem cells that have an extraordinary flexibility to be transdifferentiated into other cell types. Human adult stem cells have been transdifferentiated into insulin-producing cells [19], and could normalize hyperglycemia in streptozotocininduced diabetic mice [20], however they are in minimal quantity, their life period has limitation, and they may be already genetically altered. Their proliferation capacity is low as compared to that of ESCs; however, proliferation could be extended by genetic manipulation in tissue culture (e.g., expression of a telomerase gene). In bone-marrow, commonly used as a source of adult stem cells, the detection of cells with the properties of self-birth and multi-pedigree differentiation potential is fairly advanced [21]. Bonemarrow cells are differentiated into other types of cells in vitro and under controlled conditions [22]. Bone-marrow contains hematopoietic and mesenchymal stem cells. Mesenchymal stem cells are capable of differentiating into a number of different kinds of cells such as pancreatic b-cells [23]. Experiments on diabetic mice with totally destroyed b-cells by streptozocin show that after bone-marrow transplantation, blood glucose is normal, and survival is better [20]. These studies show the possibility of bone-marrow transplantation as a therapeutic approach for b-cell replacement; however the newly regenerated b-cells destroyed by the host immune system. While the immune destruction is a problem in bone-marrow transplantation, transplanting splenic mesenchymal cells show promising results in both pancreatic b-cells regeneration and immune destruction prevention [24]. Other sources of adult stem cells are liver and pancreas. Hepatic stem cells have the ability of being differentiated into insulin-secreting cell and expressed b-cell-specific genes in vitro and when transplanted, these cells reverse diabetes mellitus in rodents [25,26]. These cells seem to be as an appropriate source for islet transplantation; however more research is required to make it possible for clinical use. It is believed that the best place to
912 look for stem cells capable to differentiate into pancreatic b-cells is the pancreas. If it is true the limited proliferation capacity of these cells could be considered as a safety advantage, by reducing the risk of unregulated proliferation following transplantation. The concept for this belief originates from the studies of experimental models of pancreas injury [37, 27]. Human and rodent epithelium of pancreatic-duct cells [28,29] can differentiate towards a pancreatic endocrine phenotype and probably this is a place for stem cells in the pancreas from which normal renewal of islets occurs throughout life. However, a recent study raised a very critical question about the existence of pancreatic adult stem cells. Using a genetic lineage-marking technique, Dor and colleagues [30] have demonstrated that b-cell turnover under normal condition results from duplication of pre-existing b-cells themselves, and it is not the contribution of non-b-cells, such as duct cells or stem cells.
Conclusion b-Cell replacement either by transplantation or endogenous b-cell proliferation induction is believed to be the only treatment that maintains long-term glucose homeostasis; however lifelong immunosuppressive therapy and inadequate sources of transplantable islets have limited the islet transplantation and lack of knowledge in developmental biology limited the latter way. ESCs research is thought to have much greater developmental potential than adult stem cells; however it is still in the basic research phase. Existing ESC lines are not believed to be identical or ideal for generating islets or b-cells and additional ESC lines have to be established. ESCs are flexible, immortal and easily available but difficult to control them; they express immunological differences between donor and recipient. Research with ESCs derived from humans is controversial because it requires the destruction of a human embryo and/or therapeutic cloning, which some believe is a slippery slope to reproductive cloning. On the other hand, adult stem cells are already in some degree specialized, recipients may receive their own stem cells. They are flexible but they have shown mixed degree of availability. Adult stem cells are not pluripotent. They may not exist for all organs. They are difficult to purify and they cannot be maintained well outside the body. Considering the huge potential of stem cells for the treatment of several major diseases, it is clearly crucial to go forward for a number of ave-
Miszta-Lane et al. nues waiting to be explored and use all resources of stem cells in searching for the perfect stem cell to treat diabetes. It might be argued that is too soon to attempt to draw any future about stem cell replacement therapy for diabetes but both ESCs and adult stem cells currently being evaluated in pre-clinical studies and clinical trials for several specific diseases. Our Clinical Islet Transplantation Program has revealed that this kind of cell based therapy does work for the treatment of diabetes; however it needs an unlimited source of islet to be optimized. We believe the utilization of stem cells for the generation of insulin-producing b-cells in vitro will close us to the complete treatment of diabetes, and seem to be within reach in the near future.
References [1] Gepts W. Islet morphology in type I diabetes. Behring Instr Mitt 1984(75):39–41. [2] Ryan EA. Pancreas transplants: for whom? Lancet 1998;351(9109):1072–3. [3] Williams PW. Notes on diabetes treated with extract and by grafts of sheep’s pancreas. BMJ 1894;2:1303–4. [4] Shapiro AMJ, Lakey JRT, Ryan EA, et al. Islet transplantation in seven patients with type 1 diabetes mellitus using a glucocorticoid-free immunosuppressive regimen. New Engl J Med 2000;343(4):230. [5] http://www.who.int/hpr/gs.fs.diabetes.html (Aug 2005). [6] Watt FM, Hogan BLM. Out of eden:stem cells and their niches. Science 2000;287:1427–30. [7] Hubner K, Fuhrmann G, Christenson LK, Kehler J, Reinbold R, De La Fuente R, et al. Derivation of oocytes from mouse embryonic stem cells. Science 2003;300(5623):1251–6. [8] Lumelsky N, Blondel O, Laeng P, Velasco I, Ravin R, McKay R. Differentiation of embryonic stem cells to insulinsecreting structures similar to pancreatic islets. Science 2001;292(5520):1389–94. [9] Rajagopal J, Anderson WJ, Kume S, Martinez OI, Melton DA. Insulin staining of ES cell progeny from insulin uptake. Science 2003;299(5605):363. [10] Hori Y, Rulifson IC, Tsai BC, Heit JJ, Cahoy JD, Kim SK. Growth inhibitors promote differentiation of insulin-producing tissue from embryonic stem cells. Proc Natl Acad Sci USA 2002;99:16105–10. [11] Soria B, Skoudy A, Martin F. From stem cells to beta cells. Diabetologia 2001;44:407–15. [12] Kania G, Blyszczuk P, Czyz J, Navarrete-Santos A, Wobus AM. Differentiation of mouse embryonic stem cells into pancreatic and hepatic cells. Meth Enzymol 2003;365: 287–303. [13] Schuldiner M, Yanuka O, Itskovitz-Eldor J, Melton DA, Benvenisty N. Effects of eight growth factors on the differentiation of cells derived from human embryonic stem cells. Proc Natl Acad Sci USA 2000;97:11307–12. [14] Wells JM. Genes expressed in the developing endocrine pancreas and their importance for stem cell and diabetes research. Metab Res Rev 2003;19:191–201. [15] Offield MF, Jetton TL, Labosky PA, Ray M, Stein RW, Magnuson MA, et al. PDX-1 is required for pancreatic
Stem cell sources for clinical islet transplantation in type 1 diabetes
[16]
[17]
[18] [19] [20] [21]
[22]
[23]
outgrowth and differentiation of the rostral duodenum. Development 1996;122:983–95. Kim NW, Piatyszek MA, Prowse KR, et al. Specific association of human telomerase activity with immortal cells and cancer. Science 1994;266:2011–5. Sipione S, Eshpeter A, Lyon JG, Korbutt GS, Bleackley RC. Insulin expressing cells from differentiated embryonic stem cells are not beta cells. Diabetologia 2004;47:499–507. Ying QL, Nichols J, Evans EP, Smith AG. Changing potency by spontaneous fusion. Nature 2002;416(6880):545–8. Ulrich AB, Schmied BM, Standop J, Schneider MB, Pour PM. Pancreas 2002;24:111. Hess D, Li L, Martin M, Sakano S, Hill D, Strutt B, et al. Nat Biotechnol 2003;21:763. Till JE, McCulloch EA. A direct measurement of the radiation sensitivity of normal mouse bone marrow cells. Radiation Res 1961;14:213–32. Jiang Y, Jahagirdar BN, Reinhardt RL, et al. Pluripotency of mesenchymal stem cells derived from adult marrow. Nature 2002;418:41–9. Pittenger MF, Mackay AM, Beck SC, et al. Multilineage potential of adult human mesenchymal stem cells. Science 1999;284:143–7.
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[24] Kodama S, Ku ¨htreiber W, Fujimura S, Dale EA, Faustman DL. Islet regeneration during the reversal of autoimmune diabetes in NOD mice. Science 2003;302:1223–6. [25] Zalzman M, Gupta S, Giri RK, et al. Reversal of hyperglycemia in mice by using human expandable insulin-producing cells differentiated from fetal liver progenitor cells. Proc Natl Acad Sci USA 2003;100:7253–8. [26] Kojima H, Fujimiya M, Matsumura K, et al. NeuroDbetacellulin gene therapy induces islet neogenesis in the liver and reverses diabetes in mice. Nat Med 2003;9: 596–603. [27] Kanitkar M, Bhonde R. Existence of islet regeneration factors within the pancreas. Rev Diab Stud 2004;1:185–92. [28] Ramiya VK, Maraist M, Arfors KE, Schatz DA, Peck AB, Cornelius JG. Reversal of insulin-dependent diabetes using islets generated in vitro from pancreatic stem cells. Nat Med 2000;6:278–82. [29] Bonner-Weir S, Taneja M, Weir GC, et al. In vitro cultivation of human islets from expanded ductal tissue. Proc Natl Acad Sci USA 2000;97:7999–8004. [30] Dor Y, Brown J, Martinez OI, Melton DA. Adult pancreatic beta-cells are formed by self-duplication rather than stemcell differentiation. Nature 2004;429:41–6.
http://intl.elsevierhealth.com/journals/mehy
Stem cell sources for clinical islet transplantation in type 1 diabetes: Embryonic and adult stem cells Helena Miszta-Lane b,1, Mohammadreza Mirbolooki A.M. James Shapiro a,b, Jonathan R.T. Lakey a,b,*
a,b,1
,
a
Clinical Islet Transplantation Program, Department of Surgery, Faculty of Medicine and Dentistry, University of Alberta, 1074 Dentistry/Pharmacy Centre, Edmonton, Alta., Canada T6G 2N8 b Surgical-Medical Research Institute, Department of Surgery, Faculty of Medicine and Dentistry, University of Alberta, 1074 Dentistry/Pharmacy Centre, Edmonton, Alta., Canada T6G 2N8 Received 26 March 2006; accepted 29 March 2006
Summary Lifelong immunosuppressive therapy and inadequate sources of transplantable islets have led the islet transplantation benefits to less than 0.5% of type 1 diabetics. Whereas the potential risk of infection by animal endogenous viruses limits the uses of islet xeno-transplantation, deriving islets from stem cells seems to be able to overcome the current problems of islet shortages and immune compatibility. Both embryonic (derived from the inner cell mass of blastocysts) and adult stem cells (derived from adult tissues) have shown controversial results in secreting insulin in vitro and normalizing hyperglycemia in vivo. ESCs research is thought to have much greater developmental potential than adult stem cells; however it is still in the basic research phase. Existing ESC lines are not believed to be identical or ideal for generating islets or b-cells and additional ESC lines have to be established. Research with ESCs derived from humans is controversial because it requires the destruction of a human embryo and/or therapeutic cloning, which some believe is a slippery slope to reproductive cloning. On the other hand, adult stem cells are already in some degree specialized, recipients may receive their own stem cells. They are flexible but they have shown mixed degree of availability. Adult stem cells are not pluripotent. They may not exist for all organs. They are difficult to purify and they cannot be maintained well outside the body. In order to draw the future avenues in this field, existent discrepancies between the results need to be clarified. In this study, we will review the different aspects and challenges of using embryonic or adult stem cells in clinical islet transplantation for the treatment of type 1 diabetes. c 2006 Elsevier Ltd. All rights reserved.
Introduction * Corresponding author. Tel.: +1 780 492 4660; fax: +1 780 492 6335. E-mail addresses: [email protected], jlakey@ ualberta.ca (J.R.T. Lakey). 1 These authors contributed equally to this study.
Type 1 diabetes, insulin-dependent diabetes mellitus (IDDM), is an autoimmune disease caused by the progressive destruction of the insulin secreting bcells in the islets of Langerhans [1]. The discovery of insulin by Banting and Best in 1922 changed
0306-9877/$ - see front matter c 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mehy.2006.03.036
910 diabetes from a fatal disease to a chronic illness with intolerable co-morbidities and premature death. It is well known that even aggressive insulin therapy will never re-create the real-time variation of blood glucose. Furthermore, the effects of chronic hyperglycemia and peripheral hyperinsulinemia are believed to accelerate diabetic microangiopathy. That is why, b-cell replacement has been assumed to be the only treatment that reestablishes and maintains long-term glucose homeostasis with near-perfect feedback controls [2]. Transplanting extracts of pancreas in patients with diabetes was firstly performed over 100 years ago [3]; however, hastened progresses, and improved understanding of the issues that face clinical islet transplantation during the last 30 years have led this simple concept to a successful treatment for diabetes. Islet transplantation involves the isolation of islets of Langerhans from the pancreas of cadaver organ donors through complex digestion and purification processes and transplanting them into recipient’s liver. It results in near-perfect, moment-to-moment control of blood glucose, far more effectively than injected insulin. The hope is that, with tighter glucose control, the long-term complications of diabetes could be avoided. The ‘‘Edmonton Protocol’’ [4], a glucocorticoidfree immunosuppression regimen, combined with an optimal islet engraftment mass was an impressive departure from previous attempts. The Edmonton Protocol has been successfully replicated in more than 50 centers worldwide, with cumulative data from more than 500 patients. This represents a significant goal, as more patients with type 1 diabetes have now received islet implants in the past 6 years than in the entire former 30-year history of islet transplantation. However, lifelong immunosuppressive therapy and inadequate sources of transplantable islets have led the islet transplantation benefits to less than 0.5% of type 1 diabetics. It is required to find alternative sources of insulin-producing, glucose-responsive tissue to treat more than 175 million children and adult diabetics worldwide [5]. Whereas the potential risk of infection by animal endogenous viruses limits the uses of islet xeno-transplantation, deriving islets from stem cells seems to be able to overcome the current problems of islet shortages and immune compatibility. Stem cells are known as clonogenic. They have the ability to self-renew (produce identical daughter cells) and multilineage differentiation (produce daughters that are fated to differentiate) [6]. Both embryonic (derived from the inner cell mass of blastocysts) and adult stem cells (derived from
Miszta-Lane et al. Table 1 The definition of cell types as a potential source of b-cells Source of stem cells
Definition of terms
Embryonic stem cells (ESC)
Highly pluripotent stem cell with highest proliferation ability, initially derived from a blastocyst Highly pluripotent stem cells, with high proliferation ability, initially derived from the gonadal region of aborted human fetuses Derived from teratocarcinoma tissue, ESC and EGC are diploid, genetically normal, but ECC are commonly aneuploid Adult bone-marrow stem cells, giving rise to cells of the supportive marrow structure The islet stem/progenitor cells within pancreatic-ducts, from where they regenerate, differentiate and migrate to form new islets both during organogenesis and in regeneration Liver developed from endoderm during organogenesis
Embryonic germ cells (EGC)
Embryonic carcinoma cells (ECC) Mesenchymal stem cells Fetal, duct and adult pancreas stem cells
Liver stem cells
adult tissues) have shown controversial results in secreting insulin in vitro and normalizing hyperglycemia in vivo. Table 1 describes the different cell types as a potential source of b-cells. In order to draw the future avenues in this field, existent discrepancies between the results need to be clarified. In this study, we will review the different aspects and challenges of using embryonic and adult stem cells in clinical islet transplantation for the treatment of type 1 diabetes to make it clear if both resources of stem cells should be searched or one of them is prior to the other one.
Embryonic stem cells (ESCs) The most remarkable characteristic of ESCs is their potential ability to differentiate into every type of adult cell [7]. They are able to be differentiated into insulin-producing cells in culture conditions, as well. ESC-derived insulin-expressing islet-like structures were firstly reported by Lumelsky et al. They showed clusters with insulin positive cells located in the centre and surrounded by neurons. They found that majority of glucagon and somato-
Stem cell sources for clinical islet transplantation in type 1 diabetes statin positive cells surround the insulin positive cells. These cells showed intracellular insulin content of about 50-fold lower than that of normal pancreatic b-cells, and they were not able to reverse hyperglycemia in diabetic mice [8]. There is a report showing that insulin content in ESCs derived cultures may result from insulin uptake from the culture medium, rather than from endogenous synthesis [9], however transplantation of ESCs derived insulin-producing cells has reversed diabetes in animals [10], indicating that these cells do synthesis and release insulin. It has been also reported that genetically altered ESCs for insulin expression when injected into diabetic rats, improve glucose control [11]. It seems that regulated expression of transcription factors might be the reason for this discrepancy [12]. Schuldiner et al. [13] showed that both undifferentiated human embryonic stem cells and differentiated embryoid bodies expressed receptors for a number of different soluble growth factors with established effects on developmental pathways in vivo. The addition of phosphoinositide kinase inhibitors promoted differentiation of large number of ESCs towards functional b-cells [10]. According to Wells [14], embryonic development of the pancreas shares similarities with islet regeneration. In both processes, multipotent endocrine progenitor cells contained within a duct-like tube respond to signals by delaminating from the ducts, where they proliferate, differentiate, and form the islets. There are also similarities between islet regeneration and embryonic pancreas development at the gene expression level. A number of putative markers [15] transiently expressed in embryonic ducts have been suggested as indicator of islet progenitor cells. ESCs express high levels of telomerase, as well. The expression of telomerase, a ribonucleoprotein that adds telomere repeats to chromosome ends, thereby maintaining their length correlates strongly with immortality in human embryonic cell lines [16]. Therefore, problems in control of differentiation and tumorogenesity of ESC-derived insulin-producing cells remain to be overcome [17]. The number of undifferentiated ESCs exists in the graft, their ability to proliferate in an uncontrolled fashion, the number of transplanted cells, immunological rejection and the immunocompetence of the host are of important factors affecting the final outcome of ESC-derived establishments. The ability of the grafted cells to ‘‘integrate’’ with the host tissue is of the other important factors. This phenomenon may possibly rely on spontaneous fusion of the ESCs with host tissue-specific cells [18]. While undeniable evidence that true b-cells can be created in vitro from ESCs is still controver-
911
sial; ethical concerns about the use of ESCs need to be addressed and resolved.
Adult stem cells It was previously believed that stem cells are vanished soon after birth, but researches, have revealed that they exist in the adult tissues, as well. It was also believed that each of these cells could produce just one particular type of cell, however in the past few years; evidences have been issued of stem cells that have an extraordinary flexibility to be transdifferentiated into other cell types. Human adult stem cells have been transdifferentiated into insulin-producing cells [19], and could normalize hyperglycemia in streptozotocininduced diabetic mice [20], however they are in minimal quantity, their life period has limitation, and they may be already genetically altered. Their proliferation capacity is low as compared to that of ESCs; however, proliferation could be extended by genetic manipulation in tissue culture (e.g., expression of a telomerase gene). In bone-marrow, commonly used as a source of adult stem cells, the detection of cells with the properties of self-birth and multi-pedigree differentiation potential is fairly advanced [21]. Bonemarrow cells are differentiated into other types of cells in vitro and under controlled conditions [22]. Bone-marrow contains hematopoietic and mesenchymal stem cells. Mesenchymal stem cells are capable of differentiating into a number of different kinds of cells such as pancreatic b-cells [23]. Experiments on diabetic mice with totally destroyed b-cells by streptozocin show that after bone-marrow transplantation, blood glucose is normal, and survival is better [20]. These studies show the possibility of bone-marrow transplantation as a therapeutic approach for b-cell replacement; however the newly regenerated b-cells destroyed by the host immune system. While the immune destruction is a problem in bone-marrow transplantation, transplanting splenic mesenchymal cells show promising results in both pancreatic b-cells regeneration and immune destruction prevention [24]. Other sources of adult stem cells are liver and pancreas. Hepatic stem cells have the ability of being differentiated into insulin-secreting cell and expressed b-cell-specific genes in vitro and when transplanted, these cells reverse diabetes mellitus in rodents [25,26]. These cells seem to be as an appropriate source for islet transplantation; however more research is required to make it possible for clinical use. It is believed that the best place to
912 look for stem cells capable to differentiate into pancreatic b-cells is the pancreas. If it is true the limited proliferation capacity of these cells could be considered as a safety advantage, by reducing the risk of unregulated proliferation following transplantation. The concept for this belief originates from the studies of experimental models of pancreas injury [37, 27]. Human and rodent epithelium of pancreatic-duct cells [28,29] can differentiate towards a pancreatic endocrine phenotype and probably this is a place for stem cells in the pancreas from which normal renewal of islets occurs throughout life. However, a recent study raised a very critical question about the existence of pancreatic adult stem cells. Using a genetic lineage-marking technique, Dor and colleagues [30] have demonstrated that b-cell turnover under normal condition results from duplication of pre-existing b-cells themselves, and it is not the contribution of non-b-cells, such as duct cells or stem cells.
Conclusion b-Cell replacement either by transplantation or endogenous b-cell proliferation induction is believed to be the only treatment that maintains long-term glucose homeostasis; however lifelong immunosuppressive therapy and inadequate sources of transplantable islets have limited the islet transplantation and lack of knowledge in developmental biology limited the latter way. ESCs research is thought to have much greater developmental potential than adult stem cells; however it is still in the basic research phase. Existing ESC lines are not believed to be identical or ideal for generating islets or b-cells and additional ESC lines have to be established. ESCs are flexible, immortal and easily available but difficult to control them; they express immunological differences between donor and recipient. Research with ESCs derived from humans is controversial because it requires the destruction of a human embryo and/or therapeutic cloning, which some believe is a slippery slope to reproductive cloning. On the other hand, adult stem cells are already in some degree specialized, recipients may receive their own stem cells. They are flexible but they have shown mixed degree of availability. Adult stem cells are not pluripotent. They may not exist for all organs. They are difficult to purify and they cannot be maintained well outside the body. Considering the huge potential of stem cells for the treatment of several major diseases, it is clearly crucial to go forward for a number of ave-
Miszta-Lane et al. nues waiting to be explored and use all resources of stem cells in searching for the perfect stem cell to treat diabetes. It might be argued that is too soon to attempt to draw any future about stem cell replacement therapy for diabetes but both ESCs and adult stem cells currently being evaluated in pre-clinical studies and clinical trials for several specific diseases. Our Clinical Islet Transplantation Program has revealed that this kind of cell based therapy does work for the treatment of diabetes; however it needs an unlimited source of islet to be optimized. We believe the utilization of stem cells for the generation of insulin-producing b-cells in vitro will close us to the complete treatment of diabetes, and seem to be within reach in the near future.
References [1] Gepts W. Islet morphology in type I diabetes. Behring Instr Mitt 1984(75):39–41. [2] Ryan EA. Pancreas transplants: for whom? Lancet 1998;351(9109):1072–3. [3] Williams PW. Notes on diabetes treated with extract and by grafts of sheep’s pancreas. BMJ 1894;2:1303–4. [4] Shapiro AMJ, Lakey JRT, Ryan EA, et al. Islet transplantation in seven patients with type 1 diabetes mellitus using a glucocorticoid-free immunosuppressive regimen. New Engl J Med 2000;343(4):230. [5] http://www.who.int/hpr/gs.fs.diabetes.html (Aug 2005). [6] Watt FM, Hogan BLM. Out of eden:stem cells and their niches. Science 2000;287:1427–30. [7] Hubner K, Fuhrmann G, Christenson LK, Kehler J, Reinbold R, De La Fuente R, et al. Derivation of oocytes from mouse embryonic stem cells. Science 2003;300(5623):1251–6. [8] Lumelsky N, Blondel O, Laeng P, Velasco I, Ravin R, McKay R. Differentiation of embryonic stem cells to insulinsecreting structures similar to pancreatic islets. Science 2001;292(5520):1389–94. [9] Rajagopal J, Anderson WJ, Kume S, Martinez OI, Melton DA. Insulin staining of ES cell progeny from insulin uptake. Science 2003;299(5605):363. [10] Hori Y, Rulifson IC, Tsai BC, Heit JJ, Cahoy JD, Kim SK. Growth inhibitors promote differentiation of insulin-producing tissue from embryonic stem cells. Proc Natl Acad Sci USA 2002;99:16105–10. [11] Soria B, Skoudy A, Martin F. From stem cells to beta cells. Diabetologia 2001;44:407–15. [12] Kania G, Blyszczuk P, Czyz J, Navarrete-Santos A, Wobus AM. Differentiation of mouse embryonic stem cells into pancreatic and hepatic cells. Meth Enzymol 2003;365: 287–303. [13] Schuldiner M, Yanuka O, Itskovitz-Eldor J, Melton DA, Benvenisty N. Effects of eight growth factors on the differentiation of cells derived from human embryonic stem cells. Proc Natl Acad Sci USA 2000;97:11307–12. [14] Wells JM. Genes expressed in the developing endocrine pancreas and their importance for stem cell and diabetes research. Metab Res Rev 2003;19:191–201. [15] Offield MF, Jetton TL, Labosky PA, Ray M, Stein RW, Magnuson MA, et al. PDX-1 is required for pancreatic
Stem cell sources for clinical islet transplantation in type 1 diabetes
[16]
[17]
[18] [19] [20] [21]
[22]
[23]
outgrowth and differentiation of the rostral duodenum. Development 1996;122:983–95. Kim NW, Piatyszek MA, Prowse KR, et al. Specific association of human telomerase activity with immortal cells and cancer. Science 1994;266:2011–5. Sipione S, Eshpeter A, Lyon JG, Korbutt GS, Bleackley RC. Insulin expressing cells from differentiated embryonic stem cells are not beta cells. Diabetologia 2004;47:499–507. Ying QL, Nichols J, Evans EP, Smith AG. Changing potency by spontaneous fusion. Nature 2002;416(6880):545–8. Ulrich AB, Schmied BM, Standop J, Schneider MB, Pour PM. Pancreas 2002;24:111. Hess D, Li L, Martin M, Sakano S, Hill D, Strutt B, et al. Nat Biotechnol 2003;21:763. Till JE, McCulloch EA. A direct measurement of the radiation sensitivity of normal mouse bone marrow cells. Radiation Res 1961;14:213–32. Jiang Y, Jahagirdar BN, Reinhardt RL, et al. Pluripotency of mesenchymal stem cells derived from adult marrow. Nature 2002;418:41–9. Pittenger MF, Mackay AM, Beck SC, et al. Multilineage potential of adult human mesenchymal stem cells. Science 1999;284:143–7.
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[24] Kodama S, Ku ¨htreiber W, Fujimura S, Dale EA, Faustman DL. Islet regeneration during the reversal of autoimmune diabetes in NOD mice. Science 2003;302:1223–6. [25] Zalzman M, Gupta S, Giri RK, et al. Reversal of hyperglycemia in mice by using human expandable insulin-producing cells differentiated from fetal liver progenitor cells. Proc Natl Acad Sci USA 2003;100:7253–8. [26] Kojima H, Fujimiya M, Matsumura K, et al. NeuroDbetacellulin gene therapy induces islet neogenesis in the liver and reverses diabetes in mice. Nat Med 2003;9: 596–603. [27] Kanitkar M, Bhonde R. Existence of islet regeneration factors within the pancreas. Rev Diab Stud 2004;1:185–92. [28] Ramiya VK, Maraist M, Arfors KE, Schatz DA, Peck AB, Cornelius JG. Reversal of insulin-dependent diabetes using islets generated in vitro from pancreatic stem cells. Nat Med 2000;6:278–82. [29] Bonner-Weir S, Taneja M, Weir GC, et al. In vitro cultivation of human islets from expanded ductal tissue. Proc Natl Acad Sci USA 2000;97:7999–8004. [30] Dor Y, Brown J, Martinez OI, Melton DA. Adult pancreatic beta-cells are formed by self-duplication rather than stemcell differentiation. Nature 2004;429:41–6.