intervention Presentation on Diabetes

REVIEW ARTICLE

The state of the art of islet transplantation and cell therapy in type 1 diabetes

Silvia Pellegrini1 • Elisa Cantarelli1 • Valeria Sordi1 • Rita Nano1 • Lorenzo Piemonti1

Received: 15 January 2016 / Accepted: 6 February 2016 / Published online: 29 February 2016

� Springer-Verlag Italia 2016

Abstract In patients with type 1 diabetes (T1D), pan-

creatic b cells are destroyed by a selective autoimmune attack and their replacement with functional insulin-pro-

ducing cells is the only possible cure for this disease. The

field of islet transplantation has evolved significantly from

the breakthrough of the Edmonton Protocol in 2000, since

significant advances in islet isolation and engraftment,

together with improved immunosuppressive strategies,

have been reported. The main limitations, however, remain

the insufficient supply of human tissue and the need for

lifelong immunosuppression therapy. Great effort is then

invested in finding innovative sources of insulin-producing

b cells. One old alternative with new recent perspectives is the use of non-human donor cells, in particular porcine b cells. Also the field of preexisting b cell expansion has advanced, with the development of new human b cell lines. Yet, large-scale production of human insulin-producing

cells from stem cells is the most recent and promising

alternative. In particular, the optimization of in vitro

strategies to differentiate human embryonic stem cells into

mature insulin-secreting b cells has made considerable progress and recently led to the first clinical trial of stem

cell treatment for T1D. Finally, the discovery that it is

possible to derive human induced pluripotent stem cells

from somatic cells has raised the possibility that a sufficient

amount of patient-specific b cells can be derived from patients through cell reprogramming and differentiation,

suggesting that in the future there might be a cell therapy

without immunosuppression.

Keywords b Cell replacement � Islet transplantation � Xenotransplantation � Pluripotent stem cells

Introduction

The International Diabetes Federation (IDF) estimates that

415 million people worldwide have diabetes, a number that

is predicted to increase to 642 million by 2040 (http://

www.diabetesatlas.org). Type 1 diabetes (T1D), a disease

characterized by selective and progressive loss of insulin-

producing b cells caused by an autoimmune-mediated destruction, accounts for approximately 10 % of these

cases. Administration of exogenous insulin, regular blood

glucose monitoring and dietary restrictions are the funda-

mental means of treating hyperglycemia in all patients with

T1D. Although lifesaving, insulin therapy does not restore

the physiological regulation of blood glucose [1] and is not

able to prevent either the dangerous states of hypoglycemia

or long-term complications [2] and the life expectancy of

these patients is still shorter compared to that of the general

population [3]. Although new technologies like slow-re-

lease insulin or insulin pumps have been developed in the

last years and have substantially improved glycemic con-

trol as well as the quality of life of patients with T1D [4], a

fail-safe physiological regulation of systemic blood glu-

cose levels remains challenging. The only possible defini-

tive cure for this disease consists in replacing the destroyed

b cell mass capable of sensing blood sugar levels and secreting appropriate amounts of insulin in a glucose-de-

pendent manner. Increasing evidence indicates that b Cell replacement restores protection from severe hypoglycemia,

Managed by Massimo Federici.

& Lorenzo Piemonti [email protected]

1 Diabetes Research Institute, IRCCS San Raffaele Scientific

Institute, Milan, Italy

123

Acta Diabetol (2016) 53:683–691

DOI 10.1007/s00592-016-0847-z

reduces levels of glycated hemoglobin (HbA1c) and slows

progression of microvascular complications in patients

with T1D [5]. So far, the only available clinical approaches

able to restore b cell mass in patients with T1D are pan- creas or pancreatic islet transplantation, which consists in

endocrine cells infusion into the recipient’s portal vein and

requires only a minimally invasive surgical procedure

compared to the complex vascularized pancreas trans-

plantation [6–8]. The field of islet transplantation has

evolved significantly over the last three decades thanks to

the incredible efforts of the research community worldwide

with continuous improvements in islet manufacturing

process and transplantation techniques, coupled with better

patient management and the development of more effective

induction and maintenance immunosuppressive protocols

[9]. In addition, islet transplantation represents an excellent

platform toward the development of cellular therapies

aimed at the restoration of b cell function using alternative sources of b cells like xenogeneic islets or insulin-pro- ducing cells derived from the differentiation of stem cells.

This review deals with the state of the art of islet

transplantation and the most promising sources of new b cells for functional replacement in diabetes (Fig. 1).

Established procedures, ongoing clinical trials (Table 1)

and future developments of cell therapies will be discussed.

b Cell replacement with allogeneic pancreatic islets

Pancreatic islet transplantation has recently become an

accepted therapeutic option in subjects with unstable T1D.

The procedure itself may be performed as islet transplant

alone (ITA) in non-uremic patients with T1D, as simulta-

neous islet-kidney (SIK) in subjects with end-stage renal

disease or, if renal transplantation has already undergone,

as islet after kidney (IAK) transplantation. Ongoing clinical

trials are recruiting 18- to 65-year-old T1D subjects with

frequent metabolic instability (i.e., hypoglycemia, hyper-

glycemia, ketoacidosis) requiring medical treatment

despite intensive insulin therapy [10].

The first attempt of islet isolation and transplantation

was reported in 1972 by Ballinger and Lacy in chemically

induced diabetic rats [11], with Kemp et al. [12] estab-

lishing the liver as the most suitable site for islet implan-

tation. Five years later, the first islet infusion in human was

performed, with azathioprine and corticosteroid as

immunosuppressive drugs [13]. Since then, many efforts

and significant progress have been achieved in the field in

terms of human islet isolation [14], immunosuppression

strategies [15] and setting the optimal number of trans-

planted islets per kilogram of body weight [16].

Altogether these advances culminated in 2000 with the

publication of the Edmonton Protocol achieving a 100 %

insulin independence in seven patients with T1D receiving

islets from multiple donors and treated with a steroid-free

immunosuppression protocol [17]. The Edmonton Protocol

represented a fundamental proof-of-concept of the possi-

bility to achieve insulin independence through islet trans-

plantation. Few years later, the same group reported

sustained islet function as measured by the presence of

C-peptide in 73 % of their transplanted subjects with 15 %

insulin independence at 9 years after transplantation [18].

Recently, they reported a further update on long-term fol-

low-up of a cohort of the 36-patient international Immune

Tolerance Network trial having persistent graft survival at

the end of the clinical study. All patients remained free of

severe episodes of hypoglycemia and maintained HbA1c

\7.0 % showing an overall long-lasting graft function with a gradual decline in C-peptide levels during time. Impor-

tantly, the long follow-up showed long-term safety of the

procedure with the absence of severe infection, malig-

nancy, hypoglycemia and the stability of renal function

[19].

Since the initiation of the Edmonton Protocol, islet

transplant programs expanded in North America, Europe

and Australia, where alternative protocols for human islet

transplantation have been conducted in order to overcome

current limitations of the procedure, thus improving the

clinical outcome. The most recent report released by the

Collaborative Islet Transplant Registry (CITR, www.

citregistry.org) analyzes data coming from 864 islet allo-

graft recipients (686 ITA and 178 IAK) and 1679 infusions

in the era 1999–2012. A comprehensive report collecting

data available for the period 1999–2010 showed that the

rate of insulin independence at 3 years remarkably

improved during time: 27 % in the era 1999–2002, 37 % in

the era 2003–2006 and 44 % in the most recent era

2007–2010. Other parameters indicative of islet graft

function like C-peptide[0.3 ng/ml, reduction of HbA1c, resolution of severe hypoglycemia episodes and fasting

blood glucose stabilization were retained longer in the most

recent era [20]. Moreover, successful results were recently

reported by numerous European groups: The UK islet

transplantation program achieved graft function in 80 % of

transplanted patients 2 years after the first islet infusion

with a significant reduction in severe hypoglycemic epi-

sodes and the achievement and maintenance of HbA1C

\7.0 % in 70 % of the recipients [21]; the teams of Lille and the Swiss-French GRAGIL Network reached 50 and

75 % insulin independence rate during the 5-year follow-

up, respectively [22, 23]. The strong reduction in the rate of

islet graft loss during the different periods suggests that

new drugs able to improve islet engraftment and survival

and to better protect islets from the alloimmune rejection

and recurrent autoimmunity have been developed. Specif-

ically, the era 1999–2006 was dominated by the Edmonton

Protocol consisting in the administration of IL-2 receptor

684 Acta Diabetol (2016) 53:683–691

123

antagonist (i.e., daclizumab) for induction and a mam-

malian target of rapamycin (mTOR) inhibitor (i.e., sir-

olimus) in combination with a calcineurin inhibitor (CNI,

i.e., tacrolimus) for maintenance immunosuppression. In

the most recent era (2006–2010), the immunosuppressive

regimen shifted to a T cell depleting antibody with or

without a TNF-a inhibitor (i.e., etanercept) administered peri-transplant [24, 25] and an mTOR inhibitor or an

Fig. 1 Schematic representation of the most promising sources and the related strategies currently studied in order to obtain a large amount of transplantable b cells

Table 1 Clinical studies testing safety (Phase 1) and efficacy (Phase 2) of different sources of insulin-producing b cells

Source of b cells Study type

Study locations Status

Allogeneic

pancreatic islets

Islets isolated from brain-

dead organ donors

Clinical

routine

Every hospitals performing pancreatic islet

transplantation

Xenogeneic

pancreatic islets

Neonatal pig islets Phase 1/2 Hospital Infantil de Mexico, Mexico Completed, [45]

Xenogeneic

pancreatic islets

Neonatal pig islets Phase 1/2 Third Xiangy Hospital, China Completed, [46]

Xenogeneic

pancreatic islets

Neonatal pig islets Phase 1/2 Hospital Interzonal General de Agudos Eva Peron

Buenos Aires, Argentina, and Centre for Clinical

Research and Effective Practice Auckland, New

Zealand

Completed, results not

yet published

ESC-derived insulin-

producing cells

Human ESC-derived

insulin-producing cells

Phase 1/2 University of California, San Diego, USA, and

University of Alberta Hospital, Alberta, Canada

Ongoing

Acta Diabetol (2016) 53:683–691 685

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inosine monophosphate dehydrogenase inhibitor (IMPDH,

i.e., mycophenolic acid) combined with a CNI for the

maintenance therapy [26, 27]. Besides, an efficient protocol

of induction based on the use of alemtuzumab for lym-

phocyte depletion was associated with promising longer-

term function [28]. Moreover, a CNI-free immunosup-

pressive schedule was reported [29]. Finally, in the most

recent years the field moved in the direction of finding new

biologics with a lower islet cell and organ toxicity profiles:

Drugs that target co-stimulation pathways in immune cells

and/or adhesion molecules such as LFA-1, CTLA4-Ig, PD-

1/PD-L1 and CD40 [30–32] or chemokine receptors

(CXCR1/2) [33] have been tested in preclinical models and

clinical trials. Remarkably, the increasing success in the

clinical outcome underlines that improvements made in the

last decades allowed to reach results closed to that obtained

with whole pancreas transplantation [34]. At present,

however, the lack of pancreas from heart-beating brain-

dead donors, the only suitable source of human islets for

clinical use until now, strongly limits the broad application

of islet transplantation as a standard procedure. Many

approaches aimed to find alternative sources of b cells are currently intensively investigated, in particular xenogeneic

islets, immortalized b cell lines and stem cells able to differentiate into insulin-producing b cells.

b Cell replacement with xenogeneic pancreatic islets

Using pancreatic islets derived from other species seems an

obvious way of providing the large amount of islets

required for transplantation therapy. Most effort in this area

has been directed toward the use of pig islets for many

reasons: (1) Pig insulin can efficiently substitute human

insulin because they differ by only one amino acid; (2)

porcine islets regulate glucose levels in the same physio-

logic range as humans; (3) high yields of islets can be

obtained with techniques established for human islet iso-

lation and (4) pigs can be genetically modified for making

their islets more suitable for the transplantation in humans

[35]. One of the first clinical attempts made in 1994 by

Groth et al. [36] who transplanted fetal pig islet-like cell

clusters in T1D patients proved that porcine pancreatic

endocrine tissue can survive in humans although the clin-

ical benefit in these patients was barely detected. However,

two main problems have limited the use of pig islets in

humans: (1) the risk of an hyperacute immunologic rejec-

tion, because humans have natural preformed antibodies

reacting to galactose-a1,3-galactose (Gal), a saccharide expressed on cells of lower mammals but not on cells of

humans or monkeys [37] and (2) the risk of zoonosis,

because porcine endogenous retroviral (PERV) sequences

can infect several human cells in vitro and may be acti-

vated after the xenotransplant [38]. Promising findings

coming from the transplantation of pig islet transplantation

in the NHP (non-human primate) model provided the

rationale for continued development of islet xenotransplant

as a potential treatment option for T1D. Indeed, funda-

mental studies in NHP reported the long-term survival of

neonatal [39] or adult [40] porcine islets in the presence of

immunosuppression therapy. Besides, a recent study pro-

vided evidences that islets isolated from miniature pigs

infused in diabetic NHP engrafted and maintained nor-

moglycemia for more than 6 months in 4 out of 5 recipients

with low-dose immunosuppressive therapy and adoptive

transfer of expanded autologous regulatory T cells [41].

Moreover, in order to overcome the issue of the immuno-

genicity, genetically engineered pigs have been developed

and some groups have reported variable survival gains

using multiple genetically engineered pig islets trans-

planted in NHP [42, 43]. Another strategy currently studied

to avoid immunosuppression consists in islet microencap-

sulation: Islets can be enveloped within a biocompatible

membrane and isolated from the host immune system [44].

The promising results in the preclinical studies using the

stringent pig-to-NHP model [45] and the case report of

long-term function of encapsulated neonatal pig islets

transplanted in a diabetic patient without immunosuppres-

sion [46] paved the way for pursuing the potentiality of

islet xenotransplantation in extensive clinical studies. The

first clinical trial was performed in Mexico co-transplant-

ing neonatal pig islets with Sertoli cells in subcutaneous

collagen-covered device in 12 patients with T1D in the

absence of immunosuppression, but showed disappointing

results [47]. In China, transplantation of neonatal pig islets

in 22 T1D subjects treated with a multiple drug immuno-

suppressive regimen resulted in negligible clinical benefit

[48]. Other clinical trials have been currently undertaken

by Living Cell TechnologiesTM in New Zealand: They

performed phase 1/2 clinical trials in Russia, Argentina

and New Zealand (clinicaltrial.gov: NCT01739829,

NCT01736228, NCT00940173). Neonatal pig islets

encapsulated in alginate microcapsules (DIABECELL�)

were transplanted in T1D patients, and their findings are

expected to be published imminently. To date no subject, to

our knowledge, has been rendered insulin independent with

such approaches. In summary, encouraging results in pro-

longed graft survival and data concerning the safety of

transplanted pig islets have recently been obtained and,

although several concerns are still waiting for being

addressed, this strategy may represents a therapeutic

alternative in the near future.

b Cell replacement with expanded b cells

Unlike blood, skin or intestine, that are tissues with a rel-

atively rapid turnover of cells, b cells in the pancreatic

686 Acta Diabetol (2016) 53:683–691

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islets are a quiescent population with a proliferative ratio of

0.1–0.3 %/day in 1-year-old mice [49] and negligible

proliferation, except for the first years after birth or during

pregnancy, in humans [50]. During the past 30 years, many

attempts have been made to generate human b cell lines from many pancreatic sources, but insulin production by

these cells was extremely low or limited at few passages

[51, 52]. In 2005, Narushima et al. [53] reported the suc-

cessful establishment of a functional human b cell line, NAKT-15, that looked promising for cell therapy of dia-

betes, but no new reports on the utility of this cell line have

been published since then. In 2011 another human b cell line was established transducing human fetal pancreas with

a lentiviral vector that expressed SV40LT and human

telomerase reverse transcriptase (hTERT). One of the cell

lines generated with this strategy, the EndoC-bH1, was further characterized and resulted able to secrete insulin in

response to glucose stimulation, was stable at least for 80

passages and expressed many specific b cell markers, without any substantial expression of markers of other

pancreatic cell types [54]. In view of clinical use, a second

generation of human b cell lines has been recently devel- oped; the conditionally immortalized EndoC-bH2 cell line is based on Cre-mediated excision of the immortalizing

transgenes, leading to an arrest of cell proliferation and

pronounced enhancement of b cell-specific features such as insulin expression, content and secretion [55], but further

studies are required to determine the actual safety of these

cells.

b Cell replacement with stem cell-derived b cells

Currently, many opportunities for the cell therapy of sin-

gle-cell disorders like T1D are offered by stem cell dif-

ferentiation. Stem cells are, by definition, undifferentiated

cells that hold both the potential to differentiate into a large

variety of specialized cell types and the ability to go

through numerous cycles of cell division while maintaining

their undifferentiated state (self-renewal). The first

attempts focused on adult stem cells because many tissues

offered the possibility to derive progenitor cells able to

differentiate into pancreatic b-like cells, but until now none of the sources analyzed has proved able to produce ‘‘true’’

b cells capable of secreting insulin in response to glucose and normalizing glycemia in diabetic animal models [56].

So far, the most promising source of cells for cell/organ

replacement therapies is pluripotent stem cells.

Embryonic stem cells

Because of their self-renewal abilities and the capacity to

differentiate into any cell of the body, embryonic stem cells

(ESC) have always been considered the most auspicious

source for cell replacement therapies. In fact, the devel-

opment of ESC lines from the inner cell mass of early stage

human embryos [57] offered the potential to generate any

specialized cell type in large quantities, including insulin-

producing cells. Novocell, a preclinical-stage stem cell

engineering company focused on diabetes, that in 2010

changed its name into ViaCyte, developed a differentiation

protocol of human ESC into b cells, designed along the lines of pancreatic organogenesis in vivo. This protocol

brought ESC through subsequent stages on the desired

path: from definitive endoderm to posterior foregut, then to

pancreatic endoderm, progenitors of endocrine pancreas

and, finally, to hormone-producing endocrine cells. With

their five-step differentiation protocol, ViaCyte succeeded

in obtaining about 7 % of cells that expressed high levels

of proinsulin that was processed, albeit inefficiently, to

insulin and C-peptide [58]. Two other groups, using dif-

ferent culture conditions, confirmed that ESC are able to

differentiate in insulin-producing cells, albeit with a lower

efficiency [59, 60]. Subsequently, Baetge and colleagues

improved their results optimizing their differentiation

protocol and transplanting ESC-derived pancreatic pro-

genitor cells into mice such that after 3 months in vivo the

implanted cells differentiate into mature endocrine cells

that can regulate blood glucose levels after diabetes

induction [61]. The same group recently developed a

scalable and standardized system for the production of

functional pancreatic progenitors from human ESC, further

optimizing their differentiation protocol for the CyT49

ESC line [62]. Finally, on October 29, 2014, ViaCyte

announced the beginning of a phase 1/2 clinical trial

(clinicaltrial.gov: NCT02239354) and that the first patient

of this study was successfully implanted with ESC-derived

insulin-producing cells delivered under the skin in a pro-

prietary device with a selectively porous cell-impermeable

membrane, called the Encaptra� drug delivery system; this

device is designed to protect the implanted cells from

possible immune rejection, to permanently contain the cells

and prevent their distribution away from the implantation

site. This is the first time that an ESC-derived cell

replacement therapy for diabetes is studied in human sub-

jects, and it represents the culmination of a decade of effort

by the ViaCyte team (http://viacyte.com). Meanwhile,

modified or improved protocols have been established

using combinations of cytokines and small molecules, such

as fibroblast growth factors, sonic hedgehog pathway

inhibitors (KAAD-cyclopamine or SANT-1), retinoic acid,

nicotinamide, protein kinase C (PKC) activator (indolac-

tam V) or TGF-b pathway inhibitors (Alk5 inhibitor, dor- somorphin or noggin) [63–65]. Noteworthy are in

particular the directed differentiation strategies reported by

the research units of Melton and Kieffer [66, 67]. These

two groups reported an efficient approach to generate

Acta Diabetol (2016) 53:683–691 687

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in vitro 20–50 % insulin (C-peptide)-positive cells from

human ESC. Upon transplantation into immunocompro-

mised mice, the graft (composed of endocrine and ductal

cells) restored normoglycemia within 2 [66] or 6 weeks

[67], a tremendous improvement compared with the 2- to

3-month period required after transplantation of ESC-

derived pancreatic progenitors [61]. Nevertheless, the

similarities and differences between b-like cells generated by all these groups remain to be elucidated by a direct

comparison. Despite significant successes, three main

problems still limit the use of ESC-derived insulin-pro-

ducing cells. First, due to their pluripotency, undifferenti-

ated cells give rise to teratoma formation in vivo and the

transplantation of unselected differentiated cells would

inevitably lead to tumorigenesis because of the presence of

some residual undifferentiated cells [61]; several attempts

have been made to identify surface markers able to select

pancreatic progenitor cells [68, 69], but the safety of the

selected cells requires further investigation. Another

unsolved problem is related to the evidence that each ESC

line has a different propensity to give rise to pancreatic

cells [70]. Therefore, many cell lines have to be tested

(and, accordingly, the differentiation protocol must be

optimized) in order to identify a set of ESC lines that could

facilitate genetic matching of donor cells to patients and

therefore prevent graft rejection and lifelong immunosup-

pression. The last major problem, which greatly limits the

use of ESC in many countries of the world, is the presence

of ethical concerns regarding the destruction of human

embryos for the production of these cell lines.

Induced pluripotent stem cells

To overcome these obstacles and still obtain pluripotent

cells, the group of professor Yamanaka (winner of the

Nobel Prize in 2012 for this discovery) succeeded in 2006

in reprogramming adult somatic murine cells into induced

pluripotent stem cells (iPSC) through the forced expression

of 4 genes (OCT4, SOX2, KLF4 and c-Myc) [71]. One

year later, Yamanaka’s and two other groups have suc-

cessfully repeated the reprogramming process using human

somatic cells [72, 73]. Mouse and human iPSC resulted

highly comparable to ESC as these cells showed the same

morphology, the same proliferative capacity, had similar

telomerase activity, a normal karyotype, expressed surface

markers and genes that characterize ESC and were also

able to form teratomas in vivo and to differentiate into cells

of all three germ layers in vitro [71, 73].

Several strategies to differentiate iPSC into cells capable

of producing insulin have been tested, with original pro-

tocols or borrowing the experience from ESC. The first

paper that reported successful differentiation of human

iPSC into insulin-secreting cells dates back to 2008, when

the group of Zhang adapted the four-step differentiation

protocol developed for ESC from Jiang et al. [60] and

obtained for the first time b-like cells in vitro from repro- grammed human fibroblasts. Unfortunately, the efficiency

of differentiation process was very low and the total

C-peptide content was significantly lower compared to

adult b cells [74]. Subsequent studies focused on the cul- ture conditions in order to increase the efficiency of dif-

ferentiation of the iPSC into insulin-secreting cells; for

example, in 2010 the group led by Yupo Ma applied a

protocol previously successful for murine ESC [75] to

iPSC derived from adult mouse fibroblasts. With this dif-

ferentiation protocol, they were able to obtain up to 50 %

of cells capable of secreting insulin in response to glucose

stimulus from murine iPSC and, if transplanted into dia-

betic mice, these cells were capable to restore normo-

glycemia [76]. It remains to be confirmed whether the same

differentiation protocol could have the same efficiency in

differentiating human iPSC. One year later, it was reported

the differentiation of human iPSC into insulin-secreting

cells responsive to glucose using a protocol that requires

the addition, compared to ViaCyte one, of two molecules:

indolactam V [63] and GLP-1. The differentiation effi-

ciency was very low, as only 1.29 % of insulin positive

cells were obtained, and their ability to secrete insulin

in vivo has not been verified [77]. Encouraging results have

been reported by other several in vitro studies that used

protocols mimicking the mechanism of in vivo pancreas

development to guide the differentiation of iPSC into b- like cells [78–82] but with a lower efficiency compared to

ESC. Insulin-producing cells, although with low efficiency,

were also generated with iPSC derived from the repro-

gramming of fibroblasts of two patients with diabetes [83],

opening the way not only to autologous cell replacement

therapy of T1D, but also to in vitro modeling of this dis-

ease. Last year two important groups described for the first

time that pancreatic cells derived from the differentiation

of pluripotent stem cells (both embryonic and induced) are

capable to revert diabetes in mice [66, 67]. The Melton’s

group, in particular, described a 4- to 5-week in vitro dif-

ferentiation protocol which involves a combination of

sequential culture steps using factors that affect signaling

in numerous pathways, including signaling by WNT,

activin, hedgehog, TGF-b, retinoic acid and c-secretase inhibitors, and leads to the generation of *50 % of C-peptide and Nkx6.1 double-positive cells from both ESC

and iPSC [66]. These results brought to the foundation of a

company, called Semma Therapeutics (http://www.semma-

tx.com/), focused on the development of an ESC- or iPSC-

based therapy for diabetes.

In conclusion, iPSC retain the same essential properties

of ESC, included the ability to differentiate into b cells, but offer the advantage of allowing the generation of

688 Acta Diabetol (2016) 53:683–691

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autologous cells that might be useful for cell therapy.

However, the main problem of iPSC, which currently still

preclude their use in humans, is related to their intrinsic

characteristic: As pluripotent cells, like ESC, also iPSC

determine the formation of tumors when transplanted into

immunodeficient animals. In addition, other problems are

caused by the reprogramming process itself, as the use for

transfection of integrating virus like retroviruses may cause

insertional mutagenesis, interfere with gene transcription

and induce tumors formation [73]. To overcome these

obstacles, various strategies have been developed: The

removal of the oncogene c-Myc from the set of genes

required for reprogramming [84] or the use of new classes

of vectors for reprogramming that do not integrate into the

host genome [85], thereby drastically decreasing the

tumorigenicity risk without altering the pluripotency. It is

then clear that many efforts still need to be done in order to

make both processes of reprogramming and differentiation

safer and more efficient. It should also be considered that,

although iPSC offer great hope for cell replacement ther-

apy for diabetes, a potential translation in recipients with

T1D will require strategies to avoid recurrence of

autoimmunity, in the form of a selective immunosuppres-

sive therapy or of an encapsulation device for their

immunoprotection [86].

Conclusion

Insulin treatment is not a cure for patients with T1D and

does not eliminate the long-term complications associated

with the disease. Major advances have been achieved in the

field of b Cell replacement through islet transplantation, mainly due to novel immunosuppression strategies. As

limits of islet transplantation are addressed and overcome,

cellular therapy will become the choice for a wider parterre

of people with diabetes. In this scenario, more and more

insulin-secreting cells will be needed and this necessity is

strongly pushing the search for alternative sources. Xeno-

geneic islets hold a great potential, and recent studies have

marked significant progresses in controlling immune

rejection toward xenoantigens. New b cell lines have also been established, and their safety is currently under

investigation. Currently, the most significant advances

come from the stem cell field; in fact, it has been described

that human ESC and iPSC are able to generate pancreatic

progenitors and/or functional b cells in vitro that can treat diabetic mice, and a clinical trials with ESC-derived cells is

ongoing in T1D patients. Moreover, the stem cell approach

may synergize well with other developing innovations such

as the generation of immune isolating and retrievable

devices, fundamental to allow cell therapy without

immunosuppression and to overcome the safety concerns

about tumorigenic cells. It is likely that altogether these

experiences will change the way we treat T1D and lead to

new therapeutic options for patients with diabetes.

Compliance with ethical standards

Conflict of interest The authors declare that they have no conflict of interest.

Ethical standard All works cited in this review have been pub- lished in journals that require approval by the Ethics Committees of

the conducted experiments.

Human and animal rights This article does not contain any studies with human or animal subjects performed by any of the authors.

Informed consent All works cited in this review have been pub- lished in journals that require that informed consents of participants to

reported clinical trials are collected.

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