Mixed chimerism and growth factors augment β cell regeneration and reverse late-stage type 1 diabetes

Biochemical pancreatic β-cell lineage reprogramming: Various cell fate shifts

The incidence of pancreatic diseases has been continuously rising in recent years. Thus, research on pancreatic regeneration is becoming more popular. Chronic hyperglycemia is detrimental to pancreatic β-cells, leading to impairment of insulin secretion which is the main hallmark of pancreatic diseases. Obtaining plenty of functional pancreatic β-cells is the most crucial aspect when studying pancreatic biology and treating diabetes. According to the International Diabetes Federation, diabetes has become a global epidemic, with about 3 million people suffering from diabetes worldwide. Hyperglycemia can lead to many dangerous diseases, including amputation, blindness, neuropathy, stroke, and cardiovascular and kidney diseases. Insulin is widely used in the treatment of diabetes; however, innovative approaches are needed in the academic and preclinical stages. A new approach aims at synthesizing patient-specific functional pancreatic β-cells. The present article focuses on how cells from different tissues can be transformed into pancreatic β-cells.

Dysregulation of β-Cell Proliferation in Diabetes: Possibilities of Combination Therapy in the Development of a Comprehensive Treatment

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia as a result of insufficient insulin levels and/or impaired function as a result of autoimmune destruction or insulin resistance. While Type 1 DM (T1DM) and Type 2 DM (T2DM) occur through different pathological processes, both result in β-cell destruction and/or dysfunction, which ultimately lead to insufficient β-cell mass to maintain normoglycemia. Therefore, therapeutic agents capable of inducing β-cell proliferation is crucial in treating and reversing diabetes; unfortunately, adult human β-cell proliferation has been shown to be very limited (~0.2% of β-cells/24 h) and poorly responsive to many mitogens. Furthermore, diabetogenic insults result in damage to β cells, making it ever more difficult to induce proliferation. In this review, we discuss β-cell mass/proliferation pathways dysregulated in diabetes and current therapeutic agents studied to induce β-cell proliferation. Furthermore, we discuss possible combination therapies of proliferation agents with immunosuppressants and antioxidative therapy to improve overall long-term outcomes of diabetes.

Formation of pancreatic β-cells from precursor cells contributes to the reversal of established type 1 diabetes

Ig-GAD2, an antigen-specific immune modulator, requires bone marrow (BM) cell transfer in order to restore beta (β)-cell formation and induce recovery from established type 1 diabetes (T1D). The BM cells provide endothelial precursor cells (EPCs) that give rise to islet resident endothelial cells (ECs). This study shows that, during development of T1D, the immune attack causes collateral damage to the islet vascular network. The EPC-derived ECs repair and restore islet blood vessel integrity. In addition, β-cell genetic tracing indicates that the newly formed β-cells originate from residual β-cells that escaped the immune attack and, unexpectedly, from β-cell precursors. This indicates that the rejuvenated islet microenvironment invigorates formation of new β-cells not only from residual β-cells but also from precursor cells. This is twofold significant from the perspective of precursor cells as a safe reserve for restoration of β-cell mass and its promise for therapy of T1D long after diagnosis.

Amniotic Membrane Extract Protects Islets From Serum-Deprivation Induced Impairments and Improves Islet Transplantation Outcome

Islet culture prior to transplantation is a standard practice in many transplantation centers. Nevertheless, the abundant islet mass loss and function impairment during this serum-deprivation culture period restrain the success of islet transplantation. In the present study, we used a natural biomaterial derived product, amniotic membrane extract (AME), as medium supplementation of islet pretransplant cultivation to investigate its protective effect on islet survival and function and its underlying mechanisms, as well as the engraftment outcome of islets following AME treatment. Results showed that AME supplementation improved islet viability and function, and decreased islet apoptosis and islet loss during serum-deprived culture. This was associated with the increased phosphorylation of PI3K/Akt and MAPK/ERK signaling pathway. Moreover, transplantation of serum-deprivation stressed islets that were pre-treated with AME into diabetic mice revealed better blood glucose control and improved islet graft survival. In conclusion, AME could improve islet survival and function in vivo and in vitro, and was at least partially through increasing phosphorylation of PI3K/Akt and MAPK/ERK signaling pathway.

Haploidentical mixed chimerism cures autoimmunity in established type 1 diabetic mice

Clinical trials are currently testing whether induction of haploidentical mixed chimerism (Haplo-MC) induces organ transplantation tolerance. Whether Haplo-MC can be used to treat established autoimmune diseases remains unknown. Here, we show that established autoimmunity in euthymic and adult-thymectomized NOD (H-2g7) mice was cured by induction of Haplo-MC under a non-myeloablative anti-thymocyte globulin-based conditioning regimen and infusion of CD4+ T cell-depleted hematopoietic graft from H-2b/g7 F1 donors that expressed autoimmune-resistant H-2b or from H-2s/g7 F1 donors that expressed autoimmune-susceptible H-2s. The cure was associated with enhanced thymic negative selection, increased thymic Treg (tTreg) production, and anergy or exhaustion of residual host-type autoreactive T cells in the periphery. The peripheral tolerance was accompanied by expansion of donor- and host-type CD62L-Helios+ tTregs as well as host-type Helios-Nrp1+ peripheral Tregs (pTregs) and PD-L1hi plasmacytoid DCs (pDCs). Depletion of donor- or host-type Tregs led to reduction of host-type PD-L1hi pDCs and recurrence of autoimmunity, whereas PD-L1 deficiency in host-type DCs led to reduction of host-type pDCs and Helios-Nrp1+ pTregs. Thus, induction of Haplo-MC reestablished both central and peripheral tolerance through mechanisms that depend on allo-MHC+ donor-type DCs, PD-L1hi host-type DCs, and the generation and persistence of donor- and host-type tTregs and pTregs.

Reversal of autoimmunity by mixed chimerism enables reactivation of β cells and transdifferentiation of α cells in diabetic NOD mice

Cure of autoimmune type 1 diabetes (T1D) requires both reversal of autoimmunity and regeneration or resupply of insulin-producing β cells. We have observed that combination therapy with induction of haploidentical mixed chimerism and administration of gastrin and epidermal growth factor (EGF) cures firmly established T1D. The predominant source of β cell regeneration in mice comes from reactivation of dysfunctional insulin^lo β cells and transdifferentiation of α cells. These studies have provided insights into β cell regeneration mechanisms in firmly established autoimmune T1D, in particular, reactivation of the insulin^lo β cells after reversal of autoimmunity by induction of haploidentical mixed chimerism. These studies also provide a preclinical scientific basis for the feasibility of cure of long-standing T1D in humans.

Type 1 diabetes (T1D) results from the autoimmune destruction of β cells, so cure of firmly established T1D requires both reversal of autoimmunity and restoration of β cells. It is known that β cell regeneration in nonautoimmune diabetic mice can come from differentiation of progenitors and/or transdifferentiation of α cells. However, the source of β cell regeneration in autoimmune nonobese diabetic (NOD) mice remains unclear. Here, we show that, after reversal of autoimmunity by induction of haploidentical mixed chimerism, administration of gastrin plus epidermal growth factor augments β cell regeneration and normalizes blood glucose in the firmly established diabetic NOD mice. Using transgenic NOD mice with inducible lineage-tracing markers for insulin-producing β cells, Sox9⁺ ductal progenitors, Nestin⁺ mesenchymal stem cells, and glucagon-producing α cells, we have found that both reactivation of dysfunctional low-level insulin expression (insulin^lo) β cells and neogenesis contribute to the regeneration, with the latter predominantly coming from transdifferentiation of α cells. These results indicate that, after reversal of autoimmunity, reactivation of β cells and transdifferentiation of α cells can provide sufficient new functional β cells to reach euglycemia in firmly established T1D.

Pancreatic cancer triggers diabetes through TGF-β-mediated selective depletion of islet β-cells

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease that remains incurable because of late diagnosis, which renders any therapeutic intervention challenging. Most PDAC patients develop de novo diabetes, which exacerbates their morbidity and mortality. How PDAC triggers diabetes is still unfolding. Using a mouse model of KrasG12D-driven PDAC, which faithfully recapitulates the progression of the human disease, we observed a massive and selective depletion of β-cells, occurring very early at the stages of preneoplastic lesions. Mechanistically, we found that increased TGF beta (TGF-β) signaling during PDAC progression caused erosion of β-cell mass through apoptosis. Suppressing TGF-β signaling, either pharmacologically through TGF-β immunoneutralization or genetically through deletion of Smad4 or TGF-β type II receptor (TβRII), afforded substantial protection against PDAC-driven β-cell depletion. From a translational perspective, both activation of TGF-β signaling and depletion of β-cells frequently occur in human PDAC, providing a mechanistic explanation for the pathogenesis of diabetes in PDAC patients, and further implicating new-onset diabetes as a potential early prognostic marker for PDAC.

Long-Term Correction of Diabetes in Mice by In Vivo Reprogramming of Pancreatic Ducts

Direct lineage reprogramming can convert readily available cells in the body into desired cell types for cell replacement therapy. This is usually achieved through forced activation or repression of lineage-defining factors or pathways. In particular, reprogramming toward the pancreatic β cell fate has been of great interest in the search for new diabetes therapies. It has been suggested that cells from various endodermal lineages can be converted to β-like cells. However, it is unclear how closely induced cells resemble endogenous pancreatic β cells and whether different cell types have the same reprogramming potential. Here, we report in vivo reprogramming of pancreatic ductal cells through intra-ductal delivery of an adenoviral vector expressing the transcription factors Pdx1, Neurog3, and Mafa. Induced β-like cells are mono-hormonal, express genes essential for β cell function, and correct hyperglycemia in both chemically and genetically induced diabetes models. Compared with intrahepatic ducts and hepatocytes treated with the same vector, pancreatic ducts demonstrated more rapid activation of β cell transcripts and repression of donor cell markers. This approach could be readily adapted to humans through a commonly performed procedure, endoscopic retrograde cholangiopancreatography (ERCP), and provides potential for cell replacement therapy in type 1 diabetes patients.

MHC-mismatched mixed chimerism restores peripheral tolerance of noncross-reactive autoreactive T cells in NOD mice

Mixed chimerism has shown good potential to cure some autoimmune diseases and prevent tissue rejection. It is known that MHC-mismatched but not -matched mixed chimerism effectively tolerizes autoreactive T cells, even those noncross-reactive T cells that do not directly recognize donor-type antigen presenting cells [i.e., dendritic cells (DCs)]. How this is accomplished remains unknown. These studies have shown that tolerizing peripheral residual host-type noncross-reactive autoreactive T cells requires engraftment of donor-type DCs and involves a host-type DC-mediated increase in donor-type Treg cells, which associates with restoration of tolerogenic features of host-type plasmacytoid DCs and expansion of host-type Treg cells. This study suggests a previously unrecognized tolerance network among donor- and host-type DCs and Treg cells in MHC-mismatched mixed chimeras.

Autoimmune type 1 diabetes (T1D) and other autoimmune diseases are associated with particular MHC haplotypes and expansion of autoreactive T cells. Induction of MHC-mismatched but not -matched mixed chimerism by hematopoietic cell transplantation effectively reverses autoimmunity in diabetic nonobese diabetic (NOD) mice, even those with established diabetes. As expected, MHC-mismatched mixed chimerism mediates deletion in the thymus of host-type autoreactive T cells that have T-cell receptor (TCR) recognizing (cross-reacting with) donor-type antigen presenting cells (APCs), which have come to reside in the thymus. However, how MHC-mismatched mixed chimerism tolerizes host autoreactive T cells that recognize only self-MHC–peptide complexes remains unknown. Here, using NOD.Rag1^−/−.BDC2.5 or NOD.Rag1^−/−.BDC12-4.1 mice that have only noncross-reactive transgenic autoreactive T cells, we show that induction of MHC-mismatched but not -matched mixed chimerism restores immune tolerance of peripheral noncross-reactive autoreactive T cells. MHC-mismatched mixed chimerism results in increased percentages of both donor- and host-type Foxp3⁺ Treg cells and up-regulated expression of programmed death-ligand 1 (PD-L1) by host-type plasmacytoid dendritic cells (pDCs). Furthermore, adoptive transfer experiments showed that engraftment of donor-type dendritic cells (DCs) and expansion of donor-type Treg cells are required for tolerizing the noncross-reactive autoreactive T cells in the periphery, which are in association with up-regulation of host-type DC expression of PD-L1 and increased percentage of host-type Treg cells. Thus, induction of MHC-mismatched mixed chimerism may establish a peripheral tolerogenic DC and Treg network that actively tolerizes autoreactive T cells, even those with no TCR recognition of the donor APCs.

Pancreatic β Cell Regeneration as a Possible Therapy for Diabetes

Diabetes is the result of having inadequate supply of functional insulin-producing β cells. Two possible approaches for replenishing the β cells are: (1) replacement by transplanting cadaveric islets or β cells derived from human embryonic stem cells/induced pluripotent stem cells and (2) induction of endogenous regeneration. This review focuses on endogenous regeneration, which can follow two pathways: enhanced replication of existing β cells and formation of new β cells from cells not expressing insulin, either by conversion from a differentiated cell type (transdifferentiation) or differentiation from progenitors (neogenesis). Exciting progress on both pathways suggest that regeneration may have therapeutic promise.

Transplantation Tolerance through Hematopoietic Chimerism: Progress and Challenges for Clinical Translation

The perception that transplantation of hematopoietic stem cells can confer tolerance to any tissue or organ from the same donor is widely accepted but it has not yet become a treatment option in clinical routine. The reasons for this are multifaceted but can generally be classified into safety and efficacy concerns that also became evident from the results of the first clinical pilot trials. In comparison to standard immunosuppressive therapies, the infection risk associated with the cytotoxic pre-conditioning necessary to allow allogeneic bone marrow engraftment and the risk of developing graft-vs.-host disease (GVHD) constitute the most prohibitive hurdles. However, several approaches have recently been developed at the experimental level to reduce or even overcome the necessity for cytoreductive conditioning, such as costimulation blockade, pro-apoptotic drugs, or Treg therapy. But even in the absence of any hazardous pretreatment, the recipients are exposed to the risk of developing GVHD as long as non-tolerant donor T cells are present. Total lymphoid irradiation and enriching the stem cell graft with facilitating cells emerged as potential strategies to reduce this peril. On the other hand, the long-lasting survival of kidney allografts, seen with transient chimerism in some clinical series, questions the need for durable chimerism for robust tolerance. From a safety point of view, loss of chimerism would indeed be favorable as it eliminates the risk of GVHD, but also complicates the assessment of tolerance. Therefore, other biomarkers are warranted to monitor tolerance and to identify those patients who can safely be weaned off immunosuppression. In addition to these safety concerns, the limited efficacy of the current pilot trials with approximately 40-60% patients becoming tolerant remains an important issue that needs to be resolved. Overall, the road ahead to clinical routine may still be rocky but the first successful long-term patients and progress in pre-clinical research provide encouraging evidence that deliberately inducing tolerance through hematopoietic chimerism might eventually make it from dream to reality.

Murine models of transplantation tolerance through mixed chimerism: advances and roadblocks

Organ transplantation is the treatment of choice for patients with end-stage organ failure, but chronic immunosuppression is taking its toll in terms of morbidity and poor efficacy in preventing late graft loss. Therefore, a drug-free state would be desirable where the recipient permanently accepts a donor organ while remaining otherwise fully immunologically competent. Mouse studies unveiled mixed chimerism as an effective approach to induce such donor-specific tolerance deliberately and laid the foundation for a series of clinical pilot trials. Nevertheless, its widespread clinical implementation is currently prevented by cytotoxic conditioning and limited efficacy. Therefore, the use of mouse studies remains an indispensable tool for the development of novel concepts with potential for translation and for the delineation of underlying tolerance mechanisms. Recent innovations developed in mice include the use of pro-apoptotic drugs or regulatory T cell (Treg ) transfer for promoting bone marrow engraftment in the absence of myelosuppression and new insight gained in the role of innate immunity and the interplay between deletion and regulation in maintaining tolerance in chimeras. Here, we review these and other recent advances in murine studies inducing transplantation tolerance through mixed chimerism and discuss both the advances and roadblocks of this approach.

β-cell replacement sources for type 1 diabetes: a focus on pancreatic ductal cells

Thorough research on the capacity of human islet transplantation to cure type 1 diabetes led to the achievement of 3- to 5-year-long insulin independence in nearly half of transplanted patients. Yet, translation of this technique to clinical routine is limited by organ shortage and the need for long-term immunosuppression, restricting its use to adults with unstable disease. The production of new bona fide β cells in vitro was thus investigated and finally achieved with human pluripotent stem cells (PSCs). Besides ethical concerns about the use of human embryos, studies are now evaluating the possibility of circumventing the spontaneous tumor formation associated with transplantation of PSCs. These issues fueled the search for cell candidates for β-cell engineering with safe profiles for clinical translation. In vivo studies revealed the regeneration capacity of the exocrine pancreas after injury that depends at least partially on facultative progenitors in the ductal compartment. These stimulated subpopulations of pancreatic ductal cells (PDCs) underwent β-cell transdifferentiation through reactivation of embryonic signaling pathways. In vitro models for expansion and differentiation of purified PDCs toward insulin-producing cells were described using cocktails of growth factors, extracellular-matrix proteins and transcription factor overexpression. In this review, we will describe the latest findings in pancreatic β-cell mass regeneration due to adult ductal progenitor cells. We will further describe recent advances in human PDC transdifferentiation to insulin-producing cells with potential for clinical translational studies.

Growth factors and medium hyperglycemia induce Sox9+ ductal cell differentiation into β cells in mice with reversal of diabetes

We previously reported that long-term administration of a low dose of gastrin and epidermal growth factor (GE) augments β-cell neogenesis in late-stage diabetic autoimmune mice after eliminating insulitis by induction of mixed chimerism. However, the source of β-cell neogenesis is still unknown. SRY (sex-determining region Y)-box 9(+) (Sox9(+)) ductal cells in the adult pancreas are clonogenic and can give rise to insulin-producing β cells in an in vitro culture. Whether Sox9(+) ductal cells in the adult pancreas can give rise to β cells in vivo remains controversial. Here, using lineage-tracing with genetic labeling of Insulin- or Sox9-expressing cells, we show that hyperglycemia (>300 mg/dL) is required for inducing Sox9(+) ductal cell differentiation into insulin-producing β cells, and medium hyperglycemia (300-450 mg/dL) in combination with long-term administration of low-dose GE synergistically augments differentiation and is associated with normalization of blood glucose in nonautoimmune diabetic C57BL/6 mice. Short-term administration of high-dose GE cannot augment differentiation, although it can augment preexisting β-cell replication. These results indicate that medium hyperglycemia combined with long-term administration of low-dose GE represents one way to induce Sox9(+) ductal cell differentiation into β cells in adult mice.

MHC-mismatched mixed chimerism augments thymic regulatory T-cell production and prevents relapse of EAE in mice

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system with demyelination, axon damage, and paralysis. Induction of mixed chimerism with allogeneic donors has been shown to not cause graft-versus-host disease (GVHD) in animal models and humans. We have reported that induction of MHC-mismatched mixed chimerism can cure autoimmunity in autoimmune NOD mice, but this approach has not yet been tested in animal models of MS, such as experimental autoimmune encephalomyelitis (EAE). Here, we report that MHC-mismatched mixed chimerism with C57BL/6 (H-2(b)) donor in SJL/J (H-2(s)) EAE recipients eliminates clinical symptoms and prevents relapse. This cure is demonstrated by not only disappearance of clinical signs but also reversal of autoimmunity; elimination of infiltrating T, B, and macrophage cells in the spinal cord; and regeneration of myelin sheath. The reversal of autoimmunity is associated with a marked reduction of autoreactivity of CD4(+) T cells and significant increase in the percentage of Foxp3(+) Treg among host-type CD4(+) T cells in the spleen and lymph nodes. The latter is associated with a marked reduction of the percentage of host-type CD4(+)CD8(+) thymocytes and an increase of Treg percentage among the CD4(+)CD8(+) and CD4(+)CD8(-) thymocytes. Thymectomy leads to loss of prevention of EAE relapse by induction of mixed chimerism, although there is a dramatic expansion of host-type Treg cells in the lymph nodes. These results indicate that induction of MHC-mismatched mixed chimerism can restore thymic negative selection of autoreactive CD4(+) T cells, augment production of Foxp3(+) Treg, and cure EAE.

Beta Cell Mass Restoration in Alloxan-Diabetic Mice Treated with EGF and Gastrin

One week of treatment with EGF and gastrin (EGF/G) was shown to restore normoglycemia and to induce islet regeneration in mice treated with the diabetogenic agent alloxan. The mechanisms underlying this regeneration are not fully understood. We performed genetic lineage tracing experiments to evaluate the contribution of beta cell neogenesis in this model. One day after alloxan administration, mice received EGF/G treatment for one week. The treatment could not prevent the initial alloxan-induced beta cell mass destruction, however it did reverse glycemia to control levels within one day, suggesting improved peripheral glucose uptake. In vitro experiments with C2C12 cell line showed that EGF could stimulate glucose uptake with an efficacy comparable to that of insulin. Subsequently, EGF/G treatment stimulated a 3-fold increase in beta cell mass, which was partially driven by neogenesis and beta cell proliferation as assessed by beta cell lineage tracing and BrdU-labeling experiments, respectively. Acinar cell lineage tracing failed to show an important contribution of acinar cells to the newly formed beta cells. No appearance of transitional cells co-expressing insulin and glucagon, a hallmark for alpha-to-beta cell conversion, was found, suggesting that alpha cells did not significantly contribute to the regeneration. An important fraction of the beta cells significantly lost insulin positivity after alloxan administration, which was restored to normal after one week of EGF/G treatment. Alloxan-only mice showed more pronounced beta cell neogenesis and proliferation, even though beta cell mass remained significantly depleted, suggesting ongoing beta cell death in that group. After one week, macrophage infiltration was significantly reduced in EGF/G-treated group compared to the alloxan-only group. Our results suggest that EGF/G-induced beta cell regeneration in alloxan-diabetic mice is driven by beta cell neogenesis, proliferation and recovery of insulin. The glucose-lowering effect of the treatment might play an important role in the regeneration process.

PD-L1-driven tolerance protects neurogenin3-induced islet neogenesis to reverse established type 1 diabetes in NOD mice

A breakdown in self-tolerance underlies autoimmune destruction of β-cells and type 1 diabetes. A cure by restoring β-cell mass is limited by the availability of transplantable β-cells and the need for chronic immunosuppression. Evidence indicates that inhibiting costimulation through the PD-1/PD-L1 pathway is central to immune tolerance. We therefore tested whether induction of islet neogenesis in the liver, protected by PD-L1-driven tolerance, reverses diabetes in NOD mice. We demonstrated a robust induction of neo-islets in the liver of diabetic NOD mice by gene transfer of Neurogenin3, the islet-defining factor, along with betacellulin, an islet growth factor. These neo-islets expressed all the major pancreatic hormones and transcription factors. However, an enduring restoration of glucose-stimulated insulin secretion and euglycemia occurs only when tolerance is also induced by the targeted overexpression of PD-L1 in the neo-islets, which results in inhibition of proliferation and increased apoptosis of infiltrating CD4(+) T cells. Further analysis revealed an inhibition of cytokine production from lymphocytes isolated from the liver but not from the spleen of treated mice, indicating that treatment did not result in generalized immunosuppression. This treatment strategy leads to persistence of functional neo-islets that resist autoimmune destruction and consequently an enduring reversal of diabetes in NOD mice.

MHC-mismatched mixed chimerism mediates thymic deletion of cross-reactive autoreactive T cells and prevents insulitis in nonobese diabetic mice

Type 1 diabetic NOD mice have defects in both thymic negative selection and peripheral regulation of autoreactive T cells, and induction of mixed chimerism can effectively reverse these defects. Our recent studies suggest that MHC-mismatched mixed chimerism mediates negative selection of autoreactive thymocytes in wild-type NOD and TCR-transgenic NOD.Rag1(+/+).BDC2.5 mice. However, it remains unknown how mismatched I-A(b) MHC class II can mediate deletion of autoreactive T cells positively selected by I-A(g7). In the present study, we directly tested the hypothesis that mismatched MHC class II in mixed chimeras mediates deletion of cross-reactive autoreactive thymocytes. We first identify that transgenic BDC2.5 T cells from NOD.Rag1(+/+).BDC2.5 but not NOD.Rag1(-/-).BDC2.5 mice possess cross-reactive TCRs with endogenous TCRα-chains; MHC-mismatched H-2(b) but not matched H-2(g7) mixed chimerism mediates thymic deletion of the cross-reactive transgenic T cells in NOD.Rag1(+/+).BDC2.5 mice. Second, by transplanting T cell-depleted (TCD) bone marrow (BM) cells from NOD.Rag1(+/+).BDC2.5 or NOD.Rag1(-/-).BDC2.5 mice into lethally irradiated MHC-mismatched H-2(b) C57BL/6 or MHC-matched congenic B6.H-2(g7) recipients, we demonstrate that NOD.Rag1(+/+).BDC2.5 BM-derived cross-reactive transgenic T cells, but not NOD.Rag1(-/-).BDC2.5 BM-derived non-cross-reactive transgenic T cells, can be positively selected in MHC-mismatched H-2(b) thymus. Third, by cotransplanting NOD.Rag1(+/+).BDC2.5 TCD BM cells with BM cells from MHC-mismatched T cell-deficient C57BL/6 mice into lethally irradiated MHC-matched B6.H-2(g7) recipients, we demonstrate that thymic deletion of the cross-reactive transgenic T cells is dependent on MHC-mismatched donor BM-derived APCs but not on donor BM-derived T cells. Taken together, our studies indicate that MHC-mismatched mixed chimerism can mediate thymic deletion of cross-reactive autoreactive T cells that express more than one TCR.

Mig6 haploinsufficiency protects mice against streptozotocin-induced diabetes

AIMS/HYPOTHESIS

EGF and gastrin co-administration reverses type 1 diabetes in rodent models. However, the failure of this to translate into a clinical treatment suggests that EGF-mediated tissue repair is a complicated process and warrants further investigation. Thus, we aimed to determine whether EGF receptor (EGFR) feedback inhibition by mitogen-inducible gene 6 protein (MIG6) limits the effectiveness of EGF therapy and promotes type 1 diabetes development.

METHODS

We treated Mig6 (also known as Errfi1) haploinsufficient mice (Mig6 (+/-)) and their wild-type littermates (Mig6 (+/+)) with multiple low doses of streptozotocin (STZ), and monitored diabetes development via glucose homeostasis tests and histological analyses. We also investigated MIG6-mediated cytokine-induced desensitisation of EGFR signalling and the DNA damage repair response in 832/13 INS-1 beta cells.

RESULTS

Whereas STZ-treated Mig6 (+/+) mice became diabetic, STZ-treated Mig6 (+/-) mice remained glucose tolerant. In addition, STZ-treated Mig6 (+/-) mice exhibited preserved circulating insulin levels following a glucose challenge. As insulin sensitivity was similar between Mig6 (+/-) and Mig6 (+/+) mice, the preserved glucose tolerance in STZ-treated Mig6 (+/-) mice probably results from preserved beta cell function. This is supported by elevated Pdx1 and Irs2 mRNA levels in islets isolated from STZ-treated Mig6 (+/-) mice. Conversely, MIG6 overexpression in isolated islets compromises glucose-stimulated insulin secretion. Studies in 832/13 cells suggested that cytokine-induced MIG6 hinders EGFR activation and inhibits DNA damage repair. STZ-treated Mig6 (+/-) mice also have increased beta cell mass recovery.

CONCLUSIONS/INTERPRETATION

Reducing Mig6 expression promotes beta cell repair and abates the development of experimental diabetes, suggesting that MIG6 may be a novel therapeutic target for preserving beta cells.

MHC-mismatched chimerism is required for induction of transplantation tolerance in autoimmune nonobese diabetic recipients

In nonautoimmune recipients, induction of mixed and complete chimerism with hematopoietic progenitor cells from MHC (HLA)-matched or -mismatched donors are effective approaches for induction of organ transplantation immune tolerance in both animal models and patients. But it is still unclear whether this is the case in autoimmune recipients. With the autoimmune diabetic NOD mouse model, we report that, although mixed and complete MHC-mismatched chimerism provide immune tolerance to donor-type islet and skin transplants, neither mixed nor complete MHC-matched chimerism does. The MHC-mismatched chimerism not only tolerizes the de novo developed, but also the residual pre-existing host-type T cells in a mismatched MHC class II-dependent manner. In the MHC-mismatched chimeras, the residual host-type peripheral T cells appear to be anergic with upregulation of PD-1 and downregulation of IL-7Rα. Conversely, in the MHC-matched chimeras, the residual host-type peripheral T cells manifest both alloreactivity and autoreactivity; they not only mediate insulitis and sialitis in the recipient, but also reject allogeneic donor-type islet and skin grafts. Interestingly, transgenic autoreactive BDC2.5 T cells from Rag1(+/+), but not from Rag1(-/-), NOD mice show alloreactivity and mediate both insulitis and rejection of allografts. Taken together, MHC-mismatched, but not MHC-matched, chimerism can effectively provide transplantation immune tolerance in autoimmune recipients.

Depletion of host CCR7(+) dendritic cells prevented donor T cell tissue tropism in anti-CD3-conditioned recipients

We reported previously that anti-CD3 mAb treatment before hematopoietic cell transplantation (HCT) prevented graft-versus-host disease (GVHD) and preserved graft-versus-leukemia (GVL) effects in mice. These effects were associated with downregulated donor T cell expression of tissue-specific homing and chemokine receptors, marked reduction of donor T cell migration into GVHD target tissues, and deletion of CD103(+) dendritic cells (DCs) in mesenteric lymph nodes (MLN). MLN CD103(+) DCs and peripheral lymph node (PLN) DCs include CCR7(+) and CCR7(-) subsets, but the role of these DC subsets in regulating donor T cell expression of homing and chemokine receptors remain unclear. Here, we show that recipient CCR7(+), but not CCR7(-), DCs in MLN induced donor T cell expression of gut-specific homing and chemokine receptors in a retinoid acid-dependent manner. CCR7 regulated activated DC migration from tissue to draining lymph node, but it was not required for the ability of DCs to induce donor T cell expression of tissue-specific homing and chemokine receptors. Finally, anti-CD3 treatment depleted CCR7(+) but not CCR7(-) DCs by inducing sequential expansion and apoptosis of CCR7(+) DCs in MLN and PLN. Apoptosis of CCR7(+) DCs was associated with DC upregulation of Fas expression and natural killer cell but not T, B, or dendritic cell upregulation of FasL expression in the lymph nodes. These results suggest that depletion of CCR7(+) host-type DCs, with subsequent inhibition of donor T cell migration into GVHD target tissues, can be an effective approach in prevention of acute GVHD and preservation of GVL effects.

Distinctions between the islets of mice and men: implications for new therapies for type 1 and 2 diabetes

OBJECTIVE

To elucidate why diabetes is so difficult to treat despite the present tools and pharmacologic armamentarium and to provide insights into emerging therapies by describing human and rodent data that demonstrates the ability to transform progenitor cells within the adult pancreas into new islets.

METHODS

A literature review focused on the distinctions between human and rodent islets.

RESULTS

We are beginning to elucidate important differences between the architecture and composition of the islets of Langerhans in humans and rodents. In contrast to rodent islets, human islets are more heterogeneous in cellular composition and have more prominent intra-islet vascularity, with smooth muscle-containing blood vessels that are not present in rodent islets. Some studies report that more than 70% of human beta cells have direct physical contact with other cell types, whereas others describe that smaller human islets possess features more typical of rodents, while larger islets exhibit greater vascularity and a cellular distribution distinct from centrally clustered beta cells surrounded by a mantle of alpha and delta cells found in rodents.

CONCLUSIONS

The differences between the islets of mice and men may influence why treatments hailed as reversing diabetes among rodents have not been successfully translated into humans. Increased understanding of the complexities within the human islet may yield unique insights into reversing diabetes in humans.

IL-2 immunotherapy reveals potential for innate beta cell regeneration in the non-obese diabetic mouse model of autoimmune diabetes

Type-1 diabetes (T1D) is an autoimmune disease targeting insulin-producing beta cells, resulting in dependence on exogenous insulin. To date, significant efforts have been invested to develop immune-modulatory therapies for T1D treatment. Previously, IL-2 immunotherapy was demonstrated to prevent and reverse T1D at onset in the non-obese diabetic (NOD) mouse model, revealing potential as a therapy in early disease stage in humans. In the NOD model, IL-2 deficiency contributes to a loss of regulatory T cell function. This deficiency can be augmented with IL-2 or antibody bound to IL-2 (Ab/IL-2) therapy, resulting in regulatory T cell expansion and potentiation. However, an understanding of the mechanism by which reconstituted regulatory T cell function allows for reversal of diabetes after onset is not clearly understood. Here, we describe that Ab/IL-2 immunotherapy treatment, given at the time of diabetes onset in NOD mice, not only correlated with reversal of diabetes and expansion of Treg cells, but also demonstrated the ability to significantly increase beta cell proliferation. Proliferation appeared specific to Ab/IL-2 immunotherapy, as anti-CD3 therapy did not have a similar effect. Furthermore, to assess the effect of Ab/IL-2 immunotherapy well after the development of diabetes, we tested the effect of delaying treatment for 4 weeks after diabetes onset, when beta cells were virtually absent. At this late stage after diabetes onset, Ab/IL-2 treatment was not sufficient to reverse hyperglycemia. However, it did promote survival in the absence of exogenous insulin. Proliferation of beta cells could not account for this improvement as few beta cells remained. Rather, abnormal insulin and glucagon dual-expressing cells were the only insulin-expressing cells observed in islets from mice with established disease. Thus, these data suggest that in diabetic NOD mice, beta cells have an innate capacity for regeneration both early and late in disease, which is revealed through IL-2 immunotherapy.

β-Cell differentiation and regeneration in type 1 diabetes

Pancreatic insulin-producing β-cells have traditionally been viewed as a quiescent cell population. However, several recent lines of evidence indicated that like most tissues the β-cell mass is dynamically regulated with ongoing β-cell regeneration throughout life to replenish lost or damaged β-cells. In type 1 diabetes (T1D), this fine-tuned balance between β-cell death and β-cell renewal in the endocrine pancreas is lost and the deficit in β-cell mass is largely caused by autoimmune-mediated apoptosis. Currently, the concept that a cure for T1D will require both re-establishment of immunological tolerance along with replacement or regeneration of a functional β-cell mass in T1D patients is generally accepted. In this study our current understanding of the events directing β-cell replication, β-cell reprogramming from different cell types and β-cell regeneration is reviewed, in view of the results of various immunomodulatory strategies aiming at blocking autoimmune responses against pancreatic β-cells and at improving β-cell mass and function in subjects with T1D.

Testing agents for prevention or reversal of type 1 diabetes in rodents

We report the results of an independent laboratory's tests of novel agents to prevent or reverse type 1 diabetes (T1D) in the non-obese diabetic (NOD) mouse, BioBreeding diabetes prone (BBDP) rat, and multiple autoimmune disease prone (MAD) rat models. Methods were developed to better mimic human clinical trials, including: prescreening, randomization, blinding, and improved glycemic care of the animals. Agents were suggested by the research community in an open call for proposals, and selected for testing by an NIDDK appointed independent review panel. Agents selected for testing to prevent diabetes at later stages of progression in a rodent model were a STAT4 antagonist (DT22669), alpha1 anti-trypsin (Aralast NP), celastrol (a natural product with anti-inflammatory properties), and a Macrophage Inflammatory Factor inhibitor (ISO-092). Agents tested for reversal of established T1D in rodent models were: alpha1 anti-trypsin (Aralast NP), tolerogenic peptides (Tregitopes), and a long-acting formulation of GLP-1 (PGC-GLP-1). None of these agents were seen to prevent or reverse type 1 diabetes, while the positive control interventions were effective: anti-CD3 treatment provided disease reversal in the NOD mouse, dexamethasone prevented T1D induction in the MAD rat, and cyclosporin prevented T1D in the BBDP rat. For some tested agents, details of previous formulation, delivery, or dosing, as well as laboratory procedure, availability of reagents and experimental design, could have impacted our ability to confirm prior reports of efficacy in preclinical animal models. In addition, the testing protocols utilized here provided detection of effects in a range commonly used in placebo controlled clinical trials (for example, 50% effect size), and thus may have been underpowered to observe more limited effects. That said, we believe the results compiled here, showing good control and repeatability, confirm the feasibility of screening diverse test agents in an independent laboratory.

Gastrin: a distinct fate of neurogenin3 positive progenitor cells in the embryonic pancreas

Neurogenin3(+) (Ngn3(+)) progenitor cells in the developing pancreas give rise to five endocrine cell types secreting insulin, glucagon, somatostatin, pancreatic polypeptide and ghrelin. Gastrin is a hormone produced primarily by G-cells in the stomach, where it functions to stimulate acid secretion by gastric parietal cells. Gastrin is expressed in the embryonic pancreas and is common in islet cell tumors, but the lineage and regulators of pancreatic gastrin(+) cells are not known. We report that gastrin is abundantly expressed in the embryonic pancreas and disappears soon after birth. Some gastrin(+) cells in the developing pancreas co-express glucagon, ghrelin or pancreatic polypeptide, but many gastrin(+) cells do not express any other islet hormone. Pancreatic gastrin(+) cells express the transcription factors Nkx6.1, Nkx2.2 and low levels of Pdx1, and derive from Ngn3(+) endocrine progenitor cells as shown by genetic lineage tracing. Using mice deficient for key transcription factors we show that gastrin expression depends on Ngn3, Nkx2.2, NeuroD1 and Arx, but not Pax4 or Pax6. Finally, gastrin expression is induced upon differentiation of human embryonic stem cells to pancreatic endocrine cells expressing insulin. Thus, gastrin(+) cells are a distinct endocrine cell type in the pancreas and an alternative fate of Ngn3+ cells.

Recovery from overt type 1 diabetes ensues when immune tolerance and β-cell formation are coupled with regeneration of endothelial cells in the pancreatic islets

Immune modulation of pancreatic inflammation induces recovery from type 1 diabetes (T1D), but remission was not durable, perhaps because of an inability to sustain the formation and function of new pancreatic β-cells. We have previously shown that Ig-GAD2, carrying GAD 206-220 peptide, induced in hyperglycemic mice immune modulation that was able to control pancreatic inflammation, stimulate β-cell regeneration, and prevent T1D progression. Herein, we show that the same Ig-GAD2 regimen given to mice with overt T1D was unable to reverse the course of disease despite eradication of Th1 and Th17 cells from the pancreas. However, the regimen was able to sustain recovery from T1D when Ig-GAD2 was accompanied with transfer of bone marrow (BM) cells from healthy donors. Interestingly, alongside immune modulation, there was concomitant formation of new β-cells and endothelial cells (ECs) in the pancreas. The new β-cells were of host origin while the donor BM cells gave rise to the ECs. Moreover, transfer of purified BM endothelial progenitors instead of whole BM cells sustained both β-cell and EC formation and reversal of diabetes. Thus, overcoming T1D requires both immune modulation and repair of the islet vascular niche to preserve newly formed β-cells.

Emerging combinatorial hormone therapies for the treatment of obesity and T2DM

Peptide hormones and proteins control body weight and glucose homeostasis by engaging peripheral and central metabolic signalling pathways responsible for the maintenance of body weight and euglycaemia. The development of obesity, often in association with type 2 diabetes mellitus (T2DM), reflects a dysregulation of metabolic, anorectic and orexigenic pathways in multiple organs. Notably, therapeutic attempts to normalize body weight and glycaemia with single agents alone have generally been disappointing. The success of bariatric surgery, together with emerging data from preclinical studies, illustrates the rationale and feasibility of using two or more agonists, or single co-agonists, for the treatment of obesity and T2DM. Here, we review advances in the science of co-agonist therapy, and highlight promising areas and challenges in co-agonist development. We describe mechanisms of action for combinations of glucagon-like peptide 1, glucagon, gastric inhibitory polypeptide, gastrin, islet amyloid polypeptide and leptin, which enhance weight loss whilst preserving glucoregulatory efficacy in experimental models of obesity and T2DM. Although substantial progress has been achieved in preclinical studies, the putative success and safety of co-agonist therapy for the treatment of patients with obesity and T2DM remains uncertain and requires extensive additional clinical validation.

Enhancing pancreatic Beta-cell regeneration in vivo with pioglitazone and alogliptin

Aims/Hypothesis

Pancreatic beta-cells retain limited ability to regenerate and proliferate after various physiologic triggers. Identifying therapies that are able to enhance beta-cell regeneration may therefore be useful for the treatment of both type 1 and type 2 diabetes.

Methods

In this study we investigated endogenous and transplanted beta-cell regeneration by serially quantifying changes in bioluminescence from beta-cells from transgenic mice expressing firefly luciferase under the control of the mouse insulin I promoter. We tested the ability of pioglitazone and alogliptin, two drugs developed for the treatment of type 2 diabetes, to enhance beta-cell regeneration, and also defined the effect of the immunosuppression with rapamycin and tacrolimus on transplanted islet beta mass.

Results

Pioglitazone is a stimulator of nuclear receptor peroxisome proliferator-activated receptor gamma while alogliptin is a selective dipeptidyl peptidase IV inhibitor. Pioglitazone alone, or in combination with alogliptin, enhanced endogenous beta-cell regeneration in streptozotocin-treated mice, while alogliptin alone had modest effects. In a model of syngeneic islet transplantation, immunosuppression with rapamycin and tacrolimus induced an early loss of beta-cell mass, while treatment with insulin implants to maintain normoglycemia and pioglitazone plus alogliptin was able to partially promote beta-cell mass recovery.

Conclusions/Interpretation

These data highlight the utility of bioluminescence for serially quantifying functional beta-cell mass in living mice. They also demonstrate the ability of pioglitazone, used either alone or in combination with alogliptin, to enhance regeneration of endogenous islet beta-cells as well as transplanted islets into recipients treated with rapamycin and tacrolimus.

Stem cell therapy to cure type 1 diabetes: from hype to hope

Type 1 diabetes mellitus (T1D) is a chronic, multifactorial autoimmune disease that involves the progressive destruction of pancreatic β-cells, ultimately resulting in the loss of insulin production and secretion. The goal of clinical intervention is to prevent or arrest the onset and progression of autoimmunity, reverse β-cell destruction, and restore glycometabolic and immune homeostasis. Despite promising outcomes observed with islet transplantation and advancements in immunomodulatory therapies, the need for an effective cell replacement strategy for curing T1D still persists. Stem cell therapy offers a solution to the cited challenges of islet transplantation. While the regenerative potential of stem cells can be harnessed to make available a self-replenishing supply of glucose-responsive insulin-producing cells, their immunomodulatory properties may potentially be used to prevent, arrest, or reverse autoimmunity, ameliorate innate/alloimmune graft rejection, and prevent recurrence of the disease. Herein, we discuss the therapeutic potential of stem cells derived from a variety of sources for the cure of T1D, for example, embryonic stem cells, induced pluripotent stem cells, bone marrow-derived hematopoietic stem cells, and multipotent mesenchymal stromal cells derived from bone marrow, umbilical cord blood, and adipose tissue. The benefits of combinatorial approaches designed to ensure the successful clinical translation of stem cell therapeutic strategies, such as approaches combining effective stem cell strategies with islet transplantation, immunomodulatory drug regimens, and/or novel bioengineering techniques, are also discussed. To conclude, the application of stem cell therapy in the cure for T1D appears extremely promising.

Three Strikes and You're Cured

New research shows that in a mouse model of type 1 diabetes, it may be possible to abrogate autoimmunity and then exploit the ability of pancreatic β cells to regenerate, thereby restoring blood glucose regulation.