Thrombomodulin improves early outcomes after intraportal islet transplantation

Engineering Pancreatic Islets to Transiently Codisplay on Their Surface Thrombomodulin and CD47 Immunomodulatory Proteins as a Means of Mitigating Instant Blood-Mediated Inflammatory Reaction following Intraportal Transplantation

Most pancreatic islets are destroyed immediately after intraportal transplantation by an instant blood-mediated inflammatory reaction (IBMIR) generated through activation of coagulation, complement, and proinflammatory pathways. Thus, effective mitigation of IBMIR may be contingent on the combined use of agents targeting these pathways for modulation. CD47 and thrombomodulin (TM) are two molecules with distinct functions in regulating coagulation and proinflammatory responses. We previously reported that the islet surface can be modified with biotin for transient display of novel forms of these two molecules chimeric with streptavidin (SA), that is, thrombomodulin chimeric with SA (SA-TM) and CD47 chimeric with SA (SA-CD47), as single agents with improved engraftment following intraportal transplantation. This study aimed to test whether islets can be coengineered with SA-TM and SA-CD47 molecules as a combinatorial approach to improve engraftment by inhibiting IBMIR. Mouse islets were effectively coengineered with both molecules without a detectable negative impact on their viability and metabolic function. Coengineered islets were refractory to destruction by IBMIR ex vivo and showed enhanced engraftment and sustained function in a marginal mass syngeneic intraportal transplantation model. Improved engraftment correlated with a reduction in intragraft innate immune infiltrates, particularly neutrophils and M1 macrophages. Moreover, transcripts for various intragraft procoagulatory and proinflammatory agents, including tissue factor, HMGB1 (high-mobility group box-1), IL-1β, IL-6, TNF-α, IFN-γ, and MIP-1α, were significantly reduced in coengineered islets. These data demonstrate that the transient codisplay of SA-TM and SA-CD47 proteins on the islet surface is a facile and effective platform to modulate procoagulatory and inflammatory responses with implications for both autologous and allogeneic islet transplantation.

Engineering pancreatic islets with a novel form of thrombomodulin protein to overcome early graft loss triggered by instant blood-mediated inflammatory reaction

The instant blood-mediated inflammatory reaction (IBMIR) is initiated by innate immune responses that cause substantial islet loss after intraportal transplantation. Thrombomodulin (TM) is a multifaceted innate immune modulator. In this study, we report the generation of a chimeric form of thrombomodulin with streptavidin (SA-TM) for transient display on the surface of islets modified with biotin to mitigate IBMIR. SA-TM protein expressed in insect cells showed the expected structural and functional features. SA-TM converted protein C into activated protein C, blocked phagocytosis of xenogeneic cells by mouse macrophages and inhibited neutrophil activation. SA-TM was effectively displayed on the surface of biotinylated islets without a negative effect on their viability or function. Islets engineered with SA-TM showed improved engraftment and established euglycemia in 83% of diabetic recipients when compared with 29% of recipients transplanted with SA-engineered islets as control in a syngeneic minimal mass intraportal transplantation model. Enhanced engraftment and function of SA-TM-engineered islets were associated with the inhibition of intragraft proinflammatory innate cellular and soluble mediators of IBMIR, such as macrophages, neutrophils, high-mobility group box 1, tissue factor, macrophage chemoattractant protein-1, interleukin-1β, interleukin-6, tumor necrosis factor-α, interferon-γ. Transient display of SA-TM protein on the islet surface to modulate innate immune responses causing islet graft destruction has clinical potential for autologous and allogeneic islet transplantation.

Minimizing Post-Infusion Portal Vein Bleeding during Intrahepatic Islet Transplantation in Mice

Although the liver is currently accepted as the primary transplantation site for human islets in clinical settings, islets are transplanted under the kidney capsule in most rodent preclinical islet transplantation studies. This model is commonly used because murine intrahepatic islet transplantation is technically challenging, and a high percentage of mice could die from surgical complications, especially bleeding from the injection site post-transplantation. In this study, two procedures that can minimize the incidence of post-infusion portal vein bleeding are demonstrated. The first method applies an absorbable hemostatic gelatin sponge to the injection site, and the second method involves penetrating the islet injection needle through the fat tissue first and then into the portal vein by using the fat tissue as a physical barrier to stop bleeding. Both methods could effectively prevent bleeding-induced mouse death. The whole liver section showing islet distribution and evidence of islet thrombosis post-transplantation, a typical feature for intrahepatic islet transplantation, were presented. These improved protocols refine the intrahepatic islet transplantation procedures and may help laboratories set up the procedure to study islet survival and function in pre-clinical settings.

Immune checkpoint CD47 molecule engineered islets mitigate instant blood-mediated inflammatory reaction and show improved engraftment following intraportal transplantation

Instant blood-mediated inflammatory reaction (IBMIR) causes significant destruction of islets transplanted intraportally. Myeloid cells are a major culprit of IBMIR. Given the critical role of CD47 as a negative checkpoint for myeloid cells, we hypothesized that the presence of CD47 on islets will minimize graft loss by mitigating IBMIR. We herein report the generation of a chimeric construct, SA-CD47, encompassing the extracellular domain of CD47 modified to include core streptavidin (SA). SA-CD47 protein was expressed in insect cells and efficiently displayed on biotin-modified mouse islet surface without a negative impact on their viability and function. Rat cells engineered with SA-CD47 were refractory to phagocytosis by mouse macrophages. SA-CD47-engineered islets showed intact structure and minimal infiltration by CD11b+ granulocytes/macrophages as compared with SA-engineered controls in an in vitro loop assay mitigating IBMIR. In a syngeneic marginal mass model of intraportal transplantation, SA-CD47-engineered islets showed better engraftment and function as compared with the SA-control group (87.5% vs 14.3%). Engraftment was associated with low levels of intrahepatic inflammatory cells and mediators of islet destruction, including high-mobility group box-1, tissue factor, and IL-1β. These findings support the use of CD47 as an innate immune checkpoint to mitigate IBMIR for enhanced islet engraftment with translational potential.

Engineering the vasculature for islet transplantation

The microvasculature in the pancreatic islet is highly specialized for glucose sensing and insulin secretion. Although pancreatic islet transplantation is a potentially life-changing treatment for patients with insulin-dependent diabetes, a lack of blood perfusion reduces viability and function of newly transplanted tissues. Functional vasculature around an implant is not only necessary for the supply of oxygen and nutrients but also required for rapid insulin release kinetics and removal of metabolic waste. Inadequate vascularization is particularly a challenge in islet encapsulation. Selectively permeable membranes increase the barrier to diffusion and often elicit a foreign body reaction including a fibrotic capsule that is not well vascularized. Therefore, approaches that aid in the rapid formation of a mature and robust vasculature in close proximity to the transplanted cells are crucial for successful islet transplantation or other cellular therapies. In this paper, we review various strategies to engineer vasculature for islet transplantation. We consider properties of materials (both synthetic and naturally derived), prevascularization, local release of proangiogenic factors, and co-transplantation of vascular cells that have all been harnessed to increase vasculature. We then discuss the various other challenges in engineering mature, long-term functional and clinically viable vasculature as well as some emerging technologies developed to address them. The benefits of physiological glucose control for patients and the healthcare system demand vigorous pursuit of solutions to cell transplant challenges. STATEMENT OF SIGNIFICANCE: Insulin-dependent diabetes affects more than 1.25 million people in the United States alone. Pancreatic islets secrete insulin and other endocrine hormones that control glucose to normal levels. During preparation for transplantation, the specialized islet blood vessel supply is lost. Furthermore, in the case of cell encapsulation, cells are protected within a device, further limiting delivery of nutrients and absorption of hormones. To overcome these issues, this review considers methods to rapidly vascularize sites and implants through material properties, pre-vascularization, delivery of growth factors, or co-transplantation of vessel supporting cells. Other challenges and emerging technologies are also discussed. Proper vascular growth is a significant component of successful islet transplantation, a treatment that can provide life-changing benefits to patients.

Effect of liver histopathology on islet cell engraftment in the model mimicking autologous islet cell transplantation

BACKGROUND

The inflammatory milieu in the liver as determined by histopathology is different in individual patients undergoing autologous islet cell transplantation. We hypothesized that inflammation related to fatty-liver adversely impacts islet survival. To test this hypothesis, we used a mouse model of fatty-liver to determine the outcome of syngeneic islet transplantation after chemical pancreatectomy.

METHODS

Mice (C57BL/6) were fed a high-fat-diet from 6 weeks of age until attaining a weight of ≥28 grams (6-8 weeks) to produce a fatty liver (histologically > 30% fat);steatosis was confirmed with lipidomic profile of liver tissue. Islets were infused via the intra-portal route in fatty-liver and control mice after streptozotocin induction of diabetes. Outcomes were assessed by the rate of euglycemia, liver histopathology, evaluation of liver inflammation by measuring tissue cytokines IL-1β and TNF-α by RT-PCR and CD31 expression by immunohistochemistry.

RESULTS

The difference in the euglycemic fraction between the normal liver group (90%, 9/10) and the fatty-liver group (37.5%, 3/8) was statistically significant at the 18^th day post- transplant and was maintained to the end of the study (day 28) (p = 0.019, X² = 5.51). Levels of TNF-α and IL-1β were elevated in fatty-liver mice (p = 0.042, p = 0.037). Compared to controls cytokine levels were elevated after islet cell transplantation and in transplanted fatty-liver mice as compared to either fatty- or islet transplant group alone (p = NS). A difference in the histochemical pattern of CD31 could not be determined.

CONCLUSION

Fatty-liver creates an inflammatory state which adversely affects the outcome of autologous islet cell transplantation.

Recombinant and chemo-/bio-orthogonal synthesis of liposomal thrombomodulin and its antithrombotic activity

Thrombomodulin (TM) is an endothelial cell membrane protein that acts as a major cofactor in the protein C anticoagulant pathway. The EGF-like domains 4-6 of TM (TM₄₅₆) are essential for PC activation. In this study, we proposed a liposomal recombinant TM conjugate to mimic the membrane TM structure and its anticoagulant activity. First, a DSPE-PEG₂₀₀₀-TM₄₅₆ was successfully synthesized by site-specific conjugation of azido-TM₄₅₆ with DSPE-PEG₂₀₀₀-DBCO via copper-free click chemistry quantitatively. Then, liposome-TM₄₅₆ was fabricated via direct liposome formation with the DSPE-PEG₂₀₀₀-TM₄₅₆ and other lipids. This liposomal formulation of TM₄₅₆ retained protein C activation activity as that of TM₄₅₆. Also, liposome-TM₄₅₆ was much more stable and had a longer plasma half-life than TM₄₅₆ and DSPE-PEG₂₀₀₀-TM₄₅₆, respectively. Moreover, liposome-TM₄₅₆ showed in vivo anticoagulant effect by decreasing the mortality from 80% to 20% in a thrombin-induced thromboembolism mouse model. The reported liposome-TM₄₅₆ conjugate mimics the endothelial TM anticoagulation activity and may serve as an effective anticoagulant agent candidate for future development.

Novel technologies to engineer graft for tolerance induction

PURPOSE OF REVIEW

Conquering allograft rejection remains an elusive goal in spite of recent breakthroughs in the field of immunosuppression. Much of the problem lies in the toxicity and side-effects of long-term use of systemic immunosuppressant drugs, which are sometimes ineffective in controlling rejection, but also hinder establishment of transplant tolerance. In this review, we discuss novel technologies that use grafts engineered with immunomodulatory molecules as a means of inducing tolerance.

RECENT FINDINGS

Several recent studies have demonstrated the feasibility of engineering cells, tissues, or solid organ grafts with immunoregulatory biologics to achieve long termgraft survival without the use of chronic immunosuppression. This approach was shown to primarily change the ratio of T effector versus CD4+CD25+FoxP3+ T regulatory cells within the graft microenvironment in favor of attaining localized tolerance induction and maintenance.

SUMMARY

Localized immunomodulation using biologic-engineered allografts represent a new paradigm for achieving long-term graft survival in the absence of chronic use of immunosuppression. The manipulation of the graft, rather than the recipient, not only ensures short- and long-term safety by minimizing the adverse effects of immunosuppression, but also allows retention of immune competency critical for the ability of the recipient to fight infections and cancer.

Instant Blood-Mediated Inflammatory Reaction in Hepatocyte Transplantation: Current Status and Future Perspectives

Hepatocyte transplantation (HT) is emerging as a promising alternative to orthotopic liver transplantation (OLT) in patients with certain liver-based metabolic disease and acute liver failure. Hepatocytes are generally infused into the portal venous system, from which they migrate into the liver cell plates of the native organ. One of the major hurdles to the sustained success of this therapy is early cell loss, with up to 70% of hepatocytes lost immediately following infusion. This is largely thought to be due to the instant blood-mediated inflammatory reaction (IBMIR), resulting in the activation of complement and coagulation pathways. Transplanted hepatocytes produce and release tissue factor (TF), which activates the coagulation pathway, leading to the formation of thrombin and fibrin clots. Thrombin can further activate a number of complement proteins, leading to the activation of the membrane attack complex (MAC) and subsequent hepatocyte cell death. Inflammatory cells including granulocytes, monocytes, Kupffer cells, and natural killer (NK) cells have been shown to cluster around transplanted hepatocytes, leading to their rapid clearance shortly after transplantation. Current research aims to improve cell engraftment and prevent early cell loss. This has been proven successful in vitro using pharmacological interventions such as melagatran, low-molecular-weight dextran sulphate, and N-acetylcysteine (NAC). Effective inhibition of IBMIR would significantly improve hepatocyte engraftment, proliferation, and function, providing successful treatment for patients with liver-based metabolic diseases.

Advances in Local Drug Release and Scaffolding Design to Enhance Cell Therapy for Diabetes

Islet transplant is a curative treatment for insulin-dependent diabetes. However, challenges, including poor tissue survival and a lack of efficient engraftment, must be overcome. An encapsulating or scaffolding material can act as a vehicle for agents carefully chosen for the islet transplant application. From open porous scaffolds to spherical capsules and conformal coatings, greater immune protection is often accompanied by greater distances to microvasculature. Generating a local oxygen supply from the implant material or encouraging vessel growth through the release of local factors can create an oxygenated engraftment site. Intricately related to the vascularization response, inflammatory interaction with the cell supporting implant is a long-standing hurdle to material-based islet transplant. Modulation of the immune responses to the islets as well as the material itself must be considered. To match the post-transplant complexity, the release rate can be tuned to orchestrate temporal responses. Material degradation properties can be utilized in passive approaches or external stimuli and biological cues in active approaches. A combination of multiple carefully chosen factors delivered in an agent-specialized manner is considered by this review to improve the long-term function of islets transplanted in scaffolding and encapsulating materials.

THERAPY OF ENDOCRINE DISEASE: Islet transplantation for type 1 diabetes: so close and yet so far away

Over the past decades, tremendous efforts have been made to establish pancreatic islet transplantation as a standard therapy for type 1 diabetes. Recent advances in islet transplantation have resulted in steady improvements in the 5-year insulin independence rates for diabetic patients. Here we review the key challenges encountered in the islet transplantation field which include islet source limitation, sub-optimal engraftment of islets, lack of oxygen and blood supply for transplanted islets, and immune rejection of islets. Additionally, we discuss possible solutions for these challenges.

Genomic profiling of host responses to Lassa virus: therapeutic potential from primate to man

Lassa virus infection elicits distinctive changes in host gene expression and metabolism. We focus on changes in host gene expression that may be biomarkers that discriminate individual pathogens or may help to provide a prognosis for disease. In addition to assessing mRNA changes, functional studies are also needed to discriminate causes of disease from mechanisms of host resistance. Host responses that drive pathogenesis are likely to be targets for prevention or therapy. Host responses to Lassa or its related arenaviruses have been monitored in cell culture, in animal models of hemorrhagic fever, in Lassa-infected nonhuman primates and, to a limited extent, in infected human beings. Here, we describe results from those studies and discuss potential targets for reducing virus replication and mitigating disease.

Engineering biomimetic materials for islet transplantation

A closed-loop system that provides both the sensing of glucose and the appropriate dosage of insulin could dramatically improve treatment options for insulin-dependent diabetics. The intrahepatic implantation of allogeneic islets has the potential to provide this intimate control, by transplanting the very cells that have this inherent sensing and secretion capacity. Limiting islet transplantation, however, is the significant loss and dysfunction of islets following implantation, due to the poor engraftment environment and significant immunological attack. In this review, we outline approaches that seek to address these challenges via engineering biomimetic materials. These materials can serve to mimic natural processes that work toward improving engraftment, minimizing inflammation, and directing immunological responses. Biomimetic materials can serve to house cells, recapitulate native microenvironments, release therapeutic agents in a physiological manner, and/or present agents to direct cells towards desired responses. By integrating these approaches, superior platforms capable of improving long-term engraftment and acceptance of transplanted islets are on the horizon.

The role and regulation of complement activation as part of the thromboinflammation elicited in cell therapies

Cell therapies in which the cells come into direct contact with blood and other body fluids are emerging treatment procedures for patients with various diseases, such as diabetes mellitus, liver insufficiency, and graft-versus-host disease. However, despite recent progress, these procedures are associated with tissue loss caused by thromboinflammatory reactions. These deleterious reactions involve the activation of the complement and coagulation cascades and platelet and leukocyte activation, ultimately resulting in clot formation and damage to the implanted cells. In this concept review, we discuss the basic mechanisms underlying the thrombininflammatory process, with special reference to the engagement of complement and emerging strategies for the therapeutic regulation of these reactions that include the use of selective systemic inhibitors and various procedures to coat the surfaces of the cells. The coating procedures may also be applied to other treatment modalities in which similar mechanisms are involved, including whole organ transplantation, treatment with biomaterials in contact with blood, and extracorporeal procedures.

Three-dimensional islet graft histology: panoramic imaging of neural plasticity in sympathetic reinnervation of transplanted islets under the kidney capsule

Microscopic examination of transplanted islets in an ectopic environment provides information to evaluate islet engraftment, including revascularization and reinnervation. However, because of the dispersed nature of blood vessels and nerves, global visualization of the graft neurovascular network has been difficult. In this research we revealed the neurovascular network by preparing transparent mouse islet grafts under the kidney capsule with optical clearing to investigate the sympathetic reinnervation via three-dimensional confocal microscopy. Normoglycemic and streptozotocin-induced diabetic mice were used in syngeneic islet transplantation, with both groups maintaining euglycemia after transplantation. Triple staining of insulin/glucagon, blood vessels, and tyrosine hydroxylase (sympathetic marker) was used to reveal the graft microstructure, vasculature, and sympathetic innervation. Three weeks after transplantation, we observed perigraft sympathetic innervation similar to the peri-islet sympathetic innervation in the pancreas. Six weeks after transplantation, prominent intragraft, perivascular sympathetic innervation was achieved, resembling the pancreatic intraislet, perivascular sympathetic innervation in situ. Meanwhile, in diabetic recipients, a higher graft sympathetic nerve density was found compared with grafts in normoglycemic recipients, indicating the graft neural plasticity in response to the physiological difference of the recipients and the resolving power of this imaging approach. Overall, this new graft imaging method provides a useful tool to identify the islet neurovascular complex in an ectopic environment to study islet engraftment.

The role of platelets in coagulation dysfunction in xenotransplantation, and therapeutic options

Xenotransplantation could resolve the increasing discrepancy between the availability of deceased human donor organs and the demand for transplantation. Most advances in this field have resulted from the introduction of genetically engineered pigs, e.g., α1,3-galactosyltransferase gene-knockout (GTKO) pigs transgenic for one or more human complement-regulatory proteins (e.g., CD55, CD46, CD59). Failure of these grafts has not been associated with the classical features of acute humoral xenograft rejection, but with the development of thrombotic microangiopathy in the graft and/or consumptive coagulopathy in the recipient. Although the precise mechanisms of coagulation dysregulation remain unclear, molecular incompatibilities between primate coagulation factors and pig natural anticoagulants exacerbate the thrombotic state within the xenograft vasculature. Platelets play a crucial role in thrombosis and contribute to the coagulation disorder in xenotransplantation. They are therefore important targets if this barrier is to be overcome. Further genetic manipulation of the organ-source pigs, such as pigs that express one or more coagulation-regulatory genes (e.g., thrombomodulin, endothelial protein C receptor, tissue factor pathway inhibitor, CD39), is anticipated to inhibit platelet activation and the generation of thrombus. In addition, adjunctive pharmacologic anti-platelet therapy may be required. The genetic manipulations that are currently being tested are reviewed, as are the potential pharmacologic agents that may prove beneficial.

Activated protein C and its potential applications in prevention of islet β-cell damage and diabetes

Activated protein C (APC) is derived from its precursor, protein C (PC). Originally thought to be synthesized exclusively by the liver, recent reports have shown that PC is also produced by many other cells including pancreatic islet β cells. APC functions as a physiological anticoagulant with anti-inflammatory, anti-apoptotic, and barrier-stabilizing properties. APC exerts its protective effects via an intriguing mechanism requiring combinations of endothelial PC receptor, protease-activated receptors, epidermal growth factor receptor, Tie2 or CD11b, depending on cell types. Diabetes is a chronic condition resulted from the body's inability to produce and/or properly use insulin. The prevalence of diabetes has risen dramatically and has become one of the major causes of premature mortality and morbidity worldwide. Diabetes prevention is an ideal approach to reduce this burden. Type 1 and type 2 diabetes are the major forms of diabetes mellitus, and both are characterized by an autoimmune response, intraislet inflammation, β-cell apoptosis, and progressive β-cell loss. Protecting β-cell from damage is critical in both prevention and treatment of diabetes. Recent in vitro and animal studies show that APC's strong anti-inflammatory and anti-apoptotic properties are beneficial in preventing β-cell destruction and diabetes in the NOD mouse model of type 1 diabetes. Future preventive and therapeutic uses of APC in diabetes look very promising.

Anti-inflammatory strategies to enhance islet engraftment and survival

Early innate inflammatory reaction strongly affects islet engraftment and survival after intrahepatic transplantation. This early immune response is triggered by ischemia-reperfusion injury and instant blood mediated inflammatory reaction (IBMIR) occurring hours and days after islet infusion. Evidence in both mouse model and in human counterpart suggest the involvement of coagulation, complement system, and proinflammatory chemokines/cytokines. Identification and targeting of pathway(s), playing a role as "master regulator(s)" in post-transplant detrimental inflammatory events, is now mandatory to improve islet transplantation success. This review will focus on inflammatory pathway(s) differentially modulated by islet isolation and mainly associated with the early post-transplant events. Moreover, we will take into account anti-inflammatory strategies that have been tested at 2 levels: on the graft, ex vivo, during islet culture (i.e., donor) and/or on the graft site, in vivo, early after islet infusion (i.e., recipient).

Transcriptome analysis of human peripheral blood mononuclear cells exposed to Lassa virus and to the attenuated Mopeia/Lassa reassortant 29 (ML29), a vaccine candidate

Lassa virus (LASV) is the causative agent of Lassa Fever and is responsible for several hundred thousand infections and thousands of deaths annually in West Africa. LASV and the non-pathogenic Mopeia virus (MOPV) are both rodent-borne African arenaviruses. A live attenuated reassortant of MOPV and LASV, designated ML29, protects rodents and primates from LASV challenge and appears to be more attenuated than MOPV. To gain better insight into LASV-induced pathology and mechanism of attenuation we performed gene expression profiling in human peripheral blood mononuclear cells (PBMC) exposed to LASV and the vaccine candidate ML29. PBMC from healthy human subjects were exposed to either LASV or ML29. Although most PBMC are non-permissive for virus replication, they remain susceptible to signal transduction by virus particles. Total RNA was extracted and global gene expression was evaluated during the first 24 hours using high-density microarrays. Results were validated using RT-PCR, flow cytometry and ELISA. LASV and ML29 elicited differential expression of interferon-stimulated genes (ISG), as well as genes involved in apoptosis, NF-kB signaling and the coagulation pathways. These genes could eventually serve as biomarkers to predict disease outcomes. The remarkable differential expression of thrombomodulin, a key regulator of inflammation and coagulation, suggests its involvement with vascular abnormalities and mortality in Lassa fever disease.

The virulent Lassa fever virus (LASV) and the non-pathogenic Mopeia virus (MOPV) infect rodents and, incidentally, people in West Africa. The mechanism of LASV damage in human beings is unclear. There is no licensed Lassa fever vaccine and therapeutic intervention is usually too late. The ML29 vaccine candidate derived from Lassa and Mopeia viruses protects rodents and primates from Lassa fever disease. Peripheral blood mononuclear cells from healthy human subjects were exposed to either LASV or ML29 in order to identify early cellular responses that could be attributed to the difference in virulence between the two viruses. Differential expression of interferon-stimulated genes as well as coagulation-related genes could lead to an explanation for Lassa fever pathogenesis and indicate protective treatments for Lassa fever disease.

Tissue factor triggers procoagulation in transplanted mesenchymal stem cells leading to thromboembolism

Mesenchymal stem cells (MSCs) have shown extreme clinical promise as a therapeutic regenerative system in the treatment of numerous types of diseases. A recent report, however, documented lethal pulmonary thromboembolism in a patient following the administration of adipose-derived MSCs (ADSCs). In our study, we designed experiments to examine the role of tissue factor (TF), which is highly expressed at the level of mRNA and localized to the cell surface of cultured MSCs, as a triggering factor in the procoagulative cascade activated by infused MSCs. A high mortality rate of ~85% in mice was documented following intravenous infusion of mouse ADSCs within 24 h due to the observation of pulmonary embolism. Rotation thromboelastometry and plasma clotting assay demonstrated significant procoagulation by the cultured mouse ADSCs, and preconditioning of ADSCs with an anti-TF antibody or usage of factor VII deficient plasma in the assay successfully suppressed the procoagulant properties. These properties were also observed in human ADSCs, and could be suppressed by recombinant human thrombomodulin. In uncultured mouse adipose-derived cells (ADCs), the TF-triggered procoagulant activity was not observed and all mice infused with these uncultured ADCs survived after 24 h. This clearly demonstrated that the process of culturing cells plays a critical role in sensitizing these cells as a procoagulator through the induction of TF expression. Our results would recommend that clinical applications of MSCs to inhibit TF activity using anti-coagulant agents or genetic approaches to maximize clinical benefit to the patients.

The potential of endothelial colony-forming cells to improve early graft loss after intraportal islet transplantation

Early graft loss in islet transplantation means that a large amount of donor islets is required. Endothelial cells and endothelial colony-forming cells (ECFCs) have been reported to improve instant blood-mediated inflammatory reaction (IBMIR) in vitro. In this study, we examined if ECFC-coated porcine islets would prevent early graft loss in vivo. Human ECFCs were prepared from cord blood and cocultured with islets to make composite grafts. Diabetic nude mice underwent intraportal transplantation. Blood glucose levels were monitored, and morphological examination of the grafts along with analysis of the components of IBMIR and inflammatory reaction were performed with the liver tissues. The ECFC-coated islets significantly decreased blood glucose levels immediately after transplantation compared to the uncoated islets. Composite ECFC islet grafts were observed in the liver sections, associated with a more insulin(+) area compared to that of the uncoated group within 48 h after transplantation. Deposition of CD41a, C5b-9, and CD11b(+) cells was also decreased in the ECFC-coated group. Expression of porcine HMGB1 and mouse TNF-α was increased in the transplantated groups compared to the sham operation group, with a trend of a decreasing trend across the uncoated group, the ECFC-coated group, and the sham group. We demonstrated that the composite ECFC porcine islets transplanted into the portal vein of nude mice improved early graft loss and IBMIR in vivo.

Control of instant blood-mediated inflammatory reaction to improve islets of Langerhans engraftment

PURPOSE OF REVIEW

Transplantation of islets of Langerhans is an emerging treatment procedure for patients with severe type 1 diabetes, but despite recent progress the procedure is associated with massive tissue loss caused by an inflammatory reaction termed instant blood-mediated inflammatory reaction (IBMIR). This reaction involves activation of the complement and coagulation cascades, ultimately resulting in clot formation and infiltration of leukocytes into the islets, which leads to disruption of islet integrity and islet destruction.

RECENT FINDINGS

In this review we discuss basic mechanisms underlying the IBMIR and emerging strategies for therapeutic regulation of the IBMIR. These include the use of selective inhibitors of the coagulation and complement systems, different procedures to coat the surface of the islets as well as the development of composite islet-endothelial cell grafts.

SUMMARY

The IBMIR is a major cause of tissue loss in clinical islet transplantation, and most likely in other cell therapies in which cells are exposed to blood. Thus, it is an obvious target for therapeutic intervention. Due to its complexity, it is necessary to use different strategies to control the IBMIR.

Soluble donor DNA and islet injury after transplantation

INTRODUCTION

A large proportion of clinical islet transplant recipients fail to initially achieve or sustain meaningful independence from exogenous insulin use. We hypothesized that immediate allograft injury is a key constraint on independence from exogenous insulin use.

METHODS

Standard human leukocyte antigen genotyping was reviewed to identify nonshared polymorphisms between 21 prospectively recruited islet transplant recipients from a single institution and their respective donors. Human leukocyte antigen polymorphism-specific quantitative polymerase chain reaction was used to quantify donor DNA shed into blood by injured islets from serial sera acquired over the first 10 days postprocedure and examined for correlation with achievement of insulin independence.

RESULTS

Nearly fourfold higher serum concentrations of donor DNA were detected in subjects whose grafts failed to generate insulin independence. The median for the average area under the curve in recipients who did and did not achieve insulin independence was 12 (range, 1-61) and 45 (range, 14-255) donor genome equivalents (gEq)-day/mL (p=0.03), respectively.

CONCLUSIONS

These findings represent the first direct testing of allograft injury in humans undergoing islet cell transplantation. Injury to donor islets very soon after transplantation may represent an important barrier to achieving insulin independence other than adaptive immune responses targeting allografts at later times. In addition, soluble donor DNA merits further development as a quantifiable biomarker to evaluate new interventions aimed at mitigating immediate islet injury.

Advancing islet transplantation: from engraftment to the immune response

The promise and progress of islet transplantation for treating type 1 diabetes has been challenged by obstacles to patient accessibility and long-term graft function that may be overcome by integrating emerging technologies in biomaterials, drug delivery and immunomodulation. The hepatic microenvironment and traditional systemic immunosuppression stress the vulnerable islets and contribute to the limited success of transplantation. Locally delivering extracellular matrix proteins and trophic factors can enhance transplantation at extrahepatic sites by promoting islet engraftment, revascularisation and long-term function while avoiding unintended systemic effects. Cell- and cytokine-based therapies for immune cell recruitment and reprogramming can inhibit local and systemic immune system activation that normally attacks transplanted islets. Combined with antigen-specific immunotherapies, states of operational tolerance may be achievable, reducing or eliminating the long-term pharmaceutical burden. Integration of these technologies to enhance engraftment and combat rejection may help to advance the therapeutic efficacy and availability of islet transplantation.

Islet transplantation and encapsulation: an update on recent developments

Human islet transplantation can provide good glycemic control in diabetic recipients without exogenous insulin. However, a major factor limiting its application is the recipient's need to adhere to life-long immunosuppression, something that has serious side effects. Microencapsulating human islets is a strategy that should prevent rejection of the grafted tissue without the need for anti-rejection drugs. Despite promising studies in various animal models, the encapsulated human islets so far have not made an impact in the clinical setting. Many non-immunological and immunological factors such as biocompatibility, reduced immunoprotection, hypoxia, pericapsular fibrotic overgrowth, effects of the encapsulation process and post-transplant inflammation hamper the successful application of this promising technology. In this review, strategies are discussed to overcome the above-mentioned factors and to enhance the survival and function of encapsulated insulin-producing cells, whether in islets or surrogate β-cells. Studies at our center show that barium alginate microcapsules are biocompatible in rodents, but not in humans, raising concerns over the use of rodents to predict outcomes. Studies at our center also show that the encapsulation process had little or no effect on the cellular transcriptome of human islets and on their ability to function either in vitro or in vivo. New approaches incorporating further modifications to the microcapsule surface to prevent fibrotic overgrowth are vital, if encapsulated human islets or β-cell surrogates are to become a viable therapy option for type 1 diabetes in humans.

Controlling coagulation dysregulation in xenotransplantation

PURPOSE OF REVIEW

Deletion of the α1,3-galactosyltransferase (GalT) gene in pigs has removed a major xenoantigen but has not eliminated the problem of dysregulated coagulation and vascular injury. Rejecting GalT knockout organ xenografts almost invariably show evidence of thrombosis and platelet sequestration, and primate recipients frequently develop consumptive coagulopathy. This review examines recent findings that illuminate potential mechanisms of this current barrier to successful xenotransplantation.

RECENT FINDINGS

The coagulation response to xenotransplantation differs depending on the type of organ and quite likely the distinct vasculatures. Renal xenografts appear more likely to initiate consumptive coagulopathy than cardiac xenografts, possibly reflecting differential transcriptional responses. Liver xenografts induce rapid and profound thrombocytopenia resulting in recipient death within days due to bleeding; ex-vivo data suggest that liver endothelial cells and hepatocytes are responsible for platelet consumption by a coagulation-independent process.It has been proposed that expression of recipient tissue factor on platelets and monocytes is an important trigger of consumptive coagulopathy. Finally, pigs transgenic for human anticoagulants and antithrombotics are slowly but surely coming on line, but have not yet been rigorously tested to date.

SUMMARY

Successful control of coagulation dysregulation in xenotransplantation may require different combinatorial pharmacological and genetic strategies for different organs.

Permanent protection of PLG scaffold transplanted allogeneic islet grafts in diabetic mice treated with ECDI-fixed donor splenocyte infusions

Allogeneic islet cell transplantation is a promising treatment for human type 1 diabetes. Currently, human islets are transplanted via intra-portal infusions. While successful, it leads to significant early islet attrition from instant blood-mediated inflammatory reaction. An extra-hepatic site was established by transplanting islet-loaded microporous poly(lactide-co-glycolide) (PLG) scaffolds into the epididymal fat pad in syngeneic islet transplant models. This study examined this technology in allogeneic islet transplantation and determined whether transplant tolerance could be effectively induced to protect PLG scaffold transplanted allogeneic islets. The efficacy of an established tolerance induction strategy using donor splenocytes treated with ethylcarbodiimide(ECDI) was tested. ECDI-fixed donor splenocytes were infused 7 days before and 1 day after islet transplantation. Immediate normoglycemia was restored, and treated mice maintained indefinite normoglycemia whereas untreated mice rejected islet grafts within 20 days of transplantation. Interestingly, efficacy of tolerance induction was superior in PLG scaffold compared with intra-portal transplanted islets. Protection of PLG scaffold islet allografts was associated with several mechanisms of immune regulation. In summary, PLG scaffolds can serve as an alternative delivery system for islet transplantation that does not impair tolerance induction. This approach of combining tolerance induction with scaffold islet transplantation has potential therapeutic implications for human islet transplantation.

Attenuation of cross-talk between the complement and coagulation cascades by C5a blockade improves early outcomes after intraportal islet transplantation

BACKGROUND

Complement 5a factor (C5a) elicits a broad range of proinflammatory effects, including chemotaxis of inflammatory cells and cytokine release. C5a is also linked to the coagulant activity in autoimmune diseases. Therefore, C5a most likely plays a crucial role in the instant blood-mediated inflammatory reaction.

METHODS

Intraportal transplantation of 2.5 islet equivalents/g of syngeneic rat islet grafts was performed in two groups of streptozotocin-induced diabetic rats: controls and C5a inhibitory peptide (C5aIP)-treated group.

RESULTS

The thrombin-antithrombin complex was significantly suppressed in the C5aIP group (P=0.003), and both the curative rate and the glucose tolerance were significantly improved in the C5aIP group (P<0.05 and P<0.005, respectively). Expression of tissue factor on granulocytes in recipient livers was up-regulated 1 h after islet infusion (P<0.0001), which was significantly suppressed by C5aIP (P<0.005). However, C5aIP was unable to regulate tissue factor expression on isolated islets. Furthermore, no differences were detected between the groups, regarding infiltration of CD11b-positive cells and deposition of C5b-9 on the islet grafts.

CONCLUSIONS

These data suggest that C5aIP attenuates cross-talk between the complement and coagulation cascades through suppressing up-regulation of tissue factor expression on leukocytes in recipient livers but not on islet grafts, a process leading to improvement in islet engraftment. Therefore, C5aIP in combination with conventional anticoagulants could be a strong candidate strategy to control the instant blood-mediated inflammatory reaction induced in clinical islet transplantation.

Interface between hemostasis and adaptive immunity

Stress induced activation or denudation of the endothelium elicits arrest and activation of platelets with attendant triggering of coagulation, culminating in a physical barrier to limit blood loss. Recently, coagulation-activated osteopontin, chemerin, and protease-activated receptor signaling, as well as platelet-derived molecules including platelet factor 4, serotonin, P-selectin, and CD154 (CD40L) have been revealed as new links between hemostasis and adaptive immunity. The initiation of hemostasis establishes a local state of inflammation that serves as an adjuvant system for antigen presentation, consequently influencing the onset and functional characteristics of an evolving adaptive immune response. In this context, the hemostatic system and its associated signaling pathways warrant further study as novel therapeutic targets that may enhance, abrogate, or otherwise selectively direct the adaptive immune response.

Beneficial effects of desferrioxamine on encapsulated human islets--in vitro and in vivo study

As many as 2000 IEQs (islet equivalent) of encapsulated human islets are required to normalize glucose levels in diabetic mice. To reduce this number, encapsulated islets were exposed to 100 μM desferrioxamine (DFO) prior to transplantation. Cell viability, glucose-induced insulin secretion, VEGF (Vascular endothelial growth factor), HIF-1α (Hypoxia inducible factor-1 alpha), caspase-3 and caspase-8 levels were assessed after exposure to DFO for 12, 24 or 72 h. Subsequently, 1000, 750 or 500 encapsulated IEQs were infused into peritoneal cavity of diabetic mice after 24 h exposure to DFO. Neither viability nor function in vitro was affected by DFO, and levels of caspase-3 and caspase-8 were unchanged. DFO significantly enhanced VEGF secretion by 1.6- and 2.5-fold at 24 and 72 h, respectively, with a concomitant increase in HIF-1α levels. Euglycemia was achieved in 100% mice receiving 1000 preconditioned IEQs, as compared to only 36% receiving unconditioned IEQs (p < 0.001). Similarly, with 750 IEQ, euglycemia was achieved in 50% mice receiving preconditioned islets as compared to 10% receiving unconditioned islets (p = 0.049). Mice receiving preconditioned islets had lower glucose levels than those receiving unconditioned islets. In summary, DFO treatment enhances HIF-1α and VEGF expression in encapsulated human islets and improves their ability to function when transplanted.

Biomolecular surface engineering of pancreatic islets with thrombomodulin

Islet transplantation has emerged as a promising treatment for Type 1 diabetes, but its clinical impact remains limited by early islet destruction mediated by prothrombotic and innate inflammatory responses elicited upon transplantation. Thrombomodulin (TM) acts as an important regulator of thrombosis and inflammation through its capacity to channel the catalytic activity of thrombin towards generation of activated protein C (APC), a potent anticoagulant and anti-inflammatory agent. We herein describe a novel biomolecular strategy for re-engineering the surface of pancreatic islets with TM. A biosynthetic approach was employed to generate recombinant human TM (rTM) bearing a C-terminal azide group, which facilitated site-specific biotinylation of rTM through Staudinger ligation. Murine pancreatic islets were covalently biotinylated through targeting of cell surface amines and aldehydes and both islet viability and the surface density of streptavidin were maximized through optimization of biotinylation conditions. rTM was immobilized on islet surfaces through streptavidin-biotin interactions, resulting in a nearly threefold increase in the catalytic capacity of islets to generate APC.