Intracutaneous Transplantation of Islets within a Biodegradable Temporizing Matrix (BTM) as an Alternative Site for Islet Transplantation

Intra-hepatic islet transplantation for type-1 diabetes is limited by the need for multiple infusions and poor islet viability post-transplantation. The development of alternative transplantation sites is necessary to improve islet survival, and facilitate monitoring and retrieval. We tested a clinically proven Biodegradable Temporizing Matrix (BTM), a polyurethane-based scaffold, to generate a well vascularized intracutaneous "neo-dermis" within the skin for islet transplantation. In murine models, BTM did not impair syngeneic islet renal-subcapsular transplant viability or function, and facilitated diabetes cure for over 150 days. Further, BTM supported functional neonatal porcine islet transplants into RAG-1-/- mice for 400 days. Hence, BTM is non-toxic for islets. two-photon intravital imaging used to map vessel growth through time identified dense vascular networks, with significant collagen deposition and increases in vessel mass up to 30 days post-BTM implantation. In a pre-clinical porcine skin model, BTM implants created a highly-vascularized intracutaneous site by day 7 post-implantation. When syngeneic neonatal porcine islets were transplanted intracutaneously the islets remained differentiated as insulin producing cells, maintained normal islet architecture, secreted c-peptide, and survived for over 100 days. Here we show that BTM facilitates formation of an islet-supportive intracutaneous "neo-dermis" in a porcine pre-clinical model, as an alternative islet transplant site.

Bioengineered human pseudoislets form efficiently from donated tissue, compare favourably with native islets in vitro and restore normoglycaemia in mice

AIMS/HYPOTHESIS

Islet transplantation is a treatment option that can help individuals with type 1 diabetes become insulin independent, but inefficient oxygen and nutrient delivery can hamper islet survival and engraftment due to the size of the islets and loss of the native microvasculature. We hypothesised that size-controlled pseudoislets engineered via centrifugal-forced-aggregation (CFA-PI) in a platform we previously developed would compare favourably with native islets, even after taking into account cell loss during the process.

METHODS

Human islets were dissociated and reaggregated into uniform, size-controlled CFA-PI in our microwell system. Their performance was assessed in vitro and in vivo over a range of sizes, and compared with that of unmodified native islets, as well as islet cell clusters formed by a conventional spontaneous aggregation approach (in which dissociated islet cells are cultured on ultra-low-attachment plates). In vitro studies included assays for membrane integrity, apoptosis, glucose-stimulated insulin secretion assay and total DNA content. In vivo efficacy was determined by transplantation under the kidney capsule of streptozotocin-treated Rag1^-/- mice, with non-fasting blood glucose monitoring three times per week and IPGTT at day 60 for glucose response. A recovery nephrectomy, removing the graft, was conducted to confirm efficacy after completing the IPGTT. Architecture and composition were analysed by histological assessment via insulin, glucagon, pancreatic polypeptide, somatostatin, CD31 and von Willebrand factor staining.

RESULTS

CFA-PI exhibit markedly increased uniformity over native islets, as well as substantially improved glucose-stimulated insulin secretion (8.8-fold to 11.1-fold, even after taking cell loss into account) and hypoxia tolerance. In vivo, CFA-PI function similarly to (and potentially better than) native islets in reversing hyperglycaemia (55.6% for CFA-PI vs 20.0% for native islets at 500 islet equivalents [IEQ], and 77.8% for CFA-PI vs 55.6% for native islets at 1000 IEQ), and significantly better than spontaneously aggregated control cells (55.6% for CFA-PI vs 0% for spontaneous aggregation at 500 IEQ, and 77.8% CFA-PI vs 33.4% for spontaneous aggregation at 1000 IEQ; p < 0.05). Glucose clearance in the CFA-PI groups was improved over that in the native islet groups (CFA-PI 18.1 mmol/l vs native islets 29.7 mmol/l at 60 min; p < 0.05) to the point where they were comparable with the non-transplanted naive normoglycaemic control mice at a low IEQ of 500 IEQ (17.2 mmol/l at 60 min).

CONCLUSIONS/INTERPRETATION

The ability to efficiently reformat dissociated islet cells into engineered pseudoislets with improved properties has high potential for both research and therapeutic applications.

Alternative immunomodulatory strategies for xenotransplantation: CD40/154 pathway-sparing regimens promote xenograft survival

Immunosuppressive therapies that block the CD40/CD154 costimulatory pathway have proven to be uniquely effective in preclinical xenotransplant models. Given the challenges facing clinical translation of CD40/CD154 pathway blockade, we examined the efficacy and tolerability of CD40/CD154 pathway-sparing immunomodulatory strategies in a pig-to-nonhuman primate islet xenotransplant model. Rhesus macaques were rendered diabetic with streptozocin and given an intraportal infusion of ≈ 50 000 islet equivalents/kg wild-type neonatal porcine islets. Base immunosuppression for all recipients included maintenance therapy with belatacept and mycophenolate mofetil plus induction with basiliximab and LFA-1 blockade. Cohort 1 recipients (n = 3) were treated with the base regimen alone; cohort 2 recipients (n = 5) were additionally treated with tacrolimus induction and cohort 3 recipients (n = 5) were treated with alefacept in place of basiliximab, and more intense LFA-1 blockade. Three of five recipients in both cohorts 2 and 3 achieved sustained insulin-independent normoglycemia (median rejection-free survivals 60 and 111 days, respectively), compared to zero of three recipients in cohort 1. These data show that CD40/CD154 pathway-sparing regimens can promote xenoislet survival. Further optimization of these strategies is warranted to aid the clinical translation of islet xenotransplantation.

Islet xenotransplantation using gal-deficient neonatal donors improves engraftment and function

Significant deficiencies in understanding of xenospecific immunity have impeded the success of preclinical trials in xenoislet transplantation. Although galactose-α1,3-galactose, the gal epitope, has emerged as the principal target of rejection in pig-to-primate models of solid organ transplant, the importance of gal-specific immunity in islet xenotransplant models has yet to be clearly demonstrated. Here, we directly compare the immunogenicity, survival and function of neonatal porcine islets (NPIs) from gal-expressing wild-type (WT) or gal-deficient galactosyl transferase knockout (GTKO) donors. Paired diabetic rhesus macaques were transplanted with either WT (n = 5) or GTKO (n = 5) NPIs. Recipient blood glucose, transaminase and serum xenoantibody levels were used to monitor response to transplant. Four of five GTKO versus one of five WT recipients achieved insulin-independent normoglycemia; transplantation of WT islets resulted in significantly greater transaminitis. The WT NPIs were more susceptible to antibody and complement binding and destruction in vitro. Our results confirm that gal is an important variable in xenoislet transplantation. The GTKO NPI recipients have improved rates of normoglycemia, likely due to decreased susceptibility of xenografts to innate immunity mediated by complement and preformed xenoantibody. Therefore, the use of GTKO donors is an important step toward improved consistency and interpretability of results in future xenoislet studies.

CD40-specific costimulation blockade enhances neonatal porcine islet survival in nonhuman primates

The widespread clinical implementation of alloislet transplantation as therapy for type 1 diabetes has been hindered by the lack of suitable islet donors. Pig-to-human islet xenotransplantation is one strategy with potential to alleviate this shortage. Long-term survival of porcine islets has been achieved using CD154-specific antibodies to interrupt the CD40/CD154 costimulation pathway; however, CD154-specific antibodies seem unlikely candidates for clinical translation. An alternative strategy for CD40/CD154 pathway interruption is use of CD40-specific antibodies. Herein, we evaluate the ability of a chimeric CD40-specific monoclonal antibody (Chi220) to protect islet xenografts. Neonatal porcine islets (~50,000 IEQ/kg) were transplanted intraportally into pancreatectomized diabetic macaques. Immunosuppression consisted of induction therapy with Chi220 and the IL-2 receptor-specific antibody basiliximab, and maintenance therapy with sirolimus and the B7-specific fusion protein belatacept. Chi220 effectively promoted xenoislet engraftment and survival, with five of six treated recipients achieving insulin-independent normoglycemia (median rejection-free survival 59 days; mean 90.8 days, maximum 203 days). No thromboembolic phenomena were observed. CD40 represents a promising alternative to CD154 as a therapeutic target, and the efficacy of CD40-specific antibodies in islet xenotransplantation warrants further investigation.

Airway delivery of mesenchymal stem cells prevents arrested alveolar growth in neonatal lung injury in rats

RATIONALE

Bronchopulmonary dysplasia (BPD) and emphysema are characterized by arrested alveolar development or loss of alveoli; both are significant global health problems and currently lack effective therapy. Bone marrow-derived mesenchymal stem cells (BMSCs) prevent adult lung injury, but their therapeutic potential in neonatal lung disease is unknown.

OBJECTIVES

We hypothesized that intratracheal delivery of BMSCs would prevent alveolar destruction in experimental BPD.

METHODS

In vitro, BMSC differentiation and migration were assessed using co-culture assays and a modified Boyden chamber. In vivo, the therapeutic potential of BMSCs was assessed in a chronic hyperoxia-induced model of BPD in newborn rats.

MEASUREMENTS AND MAIN RESULTS

In vitro, BMSCs developed immunophenotypic and ultrastructural characteristics of type II alveolar epithelial cells (AEC2) (surfactant protein C expression and lamellar bodies) when co-cultured with lung tissue, but not with culture medium alone or liver. Migration assays revealed preferential attraction of BMSCs toward oxygen-damaged lung versus normal lung. In vivo, chronic hyperoxia in newborn rats led to air space enlargement and loss of lung capillaries, and this was associated with a decrease in circulating and resident lung BMSCs. Intratracheal delivery of BMSCs on Postnatal Day 4 improved survival and exercise tolerance while attenuating alveolar and lung vascular injury and pulmonary hypertension. Engrafted BMSCs coexpressed the AEC2-specific marker surfactant protein C. However, engraftment was disproportionately low for cell replacement to account for the therapeutic benefit, suggesting a paracrine-mediated mechanism. In vitro, BMSC-derived conditioned medium prevented O(2)-induced AEC2 apoptosis, accelerated AEC2 wound healing, and enhanced endothelial cord formation.

CONCLUSIONS

BMSCs prevent arrested alveolar and vascular growth in part through paracrine activity. Stem cell-based therapies may offer new therapeutic avenues for lung diseases that currently lack efficient treatments.

Bioartificial Organ Grafts: A View at the Beginning of the Third Millennium

An immunoisolated collection of cells, which communicate and exchange essential factors, co-stimulatory hormones, as well as providing immunoprotection and immunomodulation, can be prepared, given existing scientific and medical know-how, within two decades. These "Bioartificial Organ Grafts" have advantages relative to isolated cell therapies, including beta-cell encapsulation for diabetes treatment, and xenotransplantation, which has a de facto moratorium. This paper documents that the majority of the research for the bioartificial organ grafts has been concluded, with the remaining hurdles minimum in comparison. The use of co-encapsulation and the induction of local immune-privilege will provide a more sensitive humoral hormonal response and graft survival, without systemic immunosuppression. A call for the staged implementation of bioartificial organ grafts, based on the best available medical practice, materials, tissue and technology available, is advocated. The implementation of bioartificial organ grafts can begin within the next two years, based on allografts succeeded by genetically modified human tissue, without the need to pass through a xenograft stage.

Neonatal porcine islets exhibit natural resistance to hypoxia-induced apoptosis

BACKGROUND

Despite the success of the Edmonton protocol for human islet transplantation, an alternate source of islet tissue must be developed if beta-cell replacement therapy is to see widespread application. Neonatal porcine islets (NPI) represent one potential source of tissue. When human or rodent islets are transplanted, the majority of cells undergo hypoxia-induce apoptosis soon after the grafts are placed in the recipient. In the present study, we investigated whether NPI were similarly sensitive to hypoxia.

METHODS

NPI were exposed to hypoxia and hypoxia/reoxygenation using an in vitro hypoxic chamber. Afterwards, viability, frequency of apoptosis, and beta-cell function were evaluated. NPI and adult porcine islets were transplanted into chemically diabetic, immunodeficient mice and graft apoptosis was assessed 24 hours and seven days posttransplant.

RESULTS

NPI demonstrated a remarkable capacity to resist apoptosis and maintain insulin secretion despite severe stresses such as hypoxia/reoxygenation. One day after transplantation, NPI grafts showed limited apoptosis, confined to rare strongly insulin positive cells. In contrast, adult porcine islet grafts underwent widespread apoptosis. Western blotting revealed that NPI express high levels of at least one potent endogenous antiapoptotic protein (XIAP).

CONCLUSIONS

The majority of cells within transplanted human islets undergo apoptosis soon after portal infusion. In contrast, NPI have the capacity to resist this early posttransplant apoptosis, with likely reduced antigen release and diminished immune stimulation. NPI appear to contain a population of insulin-low to insulin-negative pre-beta-cells, which are resistant to hypoxia-induced apoptosis and still capable of differentiating into mature beta-cells.

Vascular endothelial growth factor gene therapy increases survival, promotes lung angiogenesis, and prevents alveolar damage in hyperoxia-induced lung injury: evidence that angiogenesis participates in alveolarization

BACKGROUND

Bronchopulmonary dysplasia (BPD) and pulmonary emphysema, both significant global health problems, are characterized by a loss of alveoli. Vascular endothelial growth factor (VEGF) is a trophic factor required for endothelial cell survival and is abundantly expressed in the lung.

METHODS AND RESULTS

We report that VEGF blockade decreases lung VEGF and VEGF receptor 2 (VEGFR-2) expression in newborn rats and impairs alveolar development, leading to alveolar simplification and loss of lung capillaries, mimicking BPD. In hyperoxia-induced BPD in newborn rats, air space enlargement and loss of lung capillaries are associated with decreased lung VEGF and VEGFR-2 expression. Postnatal intratracheal adenovirus-mediated VEGF gene therapy improves survival, promotes lung capillary formation, and preserves alveolar development in this model of irreversible lung injury. Combined VEGF and angiopoietin-1 gene transfer matures the new vasculature, reducing the vascular leakage seen in VEGF-induced capillaries.

CONCLUSIONS

These findings underscore the importance of the vasculature in what is traditionally thought of as an airway disease and open new therapeutic avenues for lung diseases characterized by irreversible loss of alveoli through the modulation of angiogenic growth factors.

The development of osteoblasts from stem cells to supplement fusion of the spine during surgery for AIS

Surgical correction in severe cases of AIS is often hampered by insufficient autograft bone to facilitate the fusion. The development of other sources of bone generating cells would greatly enhance the surgical. Bone marrow derived stem cells were harvested from femoral reaming during total hip arthroplasty for the purpose of differentiating into osteoblasts. Stem cells were isolated from the marrow and successfully differentiated into three cell lines (osteoblasts, chondrocytes and adipocytes) to confirm multilineage potential. Osteoblasts were developed from the stem cells and demonstrated the ability to be cultured to possibly provide a source of bone generating cells to augment surgical fusions. It is anticipated that the addition of osteoblasts created from stem cells (combined with appropriate matrix) will have significant influence on the success of AIS surgery through improvement of bone fusion.

Sildenafil improves alveolar growth and pulmonary hypertension in hyperoxia-induced lung injury

RATIONALE

Bronchopulmonary dysplasia (BPD), the chronic lung disease of preterm infants, and pulmonary emphysema, both significant global health problems, are characterized by an arrest in alveolar growth/loss of alveoli structures. Mechanisms that inhibit distal lung growth are poorly understood, but recent studies suggest that impaired vascular endothelial growth factor signaling and reduced nitric oxide (NO) production decreases alveolar and vessel growth in the developing lung, features observed in experimental oxygen-induced BPD. NO exerts its biological activity by stimulating guanosine 3',5'-cyclic monophosphate (cGMP) production.

OBJECTIVES

Because cGMP is inactivated by phosphodiesterase (PDE) enzymes, we hypothesized that the cGMP-specific PDE5 inhibitor sildenafil would promote angiogenesis and attenuate oxygen-induced lung injury in newborn rats. METHODS, MEASUREMENTS, AND MAIN RESULTS: In vitro, sildenafil (10(-4) M) increased endothelial capillary network formation of human pulmonary endothelial cells exposed to hyperoxia. In vivo, rat pups were randomly exposed from birth to normoxia, hyperoxia (95% O(2), BPD model), and hyperoxia+sildenafil (100 mg/kg/day subcutaneously). Rat pups exposed to hyperoxia showed fewer and enlarged air spaces as well as decreased capillary density, mimicking pathologic features seen in human BPD. These structural anomalies were associated with echographic (decreased pulmonary acceleration time) and structural (right ventricular hypertrophy and increased medial wall thickness) signs of pulmonary hypertension. Sildenafil preserved alveolar growth and lung angiogenesis, and decreased pulmonary vascular resistance, right ventricular hypertrophy and medial wall thickness.

CONCLUSIONS

Our findings suggest a role for the NO/cGMP pathway during alveolar development. Sildenafil may have therapeutic potential in diseases associated with impaired alveolar structures.

Mannose 6-phosphate/insulin-like growth factor II receptor is a death receptor for granzyme B during cytotoxic T cell-induced apoptosis

The serine proteinase granzyme B is crucial for the rapid induction of target cell apoptosis by cytotoxic T cells. Granzyme B was recently demonstrated to enter cells in a perforin-independent manner, thus predicting the existence of a cell surface receptor(s). We now present evidence that this receptor is the cation-independent mannose 6-phosphate/insulin-like growth factor receptor (CI-MPR). Inhibition of the granzyme B-CI-MPR interaction prevented granzyme B cell surface binding, uptake, and the induction of apoptosis. Significantly, expression of the CI-MPR was essential for cytotoxic T cell-mediated apoptosis of target cells in vitro and for the rejection of allogeneic cells in vivo. These results suggest a novel target for immunotherapy and a potential mechanism used by tumors for immune evasion.

Anti-BSA antibodies do not cross-react with the 69-kDa islet cell autoantigen ICA69

In contrast to several previously published reports, we demonstrate by a variety of antibody assays that bovine serum albumin (BSA) is not antigenically cross-reactive with the 69-kDa islet cell autoantigen (ICA69). Fast protein liquid chromatography purified BSA and highly purified recombinant human ICA69 were used to establish sensitive Western blot and ELISA assays in order to detect antibodies against these two proteins. The assays excluded BSA or powdered milk as blocking agents, since these would interfere with antibody binding. A panel of sera from diabetic individuals, first degree relatives, and normal controls showed that the majority (approximately 70%) of individuals from each group had antibodies against ICA69 as assayed by Western blots, whereas considerably fewer (approximately 13%) had anti-BSA antibodies on Western blots, and individuals with antibodies to both proteins occurred only rarely (2-3%). To explore this issue further we immunized a total of 16 individual rats, representing four different strains (bio-breeding diabetes resistant and diabetes prone, Wistar-Furth, and Sprague-Dawley), with either BSA (n = 2 of each strain) or with recombinant ICA69 (n = 2 of each strain), and for each animal pre- and postimmune antibody titres against BSA and against ICA69 were assayed separately by enzyme-linked immunoabsorbent assay. In rats immunized with BSA, anti-BSA titres increased about 100,000-fold over preimmune levels, whereas anti-ICA69 reactive antibodies were unchanged over preimmune levels. Similarly, in rats immunized with ICA69, anti-ICA69 titres rose about 100,000-fold over preimmune levels, whereas anti-BSA antibodies were unchanged over preimmune levels. Thus we find no evidence for the existence of antibody cross-reactivity between ICA69 and BSA, either in humans or in immunized rats. When our rat anti-BSA antisera were used to probe Western blots made from rat islets isolated in the strict absence of fetal calf serum, we were unable to detect a 69-kDa band, even when the islets were preincubated with gamma-interferon, a treatment which has been reported to induce the BSA cross-reactive islet antigen. We conclude that BSA is not antigenically cross-reactive with ICA69 at the antibody level, and it is highly unlikely that BSA is antigenically cross-reactive with some other 69 kD islet cell antigen.

Long-term metabolic control by rat islet grafts depends on the composition of the implant

This study examines whether the loss of metabolic control in initially normalized islet transplants can result from the inadequate composition of the donor tissue. Streptozotocin-induced diabetic rats were followed for 64 weeks after the intraportal injection of islet isografts with different composition. The implantation of 2.3 million beta-cells (10(7)/kg body wt) as particles (>100 microm diameter) of primarily insulin-positive (70%) and glucagon-positive (20%) cells succeeded in a long-term normalization of 2-h fasting glycemia, glucose tolerance, and serum fructosamine. The same metabolic control was achieved in animals with short and long durations of diabetes or when grafts were implanted under the kidney capsule. At posttransplantation (PT) week 64, insulin reserves were 60% lower than those in age-matched controls, which may account for the glucose intolerance in a few old recipients. The same type of graft containing 0.7 million beta-cells (4 x 10(6)/kg body wt) corrected these metabolic parameters for more than 12 weeks; the proportionally lower insulin reserves were sufficient for the long-term correction of 2-h fasting glycemia, but did not avoid glucose intolerance in older recipients. When the higher beta-cells number (10(7)/kg body wt) was injected as smaller particles (<100 mpm diameter) of lower purity (55% insulin-positive) and negligible glucagon content (<5% glucagon-positive), the metabolic parameters were also corrected for 12 weeks PT but then progressively returned to overt diabetes (6 of 10) or glucose intolerance (4 of 10). We concluded that long-term metabolic normalization can be achieved by islet implants in the liver or under the kidney capsule. The loss of metabolic control in older animals can be caused by the inadequate composition of the graft, with the number of beta-cells, the proportion of other endocrine and nonendocrine cells, and the particle size as influential variables.