Targeted mapping and utilization of the perihepatic surface for therapeutic beta cell replacement and retrieval in diabetic non-human primates

Introduction

Successful diabetes reversal using pancreatic islet transplantation by various groups illustrates the significant achievements made in cell-based diabetes therapy. While clinically, intraportal islet delivery is almost exclusively used, it is not without obstacles, including instant blood-mediated inflammatory reaction (IBMIR), relative hypoxia, and loss of function over time, therefore hindering long-term success. Here we demonstrate the perihepatic surface of non-human primates (NHPs) as a potential islet delivery site maximizing favorable characteristics, including proximity to a dense vascular network for adequate oxygenation while avoiding IBMIR exposure, maintenance of portal insulin delivery, and relative ease of accessibility through minimally invasive surgery or percutaneous means. In addition, we demonstrate a targeted mapping technique of the perihepatic surface, allowing for the testing of multiple experimental conditions, including a semi-synthetic hydrogel as a possible three-dimensional framework to improve islet viability.

Methods

Perihepatic allo-islet cell transplants were performed in immunosuppressed cynomolgus macaques using a targeted mapping technique to test multiple conditions for biocompatibility. Transplant conditions included islets or carriers (including hydrogel, autologous plasma, and media) alone or in various combinations. Necropsy was performed at day 30, and histopathology was performed to assess biocompatibility, immune response, and islet viability. Subsequently, single-injection perihepatic allo-islet transplant was performed in immunosuppressed diabetic cynomolgus macaques. Metabolic assessments were measured frequently (i.e., blood glucose, insulin, C-peptide) until final graft retrieval for histopathology.

Results

Targeted mapping biocompatibility studies demonstrated mild inflammatory changes with islet-plasma constructs; however, significant inflammatory cell infiltration and fibrosis were seen surrounding sites with the hydrogel carrier affecting islet viability. In diabetic NHPs, perihepatic islet transplant using an autologous plasma carrier demonstrated prolonged function up to 6 months with improvements in blood glucose, exogenous insulin requirements, and HbA1c. Histopathology of these islets was associated with mild peri-islet mononuclear cell infiltration without evidence of rejection.

Discussion

The perihepatic surface serves as a viable site for islet cell transplantation demonstrating sustained islet function through 6 months. The targeted mapping approach allows for the testing of multiple conditions simultaneously to evaluate immune response to biomaterials at this site. Compared to traditional intraportal injection, the perihepatic site is a minimally invasive approach that allows the possibility for graft recovery and avoids IBMIR.

A bioengineered artificial interstitium supports long-term islet xenograft survival in nonhuman primates without immunosuppression

Cell-based therapies hold promise for many chronic conditions; however, the continued need for immunosuppression along with challenges in replacing cells to improve durability or retrieving cells for safety are major obstacles. We subcutaneously implanted a device engineered to exploit the innate transcapillary hydrostatic and colloid osmotic pressure generating ultrafiltrate to mimic interstitium. Long-term stable accumulation of ultrafiltrate was achieved in both rodents and nonhuman primates (NHPs) that was chemically similar to serum and achieved capillary blood oxygen concentration. The majority of adult pig islet grafts transplanted in non-immunosuppressed NHPs resulted in xenograft survival >100 days. Stable cytokine levels, normal neutrophil to lymphocyte ratio, and a lack of immune cell infiltration demonstrated successful immunoprotection and averted typical systemic changes related to xenograft transplant, especially inflammation. This approach eliminates the need for immunosuppression and permits percutaneous access for loading, reloading, biopsy, and recovery to de-risk the use of "unlimited" xenogeneic cell sources to realize widespread clinical translation of cell-based therapies.

System for Scoring Severity of Acute Radiation Syndrome Response in Rhesus Macaques (Macaca mulatta)

We developed a clinical assessment tool for use in an NHP radiation model to 1) quantify severity responses for subsyndromes of the acute radiation syndrome (ARS; that is, hematopoietic and others) and 2) identify animals that required enhanced monitoring. Our assessment tool was based primarily on the MEdical TREatment ProtocOLs for Radiation Accident Victims (METREPOL) scoring system but was adapted for NHP to include additional indices (for example, behaviors) for use in NHP studies involving limited medical intervention. Male (n = 16) and female (n = 12) rhesus macaques (Macaca mulatta; 5 groups: sham and 1.0, 3.5, 6.5, and 8.5 Gy; n = 6 per group) received sham- or bilateral 60Co γ-irradiation at approximately 0.6 Gy/mn. Clinical signs of ARS and blood analysis were obtained before and serially for clinical assessment during the period of 6 h to 60 d after sham or 60Co irradiation. Minimal supportive care (that is, supplemental nutrition, subcutaneous fluid, loperamide, acetaminophen, and topical antibiotic ointment) was prescribed based on clinical observations. Results from clinical signs and assays for assessment of relevant organ systems in individual animals were stratified into ARS severity scores of normal (0), mild (1), moderate (2), and severe (3 or 4). Individual NHP were scored for maximal subsyndrome ARS severity in multiple organ systems by using the proposed ARS scoring system to obtain an overall ARS response category. One NHP died unexpectedly. The multiple-parameter ARS severity scoring tool aided in the identification of animals in the high-dose (6.5 and 8.5 Gy) groups that required enhanced monitoring.

Use and Importance of Nonhuman Primates in Metabolic Disease Research: Current State of the Field

Obesity and its multiple metabolic sequelae, including type 2 diabetes, cardiovascular disease, and fatty liver disease, are becoming increasingly widespread in both the developed and developing world. There is an urgent need to identify new approaches for the prevention and treatment of these costly and prevalent metabolic conditions. Accomplishing this will require the use of appropriate animal models for preclinical and translational investigations in metabolic disease research. Although studies in rodent models are often useful for target/pathway identification and testing hypotheses, there are important differences in metabolic physiology between rodents and primates, and experimental findings in rodent models have often failed to be successfully translated into new, clinically useful therapeutic modalities in humans. Nonhuman primates represent a valuable and physiologically relevant model that serve as a critical translational bridge between basic studies performed in rodent models and clinical studies in humans. The purpose of this review is to evaluate the evidence, including a number of specific examples, in support of the use of nonhuman primate models in metabolic disease research, as well as some of the disadvantages and limitations involved in the use of nonhuman primates. The evidence taken as a whole indicates that nonhuman primates are and will remain an indispensable resource for evaluating the efficacy and safety of novel therapeutic strategies targeting clinically important metabolic diseases, including dyslipidemia and atherosclerosis, type 2 diabetes, hepatic steatosis, steatohepatitis, and hepatic fibrosis, and potentially the cognitive decline and dementia associated with metabolic dysfunction, prior to taking these therapies into clinical trials in humans.

Successful pharmaceutical-grade streptozotocin (STZ)-induced hyperglycemia in a conscious tethered baboon (Papio hamadryas) model

BACKGROUND

Non-human primate (NHP) diabetic models using chemical ablation of β-cells with STZ have been achieved by several research groups. Chemotherapeutic STZ could lead to serious adverse events including nephrotoxicity, hepatotoxicity, and mortality.

METHODS

We implemented a comprehensive therapeutic strategy that included the tether system, permanent indwelling catheter implants, an aggressive hydration protocol, management for pain with IV nubain and anxiety with IV midazolam, moment-by-moment monitoring of glucose levels post-STZ administration, and continuous intravenous insulin therapy.

RESULTS

A triphasic response in blood glucose after STZ administration was fully characterized. A dangerous hypoglycemic phase was also detected in all baboons. Other significant findings were hyperglycemia associated with low levels of plasma leptin, insulin and C-peptide concentrations, hyperglucagonemia, and elevated non-esterified fatty acids (NEFA) concentrations.

CONCLUSIONS

We successfully induced frank diabetes by IV administering a single dose of pharmaceutical-grade STZ safely and without adverse events in conscious tethered baboons.

The multifactorial role of the 3Rs in shifting the harm-benefit analysis in animal models of disease

Ethics on animal use in science in Western society is based on utilitarianism, weighing the harms and benefits to the animals involved against those of the intended human beneficiaries. The 3Rs concept (Replacement, Reduction, Refinement) is both a robust framework for minimizing animal use and suffering (addressing the harms to animals) and a means of supporting high quality science and translation (addressing the benefits). The ambiguity of basic research performed early in the research continuum can sometimes make harm-benefit analysis more difficult since anticipated benefit is often an incremental contribution to a field of knowledge. On the other hand, benefit is much more evident in translational research aimed at developing treatments for direct application in humans or animals suffering from disease. Though benefit may be easier to define, it should certainly not be considered automatic. Issues related to model validity seriously compromise experiments and have been implicated as a major impediment in translation, especially in complex disease models where harms to animals can be intensified. Increased investment and activity in the 3Rs is delivering new research models, tools and approaches with reduced reliance on animal use, improved animal welfare, and improved scientific and predictive value.

Streptozotocin-associated lymphopenia in cynomolgus monkeys

Streptozotocin (STZ) is used to induce diabetes in experimental animals. It has a variety of adverse effects, ranging from nausea, emesis, and weight loss to liver damage, renal failure, and metabolic acidosis. STZ also has effects on the immune system, being associated with lymphopenia in rodents, the mechanism of which is not fully understood. We present data on a significant STZ-associated reduction in lymphocyte count in nonhuman primates. We report a significant reduction in absolute lymphocyte count; in 2 monkeys, the lymphopenia persisted for >100 d. However, a significant increase in absolute monocyte count was noted. Furthermore, an increase in serum monocyte chemoattractant protein-1 (MCP-1) was observed. The reduction in lymphocyte numbers may contribute to immunomodulation that may be beneficial to a subsequent islet graft, and may reduce the need for immunosuppressive therapy. The increase in monocytes and MCP-1, however, may be detrimental to the islet graft. Studies are warranted to explore the mechanism by which STZ has its effect.

The usefulness and limitations of the diabetic macaque model in evaluating long-term porcine islet xenograft survival

BACKGROUND

  Various groups have reported prolonged diabetes reversal and graft function after porcine islet transplantation into diabetic macaques using different experimental designs (macaque source, islet source, type of immunosuppression): subsequently, the International Xenotransplantation Association has published recommendations for entering a clinical trial. Our experiments showed limitations that affected consistent achievement of long-term survival. We aimed to identify these limitations and underlying causes to emphasize the translational value of this highly relevant type 1 diabetic macaque model.

METHODS

  We reviewed data from our institution and literature data on long-term porcine islet xenograft survival in the diabetic macaque model, especially focusing on aspects of incomplete diabetes reversal relative to macaque normal values. This phenomenon was compared with diabetes reversal in an allo-islet transplant model in macaques and with chronic insulin treatment of diabetic macaques, all with 180-day follow-up. This comparison enabled to identify potential model limitations and underlying causative factors.

RESULTS

  Especially in the xenograft model, the achievement of long-term graft survival revealed limitations including chronic, mild hyperglycemia and absence of body weight (BW) gain or even progressive BW loss. Metabolic incompatibilities in glycemic control (i.e., insulin kinetics) between the pig and macaque species underlie chronic, mild hyperglycemia. This phenomenon might not bear relevance for the pig-to-human species combination because the glycemic control in pigs and humans is similar and differs from that in nonhuman primates (NHP). Weight loss could be related to changes in the gastrointestinal tract related with local high exposure to orally administered immunosuppressants; these must be given at higher dose levels because of low bioavailability in macaques to achieve systemic exposure at therapeutic levels. This is aggravated by insufficient graft insulin production in proportion to the needs of macaques: this model limitation has no translational value to the pig-to-human setting. Nutritional deficits can result in incorrect interpretation of blood glucose levels and C-peptide levels regarding graft function. Likewise, nutritional status alters physiologic responses, influencing susceptibility to infectious and noninfectious complications.

CONCLUSION

  THE model-induced confounding described interferes with accurate interpretation of safety and efficacy studies, which affects the translational value of pig-to-NHP islet cell transplant studies to the pig-to-human transplant condition.