Animal Models Within Surgical Simulation: A Novel Approach to the 3 Rs.

INTRODUCTION: Development of technical skills is a vital component of surgical residency. The use of animal tissues for operative simulation leads to both the loss of animal life and financial costs for the institution. We hypothesized that maximizing tissue use from investigational large animal models after euthanasia could reduce loss of animal life and institutional costs by replacing commercially purchased tissues. METHODS: After animal euthanization, a resident and medical student team harvested porcine tissue commonly used for surgical simulation: abdominal wall, kidney, heart, spleen, and small intestine. Tissues were vacuum-sealed and frozen for future educational use. Outcomes of harvest yield and time and estimated commercial pricing of harvested porcine tissues were analyzed. RESULTS: Three timed procurements were performed with decreasing operative times (36:30, 34:00, and 30:54) and increasing harvest yields (100 cm, 160 cm, and 200 cm small bowel). Procurements were conducted within 15 min of animal euthanization. Harvested tissue was considered to be of similar quality to commercially purchased tissue. Estimated cost of procured tissues from a commercial vendor was $847 compared to $109 for direct procurement from euthanized porcine models. CONCLUSIONS: Maximizing tissue use from large animal research models is an innovative approach to adhering to the three Rs of animal research: replace, reduce, and refine. Tissue procurement provides valuable tissues for resident education and simulation, increases surgical trainee operative exposure, and decreases institutional costs.

Anti-thymoglobulin induction improves neonatal porcine xenoislet engraftment and survival.

Porcine islet xenotransplantation is a viable strategy to treat diabetes. Its translation has been limited by the pre-clinical development of a clinically available immunosuppressive regimen. We tested two clinically relevant induction agents in a non-human primate (NHP) islet xenotransplantation model to compare depletional versus nondepletional induction immunosuppression. Neonatal porcine islets were isolated from GKO or hCD46/GKO transgenic piglets and transplanted via portal vein infusion in diabetic rhesus macaques. Induction therapy consisted of either basiliximab (n = 6) or rhesus-specific anti-thymocyte globulin (rhATG, n = 6), combined with a maintenance regimen using B7 costimulation blockade, tacrolimus with a delayed transition to sirolimus, and mycophenolate mofetil. Xenografts were monitored by blood glucose levels and porcine C-peptide measurements. Of the six receiving basiliximab induction, engraftment was achieved in 4 with median graft survival of 14 days. All six receiving rhATG induction engrafted with significantly longer xenograft survival at 40.5 days (P = 0.03). These data suggest that depletional induction provides superior xenograft survival to nondepletional induction, in the setting of a costimulation blockade-based maintenance regimen.

Th17 cell inhibition in a costimulation blockade-based regimen for vascularized composite allotransplantation using a nonhuman primate model.

Vascularized composite allotransplantation (VCA) is challenged by the morbidity of immunosuppression required to prevent rejection. The use of highly specific biologics has not been well explored in VCA. Given that psoriasis is T-cell mediated, as is rejection of skin-containing VCAs, we sought to assess the role of ustekinumab and secukinumab, which are approved to treat psoriasis by inhibiting Th17 cells. We combined these agents with belatacept and steroids in a VCA nonhuman primate model. Group I consisted of belatacept and steroids, group II was belatacept, ustekinumab with steroid taper, and group III was belatacept, secukinumab with steroid taper. Three animals were transplanted in each group. In group I, the mean graft survival time until the first sign of rejection was 10 days whereas in group II and III it was 10.33 and 11 days, respectively. The immunohistochemistry analysis showed that the number of IL-17a+ cells and the intensity of IL-17a expression were significantly reduced in both dermis and hypodermis parts in groups II and III when compared to group I (P < 0.01). Ustekinumab and secukinumab led to less T-cell infiltration and IL-17a expression in the allograft but provided no benefit to belatacept and steroids in VCA survival.

Secondary lymphoid tissue and costimulation-blockade resistant rejection: A nonhuman primate renal transplant study.

Naïve T cell activation requires antigen presentation combined with costimulation through CD28, both of which optimally occur in secondary lymphoid tissues such as lymph nodes and the spleen. Belatacept impairs CD28 costimulation by binding its ligands, CD80 and CD86, and in doing so, impairs de novo alloimmune responses. However, in most patients belatacept is ineffective in preventing allograft rejection when used as a monotherapy, and adjuvant therapy is required for control of costimulation-blockade resistant rejection (CoBRR). In rodent models, impaired access to secondary lymphoid tissues has been demonstrated to reduce alloimmune responses to vascularized allografts. Here we show that surgical maneuvers, lymphatic ligation, and splenectomy, designed to anatomically limit access to secondary lymphoid tissues, control CoBRR and facilitate belatacept monotherapy in a nonhuman primate model of kidney transplantation without adjuvant immunotherapy. We further demonstrate that animals sustained on belatacept monotherapy progressively develop an increasingly naïve T and B cell repertoire, an effect that is accelerated by splenectomy and lost at the time of belatacept withdrawal and rejection. These pilot data inform the role of secondary lymphoid tissues on the development of CoBRR and the use of costimulation molecule-focused therapies.

The role of human CD46 in early xenoislet engraftment in a dual transplant model.

BACKGROUND: Membrane cofactor protein CD46 attenuates the complement cascade by facilitating cleavage of C3b and C4b. In solid organ xenotransplantation, organs expressing CD46 have been shown to resist hyperacute rejection. However, the incremental value of human CD46 expression for islet xenotransplantation remains poorly defined. METHODS: This study attempted to delineate the role of CD46 in early neonatal porcine islet engraftment by comparing Gal-knocked out (GKO) and hCD46-transgenic (GKO/CD46) islets in a dual transplant model. Seven rhesus macaques underwent dual transplant and were sacrificed at 1 hour (n = 4) or 24 hours (n = 3). Both hemilivers were recovered and fixed for immunohistochemistry (CD46, insulin, neutrophil elastase, platelet, IgM, IgG, C3d, C4d, CD68, Caspase 3). Quantitative immunohistochemical analysis was performed using the Aperio Imagescope. RESULTS: Within 1 hour of intraportal infusion of xenografts, no differences were observed between the two types of islets in terms of platelet, antibody, or complement deposition. Cellular infiltration and islet apoptotic activity were also similar at 1 hour. At 24 hours, GKO/CD46 islets demonstrated significantly less platelet deposition (P = 0.01) and neutrophil infiltration (P = 0.01) compared to GKO islets. In contrast, C3d (P = 0.38) and C4d (P = 0.45) deposition was equal between the two genotypes. CONCLUSIONS: Our findings suggest that expression of hCD46 on NPIs potentially provides a measurable incremental survival advantage in vivo by reducing early thrombo-inflammatory events associated with instant blood-mediated inflammatory reaction (IBMIR) following intraportal islet infusion.

Long-term complications of glycogen storage disease type Ia in the canine model treated with gene replacement therapy.

BACKGROUND: Glycogen storage disease type Ia (GSD Ia) in dogs closely resembles human GSD Ia. Untreated patients with GSD Ia develop complications associated with glucose-6-phosphatase (G6Pase) deficiency. Survival of human patients on intensive nutritional management has improved; however, long-term complications persist including renal failure, nephrolithiasis, hepatocellular adenomas (HCA), and a high risk for hepatocellular carcinoma (HCC). Affected dogs fail to thrive with dietary therapy alone. Treatment with gene replacement therapy using adeno-associated viral vectors (AAV) expressing G6Pase has greatly prolonged life and prevented hypoglycemia in affected dogs. However, long-term complications have not been described to date. METHODS: Five GSD Ia-affected dogs treated with AAV-G6Pase were evaluated. Dogs were euthanized due to reaching humane endpoints related to liver and/or kidney involvement, at 4 to 8 years of life. Necropsies were performed and tissues were analyzed. RESULTS: Four dogs had liver tumors consistent with HCA and HCC. Three dogs developed renal failure, but all dogs exhibited progressive kidney disease histologically. Urolithiasis was detected in two dogs; uroliths were composed of calcium oxalate and calcium phosphate. One affected and one carrier dog had polycystic ovarian disease. Bone mineral density was not significantly affected. CONCLUSIONS: Here, we show that the canine GSD Ia model demonstrates similar long-term complications as GSD Ia patients in spite of gene replacement therapy. Further development of gene therapy is needed to develop a more effective treatment to prevent long-term complications of GSD Ia.

Long-term efficacy following readministration of an adeno-associated virus vector in dogs with glycogen storage disease type Ia.

Glycogen storage disease type Ia (GSD-Ia) is the inherited deficiency of glucose-6-phosphatase (G6Pase), primarily found in liver and kidney, which causes life-threatening hypoglycemia. Dogs with GSD-Ia were treated with double-stranded adeno-associated virus (AAV) vectors encoding human G6Pase. Administration of an AAV9 pseudotyped (AAV2/9) vector to seven consecutive GSD-Ia neonates prevented hypoglycemia during fasting for up to 8 hr; however, efficacy eventually waned between 2 and 30 months of age, and readministration of a new pseudotype was eventually required to maintain control of hypoglycemia. Three of these dogs succumbed to acute hypoglycemia between 7 and 9 weeks of age; however, this demise could have been prevented by earlier readministration an AAV vector, as demonstrated by successful prevention of mortality of three dogs treated earlier in life. Over the course of this study, six out of nine dogs survived after readministration of an AAV vector. Of these, each dog required readministration on average every 9 months. However, two were not retreated until >34 months of age, while one with preexisting antibodies was re-treated three times in 10 months. Glycogen content was normalized in the liver following vector administration, and G6Pase activity was increased in the liver of vector-treated dogs in comparison with GSD-Ia dogs that received only with dietary treatment. G6Pase activity reached approximately 40% of normal in two female dogs following AAV2/9 vector administration. Elevated aspartate transaminase in absence of inflammation indicated that hepatocellular turnover in the liver might drive the loss of vector genomes. Survival was prolonged for up to 60 months in dogs treated by readministration, and all dogs treated by readministration continue to thrive despite the demonstrated risk for recurrent hypoglycemia and mortality from waning efficacy of the AAV2/9 vector. These preclinical data support the further translation of AAV vector-mediated gene therapy in GSD-Ia.