Experimental Hepatocyte Transplantation in Pigs

A non-human primate model of acute liver failure suitable for testing liver support systems

Acute hepatic failure is associated with high morbidity and mortality for which the only definitive therapy is liver transplantation. Some fraction of those who undergo emergency transplantation have been shown to recover native liver function when transplanted with an auxiliary hepatic graft that leaves part of the native liver intact. Thus, transplantation could have been averted with the development and use of some form of hepatic support. The costs of developing and testing liver support systems could be dramatically reduced by the availability of a reliable large animal model of hepatic failure with a large therapeutic window that allows the assessment of efficacy and timing of intervention. Non-lethal forms of hepatic injury were examined in combination with liver-directed radiation in non-human primates (NHPs) to develop a model of acute hepatic failure that mimics the human condition. Porcine hepatocyte transplantation was then tested as a potential therapy for acute hepatic failure. After liver-directed radiation therapy, delivery of a non-lethal hepatic ischemia-reperfusion injury reliably and rapidly generated liver failure providing conditions that can enable pre-clinical testing of liver support or replacement therapies. Unfortunately, in preliminary studies, low hepatocyte engraftment and over-immune suppression interfered with the ability to assess the efficacy of transplanted porcine hepatocytes in the model. A model of acute liver failure in NHPs was created that recapitulates the pathophysiology and pathology of the clinical condition, does so with reasonably predictable kinetics, and results in 100% mortality. The model allowed preliminary testing of xenogeneic hepatocyte transplantation as a potential therapy.

Supportive Hepatocyte Transplantation after Partial Hepatectomy Enhances Liver Regeneration in a Preclinical Pig Model

BACKGROUND

Hepatocyte transplantation (HTx) is regarded as a potential treatment modality for various liver diseases including acute liver failure. We developed a preclinical pig model to evaluate if HTx could safely support recovery from liver function impairment after partial hepatectomy.

METHODS

Pigs underwent partial hepatectomy with reduction of the liver volume by 50% to induce a transient but significant impairment of liver function. Thereafter, 2 protocols for HTx were evaluated and compared to a control group receiving liver resection only (group 1, n = 5). Portal pressure-controlled HTx was performed either immediately after surgery (group 2, n = 6) or 3 days postoperatively (group 3, n = 5). In all cases, liver regeneration was monitored by conventional laboratory tests and the novel noninvasive maximum liver function capacity (LiMAx) test with a follow-up of 4 weeks.

RESULTS

Partial hepatectomy significantly impaired liver function according to conventional liver function tests as well as LiMAx in all groups. A mean of 4.10 ± 1.1 × 108 and 3.82 ± 0.7 × 108 hepatocytes were transplanted in groups 2 and 3, respectively. All animals remained stable with respect to vital parameters during and after HTx. The animals in group 2 showed enhanced liver regeneration as observed by mean postoperative LiMAx values (621.5 vs. 331.3 μg/kg/h on postoperative day 7; p < 0.001) whereas HTx in group 3 led to a significant increase in mean liver-specific coagulation factor VII (112.2 vs. 54.0% on postoperative day 7; p = 0.003) compared to controls (group 1), respectively. In both experimental groups, thrombotic material was observed in the portal veins and pulmonary arteries on histology, despite the absence of clinical symptoms.

CONCLUSION

HTx can be performed safely and effectively immediately after a partial (50%) hepatectomy as well as 3 days postoperatively, with comparable results regarding the enhancement of liver function and regeneration.

Endothelial Cells Differentiated from Porcine Epiblast Stem Cells

Pluripotent stem cells (PSCs) have the ability of self-renewal that can retain the characteristics of the mother cell, and of pluripotency that can differentiate into several body types. PSCs typically include embryonic stem cells (ESCs) derived from the inner cell mass of the preimplantation embryo, and epiblast stem cells (EpiSCs) derived from the epiblast of postimplantation embryo. Although PSCs are able to be used by differentiation into endothelial cells as a potential treatment for vascular diseases, human ESCs and induced PSCs (iPSCs) are followed by ethical and safety issues. Pigs are anatomically and physiologically similar to humans. Therefore, the goal of this study was to establish an efficient protocol that differentiates porcine EpiSCs (pEpiSCs) into the endothelial cells for applying the treatment of human vascular diseases. As a result, alkaline phosphatase (AP)-negative (-) pEpiSCs cultured in endothelial cell growth basal medium-2 (EBM-2) differentiation medium in association with 50 ng/mL of vascular endothelial growth factor (VEGF) for 8 days were changed morphologically like the feature of endothelial cells, and expression of pluripotency-associated markers (OCT-3/4, NANOG, SOX2, and C-MYC) in porcine differentiated cells was significantly decreased (p < 0.05). Additionally, when pEpiSCs were cultured in EBM-2 + 50 ng/mL of VEGF, porcine differentiated cells represented a common endothelial cell marker positive (CD31+) but monocytes and lymphocytes marker negative (CD45-). Therefore, these results indicated that pEpiSCs cultured in EBM-2 + 50 ng/mL of VEGF culture condition were efficiently differentiated into endothelial cells for the treatment of blood vessel diseases.

Long-term observation of airway reconstruction using decellularized tracheal allografts in micro-miniature pigs at growing stage

Introduction

Decellularized tissue exhibits cell matrix-like properties, along with reduced antigenicity. We explored the potential of decellularized allogeneic trachea to restore the upper respiratory tract, focusing on pediatric application. This study specifically aimed at long-term observation of tissue regeneration using a micro-miniature pig model.

Methods

Artificial defects (15 × 15 mm) in the subglottis and trachea of micro-miniature pigs were repaired by transplantation of either allogeneic decellularized or fresh (control) tracheal patches. Pigs were evaluated in situ, by bronchoscopy, every three months, and sacrificed for histological examination at six and twelve months after transplantation.

Results

No airway symptom was observed in any pig during the observation period. Bronchoscopy revealed the tracheal lumen to be restored by fresh grafts, showing an irregular surface with remarkable longitudinal compression; these changes were mild after restoration with decellularized grafts. Histologically, while fresh graft patches were denatured and replaced by calcified tissue, decellularized patches remained unchanged throughout the observation period. There were regeneration foci of cartilage adjacent to the grafts, and some foci joined the decellularized graft uniformly, suggesting the induction of tracheal reconstitution.

Conclusion

Allogeneic decellularized tracheal tissue could serve as a promising biomaterial for tracheal restoration, especially for pediatric patients at the growing stage.

Enhancing Survival of Human Hepatocytes by Neonatal Thymectomy and Partial Hepatectomy in Micro-miniature Pigs

BACKGROUND

With the goal of in vivo cultivation of human hepatocytes that have not been sufficient in full differentiation in vitro, the advantage of neonatal thymectomy was verified on expansion of xenogeneic human hepatocyte in the micro-miniature pig (MMP).

METHODS

The thymus was excised immediately after the birth of the MMPs via cesarean section. Newborns were fed by artificial feeding under specific pathogen-free conditions. The thymectomized and nonthymectomized littermates were transplanted with human hepatocytes via a portal vein with or without partial hepatectomy at the MMP adult stage.

RESULTS

The growth of thymectomized MMPs and the sham operated littermates was not significantly different; the former weighed 1.98 ± 0.30 kg (average ± standard deviation, n = 4) and the latter weighed 2.28 ± 0.39 kg (n = 4) at 1 month of age, and 17.48 ± 1.92 kg and 16.75 ± 2.68 kg at 12 months of age. Blood thymosin α₁ concentrations in the thymectomy group were significantly lower than in the control group (0.22 ± 0.05 ng/mL vs 0.46 ± 0.16 ng/mL; n = 4, 12 months old, P = .029). After human hepatocyte transplantation, human albumin levels were detectable on day 28 in the peripheral blood of the thymectomy plus hepatectomy group (14.3 ± 4.9 ng/mL [± range, n = 2]) but were not detectable even on day 21 in the control group.

CONCLUSIONS

Neonatal thymectomy was successfully achieved in infantile MMPs born via cesarean section. These pigs were considered to be an ideal in vivo bioreactor for human hepatocytes.