Hypothermic storage of human hepatocytes for transplantation

Supercooled preservation of cultured primary rat hepatocyte monolayers

Supercooled preservation (SCP) is a technology that involves cooling a substance below its freezing point without initiating ice crystal formation. It is a promising alternative to prolong the preservation time of cells, tissues, engineered tissue products, and organs compared to the current practices of hypothermic storage. Two-dimensional (2D) engineered tissues are extensively used in in vitro research for drug screening and development and investigation of disease progression. Despite their widespread application, there is a lack of research on the SCP of 2D-engineered tissues. In this study, we presented the effects of SCP at -2 and -6°C on primary rat hepatocyte (PRH) monolayers for the first time and compared cell viability and functionality with cold storage (CS, + 4°C). We preserved PRH monolayers in two different commercially available solutions: Hypothermosol-FRS (HTS-FRS) and the University of Wisconsin (UW) with and without supplements (i.e., polyethylene glycol (PEG) and 3-O-Methyl-Α-D-Glucopyranose (3-OMG)). Our findings revealed that UW with and without supplements were inadequate for the short-term preservation of PRH monolayers for both SCP and CS with high viability, functionality, and monolayer integrity. The combination of supplements (PEG and 3-OMG) in the HTS-FRS solution outperformed the other groups and yielded the highest viability and functional capacity. Notably, PRH monolayers exhibited superior viability and functionality when stored at -2°C through SCP for up to 3 days compared to CS. Overall, our results demonstrated that SCP is a feasible approach to improving the short-term preservation of PRH monolayers and enables readily available 2D-engineered tissues to advance in vitro research. Furthermore, our findings provide insights into preservation outcomes across various biological levels, from cells to tissues and organs, contributing to the advancement of bioengineering and biotechnology.

Restored glyoxylate metabolism after AGXT gene correction and direct reprogramming of primary hyperoxaluria type 1 fibroblasts

Primary hyperoxaluria type 1 (PH1) is a rare inherited metabolic disorder characterized by oxalate overproduction in the liver, resulting in renal damage. It is caused by mutations in the AGXT gene. Combined liver and kidney transplantation is currently the only permanent curative treatment. We combined locus-specific gene correction and hepatic direct cell reprogramming to generate autologous healthy induced hepatocytes (iHeps) from PH1 patient-derived fibroblasts. First, site-specific AGXT corrected cells were obtained by homology directed repair (HDR) assisted by CRISPR-Cas9, following two different strategies: accurate point mutation (c.731T>C) correction or knockin of an enhanced version of AGXT cDNA. Then, iHeps were generated, by overexpression of hepatic transcription factors. Generated AGXT-corrected iHeps showed hepatic gene expression profile and exhibited in vitro reversion of oxalate accumulation compared to non-edited PH1-derived iHeps. This strategy set up a potential alternative cellular source for liver cell replacement therapy and a personalized PH1 in vitro disease model.

Cell therapy in end-stage liver disease: replace and remodel

Liver disease is prevalent worldwide. When it reaches the end stage, mortality rises to 50% or more. Although liver transplantation has emerged as the most efficient treatment for end-stage liver disease, its application has been limited by the scarcity of donor livers. The lack of acceptable donor organs implies that patients are at high risk while waiting for suitable livers. In this scenario, cell therapy has emerged as a promising treatment approach. Most of the time, transplanted cells can replace host hepatocytes and remodel the hepatic microenvironment. For instance, hepatocytes derived from donor livers or stem cells colonize and proliferate in the liver, can replace host hepatocytes, and restore liver function. Other cellular therapy candidates, such as macrophages and mesenchymal stem cells, can remodel the hepatic microenvironment, thereby repairing the damaged liver. In recent years, cell therapy has transitioned from animal research to early human studies. In this review, we will discuss cell therapy in end-stage liver disease treatment, especially focusing on various cell types utilized for cell transplantation, and elucidate the processes involved. Furthermore, we will also summarize the practical obstacles of cell therapy and offer potential solutions.

Effects of Pro-Inflammatory Cytokines on Hepatic Metabolism in Primary Human Hepatocytes

Three decades of hepatocyte transplantation have confirmed such a cell-based approach as an adjunct or alternative treatment to solid organ transplantation. Donor cell survival and engraftment were indirectly measured by hepatospecific secretive or released metabolites, such as ammonia metabolism in urea cycle defects. In cases of sepsis or viral infection, ammonia levels can significantly and abruptly increase in these recipients, erroneously implying rejection. Pro-inflammatory cytokines associated with viral or bacterial infections are known to affect many liver functions, including drug-metabolizing enzymes and hepatic transport activities. We examined the influence of pro-inflammatory cytokines in primary human hepatocytes, isolated from both normal donors or patients with metabolic liver diseases. Different measures of hepatocyte functions, including ammonia metabolism and phase 1-3 metabolism, were performed. All the hepatic functions were profoundly and significantly suppressed after exposure to concentrations of from 0.1 to 10 ng/mL of different inflammatory cytokines, alone and in combination. Our data indicate that, like phase I metabolism, suppression of phase II/III and ammonia metabolism occurs in hepatocytes exposed to pro-inflammatory cytokines in the absence of cell death. Such inflammatory events do not necessarily indicate a rejection response or loss of the cell graft, and these systemic inflammatory signals should be carefully considered when the immunosuppressant regiment is reduced or relieved in a hepatocyte transplantation recipient in response to such alleged rejection.

Long-term and short-term preservation strategies for tissue engineering and regenerative medicine products: state of the art and emerging trends

There is an ever-growing need of human tissues and organs for transplantation. However, the availability of such tissues and organs is insufficient by a large margin, which is a huge medical and societal problem. Tissue engineering and regenerative medicine (TERM) represent potential solutions to this issue and have therefore been attracting increased interest from researchers and clinicians alike. But the successful large-scale clinical deployment of TERM products critically depends on the development of efficient preservation methodologies. The existing preservation approaches such as slow freezing, vitrification, dry state preservation, and hypothermic and normothermic storage all have issues that somehow limit the biomedical applications of TERM products. In this review, the principles and application of these approaches will be summarized, highlighting their advantages and limitations in the context of TERM products preservation.

Human Hepatocytes Isolated from Explanted Livers: A Powerful Tool to Understand End-stage Liver Disease and Drug Screening

The use of primary human hepatocytes has been hampered by limited availability of adequate numbers of fresh and viable cells due to the ongoing shortage of liver donors. Thus, there is no surplus of healthy organs from which freshly isolated cells can be prepared when needed. However, primary hepatocytes can be successfully isolated from explanted liver specimens obtained from patients receiving orthotopic liver transplantation for decompensated liver cirrhosis or for metabolic liver disease without end-stage liver disease and are a valuable resource for the pharmaceutical industry research. This review focuses on the isolation, characterization and cryopreservation of hepatocytes derived from therapeutically resected livers with various hepatic diseases.

Microtubule Stabilization Protects Hypothermia-Induced Damage to the Cytoskeleton and Barrier Integrity of the Corneal Endothelial Cells

Purpose: To determine the impact of hypothermia on the barrier function of donor corneal endothelium, thereby enhancing the success of corneal transplantation. Methods: Primary cultures of porcine endothelial cells were subjected to hypothermia (15 h; 4°C). The impact on microtubule assembly, peri-junctional actomyosin ring (PAMR), and ZO-1 was assessed by immunocytochemistry with and without pretreatment with a microtubule-stabilizing agent (Epothilone B; EpoB; 100 nM) and a p38 MAP kinase inhibitor (SB-203580; 20 μM). In addition, EpoB-loaded PLGA nanoparticles (ENPs) prepared by nanoprecipitation technique and coated with poly-L-lysine (PLL-ENPs) were administered one-time for sustained intracellular delivery of EpoB. Results: Exposure to hypothermia led to microtubule disassembly concomitant with the destruction of PAMR and the displacement of ZO-1 at the cellular periphery, suggesting a loss in barrier integrity. These adverse effects were attenuated by pretreatment with EpoB or SB-203580. PLL-ENPs possessed a zeta potential of ∼26 mV and a size of ∼110 nm. Drug loading and entrapment efficiency were 5% (w/w) and ∼87%, respectively, and PLL-ENPs showed a biphasic release in vitro: burst phase (1 day), followed by a sustained phase (∼4 weeks). Pretreatment with PLL-ENPs (0.4 mg/mL) for 24 h stabilized the microtubules and opposed the hypothermia-induced damage to PAMR and the redistribution of ZO-1. Conclusions: Hypothermia induces microtubule disassembly via activation of p38 MAP kinase and subsequently breaks down the barrier function of the endothelium. Sustained intracellular delivery of EpoB using nanoparticles has the potential to overcome endothelial barrier failure during prolonged cold storage of donor cornea.

Cryopreservation: An Overview of Principles and Cell-Specific Considerations

The origins of low-temperature tissue storage research date back to the late 1800s. Over half a century later, osmotic stress was revealed to be a main contributor to cell death during cryopreservation. Consequently, the addition of cryoprotective agents (CPAs) such as dimethyl sulfoxide (DMSO), glycerol (GLY), ethylene glycol (EG), or propylene glycol (PG), although toxic to cells at high concentrations, was identified as a necessary step to protect against rampant cell death during cryopreservation. In addition to osmotic stress, cooling and thawing rates were also shown to have significant influence on cell survival during low temperature storage. In general, successful low-temperature cell preservation consists of the addition of a CPA (commonly 10% DMSO), alone or in combination with additional permeating or non-permeating agents, cooling rates of approximately 1ºC/min, and storage in either liquid or vapor phase nitrogen. In addition to general considerations, cell-specific recommendations for hepatocytes, pancreatic islets, sperm, oocytes, and stem cells should be observed to maximize yields. For example, rapid cooling is associated with better cryopreservation outcomes for oocytes, pancreatic islets, and embryonic stem cells while slow cooling is recommended for cryopreservation of hepatocytes, hematopoietic stem cells, and mesenchymal stem cells. Yields can be further maximized by implementing additional pre-cryo steps such as: pre-incubation with glucose and anti-oxidants, alginate encapsulation, and selecting cells within an optimal age range and functional ability. Finally, viability and functional assays are critical steps in determining the quality of the cells post-thaw and improving the efficiency of the current cryopreservation methods.

Optimisation of Storage and Transportation Conditions of Cultured Corneal Endothelial Cells for Cell Replacement Therapy

As the cornea is one of the most transplanted tissues in the body it has placed a burden on the provision of corneas from cadaveric donors. Corneal endothelial dysfunction is the leading indication for cornea transplant. Therefore, tissue engineering is emerging as an alternative approach to overcome the global shortage of transplant-grade corneas. The propagation and expansion of corneal endothelial cells has been widely reported. However, one obstacle to overcome is the transport and storage of corneal endothelial cells. In this study we investigated whether tissue engineered corneal endothelial cells can be preserved in hypothermic conditions. Human corneal endothelial cells (HCEnCs) were exposed to various temperatures (4 °C, 23 °C, and 37 °C) in both adherent and suspension storage models. Optimal storage media and storage duration was tested along with post-storage viability. Following storage and subsequent recovery at 37 °C, cell phenotype was assessed by immunofluorescence, gene and protein expression, and proliferative capacity analysis. Functionality was also assessed within a rabbit model of bullous keratopathy. Our data support our hypothesis that functional HCEnCs can be preserved in hypothermic conditions.

Deep-supercooling for extended preservation of adipose-derived stem cells

Cell preservation is an enabling technology for widespread distribution and applications of mammalian cells. Traditional cryopreservation via slow-freezing or vitrification provides long-term storage but requires cytotoxic cryoprotectants (CPA) and tedious CPA loading/unloading, cooling, and recovering procedures. Hypothermic storage around 0-4 °C is an alternative method but only works for a short period due to its high storage temperatures. Here, we report on the deep-supercooling (DSC) preservation of human adipose-derived stem cells at deep subzero temperatures without freezing for extended storage. Enabled by surface sealing with an immiscible oil phase, cell suspension can be preserved in a liquid state at -13 °C and -16 °C for 7 days with high cell viability, retention of stemness, attachment, and multilineage differentiation capacities. These results demonstrate that DSC is an improved short-term preservation approach to provide off-the-shelf cell sources for booming cell-based medicine and bioengineering.

Generation of fully functional hepatocyte-like organoids from human induced pluripotent stem cells mixed with Endothelial Cells

Despite advances in stem cell research, cell transplantation therapy for liver failure is impeded by a shortage of human primary hepatocytes (HPH), along with current differentiation protocol limitations. Several studies have examined the concept of co-culture of human induced pluripotent cells (hiPSCs) with various types of supporting non-parenchymal cells to attain a higher differentiation yield and to improve hepatocyte-like cell functions both in vitro and in vivo. Co-culturing hiPSCs with human endothelial cells (hECs) is a relatively new technique that requires more detailed studies. Using our 3D human embryoid bodies (hEBs) formation technology, we interlaced Human Adipose Microvascular Endothelial Cells (HAMEC) with hiPSCs, leading to a higher differentiation yield and notable improvements across a wide range of hepatic functions. We conducted a comprehensive gene and protein secretion analysis of our HLCs coagulation factors profile, showing promising results in comparison with HPH. Furthermore, a stage-specific glycomic analysis revealed that the differentiated hepatocyte-like clusters (HLCs) resemble the glycan features of a mature tissue rather than cells in culture. We tested our HLCs in animal models, where the presence of HAMEC in the clusters showed a consistently better performance compared to the hiPSCs only group in regard to persistent albumin secretion post-transplantation.

Mitochondrial Impairment as a Key Factor for the Lack of Attachment after Cold Storage of Hepatocyte Suspensions

Isolated primary hepatocytes, which are widely used for pharmacological and clinical purposes, usually undergo certain periods of cold storage in suspension during processing. While adherent hepatocytes were shown previously to suffer iron-dependent cell death during cold (4 °C) storage and early rewarming, we previously found little iron-dependent hepatocyte death in suspension but severely decreased attachment ability unless iron chelators were added. Here, we focus on the role of mitochondrial impairment in this nonattachment of hepatocyte suspensions. Rat hepatocyte suspensions were stored in a chloride-poor, glycine-containing cold storage solution with and without iron chelators at 4 °C. After 1 wk of cold storage in the basic cold storage solution, cell viability in suspension was unchanged, while cell attachment was decreased by >80%. In the stored cells, a loss of mitochondrial membrane potential (MMP), a decrease in adenosine triphosphate (ATP) content (2 ± 2 nmol/10⁶ cells after cold storage, 5 ± 3 nmol/10⁶ cells after rewarming vs. control 29 ± 6 nmol/10⁶ cells), and a decrease in oxygen consumption (101 ± 59 pmol sec^-1 per 10⁶ cells after rewarming vs. control 232 ± 83 pmol sec^-1 per 10⁶ cells) were observed. Addition of iron chelators to the cold storage solution increased cell attachment to 53% ± 20% and protected against loss of MMP, and cells were able to partially regenerate ATP during rewarming (15 ± 10 nmol/10⁶ cells). Increased attachment could also be achieved by addition of the inhibitor combination of mitochondrial permeability transition, trifluoperazine + fructose. Attached hepatocytes displayed normal MMP and mitochondrial morphology. Additional experiments with freshly isolated hepatocytes confirmed that impaired energy production-as elicited by an inhibitor of the respiratory chain, antimycin A-can decrease cell attachment without decreasing viability. Taken together, these results suggest that mitochondrial impairment with subsequent energy deficiency is a key factor for the lack of attachment of cold-stored hepatocyte suspensions.

Isolation, characterization and cold storage of cells isolated from diseased explanted livers

INTRODUCTION

Livers discarded after standard organ retrieval are commonly used as a cell source for hepatocyte transplantation. Due to the scarcity of organ donors, this leads to a shortage of suitable cells for transplantation. Here, the isolation of liver cells from diseased livers removed during liver transplantation is studied and compared to the isolation of cells from liver specimens obtained during partial liver resection.

METHODS

Hepatocytes from 20 diseased explanted livers (Ex-group) were isolated, cultured and stored at 4°C for up to 48 hours, and compared to hepatocytes isolated from the normal liver tissue of 14 liver lobe resections (Rx-group). The nonparenchymal cell fraction (NPC) was analyzed by flow cytometry to identify potential liver progenitor cells, and OptiPrep™ (Sigma-Aldrich) density gradient centrifugation was used to enrich the progenitor cells for immediate transplantation.

RESULTS

There were no differences in viability, cell integrity and metabolic activity in cell culture and survival after cold storage when comparing the hepatocytes from the Rx-group and the Ex-group. In some cases, the latter group showed tendencies of increased resistance to isolation and storage procedures. The NPC of the Ex-group livers contained considerably more EpCAM+ and significantly more CD90+ cells than the Rx-group. Progenitor cell enrichment was not sufficient for clinical application.

CONCLUSIONS

Hepatocytes isolated from diseased explanted livers showed the essential characteristics of being adequate for cell transplantation. Increased numbers of liver progenitor cells can be isolated from diseased explanted livers. These results support the feasibility of using diseased explanted livers as a cell source for liver cell transplantation.

Host conditioning and rejection monitoring in hepatocyte transplantation in humans

BACKGROUND & AIMS

Hepatocyte transplantation partially corrects genetic disorders and has been associated anecdotally with reversal of acute liver failure. Monitoring for graft function and rejection has been difficult, and has contributed to limited graft survival. Here we aimed to use preparative liver-directed radiation therapy, and continuous monitoring for possible rejection in an attempt to overcome these limitations.

METHODS

Preparative hepatic irradiation was examined in non-human primates as a strategy to improve engraftment of donor hepatocytes, and was then applied in human subjects. T cell immune monitoring was also examined in human subjects to assess adequacy of immunosuppression.

RESULTS

Porcine hepatocyte transplants engrafted and expanded to comprise up to 15% of irradiated segments in immunosuppressed monkeys preconditioned with 10Gy liver-directed irradiation. Two patients with urea cycle deficiencies had early graft loss following hepatocyte transplantation; retrospective immune monitoring suggested the need for additional immunosuppression. Preparative radiation, anti-lymphocyte induction, and frequent immune monitoring were instituted for hepatocyte transplantation in a 27year old female with classical phenylketonuria. Post-transplant liver biopsies demonstrated multiple small clusters of transplanted cells, multiple mitoses, and Ki67+ hepatocytes. Mean peripheral blood phenylalanine (PHE) level fell from pre-transplant levels of 1343±48μM (normal 30-119μM) to 854±25μM (treatment goal ≤360μM) after transplant (36% decrease; p<0.0001), despite transplantation of only half the target number of donor hepatocytes. PHE levels remained below 900μM during supervised follow-up, but graft loss occurred after follow-up became inconsistent.

CONCLUSIONS

Radiation preconditioning and serial rejection risk assessment may produce better engraftment and long-term survival of transplanted hepatocytes. Hepatocyte xenografts engraft for a period of months in non-human primates and may provide effective therapy for patients with acute liver failure.

LAY SUMMARY

Hepatocyte transplantation can potentially be used to treat genetic liver disorders but its application in clinical practice has been impeded by inefficient hepatocyte engraftment and the inability to monitor rejection of transplanted liver cells. In this study, we first show in non-human primates that pretreatment of the host liver with radiation improves the engraftment of transplanted liver cells. We then used this knowledge in a series of clinical hepatocyte transplants in patients with genetic liver disorders to show that radiation pretreatment and rejection risk monitoring are safe and, if optimized, could improve engraftment and long-term survival of transplanted hepatocytes in patients.

Alternative Cell Sources to Adult Hepatocytes for Hepatic Cell Therapy

Adult hepatocyte transplantation is limited by scarce availability of suitable donor liver tissue for hepatocyte isolation. New cell-based therapies are being developed to supplement whole-organ liver transplantation, to reduce the waiting-list mortality rate, and to obtain more sustained and significant metabolic correction. Fetal livers and unsuitable neonatal livers for organ transplantation have been proposed as potential useful sources of hepatic cells for cell therapy. However, the major challenge is to use alternative cell sources for transplantation that can be derived from reproducible methods. Different types of stem cells with hepatic differentiation potential are eligible for generating large numbers of functional hepatocytes for liver cell therapy to treat degenerative disorders, inborn hepatic metabolic diseases, and organ failure. Clinical trials are designed to fully establish the safety profile of such therapies and to define target patient groups and standardized protocols.

Effective Hypothermic Storage of Human Pluripotent Stem Cell-Derived Cardiomyocytes Compatible With Global Distribution of Cells for Clinical Applications and Toxicology Testing

To fully explore the potential of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs), efficient methods for storage and shipment of these cells are required. Here, we evaluated the feasibility to cold store monolayers and aggregates of functional CMs obtained from different PSC lines using a fully defined clinical-compatible preservation formulation and investigated the time frame that hPSC-CMs could be subjected to hypothermic storage. We showed that two-dimensional (2D) monolayers of hPSC-CMs can be efficiently stored at 4°C for 3 days without compromising cell viability. However, cell viability decreased when the cold storage interval was extended to 7 days. We demonstrated that hPSC-CMs are more resistant to prolonged hypothermic storage-induced cell injury in three-dimensional aggregates than in 2D monolayers, showing high cell recoveries (>70%) after 7 days of storage. Importantly, hPSC-CMs maintained their typical (ultra)structure, gene and protein expression profile, electrophysiological profiles, and drug responsiveness.

SIGNIFICANCE

The applicability of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) in the clinic/industry is highly dependent on the development of efficient methods for worldwide shipment of these cells. This study established effective clinically compatible strategies for cold (4°C) storage of hPSC-CMs cultured as two-dimensional (2D) monolayers and three-dimensional (3D) aggregates. Cell recovery of 2D monolayers of hPSC-CMs was found to be dependent on the time of storage, and 3D cell aggregates were more resistant to prolonged cold storage than 2D monolayers. Of note, it was demonstrated that 7 days of cold storage did not affect hPSC-CM ultrastructure, phenotype, or function. This study provides important insights into the cold preservation of PSC-CMs that could be valuable in improving global commercial distribution of hPSC-CMs.

Improvement of short-term hypothermic preservation of microencapsulated hepatocytes

OBJECTIVES

To determine the optimal storage solution containing suitable protective agents for the preservation of microencapsulated hepatocytes at 4 °C as well as the optimum incubation time after hypothermic preservation.

RESULTS

L15 was the optimum solution for both maintaining microcapsule integrity and cell viability. Furthermore, 5 %(v/v) PEG (20 or 35 kDa) added to Leibovitz-15 medium was optimal for microencapsulated C3A cells, enhancing cell viability and liver-specific functions, including albumin and urea synthesis as well as CYP1A2 and CYP3A4 activities. The transcription levels of several CYP450-related genes were also dramatically increased in cells incubated in the optimal solution. Pre-incubation for 2 h was the optimal time for restoring favorable levels of CYP1A2 and CYP3A4 activities in microencapsulated C3A cells for short term, 2 day storage.

CONCLUSIONS

Leibovitz-15 medium supplemented with 5 % (v/v) PEG is a promising cold solution for microencapsulated hepatocytes at 4 °C, with an incubation of 2 h at 37 °C after hypothermic preservation being the best incubation duration for further cell application.

Development of novel tools for the in vitro investigation of drug-induced liver injury

INTRODUCTION

Due to its complex mechanisms and unpredictable occurrence, drug-induced liver injury (DILI) complicates drug identification and classification. Since species-specific differences in metabolism and pharmacokinetics exist, data obtained from animal studies may not be sufficient to predict DILI in humans.

AREAS COVERED

Over the last few decades, numerous in vitro models have been developed to replace animal testing. The advantages and disadvantages of commonly used liver-derived in vitro models (e.g., cell lines, hepatocyte models, liver slices, three-dimensional (3D) hepatospheres, etc.) are discussed. Toxicogenomics-based methodologies (genomics, epigenomics, transcriptomics, proteomics and metabolomics) and next-generation sequencing have also been used to enhance the reliability of DILI prediction. This review presents an overview of the currently used alternative toxicological models and of the most advanced approaches in the field of DILI research.

EXPERT OPINION

It seems unlikely that a single in vitro system will be able to mimic the complex interactions in the human liver. Three-dimensional multicellular systems may bridge the gap between conventional 2D models and in vivo clinical studies in humans and provide a reliable basis for hepatic toxicity assay development. Next-generation sequencing technologies, in comparison to microarray-based technologies, may overcome the current limitations and are promising for the development of predictive models in the near future.

New Tools in Experimental Cellular Therapy for the Treatment of Liver Diseases

The current standard of care for end stage liver disease is orthotopic liver transplantation (OLT). Through improvement in surgical techniques, immunosuppression, and general medical care, liver transplantation has become an effective treatment over the course of the last half-century. Unfortunately, due to the limited availability of donor organs, there is a finite limit to the number of patients who will benefit from this therapy. This review will discuss current research in experimental cellular therapies for acute, chronic, and metabolic liver failure that may be appropriate when liver transplantation is not an immediate option.

Clinical Hepatocyte Transplantation: Practical Limits and Possible Solutions

Since the first human hepatocyte transplants (HTx) in 1992, clinical studies have clearly established proof of principle for this therapy as a treatment for patients with acquired or inherited liver disease. Although major accomplishments have been made, there are still some specific limitations to this technology, which, if overcome, could greatly enhance the efficacy and implementation of this therapy. Here, we describe what in our view are the most significant obstacles to the clinical application of HTx and review the solutions currently proposed. The obstacles of significance include the limited number and quality of liver tissues as a cell source, the lack of clinical grade reagents, quality control evaluation of hepatocytes prior to transplantation, hypothermic storage of cells prior to transplantation, preconditioning treatments to enhance engraftment and proliferation of donor cells, tracking or monitoring cells after transplantation, and the optimal immunosuppression protocols for transplant recipients.

Cold Preservation of Human Adult Hepatocytes for Liver Cell Therapy

Hepatocyte transplantation is a promising alternative therapy for the treatment of hepatic failure, hepatocellular deficiency, and genetic metabolic disorders. Hypothermic preservation of isolated human hepatocytes is potentially a simple and convenient strategy to provide on-demand hepatocytes in sufficient quantity and of the quality required for biotherapy. In this study, first we assessed how cold storage in three clinically safe preservative solutions (UW, HTS-FRS, and IGL-1) affects the viability and in vitro functionality of human hepatocytes. Then we evaluated whether such cold-preserved human hepatocytes could engraft and repopulate damaged livers in a mouse model of liver failure. Human hepatocytes showed comparable viabilities after cold preservation in the three solutions. The ability of fresh and cold-stored hepatocytes to attach to a collagen substratum and to synthesize and secrete albumin, coagulation factor VII, and urea in the medium after 3 days in culture was also equally preserved. Cold-stored hepatocytes were then transplanted in the spleen of immunodeficient mice previously infected with adenoviruses containing a thymidine kinase construct and treated with a single dose of ganciclovir to induce liver injury. Engraftment and liver repopulation were monitored over time by measuring the blood level of human albumin and by assessing the expression of specific human hepatic mRNAs and proteins in the recipient livers by RT-PCR and immunohistochemistry, respectively. Our findings show that cold-stored human hepatocytes in IGL-1 and HTS-FRS preservative solutions can survive, engraft, and proliferate in a damaged mouse liver. These results demonstrate the usefulness of human hepatocyte hypothermic preservation for cell transplantation.

Explanted diseased livers - a possible source of metabolic competent primary human hepatocytes

Being an integral part of basic, translational and clinical research, the demand for primary human hepatocytes (PHH) is continuously growing while the availability of tissue resection material for the isolation of metabolically competent PHH remains limited. To overcome current shortcomings, this study evaluated the use of explanted diseased organs from liver transplantation patients as a potential source of PHH. Therefore, PHH were isolated from resected surgical specimens (Rx-group; n = 60) and explanted diseased livers obtained from graft recipients with low labMELD-score (Ex-group; n = 5). Using established protocols PHH were subsequently cultured for a period of 7 days. The viability and metabolic competence of cultured PHH was assessed by the following parameters: morphology and cell count (CyQuant assay), albumin synthesis, urea production, AST-leakage, and phase I and II metabolism. Both groups were compared in terms of cell yield and metabolic function, and results were correlated with clinical parameters of tissue donors. Notably, cellular yields and viabilities were comparable between the Rx- and Ex-group and were 5.3±0.5 and 2.9±0.7×10⁶ cells/g liver tissue with 84.3±1.3 and 76.0±8.6% viability, respectively. Moreover, PHH isolated from the Rx- or Ex-group did not differ in regards to loss of cell number in culture, albumin synthesis, urea production, AST-leakage, and phase I and II metabolism (measured by the 7-ethoxycoumarin-O-deethylase and uracil-5′-diphosphate-glucuronyltransferase activity). Likewise, basal transcript expressions of the CYP monooxygenases 1A1, 2C8 and 3A4 were comparable as was their induction when treated with a cocktail that consisted of 3-methylcholantren, rifampicin and phenobarbital, with increased expression of CYP 1A1 and 3A4 mRNA while transcript expression of CYP 2C8 was only marginally changed. In conclusion, the use of explanted diseased livers obtained from recipients with low labMELD-score might represent a valuable source of metabolically competent PHH which are comparable in viability and function to cells obtained from specimens following partial liver resection.

Rapid and sensitive assessment of human hepatocyte functions

Transplantation of human hepatocytes (HTx) has gained recognition as a bridge to, or an alternative to, orthotopic liver transplantation for patients with acute liver failure or genetic defects in liver function. Although the quality of the hepatocytes used for cell transplantation is critical, no consensus exists on protocols to assess the function of hepatocytes prior to HTx. Application of this cell therapy in clinical practice could be aided by fast and reliable assays to evaluate the functional competence of isolated hepatocytes prior to clinical transplantation. Traditional assays for measuring metabolic functions in primary hepatocytes frequently involve highly technical equipment, time-consuming methods, and large numbers of cells. We describe a novel approach for the rapid assessment of the metabolic capabilities of human hepatocytes. This report details simple procedures to evaluate 11 endpoints from cells isolated from human liver that can be performed by a single operator within approximately 2 h of isolation. Longer term cultured hepatocytes were also analyzed to determine if the results from the 2-h tests were predictive of long-term hepatic function. The assays simultaneously measure five cytochrome P450 activities, one phase II activity, plating efficiency, and ammonia metabolism in addition to viability and cell yield. The assays require fewer than 20 million cells and can be completed using commonly available and inexpensive laboratory equipment. The protocol details methods that can be used in a time frame that would allow analysis of hepatic functions in freshly isolated hepatocytes prior to their use for clinical transplantation.