Immunological aspects of liver cell transplantation

Kupffer cells abrogate homing and repopulation of allogeneic hepatic progenitors in injured liver site

BACKGROUND

Allogeneic hepatocyte transplantation is an emerging approach to treat acute liver defects. However, durable engraftment of the transplanted cells remains a daunting task, as they are actively cleared by the recipient's immune system. Therefore, a detailed understanding of the innate or adaptive immune cells-derived responses against allogeneic transplanted hepatic cells is the key to rationalize cell-based therapies.

METHODS

Here, we induced an acute inflammatory regenerative niche (3-96 h) on the surface of the liver by the application of cryo-injury (CI) to systematically evaluate the innate immune response against transplanted allogeneic hepatic progenitors in a sustained micro-inflammatory environment.

RESULTS

The resulting data highlighted that the injured site was significantly repopulated by alternating numbers of innate immune cells, including neutrophils, monocytes and Kupffer cells (KCs), from 3 to 96 h. The transplanted allo-HPs, engrafted 6 h post-injury, were collectively eliminated by the innate immune response within 24 h of transplantation. Selective depletion of the KCs demonstrated a delayed recruitment of monocytes from day 2 to day 6. In addition, the intrasplenic engraftment of the hepatic progenitors 54 h post-transplantation was dismantled by KCs, while a time-dependent better survival and translocation of the transplanted cells into the injured site could be observed in samples devoid of KCs.

CONCLUSION

Overall, this study provides evidence that KCs ablation enables a better survival and integration of allo-HPs in a sustained liver inflammatory environment, having implications for rationalizing the cell-based therapeutic interventions against liver defects.

Hepatocyte transplantation: The progress and the challenges

Numerous studies have shown that hepatocyte transplantation is a promising approach for liver diseases, such as liver-based metabolic diseases and acute liver failure. However, it lacks strong evidence to support the long-term therapeutic effects of hepatocyte transplantation in clinical practice. Currently, major hurdles include availability of quality-assured hepatocytes, efficient engraftment and repopulation, and effective immunosuppressive regimens. Notably, cell sources have been advanced recently by expanding primary human hepatocytes by means of dedifferentiation in vitro. Moreover, the transplantation efficiency was remarkably improved by the established preparative hepatic irradiation in combination with hepatic mitogenic stimuli regimens. Finally, immunosuppression drugs, including glucocorticoid and inhibitors for co-stimulating signals of T cell activation, were proposed to prevent innate and adaptive immune rejection of allografted hepatocytes. Despite remarkable progress, further studies are required to improve in vitro cell expansion technology, develop clinically feasible preconditioning regimens, and further optimize immunosuppression regimens or establish ex vivo gene correction-based autologous hepatocyte transplantation.

Successful induction of human chemically induced liver progenitors with small molecules from damaged liver

BACKGROUND

Human chemically induced liver progenitors (hCLiP) induced by small molecules produced by mature hepatocytes can potentially overcome issues related to hepatocyte transplantation, such as graft rejection or donor shortage. However, to our knowledge, no studies have explored the induction of hCLiP from mature hepatocytes (MHs) in damaged liver, indicated for liver transplantation.

METHODS

Liver tissues were collected from surgically resected livers, including damaged livers, of 86 patients at our department, and hepatocytes were isolated using the collagenase perfusion method. Hepatocytes isolated from 33 of these 86 donors were cultured in YAC medium containing Y-27632 (ROCK inhibitor), A-83-01 (TGF-β type I receptor inhibitor), and CHIR99021 (GSK-3 inhibitor) to induce hCLiP, and their functions were assessed.

RESULTS

Hepatocytes were isolated regardless of the liver fibrosis classifications (viability: F0,1: 87.2 ± 13.2%; F2,3: 87.8 ± 13.1%; and F4: 86.3 ± 4.2%). Most hepatocytes cultured in the YAC medium acquired the liver progenitor cell (LPC) gene. The expression of MH markers (ALB, HNF4α, G6PC, and CYP1A2) was lower in hCLiP than in MHs before reprogramming. Reverse transcription-polymerase chain reaction revealed that hCLiP markers (e.g., EpCAM, SOX9, CK19, and CD133) exhibited higher expression in LPCs than in MHs. Furthermore, hCLiPs had the ability to differentiate into hepatocytes, and were engrafted on the liver surface as mature hepatocytes.

CONCLUSION

Hepatocytes could be isolated from damaged liver. Furthermore, hCLiP may be obtained from hepatocytes isolated from damaged liver and may differentiate into MHs in vitro. Autologous hCLiP can potentially be transplanted without tumorigenesis and remodel damaged liver.

Transplantation of SDF-1α-loaded liver extracellular matrix repopulated with autologous cells attenuated liver fibrosis in a rat model

Cell-based therapy and tissue engineering are promising substitutes for liver transplantation to cure end-stage liver disorders. However, the limited sources for healthy and functional cells and poor engraftment rate are main challenges to the cell-based therapy approach. On the other hand, feasibility of production and size of bioengineered tissues are primary bottlenecks in tissue engineering. Here, we induce regeneration in a rat fibrotic liver model by transplanting a natural bioengineered scaffold with a native microenvironment repopulated with autologous stem/progenitor cells. In the main experimental group, a 1 mm³ stromal derived factor-1α (SDF-1α; S) loaded scaffold from decellularized liver extracellular matrix (LEM) was transplanted (Tx) into a fibrotic liver and the endogenous stem/progenitor cells were mobilized via granulocyte colony stimulating factor (G-CSF; G) therapy. Four weeks after transplantation, changes in liver fibrosis and necrosis, efficacy of cell engraftment and differentiation, vasculogenesis, and liver function recovery were assessed in this (LEM-TxSG) group and compared to the other groups. We found significant reduction in liver fibrosis stage in the LEM-TxSG, LEM-TxS and LEM-TxG groups compared to the control (fibrotic) group. Liver necrosis grade, and alanine transaminase (ALT) and aspartate transaminase (AST) levels dramatically reduced in all experimental groups compared to the control group. However, the number of engrafted cells into the transplanted scaffold and ratio of albumin (Alb) positive cells per total incorporated cells were considerably higher in the LEM-TxSG group compared to the LEM-Tx, LEM-TxS and LEM-TxG groups. Serum Alb levels increased in the LEM-Tx, LEM-TxS, and LEM-TxG groups, and was highest in the LEM-TxSG group, which was significantly more than the fibrotic group. Small vessel formation in the LEM-TxSG group was significantly higher than the LEM-Tx and LEM-TxS groups. Totally, these findings support application of the in vivo tissue engineering approach as a possible novel therapeutic strategy for liver fibrosis.

Molecularly Tailored Interface for Long-Term Xenogeneic Cell Transplantation

Encapsulation of therapeutic cells in a semipermeable device can mitigate the need for systemic immune suppression following cell transplantation by providing local immunoprotection while being permeable to nutrients, oxygen, and different cell-secreted biomolecules. However, fibrotic tissue deposition around the device has been shown to compromise the long-term function of the transplanted cells. Herein, a macroencapsulation device design that improves long-term survival and function of the transplanted cells is reported. The device is comprised of a semipermeable chitosan pouch with a tunable reservoir and molecularly engineered interface. The chitosan pouch interface decorated with 1,12-dodecanedioic acid (DDA), limits the cell adhesion and vigorous foreign body response while maintaining the barrier properties amenable to cell encapsulation. The device provides long-term protection to the encapsulated human primary hepatocytes in the subcutaneous space of immunocompetent mice. The device supports the encapsulated cells for up to 6 months as evident from cell viability and presence of human specific albumin in circulation. Solutions that integrate biomaterials and interfacial engineering such as the one described here may advance development of easy-to manufacture and retrievable devices for the transplantation of therapeutic cells in the absence of immunosuppression.

Pluripotent Stem Cell-Derived Hepatocytes Inhibit T Cell Proliferation In Vitro through Tryptophan Starvation

Regenerative medicine aims to replace damaged tissues by stimulating endogenous tissue repair or by transplanting autologous or allogeneic cells. Due to their capacity to produce unlimited numbers of cells of a given cell type, pluripotent stem cells, whether of embryonic origin or induced via the reprogramming of somatic cells, are of considerable therapeutic interest in the regenerative medicine field. However, regardless of the cell type, host immune responses present a barrier to success. The aim of this study was to investigate in vitro the immunological properties of human pluripotent stem cell (PSC)-derived hepatocyte-like cells (HLCs). These cells expressed MHC class I molecules while they lacked MHC class II and co-stimulatory molecules, such as CD80 and CD86. Following stimulation with IFN-γ, HLCs upregulated CD40, PD-L1 and MHC class I molecules. When co-cultured with allogeneic T cells, HLCs did not induce T cell proliferation; furthermore, when T cells were stimulated via αCD3/CD28 beads, HLCs inhibited their proliferation via IDO1 and tryptophan deprivation. These results demonstrate that PSC-derived HLCs possess immunoregulatory functions, at least in vitro.

Hepatocyte organoids and cell transplantation: What the future holds

Historically, primary hepatocytes have been difficult to expand or maintain in vitro. In this review, we will focus on recent advances in establishing hepatocyte organoids and their potential applications in regenerative medicine. First, we provide a background on the renewal of hepatocytes in the homeostatic as well as the injured liver. Next, we describe strategies for establishing primary hepatocyte organoids derived from either adult or fetal liver based on insights from signaling pathways regulating hepatocyte renewal in vivo. The characteristics of these organoids will be described herein. Notably, hepatocyte organoids can adopt either a proliferative or a metabolic state, depending on the culture conditions. Furthermore, the metabolic gene expression profile can be modulated based on the principles that govern liver zonation. Finally, we discuss the suitability of cell replacement therapy to treat different types of liver diseases and the current state of cell transplantation of in vitro-expanded hepatocytes in mouse models. In addition, we provide insights into how the regenerative microenvironment in the injured host liver may facilitate donor hepatocyte repopulation. In summary, transplantation of in vitro-expanded hepatocytes holds great potential for large-scale clinical application to treat liver diseases.

Artificial cells for the treatment of liver diseases

Liver diseases have become an increasing health burden and account for over 2 million deaths every year globally. Standard therapies including liver transplant and cell therapy offer a promising treatment for liver diseases, but they also suffer limitations such as adverse immune reactions and lack of long-term efficacy. Artificial cells that mimic certain functions of a living cell have emerged as a new strategy to overcome some of the challenges that liver cell therapy faces at present. Artificial cells have demonstrated advantages in long-term storage, targeting capability, and tuneable features. This article provides an overview of the recent progress in developing artificial cells and their potential applications in liver disease treatment. First, the design of artificial cells and their biomimicking functions are summarized. Then, systems that mimic cell surface properties are introduced with two concepts highlighted: cell membrane-coated artificial cells and synthetic lipid-based artificial cells. Next, cell microencapsulation strategy is summarized and discussed. Finally, challenges and future perspectives of artificial cells are outlined. STATEMENT OF SIGNIFICANCE: Liver diseases have become an increasing health burden. Standard therapies including liver transplant and cell therapy offer a promising treatment for liver diseases, but they have limitations such as adverse immune reactions and lack of long-term efficacy. Artificial cells that mimic certain functions of a living cell have emerged as a new strategy to overcome some of the challenges that liver cell therapy faces at present. This article provides an overview of the recent progress in developing artificial cells and their potential applications in liver disease treatment, including the design of artificial cells and their biomimicking functions, two systems that mimic cell surface properties (cell membrane-coated artificial cells and synthetic lipid-based artificial cells), and cell microencapsulation strategy. We also outline the challenges and future perspectives of artificial cells.

A Preconditioning Strategy to Augment Retention and Engraftment Rate of Donor Cells During Hepatocyte Transplantation

BACKGROUND

Hepatocyte transplantation has been extensively investigated as an alternative to orthotopic liver transplantation. However, its application in routine clinical practice has been restricted because of low initial engraftment and subsequent repopulation.

METHODS

Using mice as a model, we have developed a minimally invasive and nontoxic preconditioning strategy based on preadministration of antibodies against hepsin to increase donor hepatocyte retention and engraftment rate.

RESULTS

Liver sinusoid diameters decreased significantly with antihepsin pretreatment, and graft cell numbers increased nearly 2-fold in the recipients' liver parenchyma for 20 days after hepatocyte transplantation. Postoperative complications such as hepatic ischemia injury or apparent immune cell accumulation were not observed in recipients. In a hemophilia B mouse model, antihepsin preconditioning enhanced the expression and clotting activity of coagulation factor IX (FIX) to nearly 2-fold that of immunoglobulin G-treated controls and maintained higher plasma FIX clotting activity relative to the prophylactic range for 50 days after hepatocyte transplantation. Antihepsin pretreatment combined with adeno-associated virus-transduced donor hepatocytes expressing human FIX-Triple, a hyperfunctional FIX variant, resulted in plasma FIX levels similar to those associated with mild hemophilia, which protected hemophilia B mice from major bleeding episodes for 50 days after transplantation. Furthermore, antihepsin pretreatment and repeated transplantation resulted in extending the therapeutic period by 30 days relative to the immunoglobulin G control.

CONCLUSIONS

Thus, this antihepsin strategy improved the therapeutic effect of hepatocyte transplantation in mice with tremendous safety and minimal invasion. Taken together, we suggest that preconditioning with antihepsin may have clinical applications for liver cell therapy.

Effect of ultraviolet irradiation on immunogenicity and biological activity of primary adult human hepatocytes

BACKGROUND

The immune rejection of the recipient is the main factor affecting the therapeutic effect of hepatocyte transplantation, and ultraviolet can cause immunosuppression. Appropriate intensity of ultraviolet irradiation can not only reduce the immunogenicity of hepatocytes, but also avoid excessive damage to hepatocytes caused by ultraviolet irradiation, so as to better preserve the stability of hepatocytes and cell synthesis function.

AIM

To investigate the effect of ultraviolet radiation on the immunogenicity and biological activity of primary adult human hepatocytes.

METHODS

Hepatocytes were isolated from benign adult liver tissues by collagenase perfusion and divided into a control group (0 J/m²) and four experimental groups with different UV irradiation intensities (200, 350, 550, and 750 J/m²). Trypan blue and CCK-8 were used to detect the cell viability. Mitochondrial membrane potential changes were detected with JC-1 dye. The proliferation of recipient T cells was determined by mixed lymphocyte hepatocyte culture (MLHC). The levels of albumin and lactate dehydrogenase in culture supernatant were tested.

RESULTS

The viable rate of newly isolated hepatocytes was more than 90%. CCK-8 detection revealed that the viability of hepatocytes in the 200 J/m² group was the highest, which had no significant difference compared with that of the control group, but was significantly higher than that of other experimental groups. In the presence of JC-1 dye, the hepatocytes in the control group and the 200 J/m² group mainly exhibited red fluorescence, and brown (350 J/m²), yellow green (550 J/m²), and green (750 J/m²) changes were noted with the increase of irradiation intensity. The OD value of the 200 J/m² group was the highest, which had no significant difference compared with that of the control group, indicating that the membrane potential of hepatocytes was stable and the cell activity was the best; with the increase of irradiation intensity, the membrane potential of hepatocytes decreased significantly. The MLHC test showed that the 200 J/m²-irradiated hepatocytes had a significantly reduced lymphocyte proliferative ability compared with the control group, while that in the 350, 550, and 750 J/m² irradiation groups was increased. Biochemical test showed that the level of albumin was the highest in the 200 J/m² group, which had no difference compared with that of the control group. On the third day of culture, the secretory and synthetic functions of hepatocytes were in the best state.

CONCLUSION

Ultraviolet radiation at an intensity of 200 J/m² can reduce the ability of adult primary hepatocytes to cause T cell proliferation, while the vitality and synthesis function of hepatocytes are well preserved.

Alloresponses of Mixed Lymphocyte Hepatocyte Culture to Immunosuppressive Drugs as an In-Vitro Model of Hepatocyte Transplantation

Background

Hepatocyte transplantation (HCTx) has the potential for the treatment of end-stage liver disease. However, failure of engraftment and the long-term acceptance of cellular allografts remain significant challenges for its clinical application. The aim of this study was to investigate the efficacy of the immunosuppressive agents, Cyclosporine, Everolimus, and Belatacept to suppress the alloresponse of primary human hepatocytes in a mixed lymphocyte-hepatocyte culture (MLHC) and their potential hepatotoxicity in vitro.

Material/Methods

Primary human hepatocytes were co-cultured with allogeneic peripheral blood mononuclear cells (PBMCs) in an MLHC. Proliferative alloresponses were determined by flow cytometry, and cytokine secretion was measured using Luminex-based multiplex technology. Using an MLHC, the alloresponses of primary human hepatocytes were compared in the presence and absence of Cyclosporine, Everolimus, and Belatacept. Cultured primary human hepatocytes were assessed for the production of albumin, urea, aspartate transaminase (AST) and DNA content. Metabolic activity was determined with the MTT assay.

Results

Immune responses induced by primary human hepatocytes were effectively suppressed by Cyclosporine, Everolimus, and Belatacept. Everolimus significantly reduced the metabolic activity of primary human hepatocytes in vitro, suggesting impairment of cell viability. However, further functional analysis showed no significant differences between treated and untreated controls.

Conclusions

Cyclosporine, Everolimus, and Belatacept suppressed the alloresponse of primary human hepatocytes in an MLHC without significant cytotoxicity or functional cell impairment.

Decellularized liver transplant could be recellularized in rat partial hepatectomy model

In situ recellularization of the liver decellularized scaffold is a potential therapeutic alternative for liver transplantation. We aimed to develop an in situ procedure for recellularization of the rat liver using sodium lauryl ether sulfate (SLES) compared with Triton X-100/SDS. Rat liver specimens were rinsed with PBS, decellularized with either Triton X-100/SDS or SLES, and finally rinsed by distilled water. The efficiency of decellularized liver scaffolds was evaluated by histological, confocal Raman microscopy, histochemical staining, and DNA quantification assessments. Finally, in vivo studies were done to assess the biocompatibility of the liver scaffold by serum biochemical parameters and the recellularization capacity by histological and immunohistochemistry staining. Findings confirmed the preservation of extracellular matrix (ECM) components such as reticular, collagen, glycosaminoglycans, and neutral carbohydrates in both Triton X-100/SDS- and SLES-treated livers. Hoechst, feulgen, Hematoxylin and eosin, and DNA quantification assessments confirmed complete genetic content removal. The serological parameters showed no adverse impact on the liver functions. Transplantation of SLES-treated cell-free decellularized liver showed extensive neovascularization along with migration of the fibrocytes and adipocytes and some immune cells. Also, immunohistochemical staining showed that the oval cells, stellate cells, cholangiocytes and hepatocytes invaded extensively into the graft. It is concluded that SLES can be considered as a promising alternative in the liver decellularization process, and the transplanted decellularized liver can appropriately be revascularized and regenerated.

Silencing of HLA class I on primary human hepatocytes as a novel strategy for reduction in alloreactivity

In contrast to the whole liver, primary hepatocytes are highly immunogenic. Thus, alternative strategies of immunomodulation after hepatocyte transplantation are of special interest. Silencing of HLA class I expression is expected to reduce the strength of allogeneic immune responses and to improve graft survival. In this study, primary human hepatocytes (PHH) were isolated using a two-step-collagenase perfusion-technique and co-cultured with allogeneic lymphocytes in terms of a mixed lymphocyte hepatocyte culture. Expression of HLA class I on PHH was silenced using lentiviral vectors encoding for β2-microglobulin-specific short hairpin RNA (shβ2m) or non-specific shRNA (shNS) as control. The delivery of shβ2m into PHH caused a decrease by up to 96% in β2m transcript levels and a down-regulation of HLA class I cell surface expression on PHH by up to 57%. Proliferative T cell alloresponses against HLA-silenced PHH were significantly lower than those observed form fully HLA-expressing PHH. In addition, significantly lower secretion of pro-inflammatory cytokines was observed. Levels of albumin, urea and aspartate-aminotransferase did not differ in supernatants of cultured PHH. In conclusion, silencing HLA class I expression on PHH might represent a promising approach for immunomodulation in the transplant setting without compromising metabolic function of silenced hepatocytes.

Clinical use of an immune monitoring panel in liver transplant recipients: A prospective, observational study

Immunosuppressive therapy greatly contributed to making liver transplantation the standard treatment for end-stage liver diseases. However, it remains difficult to predict and measure the efficacy of pharmacological immunosuppression. Therefore, we used a panel of standardized, commonly available, biomarkers with the aim to describe their changes in the first 3 weeks after the transplant procedure and assess if they may help therapeutic drug monitoring in better tailoring the dose of the immunosuppressive drugs. We prospectively studied 72 consecutive patients from the day of liver transplant (post-operative day #0) until the post-operative day #21. Leukocytes, neutrophils, lymphocytes (CD4+, CD8+), natural killer cells, monocytes, immunoglobulins and tacrolimus serum levels were measured on peripheral blood (at day 0, 3, 7, 14, 21 after surgery). Patients who developed infections showed significantly higher CD64+ monocytes on post operative day #7. IgG levels were lower on post operative day #3 among patients who later developed infections. We also found that a sharp decrease in IgA from post operative day #0 to 3 (-226 mg/dL in the ROC curve analysis) strongly correlates with the onset of infections among HCV- patients. No specific markers of rejection emerged from the tested panel of markers. Our results show that some early changes in peripheral blood white cells and immunoglobulins may predict the onset of infections and may be useful in modulating the immunosuppressive therapy. However, a panel of commonly available, standardized biomarkers do not support in improving therapeutic drug monitoring ability to individualize immunosuppressive drugs dosing.

3D human liver tissue from pluripotent stem cells displays stable phenotype in vitro and supports compromised liver function in vivo

Liver disease is an escalating global health issue. While liver transplantation is an effective mode of therapy, patient mortality has increased due to the shortage of donor organs. Developing renewable sources of human liver tissue is therefore attractive. Pluripotent stem cell-derived liver tissue represents a potential alternative to cadaver derived hepatocytes and whole organ transplant. At present, two-dimensional differentiation procedures deliver tissue lacking certain functions and long-term stability. Efforts to overcome these limiting factors have led to the building of three-dimensional (3D) cellular aggregates. Although enabling for the field, their widespread application is limited due to their reliance on variable biological components. Our studies focused on the development of 3D liver tissue under defined conditions. In vitro generated 3D tissues exhibited stable phenotype for over 1 year in culture, providing an attractive resource for long-term in vitro studies. Moreover, 3D derived tissue provided critical liver support in two animal models, including immunocompetent recipients. Therefore, we believe that our study provides stable human tissue to better model liver biology 'in the dish', and in the future may permit the support of compromised liver function in humans.

Hepatocyte-induced CD4+ T cell alloresponse is associated with major histocompatibility complex class II up-regulation on hepatocytes and suppressible by regulatory T cells

Hepatocyte transplantation is a promising therapeutic approach for various liver diseases. Despite the liver's tolerogenic potential, early immune-mediated loss of transplanted cells is observed, and longterm acceptance has not been achieved yet. Patients deemed tolerant after liver transplantation presented an increased frequency of regulatory T cells (Tregs), which therefore also might enable reduction of posttransplant cell loss and enhance longterm allograft acceptance. We hence characterized hepatocyte-induced immune reactions and evaluated the immunomodulatory potential of Tregs applying mixed lymphocyte cultures and mixed lymphocyte hepatocyte cultures. These were set up using peripheral blood mononuclear cells and primary human hepatocytes, respectively. Polyclonally expanded CD4⁺ CD25^high CD127^low Tregs were added to cocultures in single-/trans-well setups with/without supplementation of anti-interferon γ (IFNγ) antibodies. Hepatocyte-induced alloresponses were then analyzed by multicolor flow cytometry. Measurements indicated that T cell response upon stimulation was associated with IFNγ-induced major histocompatibility complex (MHC) class II up-regulation on hepatocytes and mediated by CD4⁺ T cells. An indirect route of antigen presentation could be ruled out by use of fragmented hepatocytes and culture supernatants of hepatocytes. Allospecific proliferation was accompanied by inflammatory cytokine secretion. CD8⁺ T cells showed early up-regulation of CD69 despite lack of cell proliferation in the course of coculture. Supplementation of Tregs effectively abrogated hepatocyte-induced alloresponses and was primarily cell contact dependent. In conclusion, human hepatocytes induce a CD4⁺ T cell alloresponse in vitro, which is associated with MHC class II up-regulation on hepatocytes and is susceptible to suppression by Tregs. Liver Transplantation 24 407-419 2018 AASLD.

Hepatocyte transplantation: past efforts, current technology, and future expansion of therapeutic potential

Hepatic cell transplantation (HCT) continues to garner interest as an alternative to orthotopic liver transplantation and the attendant donor shortage. When compared with solid organ transplantation, advantages of cell transplantation include the potential to treat more patients with a considerably less invasive procedure, the ability to utilize organs otherwise unsuitable for transplant, and leaving the native organ in situ with the potential for regeneration. While studies date back to the early 1960s, advancement of clinical application has been slow due in part to limitations of suitable tissue supplies and reproducible robust techniques. Compared with orthotopic liver transplantation, there are fewer absolute contraindications for donor selection. And, current techniques used to harvest, isolate, store, and even transfuse cells vary little between institutions. Significant variation is seen due to a lack of consensus with maintenance therapy. Although the ideal recipient has not been clearly identified, the most significant results have been demonstrated with correction of congenital metabolic liver disorders, with a few trials examining its utility in cirrhotics and more recently acute liver failure. The most exciting new topic of discussion examines techniques to improve engraftment, with many such as ischemic preconditioning and nonselective partial embolization (microbead therapy), while not yet used in HCT study, showing promise in solid organ research. Advancements in HCT, although slow in progress, have great potential in the ability to alleviate the burden faced in solid organ transplantation and possibly become a long-term viable option, beyond that of a bridge or salvage therapy.

Human hepatocyte transplantation for liver disease: current status and future perspectives

Liver transplantation is the accepted treatment for patients with acute liver failure and liver-based metabolic disorders. However, donor organ shortage and lifelong need for immunosuppression are the main limitations to liver transplantation. In addition, loss of the native liver as a target organ for future gene therapy for metabolic disorders limits the futuristic treatment options, resulting in the need for alternative therapeutic strategies. A potential alternative to liver transplantation is allogeneic hepatocyte transplantation. Over the last two decades, hepatocyte transplantation has made the transition from bench to bedside. Standardized techniques have been established for isolation, culture, and cryopreservation of human hepatocytes. Clinical hepatocyte transplantation safety and short-term efficacy have been proven; however, some major hurdles-mainly concerning shortage of donor organs, low cell engraftment, and lack of a long-lasting effect-need to be overcome to widen its clinical applications. Current research is aimed at addressing these problems, with the ultimate goal of increasing hepatocyte transplantation efficacy in clinical applications.

Clinical Hepatocyte Transplantation: What Is Next?

Purpose of review

Significant recent scientific developments have occurred in the field of liver repopulation and regeneration. While techniques to facilitate liver repopulation with donor hepatocytes and different cell sources have been studied extensively in the laboratory, in recent years clinical hepatocyte transplantation (HT) and liver repopulation trials have demonstrated new disease indications and also immunological challenges that will require the incorporation of a fresh look and new experimental approaches.

Recent findings

Growth advantage and regenerative stimulus are necessary to allow donor hepatocytes to proliferate. Current research efforts focus on mechanisms of donor hepatocyte expansion in response to liver injury/preconditioning. Moreover, latest clinical evidence shows that important obstacles to HT include optimizing engraftment and limited duration of effectiveness, with hepatocytes being lost to immunological rejection. We will discuss alternatives for cellular rejection monitoring, as well as new modalities to follow cellular graft function and near-to-clinical cell sources.

Summary

HT partially corrects genetic disorders for a limited period of time and has been associated with reversal of ALF. The main identified obstacles that remain to make HT a curative approach include improving engraftment rates, and methods for monitoring cellular graft function and rejection. This review aims to discuss current state-of-the-art in clinical HT and provide insights into innovative approaches taken to overcome these obstacles.

Emerging advancements in liver regeneration and organogenesis as tools for liver replacement

PURPOSE OF REVIEW

Although the liver possesses a unique, innate ability to regenerate through mass compensation, transplantation remains the only therapy when damage outpaces regeneration, or liver metabolic capacity is irreversibly impacted. Recent insight from developmental biology has greatly influenced the advancement of alternative options to transplantation in these settings.

RECENT FINDINGS

Factors known to direct liver cell specification, expansion, and differentiation have been used to generate hepatocyte-like cells from stem and somatic cells for developing cell therapies. Additionally, interactions between hepatic epithelial and nonepithelial cells key to establishing hepatic architecture have been used in tissue engineering approaches to advance self-organizing hepatic organoids and bioartificial liver devices. Simultaneously, recent clinically applicable advances in human hepatocyte transplantation and promotion of innate hepatic regeneration have been limited.

SUMMARY

Although mature hepatocytes have the potential to bridge to, or replace whole organ transplantation, limits in the ability to obtain healthy cells, stabilize in-vitro expansion, cryopreserve, and alleviate rejection, still exist. Alternative sources for generating hepatocytes hold promise for cell therapy and tissue engineering. These may allow generation of autologous or universal donor cells that eliminate the need for immunosuppression; however, limits exist regarding hepatocyte maturity and efficacy at liver repopulation, as well as applicability to human chronic liver disease.