Human monocyte-derived neohepatocytes: a promising alternative to primary human hepatocytes for autologous cell therapy.

BACKGROUND: There is growing interest in new therapeutic options for the treatment of end-stage liver diseases. In addition to mechanical devices supporting liver function, such as bioreactors, the transplantation of hepatocyte-like cells derived from (adult) stem cells offer great perspectives. We have generated hepatocyte-like (NeoHep) cells from terminally differentiated peripheral blood monocytes and, in this study, have evaluated these cells as a possible tool for autologous cell therapy. METHODS: Peripheral blood monocytes were cultured under conditions that promote hepatocyte-like differentiation and were characterized for hepatocyte marker expression by reverse-transcriptase polymerase chain reaction, immunohistochemistry, and immunoblotting and for specific secretory and metabolic functions with the appropriate biochemical assays. RESULTS: NeoHep cells resembled primary human hepatocytes with respect to morphology, expression of hepatocyte markers (albumin, cytochrome P450 isoenzymes, asialoglycoprotein receptor, coagulation factor VII), various secretory and metabolic functions (albumin secretion, urea production, lactate formation, and lactate dehydrogenase and aspartate transaminase release), and drug detoxification activities (phase I metabolization of ethoxycoumarin into 7OH-coumarin after stimulation with 3-methylcholanthren, induction of CYP3A4 activity, and phase II metabolization through UDP-glucuronidation of 4-methyl-umbelliferone). CONCLUSIONS: These data convincingly show that NeoHep cells display a phenotype and specific in vitro metabolic functions that are quantitatively and qualitatively comparable in part with those of primary human hepatocytes. These cells could thus be clinically applied in an autologous setting for the treatment of end-stage liver diseases or for improving liver function in patients who have undergone critical liver-mass resection.

Generation of human hepatocytes by stem cell technology: definition of the hepatocyte.

Since 1999, numerous articles have reported the generation of hepatocytes from different types of extrahepatic stem or precursor cells. This opens exciting new possibilities for pharmacology and toxicology, as well as for cell therapy. Hepatocyte marker expression, including albumin, cytokeratin 18, c-met, alpha-fetoprotein and cytochrome P450 3A4 and -2B6, has been observed after transplantation of different types of human stem cells into the liver of laboratory animals or in vitro after incubation with cytokines. These intriguing observations have prompted scientists to classify stem cell-derived cell populations as hepatocytes. However, this conclusion may be premature. It has been shown that factors of the liver microenvironment can induce expression of a limited number of hepatocyte marker genes in nonhepatic cell types. To conclude on the grounds of a limited number of markers that these cells are true hepatocytes is not indicated. In this case one should carefully evaluate crucial hepatocyte-defining enzymatic properties. The present article: i) reviews studies describing the fate of extrahepatic human stem and precursor cells in livers of laboratory animals, including the possibility of cell fusion; and ii) critically discusses the phenotype of stem cells after application of various differentiation protocols aimed at generating human hepatocytes. In addition, the necessary criteria needed for defining a true hepatocyte are suggested. Establishing the necessary properties for stem cell-derived hepatocytes is timely and reasonable, and thus avoids further misleading semantic confusion. Finally, it is essential to understand that the definition of a bona fide hepatocyte should not be limited to qualitative assays, such as reverse transcriptase polymerase chain reaction and immunohistochemistry, but has to include a quantitative analysis of enzymatic activities, which allows direct comparison with primary hepatocytes. Although the stem cell-derived-hepatocyte does not yet exist there is a good chance that this aim may be achieved in the future.

[Stem cells and liver replacement]. / Stammzellen und Leberersatz.

Reproducible stem cell programmability, either embryonic or adult in nature, will open a variety of clinical application strategies for the treatment of tissue injuries, degenerated organs and body components, respectively, in the future. In addition, stem cells will be used to complement metabolically or genetically caused diseases. Pluripotent plasticity of stem cells describes their ability to be programmed into target cells encountered in all three germ layers during embryologic development. Here, we review future application modalities for the clinical use of cellular-derived products and therapeutics for patients presenting with liver diseases. This overview is designed as a state-of-the-art survey taking into account current knowledge and published work. It includes a diversified description of biological advantages and disadvantages of different types of stem cells, considers related ethical aspects and outlines clinically required parameters for the use of stem cells in humans. Successful application of stem cell-associated therapeutics in man will be closely related with ensuing patient risk profiles, stringent indications, long-term patient outcomes and will be determined by cost-benefit efficacy.

Programmable cells of monocytic origin (PCMO): a source of peripheral blood stem cells that generate collagen type II-producing chondrocytes.

The focus of this study was a new adult pluripotent cell derived from human peripheral blood monocytes identified as a "programmable cell of monocytic origin" (PCMO). In contrast to bone marrow-derived stem cells, these cells can be harvested from peripheral venous blood without aspiration of the bone marrow and have multilineage potential comparable to that of mesenchymal stem cells (MSC). The aim of this study was to evaluate the potential of PCMOs to differentiate into collagen type II-producing chondrocytes using various extrinsic cues (TGFbeta-1, IGF-1, BMP-2, and BMP-7). Collagen type I and II proteins were localized using immunohistochemistry and quantified by enzyme-linked immunosorbent assays (ELISA). The shape of the differentiating PCMOs was monitored with electron microscopy. Collagen type I and II messenger RNA expression was analyzed using real-time reverse transcriptase-polymerase chain reaction (RT PCR) and regular RT PCR. Immunohistochemistry revealed a strong accumulation of collagen type II after a 6-week incubation period with BMP-2, BMP-7, TGF-beta, IGF-I, and TGF-beta, and IGF-1. Collagen type I was only mildly induced by the applied stimulants. Electron microscopy findings showed a shift from a monocyte-like structure to a chondrocyte-like structure after 2 weeks of stimulation. Stimulation of PCMOs with BMP-2, BMP-7, TGF-beta, IGF-I, and TGF-beta, and IGF-1 induced a chondrogenic differentiation with continuous expression of collagen type II mRNA and protein over several weeks time. Collagen type I and II expression in undifferentiated PCMOs or in control cells incubated without any stimulant was not detected. PCMOs have the potential to differentiate into collagen type II synthesizing chondrocytes. The ability to reprogram and differentiate PCMOs from peripheral blood into sizable quantities might enable their clinical application in cartilage repair after mechanical injury or in cases of osteoarthritis.

Transforming growth factor-beta (TGF-beta) type I receptor/ALK5-dependent activation of the GADD45beta gene mediates the induction of biglycan expression by TGF-beta.

We have recently shown that induction of biglycan (BGN) expression by transforming growth factor-beta1 (TGF-beta1) required sequential activation of both Smad and p38 mitogen-activated protein kinase signaling (Ungefroren, H., Lenschow, W., Chen, W.-B., and Kalthoff, H. (2003) J. Biol. Chem. 278, 11041-11049). Here, we have analyzed the receptors through which TGF-beta1 controls expression of BGN and GADD45beta, the latter of which is postulated to link early Smad signaling to delayed activation of p38. Ectopic expression of a dominant-negative mutant of the TGF-beta type II receptor in PANC-1 cells abrogated TGF-beta-induced BGN up-regulation. Similarly, inhibition of the TGF-beta type I receptor/ALK5 with either SB431542 or by enforced stable expression of a kinase-dead mutant greatly attenuated the TGF-beta effect on both BGN and GADD45beta expression in PANC-1 and MG-63 cells. The enhancing effect of ALK5 on TGF-beta-mediated GADD45beta and BGN expression and on GADD45beta promoter activity was also dependent on its ability to activate Smad signaling, because an ALK5 mutant defective in Smad activation (TbetaRImL45) but with an otherwise functional kinase domain failed to mediate these responses. The TGF-beta/ALK5 effect on p38 activation and BGN expression was mimicked by overexpression of GADD45beta alone (in the absence of TGF-beta stimulation) and suppressed upon antisense inhibition of GADD45beta expression. These results show that TGF-beta induces BGN expression through (the Smad-activating function of) ALK5 and GADD45beta and suggest that the sensitivity of MyD118 to activation by TGF-beta, which varies between tissues, ultimately determines the strength of the TGF-beta effect on BGN.

Differentiation of in vitro-modified human peripheral blood monocytes into hepatocyte-like and pancreatic islet-like cells.

BACKGROUND & AIMS: Adult stem cells provide a promising alternative for the treatment of diabetes mellitus and end-stage liver diseases. We evaluated the differentiation potential of human peripheral blood monocytes into hepatocyte-like and pancreatic islet-like cells. METHODS: Monocytes were treated with macrophage colony-stimulating factor and interleukin 3 for 6 days, followed by incubation with hepatocyte and pancreatic islet-specific differentiation media. Cells were characterized by flow cytometry, gene-expression analysis, metabolic assays, and transplantation for their state of differentiation and tissue-specific functions. RESULTS: In response to macrophage colony-stimulating factor and interleukin 3, monocytes resumed cell division in a CD115-dependent fashion, which was associated with a down-regulation of the PRDM1 and ICSBP genes. These programmable cells of monocytic origin were capable of differentiating into neohepatocytes, which closely resemble primary human hepatocytes with respect to morphology, expression of hepatocyte markers, and specific metabolic functions. After transplantation into the liver of severe combined immunodeficiency disease/nonobese diabetic mice, neohepatocytes integrated well into the liver tissue and showed a morphology and albumin expression similar to that of primary human hepatocytes transplanted under identical conditions. Programmable cells of monocytic origin-derived pancreatic neoislets expressed beta cell-specific transcription factors, secreted insulin and C peptide in a glucose-dependent manner, and normalized blood glucose levels when xenotransplanted into immunocompetent, streptozotocin-treated diabetic mice. Programmable cells of monocytic origin retained monocytic characteristics, notably CD14 expression, a monocyte-specific methylation pattern of the CD115 gene, and expression of the transcription factor PU.1. CONCLUSIONS: The ability to reprogram, expand, and differentiate peripheral blood monocytes in large quantities opens the real possibility of the clinical application of programmable cells of monocytic origin in tissue repair and organ regeneration.

Tolerance-inducing strategies in transplantation surgery-current status and perspectives.

BACKGROUND: Life-long immunosuppressive medication has to be administered to the majority of solid-organ recipients after transplantation of genetically mismatched organs in order to circumvent acute graft loss due to alloreactive rejection responses triggered by the host's immune system. However, life-long suppression of the immune system implicitly limits the host's ability to respond appropriately to infectious, fungal and carcinogenic threats. Simultaneously non-targeted inhibition of immunological defense mechanisms coincides with substantial morbidity and mortality for the host. Thus, for the past five decades research in the field of transplantation medicine has focused on innovative strategies to induce graft tolerance to donor alloantigens, a state in which the recipient's lymphocytes have learned to accept the foreign organ or tissue as "self" or "non-dangerous" without the need of chronic immunosuppression. Achieving that specific goal of donor-specific tolerance would not only minimize the risk of the recipient to suffer from serious side effects resulting from continuous immunosuppressive therapy, but would also prevent loss of long-term graft function caused by chronic rejection processes. Recently, numerous insights into the dynamic interrelationships of host immune responses elicited by donor antigen-presentation, either on the graft itself or on specialized antigen-presenting cells, have substantially broadened our understanding of the cascade of events that result in the acquisition of tolerance. METHOD: We highlight areas of research that are currently particularly helpful not only to set up new strategies to induce donor-specific tolerance or long-term graft acceptance, but also to identify and describe parameters which serve to characterize those patients who have acquired a state of tolerance and are safe to be weaned off from their immunosuppressive regimen.

Long-term culture and differentiation of rat embryonic stem cell-like cells into neuronal, glial, endothelial, and hepatic lineages.

The in vitro differentiation of mouse embryonic stem cells into different somatic cell types such as neurons, endothelial cells, or myocytes is a well-established procedure. Long-term culture of rat embryonic stem cells is known to be hazardous, and attempts to differentiate these cells in vitro so far have been unsuccessful. We herein describe stable long-term culture of an alkaline phosphatase-positive rat embryonic stem cell-like cell line (RESC) and its differentiation into neuronal, endothelial, and hepatic lineages. RESCs were characterized by typical growth in single cells as well as in embryoid bodies when cultured in the presence of leukemia inhibitory factor. RESC expressed stage-specific-embryonic antigen-1 and the major histocompatibility complex class I molecule. For neuronal differentiation, cells were incubated with medium containing 10(-6) M retinoic acid for 14 days. For endothelial differentiation, RESCs were grown on Matrigel for 14 days, and for induction of hepatocyte-specific antigen expression, RESCs were grown in medium supplemented with fibroblast growth factor-4. Differentiated cells exhibited typical morphological changes and expressed neuronal (nestin, mitogen-activated protein-2, synaptophysin), glial (S100, glial fibrillary acid protein), endothelial (panendothelial antibody, CD31) and hepatocyte-specific (alpha-fetoprotein [alphaFP], albumin, alpha-1-antitrypsin, CK18) antigens. In addition, expression of hepatocyte-specific genes (alphaFP, transthyretin, carbamoyl-phosphate synthetase, and coagulation factor-2) was detected by reverse transcription polymerase chain reaction. We were able to culture RESCs under stable, long-term conditions and to initiate programmed differentiation of RESCs to endothelial, neuronal, glial, and hepatic lineages in the rat species.

Induction, expression and maintenance of cytochrome P450 isoforms in long-term cultures of primary human hepatocytes.

Within the past decade, tremendous progress has been made in the isolation and culture of human hepatocytes for drug metabolism and toxicology, which could potentially reduce the number of animal experiments performed. However, human hepatocyte cultures are still not widely used for preclinical drug testing, partly due to inconsistent supply and quality of human tissue. Thus, the aim of this study was to evaluate primary cultured human hepatocytes from different patients over a study period of 14 days, by assays that characterise cell quality and function. We found urea production and albumin synthesis in all cell cultures over at least 7 days. Cytochrome P4501A2, CYP2D6, and CYP3A4 protein expression was demonstrated by Western Blot analysis and CYP1A1/2 and CYP3A4 induction by 3-methylcholantrene, phenobarbital or rifampicin over 14 days. In addition, we saw that UDP-glucoronyltransferase activity was preserved in human hepatocytes over 2 weeks. In conclusion, we could show that primary human hepatocytes isolated from discarded liver tissue can consistently be kept in culture over a long time period and are therefore well suited for preclinical drug testing.

Retroviral endostatin gene transfer inhibits growth of human lung cancer in a murine orthotopic xenotransplant model.

BACKGROUND AND AIMS: The administration of endostatin, a potent anti-angiogenic agent, will be required for extended periods of time as a cancer treatment. The aim of the present study was to induce endogenous endostatin secretion in a continuous fashion, based on retroviral gene transfer. The tumor response was evaluated in an orthotopic murine tumor model of human lung cancer. MATERIALS AND METHODS: Human non-small-cell lung cancer cells (KNS 62) were retrovirally transduced with the human endostatin gene. An orthotopic murine xenotransplant model was used to investigate tumor growth, metastases and survival. After 4 weeks of subcutaneous growth, endostatin expression was measured by immunoblot analysis in tumor lysates. RESULTS: The growth of the subcutaneous tumors was significantly delayed, and orthotopic tumor growth and pleural metastases were significantly reduced in endostatin-transduced KNS 62 tumors. Prolongation of survival subsequent to orthotopic tumor induction was demonstrated. Strong endostatin expression was found in subcutaneous tumors after 4 weeks. CONCLUSION: Retroviral transduction of the human endostatin gene is capable of achieving long-term endostatin expression. Endostatin transduction provides significant anti-tumor effects with regard to local tumor growth, metastases and survival.