Use of hepatocyte and stem cells for treatment of post-resectional liver failure: Are we there yet?

Liver International

Volumn 31, Issue 6, 2011, Pages 773-784

  Ezzat, Tarek M ^a,b   Dhar, Dipok K ^a   Newsome, Philip N ^c   Malagó, Massimo ^a   Olde Damink, Steven W M ^a,d  

^a UNIVERSITY COLLEGE LONDON   (United Kingdom)

^b ALEXANDRIA UNIVERSITY   (Egypt)

^c University of Birmingham   (United Kingdom)

^d MAASTRICHT UNIVERSITY MEDICAL CENTER   (Netherlands)

Author keywords

Cell transplantation; Liver failure; Liver regeneration; Liver resection; Stem cells

Indexed keywords

BILIRUBIN; FLUOROURACIL; FRESH FROZEN PLASMA; IRINOTECAN; OXALIPLATIN;

ADULT STEM CELL; ARTIFICIAL EMBOLISM; BILIRUBIN BLOOD LEVEL; CELL PROLIFERATION; EMBRYONIC STEM CELL; FATTY LIVER; HEMATOPOIETIC STEM CELL TRANSPLANTATION; HEPATOCYTE TRANSPLANTATION; HUMAN; LIVER FAILURE; LIVER METASTASIS; LIVER REGENERATION; LIVER RESECTION; LIVER TRANSPLANTATION; MESENCHYMAL STEM CELL; MESENCHYMAL STEM CELL TRANSPLANTATION; NONHUMAN; PARTIAL HEPATECTOMY; PLURIPOTENT STEM CELL; POST RESECTIONAL LIVER FAILURE; POSTOPERATIVE COMPLICATION; REVIEW; STEM CELL TRANSPLANTATION;

EID: 79958036682     PISSN: 14783223     EISSN: 14783231     Source Type: Journal    
DOI: 10.1111/j.1478-3231.2011.02530.x     Document Type: Review

References (123)

1. Squires RH, Shneider BL, Bucuvalas J, et al. Acute liver failure in children: the First 348 patients in the pediatric acute liver failure study group. J Pediatr 2006; 148: 652-8.
2. Williams R. Classification, etiology, and considerations of outcome in acute liver failure. Semin Liver Dis 1996; 16: 343-8.
3. Sokal EM, Goldstein D, Ciocca MJ, et al. End-stage disease working group. End-stage liver disease and liver transplant: current situation and key issues. J Pediatr Gastroenterol Nutr 2008; 47: 239-46.
4. Lucey MR, Schaubel DE, Guidinger MK, Tome S, Merion RM. Effect of alcoholic liver disease and hepatitis C infection on waiting list and posttransplant mortality and transplant survival benefit. Hepatology 2009; 50: 400-6.
5. van den Broek MA, van Dam RM, Malagó M, et al. Feasibility of randomized controlled trials in liver surgery using surgery-related mortality or morbidity as endpoint. Br J Surg 2009; 96: 1005-14.
6. Otsuka Y, Duffy JP, Saab S, et al. Post resection hepatic failure: successful treatment with liver transplantation. Liver Transplant 2007; 13: 672-9.
7. Mayo SC, Pawlik TM. Current management of colorectal hepatic metastasis. Expert Rev Gastroenterol Hepatol 2009; 3: 131-44.
8. Khan SA, Toledano MB, Taylor-Robinson SD. Epidemiology, risk factors, and pathogenesis of cholangiocarcinoma. HPB (Oxf.) 2008; 10: 77-82.
9. Pawlik TM, Schlick RD, Choti MA. Expanding criteria for resectability of colorectal liver metastasis. Oncologist 2008; 13: 51-64.
10. Mathijssen RH, Van Alphen RJ, Verweij J, et al. Clinical pharmacokinetics and metabolism of irinotecan (CP-11). Clin Cancer Res 2001; 7: 2182-94.
11. Vauthey JN, Pawlik TM, Ribero D, et al. Chemotherapy regimen predicts steatohepatitis and an increase in 90-day mortality after surgery for hepatic colorectal metastases. J Clin Oncol 2006; 24: 2065-72.
12. Schiffer E, Frossard JL, Rubbia-Brandt L, Mentha G, Pastor CM. Hepatic regeneration is decreased in a rat model of sinusoidal obstruction syndrome. J Surg Oncol 2009; 99: 439-46.
13. Cescon M, Vetrone G, Grazi GL, et al. Trends in perioperative outcome after Hepatic resection: analysis of 1500 consecutive unselected cases over 20 years. Ann Surg 2009; 249: 995-1002.
14. Karoui M, Penna C, Amin-Hashem M, et al. Influence of preoperative chemotherapy on the risk of major hepatectomy for colorectal liver metastases. Ann Surg 2006; 243: 1-7.
15. Kiuchi T, Kasahara M, Uryuhara K, et al. Impact of graft size mismatching on graft prognosis in liver transplantation from living docnors. Transplantation 1999; 67: 321-7.
16. Mullen JT, Ribero D, Reddy SK, et al. Hepatic insufficiency and mortality in 1, 059 noncirrhotic patients undergoing major hepatectomy. J Am Coll Surg 2007; 204: 854-62.
17. Van den Broek MA, Olde Damink SW, Dejong CH, et al. Liver failure after partial Hepatic resection: definition, pathophysiology, risk factors and treatment. Liver Int 2008; 28: 767-80.
18. Schindl MJ, Redhead DN, Fearon KC, Garden OJ, Wigmore SJ. Edinburgh Liver Surgery and Transplantation Experimental Research Group (eLISTER). The value of residual liver volume as a predictor of hepatic dysfunction and infection after major liver resection. Gut 2005; 54: 289-96.
19. Morris-Stiff G, Gomez D, Prasad R. Quantitative assessment of hepatic function and its relevance to the liver surgeon. J Gastrointest Surg 2009; 13: 374-85.
20. Yachida S, Wakabayashi H, Okano K, Suzuki Y. Prediction of posthepatectomy hepatic functional reserve by serum hyaluronate. Br J Surg 2009; 96: 501-8.
21. Poon RT, Fan ST, Lo CM, et al. Improving perioperative outcome expands the role of hepatectomy in management of benign and malignant hepatobiliary diseases: analysis of 1222 consecutive patients from a prospective database. Ann Surg 2004; 240: 698-708.
22. Richter B, Schmandra TC, Golling M, Bechstein WO. Nutritional support after open liver resection: a systemic review. Dig Surg 2006; 23: 139-45.
23. Sewnath ME, Karsten TM, Prins MH, et al. A meta-analysis on the efficacy of preoperative biliary drainage for tumours causing obstructive jaundice. Ann Surg 2002; 236: 17-27.
24. Van der Gaag NA, Rauws EA, Van Eijck CH, et al. Preoperative biliary drainage for cancer of the head of the pancreas. N Eng J M 2010; 14: 129-37.
25. Broering DC, Hillert C, Krupski G, et al. Portal vein embolization vs. portal vein ligation for induction of hypertrophy of the future liver remnant. Gastrointest Surg 2002; 6: 905-13.
26. Liu H, Zhu S. Present status and future perspectives of preoperative portal vein embolization. Am J Surg 2009; 197: 686-90.
27. Mochida S, Ogata I, Hirata K, et al. Provocation of massive hepatic necrosis by endotoxin after partial hepatectomy in rats. Gastroenterology 1990; 99: 771-7.
28. Vassiliou I, Arkadopoulos N, Stafyla V, et al. The introduction of a simple maneuver to reduce the risk of postoperative bleeding after major hepatectomies. J Heapatobiliary Pancreat Surg 2009; 16: 552-6.
29. Gurusamy KS, Kumar Y, Pamecha V, Sharma D, Davidson BR. Ischaemic pre- conditioning for elective liver resections performed under vascular occlusion. Cochrane Dtabase Syst Rev 2009; (1): CD007629.
30. Gomez D, Homer-Vanniasinkam S, Graham AM, Prasad KR. Role of Ischaemic preconditioning in liver regeneration following major liver resection and transplantation. Gastroenterology 2007; 13: 657-70.
31. Onodera K, Yonekawa M, Kawamura A. Artificial liver support at present and in the future. J Artif Organs 2006; 9: 17-28.
32. Sen S, Williams R, Jalan R. Emerging indications for albumin dialysis. Am J Gastroenterol 2005; 100: 468-75.
33. Chamuleau RA, Poyck PP, Van de Kerkhove MP. Bioartificial liver: its pros and cons. Ther Apher Dial 2006; 10: 168-74.
34. Selden C, Hodgson H. Cellular therapies for liver replacement. Transpl Immunol 2004; 12: 273-88.
35. Yu CB, Pan XP, Li LJ. Progress in bioreactors of bioartificial livers. Hepatobiliary Pancreat Dis Int 2009; 8: 134-40.
36. Sipe JD. Tissue engineering and regenerative medicine. Ann NY Acad Sci 2002; 961: 1-9.
37. Ehnert S, Glanemann M, Schmitt A, et al. The possible use of stem cells in regenerative medicine: dream or reality? Langenbecks Arch Surg 2009; 394: 985-97.
38. Fausto N, Laird AD, Webber EM. Liver regeneration 2. Role of growth factors and cytokines in hepatic regeneration. FASEB J 1995; 9: 1527-36.
39. Fausto N. Liver regeneration and repair: hepatocytes, progenitor cells, and stem cells. Hepatology 2004; 39: 1477-87.
40. Flohr TR, Bonatti H, Brayman KL, Pruett TL. The use of stem cells in liver diseases. Curr Opin Organ Transplant 2009; 14: 64-71.
41. Garcea G, Maddern GJ. Liver failure after major hepatic resection. J Hepatobiliary Pancreat Surg 2009; 16: 145-55.
42. Sowa JP, Best J, Benko T, et al. Extent of liver resection modulates the activation of transcription factors and the production of cytokines involved in liver regeneration. World J Gastroenterol 2008; 14: 7093-100.
43. Farber E. Similarities of the sequence of the early histological changes induced in the liver of the rat by ethionine, 2-acetylaminofluorene, and 3'-methyl-4-dimethylaminoazobenzene. Cancer Res 1956; 16: 142-8.
44. Faris RA, Konkin T, Halpert G. Liver stem cells: a potential source of hepatocytes for the treatment of human liver disease. Artif Organs 2001; 25: 513-21.
45. Alison M, Golding M, Lalani EN. Wholesale hepatocytic differentiation in the rat from ductular oval cells, the progeny of biliary stem cells. J Hepatol 1997; 26: 343-52.
46. Fausto N, Campbell JS. The role of hepatocytes and oval cells in liver regeneration and repopulation. Mech Dev 2003; 120: 117-30.
47. Kuwahara R, Kofman AV, Landis CS, et al. The hepatic stem cell niche: identification by label-retaining cell assay. Hepatology 2008; 47: 1994-2002.
48. Gaudio E, Carpino G, Cardinale V, et al. New insights into liver stem cells. Dig Liver Dis 2009; 41: 455-62.
49. Sell S. Heterogeneity and plasticity of hepatocyte lineage cells. Hepatology 2001; 33: 738-50.
50. Tremblay KD, Zaret KS. Distinct populations of endoderm cells converge to generate the embryonic liver bud and ventral foregut tissues. Dev Biol 2005; 280: 87-99.
51. Lee SP, Savard CE, Kuver R. Gallbladder epithelial cells that engraft in mouse liver can differentiate into hepatocyte-like cells. Am J Pathol 2009; 174: 842-53.
52. Baccarani U, Sanna A, Cariani A, et al. Isolation of human hepatocytes from livers rejected for liver transplantation on a national basis: results of a 2-year experience. Liver Transplant 2003; 9: 506-12.
53. Allen KJ, Soriano HE. Liver cell transplantation: the road to clinical applications. J Lab Clin Med 2001; 138: 298-312.
54. Fisher RA, Strom SC. Human hepatocyte transplantation: worldwide results. Transplantation 2006; 82: 441-9.
55. Nussler A, Konig S, Ott M, et al. Present status and perspectives of cell-based Therapies for liver diseases. J Hepatol 2006; 45: 144-59.
56. Sigot V, Mediavilla MG, Furno G, Rodríguez JV, Guibert EE. A simple and effective method to improve intraspenic rat hepatocyte transplantation. Cell Transplant 2004; 13: 775-81.
57. Gupta S, Rajvanshi P, Sokhi R, et al. Entry and integration of transplanted hepatocytes in rat liver plates occur by disruption of hepatic sinusoidal endothelium. Hepatology 1999; 29: 509-19.
58. Mula N, Cubero FG, Codesal J, et al. Survival of allogenic hepatocytes into the thymus. Cell Tissues Organs 2008; 188: 270-9.
59. Baldini E, Cursio R, De Sousa G, et al. Peritoneal implantation of cryopreserved encapsulated porcine hepatocytes in rats without immunosuppression: viability and function. Transplant Proc 2008; 40: 2049-52.
60. Mei J, Sgroi A, Mai G, et al. Improved survival of fulminant liver failure by transplantation of microencapsulated cryopreserved porcine hepatocytes in mice. Cell Transplant 2009; 18: 101-10.
61. Glanemann M, Gaebelein G, Nussler N, et al. Transplantation of monocyte- derived hepatocyte-like cells (NeoHeps) improves survival in a model of acute liver failure. Ann Surg 2009; 249: 149-54.
62. Pietrosi G, Vizzini GB, Gruttadauria S, Gridelli B. Clinical applications of hepatocyte transplantation. World J Gastroenterol 2009; 15: 2074-7.
63. Rajvanshi P, Kerr A, Bhargava KK, Burk RD, Gupta S. Efficacy and safety of repeated hepatocyte transplantation for significant liver repopulation in rodents. Gastroenterology 1996; 111: 1092-110.
64. Smalley M, Leiper K, Tootle R, et al. Immortalization of human hepatocytes by temperature-sensitive SV40 large-T antigen. In Vitro Cell Dev Biol Anim 2001; 37: 166-8.
65. Khetani SR, Bhatia SN. Microscale culture of human liver cells for drug development. Nat Biotechnol 2008; 26: 120-6.
66. Ito M, Nagata H, Miyakawa S, Fox IJ. Review of hepatocyte transplantation. J Hepatobiliary Pancreat Surg 2009; 16: 97-100.
67. Nagy A, Gócza E, Diaz EM, et al. Embryonic stem cells alone are able to support fetal development in the mouse. Development 1990; 110: 815-21.
68. Xu RH, Chen X, Li DS, et al. BMP4 initiates human embryonic stem cells differentiation to trophoblast. Nat Biotechnol 2002; 20: 1261-4.
69. Polak JM, Bishop AE. Stem cells and tissue engineering: past, present, and future. Ann NY Acad Sci 2006; 1068: 352-66.
70. Takahashi K, Yamanaka S. Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell 2006; 126: 663-76.
71. Aoi T, Yae K, Nakagawa M, et al. Generation of pluripotent stem cells from adult mouse liver and stomach cells. Science 2008; 321: 699-702.
72. Park IH, Zhao R, West JA, et al. Reprogramming of human somatic cells to pluripotency with defined factors. Nature 2008; 451: 141-6.
73. Zhou Q, Brown J, Kanarek A, Rajagopal J, Melton DA. In vivo reprogramming of adult pancreatic exocrine cells to B-cells. Nature 2008; 455: 627-32.
74. Berninger B, Costa MR, Koch U, et al. Functional properties of neurons derived from in vitro reprogrammed postnatal astroglia. J Neurosci 2007; 27: 8654-64.
75. Okita K, Ichisaka T, Yamanaka S. Generation of germline-competent induced pluripotent stem cells. Nature 2007; 448: 313-17.
76. Colman A, Dreesen O. Induced pluripotent stem cells and the stability of the differentiated state. EMBO Rep 2009; 10: 714-21.
77. Lyra AC, Soares MB, Dos Santos RR. Bone marrow stem cells and liver diseases. Gut 2007; 56: 716-24.
78. Pittenger MF, Mackay AM, Beck SC, et al. Multilineage potential of adult human mesenchymal stem cells. Science 1999; 284: 143-47.
79. Bobis S, Jarocha D, Majka M. Mesenchymal stem cells: characteristics and clinical applications. Folia Histochem Cytobiol 2006; 44: 215-30.
80. Liu ZJ, Zhuge Y, Velazquez OC. Trafficking and differentiation of mesenchymal stem cells. J Cell Biochem 2009; 106: 984-91.
81. Kassem M, Kristiansen M, Abdallah BM. Mesenchymal stem cells: cell biology and potential use in therapy. Basic Clin Pharmacol Toxicol 2004; 95: 209-14.
82. Thorgeirsson SS, Grisham JW. Hematopoietic cells as hepatocyte stem cells: a critical review of the evidence. Hepatology 2006; 43: 2-8.
83. Simonsen JL, Rosada C, Serakinci N, et al. Telomerase expression extends the proliferative life-span and maintains the osteogenic potential of human bone marrow stromal cells. Nat Biotech 2002; 20: 592-6.
84. Forbes SJ, Russo FP, Rey V, et al. A significant proportion of myofibroblasts are of bone marrow origin in human liver fibrosis. Gastroenterology 2004; 126: 955-63.
85. Abdalla EK, Adam R, Bilchik AJ, et al. Improving resectability of hepatic colorectal metastases: expert consensus statement. Ann Surg Oncol 2006; 13: 1271-80.
86. DeLeve LD, McCuskey RS, Wang X, et al. Characterization of a reproducible rat model of hepatic veno-occlusive disease. Hepatology 1999; 29: 1779-91.
87. Harb R, Xie G, Lutzko C, et al. Bone marrow progenitor cells repair rat hepatic sinusoidal endothelial cells after liver injury. Gastroenterology 2009; 137: 704-12.
88. Vaquero J, Zurita M. Bone marrow stromal cells for spinal cord repair: a challenge for contemporary neurobiology. Histol Histopathol 2009; 24: 107-16.
89. Schächinger V, Erbs S, Elsässer A, et al. Intracoronary bone marrow-derived progenitor cells in acute myocardial infarction. Antioxid Redox Signal 2006; 355: 1210-21.
90. Witkowski P, Zakai SB, Rana A, Sledzinski Z, Hardy MA. Pancreatic islet transplantation, what has been achieved since Edmonton break-through. Ann Transplant 2006; 11: 5-13.
91. Baeyens L, Bouwens L. Can b-cells be derived from exocrine pancreas? Diabetes Obes Metab 2008; 10: 170-8.
92. Martin GR. Isolation of pluripotent cell line from early mouse embryos cultured in medium conditioned by teratocarcinoma stem cells. Proct Natl Acad Sci 1981; 78: 7634-38.
93. Liedtke C, Streetz KL. Hepatocytes from embryonic stem cells: Prometheus revisited? Hepatology 2007; 45: 829-30.
94. Pan YL, Cai JY, Hu AB. Differentiation of hepatocytes from mouse embryonic stem cells and its significance. Hepatobiliary Pancreat Dis Int 2005; 4: 291-4.
95. Chinzei R, Tanaka Y, Shimizu-Saito K, et al. Embryoid-body cells derived from a mouse embryonic stem cell line show differentiation into functional hepatocytes. Hepatology 2002; 36: 22-9.
96. Payne CM, Samuel K, Pryde A, et al. Persistence of functional hepatocyte-like cells in immune-compromised mice. Liver Int 2011; 31: 254-62.
97. Hamazaki T, Liboshi Y, Oka M, et al. Hepatic maturation in differentiating embryonic stem cells in vitro. FEBS Lett 2001; 497: 15-9.
98. Hay DC, Fletcher J, Payne C, et al. Highly efficient differentiation of hESCs to functional hepatic endoderm requires ActivinA and Wnt3a signaling. Proc Natl Acad Sci USA 2008; 105: 12301-6.
99. Kumashiro Y, Asahina K, Ozeki R, et al. Enrichment of hepatocytes differentiated from mouse embryonic stem cells as a transplantable source. Transplantation 2005; 79: 550-7.
100. Moriya K, Yoshikawa M, Ouji Y, et al. Embryonic stem cells reduce liver fibrosis in CCL4-treated mice. Int J Exp Pathol 2008; 89: 401-9.
101. Moore RN, Dasgupta A, Rajaei N, et al. Enhanced differentiation of embryonic stem cells using co-cultivation with hepatocytes. Biotechnol Bioeng 2008; 101: 1332-43.
102. Kubo A, Shinozaki K, Shannon JM, et al. Development of definitive endoderm from embryonic stem cells in culture. Development 2004; 131: 1651-62.
103. Zhou M, Li P, Tan L, et al. Differentiation of mouse embryonic stem cells into hepatocytes induced by a combination of cytokines and sodium butyrate. J Cell Biochem 2010; 109: 606-14.
104. Chen L, Tredget EE, Liu C, Wu Y. Analysis of allogenicity of mesenchymal stem cells in engraftment and wound healing in mice. PLoS One 2009; 4: e7119.
105. Krampera M, Glennie S, Dyson J, et al. Bone marrow mesenchymal stem cells inhibit the response of naive and memory antigen-specific T cells to their cognate peptide. Blood 2003; 101: 3722-9.
106. Di Nicola M, Carlo-Stella C, Magni M, et al. Human bone marrow stromal cells suppress T-lymphocyte proliferation induced by cellular or nonspecific mitogenic stimuli. Blood 2002; 99: 3838-43.
107. Taniguchi H, Toyoshima T, Fukao K, Nakauchi H. Presence of hematopoietic stem cells in the adult liver. Nat Med 1996; 2: 198-203.
108. Tang YL, Zhao Q, Qin Q, et al. Paracrine action enhances the effects of autologous mesenchymal stem cell transplantation on vascular regeneration in rat model of myocardial infarction. Ann Thorac Surg 2005; 80: 229-36.
109. Bruno S, Grange C, Deregibus MC, et al. Mesenchymal stem cell-derived microversicles protect against acute tubular injury. J Am Soc Nephrol 2009; 20: 1053-67.
110. Van Poll D, Parekkadan B, Cho CH, et al. Mesenchymal stem cell-derived molecules directly modulate hepatocellular death and regeneration in vitro and in vivo. Hepatology 2008; 47: 1634-43.
111. Herrera MB, Fonsato V, Gatti S, et al. Human liver stem cell-derived microvesicles accelerate hepatic regeneration in hepatectomized rats. J Cell Mol Med 2010; 14: 1605-18.
112. Yu Y, Yao AH, Chen N, et al. Mesenchymal stem cells over-expressing hepatocyte growth factor improves small-for size liver grafts regeneration. Mol Ther 2007; 15: 1382-9.
113. Son BR, Marquez-Curtis LA, Kucia M, et al. Migration of bone marrow and cord Blood mesenchymal stem cells in vitor is regulated by stromal-derived factor-1-CXCR4 and Hepatocyte Growth Factor-c-met Axes and involves matrix metalloproteinases. Stem cells 2006; 24: 1254-64.
114. Hattori K, Heissig B, Tashiro K, et al. Plasma elevation of stromal cell-derived factor-1 induces mobilization of mature and immature hematopoietic progenitor and stem cells. Blood 2001; 97: 3354-60.
115. Mao L, Qiu YD, Fang S, et al. Liver progenitor cells activated after 30% small-for-size liver transplantation in rats: a preliminary study. Transplant Proc 2008; 40: 1635-40.
116. Peichev M, Naiyer AJ, Pereira D, et al. Expression of VEGFR-2 and AC133 by Circulating human CD34+ cells identifies a population of functional endothelial precursors. Blood 2000; 95: 952-8.
117. Lemoli RM, Catani L, Talarico S, et al. Mobilization of bone marrow-derived hematopoietic and endothelial stem cells after orthotopic liver transplantation and liver resection. Stem Cells 2006; 24: 2817-25.
118. To LB, Haylock DN, Simmons PJ, Juttner CA. The biology and clinical uses of blood stem cells. Blood 1997; 89: 2233-58.
119. Pai M, Zacharoulis D, Milicevic MN, et al. Autologous infusion of expanded mobilized adult bone marrow-derived CD34+ cells into patients with alcoholic liver cisshosis. Am J Gastroenterol 2008; 103: 1952-8.
120. Stutchfield BM, Rashid S, Forbes SJ, Wigmore SJ. Practical barriers to delivering autologous bone marrow stem cell therapy as an adjunct to liver resection. Stem Cells Dev 2010; 19: 155-62.
121. Gehling UM, Willems M, Dandri M, et al. Partial hepatectomy induces mobilization of a unique population of haematopoietic progenitor cells in human healthy liver donors. J Hepatol 2005; 43: 845-53.
122. Am Esch JS II, Knoefel WT, Klein M, et al. Portal application of autologous CD 133 bone marrow cells to the liver: a novel concept to support hepatic regeneration. Stem Cells 2005; 23: 463-70.
123. Fürst G, Schulte am Esch J, Poll LW, et al. Portal vein embolization and autologous CD133+ bone marrow stem cells for liver regeneration: initial experience. Radiology 2007; 243: 171-9.