LIVER CELL TRANSPLANTATION

By Dr. Humberto Soriano

North Western University and Children Memorial Medical Center, Chicago,USA

Liver cell transplantation is a procedure that shows great promise for the treatment of many diseases now treated definitively only with whole organ transplantation. Organ transplantation involves major surgery, requires the use of scarce donor organs, is expensive and requires life-long immunosuppression. Potential advantages of cell transplantation include a simpler, safer, less costly procedure that takes advantage of currently discarded liver segments, and could use stem or in-vitro expanded cells. To isolate human hepatocytes, the donor liver is taken to the cell transplant laboratory and is perfused with a calcium chelator to separate desmosomal cell-cell contact followed by collagenase to digest the organ's supporting structure. Liver cells are filtered through decreasing size meshes and suspended in special nutrient medium. Critical steps in the isolation and freezing of primary hepatocytes can prevent cell death and optimize cell recovery. The harvested cells can be used soon after isolation or stored frozen to be thawed when needed by a patient with liver disease. Candidate diseases for liver cell therapy include acute liver failure, liver based metabolic diseases and chronic liver disease. There are much animal data on the effectiveness of this treatment for these conditions. There are mounting data on the safety and potential effectiveness of liver cell transplantation in humans. It is now widely accepted that liver cells have great regenerative capacity in vivo. This proliferative capacity enables transplanted cells to reconstitute injured, or metabolically defective, liver tissue. Liver cells can be infused into the portal vein or spleen from where cells migrate to the liver and take up permanence residence and perform the normal liver metabolic functions, including removal of toxins and the synthesis of coagulation factors. Full regeneration of a mouse liver can be accomplished after infusion of a few thousand cells. Hepatocellular transplantation has been performed in humans with encouraging results. As a treatment for cirrhosis, patients in Japan underwent partial hepatectomy and the isolated cells were infused into the spleen in an attempt to provide enhanced metabolic function. The transplanted cells could be detected in the spleen by radio-imaging techniques but only mild metabolic improvement occurred 2. As a target for ex-vivo gene therapy, autologous LDL-receptor transfected hepatocytes were used in an attempt to correct familial hypercholesterolemia. The procedure was performed safely in five patients but with modest metabolic correction. Recently, a patient with Crigler-Najjar syndrome, an inherited defect of bilirubin conjugation, was treated with hepatocytes and her serum bilirubin concentration decreased 3. Hepatocellular transplantation was also used to treat adult patients with advanced liver failure at the University of Pittsburgh. A decrease in the serum ammonia concentrations was shown, and three patients survived until a whole donor organ was available. Liver cell transplantation with encouraging results was also performed at the University of Denver. Our experience in children showed that liver cell infusions are safe and may be lifesaving as treatment for fulminant liver failure 4. Several approaches are actively investigated to offer a potential solution to the limited availability of hepatocytes including the development of stem cells, use of bone marrow5, in-vitro expansion of primary hepatocytes and use of conditionally immortalized hepatocytes. Transfection of liver cells with a variant of the SV-40 large-T antigen gene provides a temperature-sensitive control of cell cycle proteins. In culture, cell division proceeds under the direction of this transfected gene at 33oC. Once hepatocytes are transplanted, normal body temperature results in cessation of replication. In animal studies, such transplants have been shown to improve survival in acute liver failure and have a favorable impact on hepatic encephalopathy6. Concerns for potential tumorigenesis need to be allayed whenever cells are expanded in-vitro. In summary, liver cell transplantation could become a safer, less invasive and less expensive treatment for some patients with liver disease. One advantage of cell infusions to treat acute liver failure is that they can be used early in the disease, as a potential bridge to recovery, without committing the patient to lifelong immune suppression. Patients with acute, chronic and metabolic liver diseases are subjects of ongoing clinical trials of liver cell transplantation. Cell transplantation is already an established clinical tool in the realm of hematology. Cell transplantation is likely to become a clinical tool for the treatment of other diseased organs and the liver appears to be next "giant leap" in this rapidly advancing field.

Fig: Male and Female Hepatocytes Within a Hepatic Chord of Recipient of Human Liver Cell Transplantation Fluorescence in Situ Hybridization for Chromosomes X, Y and 18

References:

1. Gupta S, Chowdhury JR. Hepatocyte transplantation: back to the future. Hepatology 1992; 15:156-161.
2. Mito M, Kusano M. Hepatocyte transplantation in man. Cell Transplant 1993; 2:65-74.
3. Fox IJ, Chowdhury JR, Kaufman SS, et al. Treatment of the Crigler-Najjar syndrome type I with hepatocyte transplantation. N Engl J Med 1998; 338:1422-1426.
4. Soriano HE, Wood RP, Kang DC, et al. Hepatocellular transplantation (HCT) in children with fulminant liver failure. Hepatology 1997; 30:239A.
5. Petersen BE, Bowen WC, Patrene KD, et al. Bone Marrow as a Potential Source of Hepatic Oval Cells. Science 284:1168-1170.
6. Schumacher IK, Okamoto T, Kim BH, et al. Transplantation of conditionally immortalized hepatocytes to treat hepatic encephalopathy. Hepatology 1996; 24:337-342.