Hepatocyte transplantation : experimental and clinical studies

Abstract

Hepatocyte transplantation is an experimental treatment for patients with end-stage liver disease and inborn metabolic liver disorders. Studies in animal models and human trials have shown that allogenic hepatocytes infused through the portal vein physiologically integrate into the liver parenchyma, replacing missing liver function. Current research data provide a proof of principle for clinical hepatocyte transplantation in a wide range of liver diseases. However, most patients ultimately undergo whole organ liver transplantation due to insufficient graft function. Thus, the efficacy and long-term results of clinical hepatocyte transplantation must be improved before this treatment can be introduced into routine clinical care.

The present thesis summarizes experimental and clinical studies with the general aim of identifying current limitations and improving outcomes of hepatocyte transplantation.

Paper I investigates strategies for improving short-term preservation of isolated human hepatocytes. Human hepatocytes are usually cold stored for prolonged periods between isolation and infusion. We found that isolated human hepatocytes undergo cell death and lose hepatocyte-specific function during this cold storage period. An alternative technique of liver tissue storage and repeated isolations led to improved viability and function of isolated hepatocytes before infusion.

In Papers II and III, a hepatocyte transplantation model was established in the ApoE knockout mouse. Clinically relevant animal models are necessary for developing new treatment strategies. The ApoE knockout mouse is an ideal model of an inherited metabolic liver disease. ApoE is mainly produced by hepatocytes and its deficiency results in extrahepatic disease. ApoE (−/−) mice display severe hypercholesterolemia leading to premature atherosclerosis. We observed that transplanted wild-type hepatocytes integrated into the liver and excreted ApoE, and that this serum ApoE correlated with hepatic donor cell engraftment. Transplantation without preconditioning treatment resulted in serum ApoE levels of 1–2% of wild-type levels, which did not affect hypercholesterolemia. However, pretreatment with retrorsine gave donor hepatocytes a growth advantage, resulting in progressive repopulation of up to 55% of the recipient liver. This increased repopulation by donor hepatocytes led to normalization of hypercholesterolemia and prevention of atherosclerosis.

Paper IV evaluated the safety and efficacy of partial hepatectomy preconditioning with hepatocyte transplantation in two patients with Crigler-Najjar syndrome type I. Partial hepatectomy in combination with hepatocyte transplantation was safe and induced a regenerative response. Serum bilirubin decreased to approximately 50% of pretransplant concentrations, and allograft function was further confirmed by detection of bilirubin diglucuronides in bile after transplantation. However, both patients lost graft function in association with the emergence of donor-specific HLA antibodies.