Alpha-1 antitrypsin to improve the efficacy of hepatocyte transplantation in children with liver-based metabolic disease

Hepatocyte (Liver cell) transplantation is an alternative to liver transplantation for certain conditions. It involves the transplantation of the cells into the patient's liver, usually via the main vein supplying the liver, in a minimally invasive way. Patients for whom this treatment is especially suitable are those who are missing a particular enzyme which is made in the liver cell. This leads to buildup of toxic waste products and consequent irreversible brain injury. Two such conditions: Crigler-Najjar syndrome (where bilirubin cannot be broken down), and the urea cycle defects (where ammonia is not eliminated), cause profound brain injury due to accumulation of these toxic compounds. Replacing the whole liver, to replace the missing enzyme, is an option but comes at a high price as this involves major surgery, often with complications, a prolonged hospital stay, and leaves no fallback if the transplant fails. Furthermore, the donor organ pool is particularly small for children, who will need part of an adult liver. Thus the wait for a suitable organ may be years for children who have an extremely poor quality of life and with the potential to develop a metabolic 'crisis' at any point in time. In addition, they only actually need a fraction of liver in order to correct the deficiency. There is thus a redundancy in replacing a whole liver, particularly in view of the restricted resource and large demand. Hepatocytes are isolated from livers that don't meet the criteria for organ transplantation, and so they are an excellent use of an otherwise unusable resource. They can be frozen and stored and thus are available off the shelf. Hepatocyte transplantation also allows the patients own liver to be preserved while providing 10-15% of the liver function, i.e. sufficient function from the otherwise deficient enzyme to correct the disease. We know that, at time of infusion into the portal vein, the cells encounter attack from the innate immune system: blood begins to clot, proteins are released, attracting the defence cells of the body, and hepatocytes are destroyed before they can reach the liver to engraft and settle. Conventional immuno-suppression including steroids doesn't allow to overcome this and so, more than ninety percent of cells are destroyed before they have the opportunity to engraft. Alpha-1 antitrypsin (AAT) is a protein made in liver cells and has a range of effects which can block a lot of the adverse effects of inflammation without the side effects of most conventional immunosuppressants, which leave the body vulnerable to attack from infection and cause poor wound healing. AAT is used in clinical trials world-wide, in a variety of conditions which are influenced by inflammation such as type 1 diabetes and ischaemic heart disease. Considerable success of AAT as an immune system modifier has also been seen in the field of islet transplantation in patients with diabetes, where these insulin producing cells are also transplanted into the liver. We wish to test the use of AAT in the field of hepatocyte transplantation as we believe that it will lead to improved engraftment of cells in the liver and thus, better medium- to long-term function of the cells, making a significant difference to those treated. We predict that the mechanism through which this occurs will be the suppression of the innate (immediate) immune system and we will measure both the function of the cells in terms of supplying the missing enzyme as well as the effect that AAT has on the immediate immune response once these cells are infused. Though hepatocyte transplantation is a small field, it can result in life-changing treatment for children with devastating liver-based disease. Should we demonstrate the success of this therapy using AAT, this will give further credence to the use of AAT as an effective and safe immuno-modulator, in the context of transplantation in general, and in other inflammatory conditions.

Hepatocyte transplantation (HT) is an alternative treatment to liver transplantation for certain inborn errors of metabolism, to date demonstrating some success, but not fulfilling its long-term promise. One of the major hurdles to sustained success of this therapy is the early cell loss of ~70% of hepatocytes following their infusion. This is largely due to the instant blood-mediated inflammatory reaction (IBMIR), with activation of complement and coagulation pathways. Effective inhibition of IBMIR should significantly improve hepatocyte engraftment and function. Alpha-1 antritrypsin (AAT) is an endogenous protease with anti-inflammatory, anti-thrombotic and anti-apoptotic effects. AAT significantly improves efficacy of islet transplantation in models of diabetes. A cynomolgous model of diabetes showed islet function for more than 700 days in those treated with AAT (versus 90 days in controls). As there are several parallels between islet transplantation and HT we hypothesize that a similar effect will be seen in HT. We have shown in vitro that AAT is significantly anti-thrombotic and anti-inflammatory in a Chandler loop containing human hepatocytes and whole blood. Metabolic activity was improved in hepatocytes cultured in AAT. The proposed project will test proof of principle that AAT use in hepatocyte transplantation improves engraftment and function of cells in small animal models. Following on from this a phase IIa non-randomised open-label clinical trial will study AAT in prevention of the IBMIR in children undergoing hepatocyte transplantation for two forms of liver-based metabolic disease: Crigler-Najjar syndrome and Urea Cycle Defects. The primary outcome measure will be of efficacy (demonstrable recovery of enzyme activity) at 24 weeks post transplant which will be measured using disease-specific markers. A proteomic approach will develop biomarkers of cell survival and function and explore the mode of action of AAT in animal models and clinical trial.

The treatment of liver-based metabolic disease could be transformed by the use of alpha-1 antitrypsin (AAT) in the context of hepatocyte transplantation.
The incidence of urea cycle disorders (UCD) is approximately 1 in 35,000 and of Crigler-Najjar syndrome (CN) is 1 per 1,000,000. Though rare, the consequences for these diseases are devastating, with a high mortality (25% in early infancy) and a major burden of disease in terms of neurological disability, need for treatment and frequent hospitalisation.
If hepatocyte transplantation is combined with AAT therapy to create an effective therapy for these conditions, the major burden of medication (UCD) and phototherapy (CN) would be minimised, and improved neurological outcomes would result, thus also minimising the need for liver transplantation.
The decrease in competition for organs for transplantation (metabolic liver disease is the indication for 10% of liver transplantation in children) would therefore decrease the mortality on the waiting list for other conditions such as biliary atresia demand for organs outstrips supply at the current time.
Other indications for hepatocyte transplantation will become possible targets for this therapy should it prove effective; such indication could be acute on chronic liver failure, in which mortality is extremely high and in whom immunosuppression should ideally be minimised. Other types of cell therapy would also benefit from a targeted immunosuppression with minimal side effects, which is expected from using AAT.
This study will also aim to uncover fundamental information about how AAT influences the innate immune response to an incoming graft or an inflammatory stimulus. The knowledge produced will not only allow Hepatocyte Transplantation to fulfil its potential as an effective therapy, but the potential of AAT as an immunomodulatory agent will be developed and will have a direct benefit in the future of transplantation and in therapy of other inflammatory diseases.