Redirecting T cells to overcome tolerance in chronic HBV infection

Hepatitis B virus remains one of the top ten killers in the world today, causing around a million deaths every year from chronic liver disease. There is a vaccine to prevent spread, but this is of no use to the 400 million people estimated to already be chronically infected. There are now a number of drugs available to treat hepatitis B infection but these typically only suppress the virus rather than clear it; when the patient stops the treatment the virus level comes back up. There is no effective drug therapy for the end-stage complications of liver failure and liver cancer.
The goal of the work proposed here is to allow us to develop a type of treatment to safely boost immune control of hepatitis B virus infection. We would like to harness the natural ability of a component of the immune system called T cells to control this virus. There are very few of the right type of T cells left in patients with chronic hepatitis B virus infection, so we will genetically engineer the patients? T cells to regain the ability to fight against hepatitis B virus. This proposal aims to look into how effective these genetically engineered T cells will be at combatting hepatitis B virus when it is in the liver, by mimicking this situation in a test tube and in a mouse model. Our findings will provide essential information for the future application of this approach to hepatitis and other chronic infections and tumours.

The anti-viral T cell response is markedly depleted in patients with chronic HBV infection (CHB); this limits the chances of achieving sustained responses to antiviral therapy and therapeutic vaccination. One way to circumvent this is to re-direct the specificity of existing T cells using retroviral TCR gene transfer, an approach that has shown promise in the immunotherapy of tumours. We hypothesise that T cell tolerance in CHB can be overcome by re-directing the specificity of T cells, providing a powerful immunotherapeutic adjunct to the therapy of this infection and sequelae such as hepatocellular carcinoma (HCC).
We have cloned TCRs directed against two HLA-A2 restricted HBV epitopes and shown that TCR gene transfer to T cells from patients with CHB endows them with appropriate functional specificity in vitro. These targets were selected because they are immunodominant in the circulation of patients who have successfully controlled HBV infection. It is now critical to determine whether these epitopes are presented in the livers of patients with different pathological manifestations of CHB, allowing the re-directed T cells to recognise infected hepatocytes. We will address this aim by applying recently developed TCR-like mAbs specific for HBV peptides bound to HLA-A2 to stain liver sections from patients with well-defined histological stages of CHB, including HCC. We will then test for functional recognition of HBV-infected hepatocytes using the TCR re-directed T cells in vitro.
T cell exhaustion in CHB is thought to result from the combination of persistent high-level antigen exposure in the context of the tolerogenic liver environment; some of the mechanisms mediating this have now been defined. Our second aim is therefore to investigate whether re-directed T cells will be resistant to inactivation or deletion when they encounter their cognate antigen in the HBV-infected liver. We will test whether the livers of patients with CHB express a balance of co-stimulatory and co-inhibitory ligands favouring T cell exhaustion and what impact this has on the function and survival of re-directed T cells in vitro. We will then analyse the in vivo survival, homing and function of TCR re-directed T cells in NOD/SCID mice, as assessed by their ability to eradicate tumours derived from an HCC cell line transfected with HBV.
Our findings will extend our understanding of HBV pathogenesis and hepatic tolerance and will directly inform further developments of the TCR gene transfer approach to immunotherapy.