REDIRECTION OF T CELLS AGAINST HBV INFECTED CELLS USING SINGLE CHAIN ANTIBODY FRAGMENTS

Background: Worldwide about 350 million individuals suffer from chronic HBV infection and are at risk to develop hepatocellular carcinoma or liver cirrhosis. Upon antiviral therapy, viral replication is stopped, but the viral genome is rarely eliminated, and HBV surface antigen is still produced by infected cells. Thus, a potent artificial T cell response resulting in killing of residual infected cells, could be a promising addition to antiviral medication. The aim of our work therefore is to establish T cells with chimeric T cell receptors (TCRs) to target HBV infected hepatocytes.

Methods: Single chain fragments (scFv) directed against the HBV S-protein or against the preS1 domain of L protein were used for MHC independent recognition of antigen on the surface of infected cells. These scFvs were fused to a TCR construct, including the transmembrane- and signalling domains of the CD3z chain of the TCR and the signalling domain of the costimulatory CD28 receptor. The resulting TCR construct was introduced into preactivated primary human T cells using retroviral vectors. TCRs directed to unrelated antigens served as control. Transduced T cells were tested for the expression of chimeric TCRs by FACS analysis, and co-cultured with target cells replicating HBV.

Results: Upon antigen recognition, T cells bearing the chimeric receptors secreted IFNg and IL2. A functional T cell response resulted in up to 80% specific killing of HBV positive target hepatoma cells at an effector: target ratio of 1: 16–1: 4. This compared to maximally 10% unspecific killing of HBV negative cells, as determined by XTT viability testing. Primary human hepatocytes infected with HBV were also effectively killed.

Conclusion: Thus, we were able to redirect T cells to HBV infected cells by introducing chimeric TCRs which may be a usefull tool for adoptive immunotherapy of chronic hepatitis B after antiviral treatment.

Schlüsselwörter

Hepatitis B - Immuntherapie