T cells redirected by a chimeric antigen receptor efficiently control Hepatitis B Virus replication in an immunocompetent mouse model

Background & Aims: Current antivirals suppress HBV but do not clear the infection. For virus clearance strong effector T cell responses are needed, which are sparse in chronically infected individuals. Cell therapy using T cells redirected by HBV-specific receptors may clear HBV and help to prevent and treat HBV-associated liver cancer. We designed a chimeric antigen receptor (CAR) that is composed of a single chain antibody fragment binding to HBsAg and CD28/CD3z signaling domains. This study aimed to proof feasibility of this approach in vivo addressing the following challenges: (i) T cell-depletion to generate space for cell engraftment in chronic virus carriers is too perilous, (ii) viral antigens circulating in high amounts may inactivate transferred T cells or (iii) trigger uncontrolled immune damage.

Methods: Primary murine CD8+ T cells were isolated, stimulated using an optimized protocol and grafted with CARs by retroviral transduction. A CAR that binds HBV envelope proteins and transfers activation signals to the T cell was compared to a control CAR without a proper signaling domain and a CAR not binding HBV proteins.

Results: CD8+ T cells engineered to express an HBV-specific CAR, which recognizes HBV envelope proteins of various subtypes on infected hepatocytes, were able to engraft and expand in immune competent HBV transgenic mice. Following adoptive transfer CAR-grafted T cells targeted the liver, remained functional in vivo, rapidly and efficiently controlled HBV replication while causing only transient liver damage. The large amount of circulating viral antigens neither impaired nor over-activated the transferred T cells.

Conclusion: HBV-specific cell therapy with CAR-engineered T cells bears the potential to treat chronic hepatitis B and HBV-associated hepatocellular carcinoma irrespective of the patient's individual HLA-type.