T-Cell Receptor Grafting allows Control of Hepatitis B Virus Infection

T cell therapy is a promising means to treat chronic hepatitis B virus (HBV) infection and HBV-associated hepatocellular carcinoma. T cells engineered to express an HBV-specific T cell receptor (TCR) may achieve cure of HBV infection upon adoptive transfer. We investigated the potential of T cells genetically modified by retroviral transduction to express high affinity HLA-A2-restricted, HBV envelope- or core-specific TCRs to cure HBV infection.

TCR-grafted CD4+and CD8+ T cells were tested for their antiviral activity in vitro when co-cultured with HBV-infected HepG2-NTCP cells and in vivo when injected into HBV-infected human liver chimeric mice repopulated with HLA-A2-matched primary human hepatocytes (PHH).

Upon expression of HBV-specific high affinity TCRs, both CD8+and CD4+ T cells from healthy donors, as well as those from chronic hepatitis B patients, became polyfunctional effector cells that were able to contain HBV infection in vitro. Most of the antiviral activity of CD8+ T cells and core-specific CD4+ T cells was mediated by killing of HBV-infected target cells in vitro. On the other hand, TCR-grafted S-specific CD4+ T cells also induced cccDNA degradation via IFN-γ and TNF-α secretion. After a single T cell injection into humanized mice, viremia, HBeAg and HBsAg dropped by 4 – 5 log to undetectable levels. Such serological effects reflected the strong reduction of all intrahepatic virological markers, such as HBcAg and pgRNA, and undetectable levels of cccDNA after 8 weeks. One week post T cell injection, alanine amino transferase levels peaked transiently and normalized thereafter. As indicated by a drop of human serum albumin (HSA) and immunofluorescence staining of liver sections, T cell injection provoked clearance of infected hepatocytes even in mice with high infection rates, while in mice with lower infection rates at base line, a large proportion of human hepatocytes survived. Ki67-staining and HSA rebound indicated the potential of PHH to proliferate to compensate for cell loss. Although discontinuation of treatment with the HBV entry inhibitor Myrcludex B (MyrB) 3 weeks post T cell transfer led eventually to viral rebound in these immunodeficient mice, co-treatment of mice with MyrB guaranteed the maintenance of very low to undetectable levels of HBV serological and intrahepatic markers for the entire observation period (13 weeks).

These data demonstrate that T cells stably transduced with TCRs of high functional avidity represent an interesting therapeutic approach for chronic hepatitis B and HBV-induced hepatocellular carcinoma, since they have the potential to mediate clearance of HBV-infected cells causing limited injury in livers with low infection rates. Co-treatment with the entry inhibitor MyrB can ensure long-term control of HBV infection.