Can Nonlytic T cells be Engineered to Fight HBV Infection?
Nonlytic T cells with receptors engineered to recognize HBV suppress virus replication in hepatocytes and limit infection of mice by activating APOBEC3, researchers report in the July issue of Gastroenterology. These cells are not hepatotoxic and might be developed for treatment of chronic HBV infection.
T cells control chronic viral infections, and virus-specific TCR-redirected T cells recognize viral-infected cells in culture and in animal models. T-cell therapies are in development for persistent HBV and HCV infections. These infections are characterized by defects of antigen-specific T cells, and the viruses can be controlled with recovery of T cell function. However, T cells can cause liver damage.
One approach to restoring the lack of virus-specific T-cell response in patients with chronic hepatic viral infections is to genetically engineer patients’ own (autologous) T cells to express an HBV- or HCV-specific TCRs. Serene Koh et al created nonlytic T cells with TCRs that recognize HBV or HCV peptide–HLA complexes.
Koh et al electroporated resting T cells or T cells activated by anti-CD3 with mRNAs encoding HBV- or HCV-specific TCRs and tested their ability to suppress HBV or HCV replication, without lysis, in 2D and 3D cultures of HepG2.2.15 cells and HBV-infected HepG2-hNTCP cells (see figure).
The authors observed a 64% reduction in HBV DNA, accompanied by more than 80% reduction in levels of pregenomic (pg)RNA and covalently closed circular DNA (cccDNA), in HBV-infected HepG2-hNTCP after 24 hours of incubation with the engineered T cells at a 1:1 effector cell–to–target cell (E:T) ratio. Less pronounced antiviral effects were induced at a 1:3 E:T ratio, which produced a 50% reduction in pgRNA and cccDNA.
Koh et al showed that these engineered resting T cells had similar production of interferon gamma (IFNG), but lower levels of perforin and granzyme, compared with activated T cells. So, the engineered T cells appear to have antiviral activity without causing hepatocellular damage.
Although T-cell secretion of IFNG was required to inhibit HCV replication, the HBV-specific TCR-reprogrammed resting T cells reduced HBV replication through intracellular activation of apolipoprotein B mRNA editing enzyme, catalytic polypeptide 3 (APOBEC3). The mechanism of APOBEC3 intracellular activation involved temporal expression of lymphotoxin beta receptor ligands on resting T cells after TCR-mediated antigen recognition and activation of lymphotoxin beta receptor in infected cells.
Koh et al injected the TCR-reprogrammed T cells into HBV-infected urokinase-type plasminogen activator/SCID/interleukin 2γ mice with humanized livers. The activated and the resting engineered T cells effectively suppressed HBV replication. Koh et al found no increase in levels of aminotransferase or markers of inflammation in livers of the mice given the engineered resting T cells..
The authors conclude that antiviral nonlytic T cells can be engineered, via transfer of virus-specific TCR mRNA, to resting primary human T cells, without extensive pre-activation and culture or selection of particular subsets. They say that these cells, due to their inability to activate liver inflammation, might be used in treatment of persistent hepatic viral infections. Induction of APOBEC3B activity in hepatocytes has been previously proposed to inhibit HBV replication and destabilize HBV cccDNA.
Koh et al state that compared with antiviral treatment with nucleoside analogues, which requires in the same mouse system approximately 1 month to achieve a 2-log decrease of viremia, mice that received the engineered T cells had substantially lower levels of viremia and of HBV RNA. Furthermore, pathways with the potential to lower cccDNA had been activated.