Natural Killer T Cell Activation Inhibits Hepatitis B Virus Replication in Vivo

Abstract

We have previously reported that hepatitis B virus (HBV)–specific CD8+ cytotoxic T lymphocytes and CD4+ helper T lymphocytes can inhibit HBV replication in the liver of HBV transgenic mice by secreting interferon (IFN)-γ when they recognize viral antigen. To determine whether an activated innate immune system can also inhibit HBV replication, in this study we activated natural killer T (NKT) cells in the liver of HBV transgenic mice by a single injection of α-galactosylceramide (α-GalCer), a glycolipid antigen presented to Vα14+NK1.1+ T cells by the nonclassical major histocompatibility complex class I–like molecule CD1d. Within 24 h of α-GalCer injection, IFN-γ and IFN-α/β were detected in the liver of HBV transgenic mice and HBV replication was abolished. Both of these events were temporally associated with the rapid disappearance of NKT cells from the liver, presumably reflecting activation-induced cell death, and by the recruitment of activated NK cells into the organ. In addition, prior antibody-mediated depletion of CD4+ and CD8+ T cells from the mice did not diminish the ability of α-GalCer to trigger the disappearance of HBV from the liver, indicating that conventional T cells were not downstream mediators of this effect. Finally, the antiviral effect of α-GalCer was inhibited in mice that are genetically deficient for either IFN-γ or the IFN-α/β receptor, indicating that most of the antiviral activity of α-GalCer is mediated by these cytokines. Based on these results, we conclude that α-GalCer inhibits HBV replication by directly activating NKT cells and by secondarily activating NK cells to secrete antiviral cytokines in the liver. In view of these findings, we suggest that, if activated, the innate immune response, like the adaptive immune response, has the potential to control viral replication during natural HBV infection. In addition, the data suggest that therapeutic activation of NKT cells may represent a new strategy for the treatment of chronic HBV infection.

Tim‐3 blockade promotes iNKT cell function to inhibit HBV replication

“…As shown in Figure 4, α‐Galcer augmented the expression of IFN‐γ or CD107a in NK cells as well as CD8 + T cells (Figure 4B,D). At the same time, the percentage of NK cells was increased (Figure 4A), which was consistent with previous reports 13. But α‐Galcer did not obviously impact CD8 + T cells frequency (Figure 4C).…”

“…It has been previously reported that α‐Galcer inhibits HBV replication in HBV‐Tg mice 13. To address whether Tim‐3 promotes α‐Galcer‐initiated HBV inhibition, HBV‐Tg mice were treated with α‐Galcer alone (α‐Galcer +IgG) or α‐Galcer combined with anti‐Tim‐3 (α‐Galcer+aTim‐3).…”

“…Activated iNKT cells can secrete large amounts of IFN‐γ/TNF‐α/CD107a, but due to α‐Galcer induced strikingly decrease in iNKT cell number, the overall antiviral effect of α‐Galcer on iNKT cells is doubtful. Thus, the subsequent activation of NK/CD8 + T cells owing to IFN‐γ becomes the most powerful forces against HBV replication 13. Even though NK/CD8 T cells will take the place of overactivated iNKT cells, a randomized placebo‐controlled trial still failed to detect the success inhibition of HBV DNA in α‐Galcer‐treated patients with CHB, which we had to attribute this failure to the poor tolerance of α‐Galcer or the obvious drop of iNKT cell number 19.…”

“…iNKT cells, on activation, can produce both Th1 cytokines such as IFN‐γ and Th2 cytokines such as IL‐4/IL‐13 within a few hours, the intensity and magnitude of which are closely related to various disease outcome such as cancer and infection 9, 10, 11, 12. Increasing evidence suggests that iNKT cells play a key role in anti‐HBV immunity 13, 14, 15. In a clinical research, the per cent of peripheral iNKT cells was decreased in patients with CHB, but antiviral treatment increased their frequencies,16, 17 which meant that iNKT cells might be linked to CHB development.…”

“…α‐Galcer could promote the induction and proliferation of HBV‐specific cytotoxic T lymphocytes (CTLs) 18. Moreover, α‐Galcer was proved to inhibit HBV replication by directly activating iNKT cells and by secondarily activating natural killer (NK) cells to secrete antiviral IFN‐γ or IFN‐α/β 13. Therefore, improving iNKT cell function using α‐Galcer seems a feasible strategy for clinical practice of curing patients with CHB.…”