Inhibitory Phenotype of HBV-Specific CD4+ T-Cells Is Characterized by High PD-1 Expression but Absent Coregulation of Multiple Inhibitory Molecules

Abstract

BackgroundT-cell exhaustion seems to play a critical role in CD8+ T-cell dysfunction during chronic viral infections. However, up to now little is known about the mechanisms underlying CD4+ T-cell dysfunction during chronic hepatitis B virus (CHB) infection and the role of inhibitory molecules such as programmed death 1 (PD-1) for CD4+ T-cell failure.MethodsThe expression of multiple inhibitory molecules such as PD-1, CTLA-4, TIM-3, CD244, KLRG1 and markers defining the grade of T-cell differentiation as CCR7, CD45RA, CD57 and CD127 were analyzed on virus-specific CD4+ T-cells from peripheral blood using a newly established DRB1*01-restricted MHC class II Tetramer. Effects of in vitro PD-L1/2 blockade were defined by investigating changes in CD4+ T-cell proliferation and cytokine production.ResultsCD4+ T-cell responses during chronic HBV infection was characterized by reduced Tetramer+CD4+ T-cell frequencies, effector memory phenotype, sustained PD-1 but low levels of CTLA-4, TIM-3, KLRG1 and CD244 expression. PD-1 blockade revealed individualized patterns of in vitro responsiveness with partly increased IFN-γ, IL-2 and TNF-α secretion as well as enhanced CD4+ T-cell expansion almost in treated patients with viral control.ConclusionHBV-specific CD4+ T-cells are reliably detectable during different courses of HBV infection by MHC class II Tetramer technology. CD4+ T-cell dysfunction during chronic HBV is basically linked to strong PD-1 upregulation but absent coregulation of multiple inhibitory receptors. PD-L1/2 neutralization partly leads to enhanced CD4+ T-cell functionality with heterogeneous patterns of CD4+ T-cell rejunivation.

Clinical blockade of PD1 and LAG3 — potential mechanisms of action

“…PD1 expression has been shown in chronic infection models to correspond to dysfunctional virusspecific CD4 + T cells 72 …”

Immune checkpoint blockade in infectious diseases

“…These exhausted antigen-specific CD8 + T cells are prone to apoptosis through co-expression of the pro-apoptotic protein BIM 86 . In contrast, HBV-specific CD4 + T cells, defined by MHC Class II tetramers and HBV core peptides, expressed increased levels of PD-1, but no increase in CTLA4, TIM3, KLRG1 and CD244 89 (summarised in Figure 3). …”

“…In contrast, only PD-1 blockade partially improved HBV-specific CD4 + T cell functions with production of IFN-γ, IL-2 and tumour necrosis factor-α (TNFα) 89 . Checkpoint blockade, used either alone or in combination may potentially enhance production of HBV-specific CD8 + T cells and even production of antibody to HBsAg, but there are significant theoretical risks including increased infiltration of reinvigorated T cells into the liver which could trigger inflammation, but this has not been demonstrated in pre-clinical studies or recent clinical trials.…”

Mechanism of Kupffer cells in hepatitis infected by hepatitis B and C virus

“…The level of PD-L1,PD-L2 and PD-1 are all higher in the chronic HBV / HCV infected patients in comparison with healthy individuals, and are considered to have relations to the severity of the infection. [28] And the continuous presentation of inhibitors such as PD-1 and TIM-3 might involve with the function and exhaustion of CD+8 T and CD+4 T. 29 Nevertheless, the up-regulation of inhibitory receptors,which are based on the macrophages of the liver and the inflammatory activities involved with macrophages caused directly by the infection of HBV/HCV or by the mechanism of negative feedback after ongoing inflammation, still remains uncertain.…”