Antigen-specificity determines virus-specific CD8 T-cell exhaustion profile in chronic HBV infection

Background and Aim:

Chronic viral infection results in a phenomenon called T-cell exhaustion that is characterized by the progressive loss of virus-specific CD8 T-cell effector functions and the upregulation of inhibitory receptors (e.g. PD1). Studies in the LCMV mouse model as well as in human chronic HCV infection revealed that exhausted virus-specific CD8 T cells are heterogeneous and consist of terminally exhausted (PD1^hiCD127-) and less differentiated memory-like (PD1^intCD127) subsets. Notably, these subpopulations differ in their phenotypic and functional properties. In this study we aimed to define subsets of exhausted virus-specific CD8 T cells in chronic HBV infection focusing on different antigen-specificities.

Methods:

We analyzed CD8 T-cell populations in chronically HBV-infected patients (n = 61) specific for two well-described HLA-A*02-restricted HBV epitopes (core₁₈, pol₄₅₅) by performing tetramer-based magnetic bead enrichment followed by complex multicolour flow cytometry. Additionally, we performed peptide-specific in vitro expansion assays for 14 days to assess proliferative potential and cytokine production.

Results:

Our data revealed that exhausted epitope-specific CD8 T cells in chronic HBV infection were heterogeneous. Co-expression analyses of PD1 and CD127 showed that exhausted HBV-specific CD8 T cells could be subdivided into PD1 cells that either expressed or did not express CD127 as it has already been shown for HCV-specific CD8 T cells. Interestingly, core₁₈-specific CD8 T-cell populations were predominantly PD1 CD127 while a notable proportion of pol₄₅₅-specific CD8 T cells lacked CD127 expression. Furthermore, analysis of inhibitory receptors and homeostatic factors revealed distinct differentiation patterns with higher KLRG1 and lower TCF1 and BCL2 expression of pol₄₅₅- versus core₁₈-specific CD8 T cells. Importantly, functional analysis after peptide-specific in vitro expansion demonstrated a proliferative advantage of core₁₈-specific CD8 T cells and furthermore revealed increased functionality in terms of cytokine production and degranulation when compared to pol₄₅₅-specific CD8 T-cell populations.

Conclusion:

In sum, HBV-specific CD8 T-cell populations in chronically infected patients are heterogeneous and show distinct phenotypic exhaustion profiles and functional capacities depending on their antigen-specificity. This might play an important role in the design of immunotherapeutic approaches targeting CD8 T cells to cure chronic hepatitis B.