Exhausted phenotype of circulating CD8⁺ T cell subsets in hepatitis B virus carriers

Chronic hepatitis B virus (HBV) infection is characterized by the presence of dysfunctional exhausted CD8⁺ T cells that hamper viral control. We investigated the phenotypic heterogeneity of exhausted CD8⁺ T cells in HBV carriers.

We enrolled 31 HBV carriers and 23 healthy controls (HCs) in our study. Peripheral blood mononuclear cells (PBMCs) were isolated, and flow cytometry was used to determine the phenotypic distribution of CD8⁺ T cell subsets. Expression of cytokines such as TNF-α and IFN-γ was detected by quantitative reverse transcription-PCR, a fluorescence flow cytometry-based immunomicrobead assay and flow cytometry.

There were no significant differences in the baseline characteristics between the 31 HBV carriers and the 23 sex- and age-matched HCs. CD8⁺ T cells exhibited higher levels of inhibitory receptors (TIM3 and PD1) in the HBV carriers than in the HCs (P < 0.05); in particular, Tfc cells (CXCR5⁺CD25^-) expressed higher levels of TIM3 and PD1 than non-Tfc cells in the HBV carriers. In addition, among the subsets of Tc cells, the Tc17 (CXCR5^-CD25^-CCR6⁺) subset displayed increased expression of TIM3 and LAG3 in the HBV carriers. Our findings further showed that CD8⁺ T cells produced lower levels of IFN-γ, TNF-α, and Granzyme B. Paired analysis of the Tfc subset and the Tc subset indicated that higher levels of cytokines (IFN-γ and TNF-α) were produced by the Tfc subset in the HBV carriers. Among the Tc subsets, the Tc17 subset produced lower levels of cytokines.

The Tfc subset exhibited an enhanced exhausted phenotype but possessed some functional properties during chronic HBV infection, while the Tc subset showed a lower functional level. The identification of these unique subsets may provide a potential immunotherapeutic target in chronic HBV infection.