Impact of HBsAg on HBV-specific immune responses in HBeAg negative patients with chronic hepatitis B

Introduction:

Worldwide 250 million people are persistently infected with hepatitis B virus (HBV) leading to 686.000 deaths annually. The level of hepatitis surface antigen (HBsAg) produced by HBV-infected hepatocytes could have an immunomodulatory role in HBV infected patients. However, the correlation between HBsAg level and HBV-specific T cell immune responses in patients with chronic HBV (CHB) and HBeAg negative has not been well defined.

Aim:

We investigated HBV-specific immune responses in HBeAg negative patients with different levels of HBsAg during the natural course of chronic hepatitis B.

Methods:

44 HBeAg negative patients were categorized into 4 groups based on their HBsAg level (HBsAg < 100 IU/ml, HBsAg 100 – 999 IU/ml, HBsAg 1.000 – 9.999 IU/ml, HBsAg ≥10.000 IU/ml). PBMCs were isolated from these patients and different subsets of immune cells were phenotypically characterized using 14 color flow cytometry. Furthermore, IFNγ+ HBV-specific T cell responses were measured after in vitro culture with overlapping peptides covering polymerase, surface and core of HBV genotype D in the presence or absence of anti-PD-L1 antibody.

Results:

Patients with different levels of HBsAg showed similar frequencies of memory, naïve and effector T cells, γδ T cells, Treg cells, MAIT cells, B cells, NK cells, monocytes and DCs. Interestingly, the frequency of γδ T cells, Treg cells and CD1c- myeloid DCs was significantly increased in CHB patients compared to healthy individuals.

Stimulation of PBMCs with HBV overlapping peptides induced core- and polymerase-specific T cell responses. However, surface-specific T cell responses were hardly detectable. We observed a trend towards higher HBV-specific T cells in patients with HBsAg < 100 IU/ml. In patients with HBsAg ≥10.000 IU/ml a high variability of T cell responses were detected. Interestingly, in these patients stronger T cell responses were associated with young age, female gender and low HBV DNA. In general, CD4+ T cell response to in vitro stimulation with HBV overlapping peptides was stronger than CD8+ T cell responses. Blocking the PD-1/PD-L1 pathway during in vitro culture significantly increased the core-specific T cell response in patients with HBsAg < 100 IU/ml.

Conclusion:

Our data suggests that HBsAg level per se may have only a minor impact on the cellular immune responses. Patients with HBsAg < 100 IU/ml, showed slightly stronger T cell responses to in vitro HBV peptide stimulation especially after using checkpoint inhibitors. Therefore, patients with low HBsAg levels may demonstrate better responses to immune-modulatory treatment.