Enhancing HBV-specific T cell responses through a combination of epigenetic modulation and immune checkpoint inhibition

Objective: Chronic hepatitis B virus (HBV) infection results in the exhaustion of HBV-specific T cells and the development of epigenetic imprints that impair immune responses and limit the effectiveness of immune checkpoint inhibitor (ICI) monotherapy, such as αPD-L1. This study aimed to determine whether the DNA methyltransferase inhibitor decitabine (DAC) can reverse these epigenetic imprints and enhance the efficacy of ICI in restoring HBV-specific T cell responses. Methods: We investigated HBV-specific CD4⁺ and CD8⁺ T cell responses by 10-day in vitro stimulation of peripheral blood mononuclear cells (PBMCs) from patients with chronic HBV infection. PBMCs were stimulated with HBV core-specific overlapping peptide pools and HLA-A*02-restricted peptides, including core₁₈ and pol₄₅₅. The immunomodulatory effect of the combination of DAC/αPD-L1 was assessed via flow cytometry. Responder stratification was investigated by comparison of clinical characteristics, ex vivo DNA methylation analysis of PBMCs, and determination of IFNγ plasma levels. Results: Treatment with DAC and αPD-L1 enhanced HBV-specific CD4⁺ T cell responses in a significant proportion of 53 patients, albeit with variability. The effect was independent of the HBcrAg level. Ex vivo DNA methylation revealed hypermethylation of key genes like IFNG among DAC-responders versus non-responders, supported by altered ex vivo IFNγ plasma levels. Further analysis of HBV-specific CD8⁺ T cell responses in 22 HLA-A*02-positive patients indicated distinct response patterns between HBV-core₁₈- and HBV-pol₄₅₅-specific T cells, with pol₄₅₅-specific CD8⁺ T cells showing increased susceptibility to DAC/αPD-L1, surpassing αPD-L1 monotherapy response. Conclusions: The combination of DAC and αPD-L1 shows promising effects in improving HBV-specific T cell responses in vitro. Our study highlights the potential of remodeling exhaustion-associated epigenetic signatures to enhance HBV-specific T cell restoration, suggesting a novel immunotherapeutic avenue for chronic HBV infections.