The CD8+ T cell exhaustion mechanisms in chronic hepatitis B infection and immunotherapeutic strategies: a systematic review

The hepatitis B virus (HBV) continues to be a leading cause of morbidity and mortality worldwide. In developing countries, HBV is the most common etiology of those liver diseases such as chronic hepatitis B (CHB), acute hepatitis B (AHB), acute-on-chronic liver failure (ACLF), liver cirrhosis (LC), and hepatocellular carcinoma (HCC). CD8+ T cell exhaustion is a condition of T cell malfunction and reduction that plays a crucial role in the progression of HBV infection.This systematic review attempts to evaluate the main inhibitory mechanisms involved in CD8+ T cell exhaustion, in different clinical phases of HBV infection and relation to disease progression. A systematic search in PubMed, Web of Science, and Scopus was performed to identify articles published in English till October 2022.According to the numerous conducted studies, we conclude that CD8+ T cell exhaustion commonly occurs in the tumoral and chronic suppressive environment and CHB and HCC patients; furthermore, this phenomenon is less seen in AHB and ACLF patients. The emergence of surficial inhibitory receptors (IRs) on CD8+ T cells is the leading cause of exhaustion, and programmed cell death protein-1 (PD-1) has much importance among the others.