CHB: Chronic hepatitis B, NA: Nucleotide analog, HBsAg: Hepatitis B surface antigen, HCC: Hepatocellular carcinoma, IL-21: Interleukin 21, TDF: Tenofovir disoproxil fumarate, PEG-IFN: Pegylated interferon , FASGL: Fas ligand, CCL4: Chemokine ligands 4. Here, IL21 is linked to chronic hepatitis B virus infection.