Hepatitis B virus covalently closed circular DNA homeostasis is independent of the lymphotoxin pathway during chronic HBV infection

Current treatment options for patients with chronic hepatitis B virus (HBV) infection are not curative as they are not effective in eliminating covalently closed circular DNA (cccDNA). cccDNA is a stable template for HBV transcription in the nucleus of hepatocytes and is thought to be one of the main factors responsible for HBV persistence. Recently, activation of the lymphotoxin beta receptor (LT beta R) has been shown to trigger degradation of cccDNA through induction of cytidine deaminases of the APOBEC3 family in HBV cell culture model systems. To assess the presence and relevance of such mechanisms in the liver of chronically HBV-infected patients, we compared intrahepatic cccDNA levels with the expression levels of lymphotoxins and some of their target genes (eg APOBEC deaminases) in liver biopsy tissue. Our results confirm elevated gene expression levels of components of the lymphotoxin pathway including lymphotoxin alpha (LT alpha), lymphotoxin beta (LT beta), APOBEC3B (A3B) and APOBEC3G (A3G) in the chronically HBV-infected liver compared to uninfected liver. Furthermore, expression levels of the genes of the APOBEC deaminase family were correlated with those of LTa and LT beta gene expression, consistent with lymphotoxin-mediated up-regulation of APOBEC gene expression. However, intrahepatic cccDNA and HBV replication levels were not correlated with LT alpha, LT beta and APOBEC gene expression. In conclusion, these results suggest that although the lymphotoxin pathway is activated in the chronically HBV-infected liver, it has no major impact on HBV cccDNA metabolism in chronic HBV infection.