Biological and clinical significance of classic and innovative virological parameters in the pathogenesis and in the clinical management of HBV infection

The integrated use of HBV serological markers plays a crucial role for a correct diagnosis and management of HBV infection. Among them, HBsAg quantification has been proposed to reflect the burden of intrahepatic reservoir of HBV infection and is so far used for a proper staging of chronic HBV infection. Nevertheless, HBV is characterised by a high degree of genetic variability, particularly in the gene coding for HBV surface antigen. Its impact on HBsAg quantification has not been clarified yet. In this light, chapter 2 highlights how specific mutations in the C-terminus domain of HBsAg can affect the HBsAg release from hepatocytes by altering the structure of this domain. This can potentially lead to a clinical misinterpretation of HBsAg levels, thus providing an altered information on the burden of intrahepatic HBV reservoir. Chapter 3 shows how some HBsAg mutations can promote the hyper-glycosylation of HBsAg. The new N-glycosylation sites can mask the epitopes target of neutralizing antibodies, hampering the HBsAg recognition by the immune system and by the diagnostic assays, thus leading false-negative HBsAg results. Lastly, in chapter 4 we focused on the issue of occult HBV infection whose diagnosis is still so far challenging. In particular, we reported a clinical case of a paediatric patient who contracted a seronegative occult HBV infection in the setting of liver transplantation despite anti-HBV vaccination. The use of new highly-sensitive methods based on droplet digital PCR and Next Generation Sequencing allows to demonstrate the presence of a transcriptionally active intrahepatic HBV reservoir and the selection of viral quasispecies characterised by an enrichment of immuneescape mutations. Overall findings highlight the pathobiological complexity of HBV infection and the importance to know the biological and clinical relevance of HBV biomarkers and factors affecting their 7 detection/quantification. This is crucial in order to achieve a personalised management of HBV infection.