Serological studies into the natural history of chronic hepatitis B

© 2011 Dr. Tin Quang Nguyen.Chronic hepatitis B (CHB) infection represents a global health problem, with an estimated 400 million people affected worldwide. The potential long term sequelae includes cirrhosis, hepatic decompensation and hepatocellular carcinoma. The paradigm for treatment of chronic hepatitis B virus (HBV) is evolving with the advent of newer medications, improved laboratory assay sensitivity and an increased understanding of the natural history of chronic infection. The natural history of CHB is typically regarded as consisting of four phases which are classified by specific biochemical, serological and virological characteristics, including serum ALT levels, HBeAg serostatus and HBV DNA titre. Whilst serum HBsAg is the serological hallmark of HBV infection, measurement of the serum HBsAg titre is currently not required for the distinction between the different phases of CHB, and is also not routinely assessed during antiviral therapy. The first aim of this thesis was to perform a detailed cross-sectional examination of the baseline HBsAg titres in the different phases of the natural history of CHB. The cohort of patients with CHB that were evaluated included adult patients attending a tertiary centre, pregnant women and a paediatric group. This study demonstrated that median baseline HBsAg titres differed between the four phases of CHB, with higher titres in HBeAg positive compared to HBeAg negative patients. Furthermore there was an apparent “disconnect” between HBsAg titres and HBV DNA in the different phases of CHB. It was hypothesized that these findings may be due to the expression of HBsAg from integrated viral envelope sequences instead of HBsAg production off mRNA derived from the HBV cccDNA template, or due to differences in the immune regulation of viral replication during different phases of infection. The second aim of this thesis was to evaluate the changes in serum HBsAg titres during long term therapy with oral nucleos(t)ide agents (NA). HBsAg clearance and seroconversion represent the ultimate endpoint in antiviral in CHB. Although clinical trials have suggested a benefit in monitoring baseline and on-treatment serum HBsAg titres during Peg-IFN therapy in predicting virological responses, there is little data on the effect of oral NA on HBsAg titres. In this thesis, different patterns of HBsAg decline during oral NA therapy were observed, although overall the on- treatment reduction in HBsAg titres were modest in comparison to that previously described in the literature with Peg-IFN therapy. This was attributed to the indirect affect of oral NAs on HBsAg synthesis via inhibition of the intracellular cccDNA conversion pathway, with a subsequent decline in pre-existing cccDNA molecules over time. Serum anti-HBs is usually only detectable on current commercial assays once HBsAg seroclearance has occurred, and is thought to be due anti-HBs complexing into immune aggregates with the excess envelope proteins. The third aim of this thesis was to test the serum and the B-cell component of peripheral blood mononuclear cells (PBMCs) for anti-HBs in patients who also test positive for serum HBsAg. A minority of patients had detectable anti-HBs by the commercial immunoassay. It was hypothesized that there would be a higher proportion of patients with detectable anti-HBs in the B-cell component of PBMCs. Unfortunately, anti-HBs was not detected in the lysate of B-cells using two commercial immunoassays, and an in-house enzyme linked immunosorbent assay (ELISA) could not be optimised for technical reasons. In conclusion, the measurement of baseline and on-treatment HBsAg titres has the potential to become the next focus of translational and clinical research in CHB. In the context of the natural history of CHB, monitoring of baseline HBsAg titres may facilitate an improved understanding of the interplay between HBV with the innate and adaptive immune response. Finally, monitoring of HBsAg titres may allow the development of new algorithms to individualise patient therapy, and also encourage further study of novel therapeutic strategies which more directly affect HBsAg levels