Browsing by Author "Burak, Kelly Warren"

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    Persistent Hepatitis B Virus in Hepatic and Extrahepatic Reservoirs in Hepatitis B Virus Related Oncogenesis
    (2020-05-04) Lau, Keith Chi Kei; Coffin, Carla S.; Burak, Kelly Warren; Mahoney, Douglas J.; van Marle, Guido
    Chronic infection by Hepatitis B virus (HBV) may result in hepatocellular carcinoma (HCC). Numerous viral factors are associated with oncogenesis and development of HCC, including integration, genetic variations in the X/basal core promoter/precore (X/BCP/PC) region, and occult infection. Although primarily hepatotropic, HBV is frequently found in circulating peripheral blood mononuclear cells (PBMCs) of the lymphoid system. Few studies have characterized this extrahepatic reservoir particularly in HBV-related HCC individuals. In this thesis, we hypothesized that pro-oncogenic HBV is present in both liver and extrahepatic reservoirs in chronic HBV (CHB) carriers with and without malignant disease. A highly sensitive molecular tool for accurate detection of low-level HBV and determination of genotype is described in this thesis. Subsequently, this technique was applied to plasma and PBMCs from post-liver transplant CHB carriers in combination with next generation sequencing to identify HCC-associated viral genotypes and genetic variants. The lymphoid reservoir in 32 CHB carriers with HCC and a representative patient with an extrahepatic lymphoid malignancy (i.e., dendritic cell sarcoma [DCS]), was evaluated for pro-oncogenic HBV. Interestingly, integrated virus was identified in genes implicated in cancer development in liver, PBMCs and DCS tumor. HCC-associated X/BCP/PC variants and genotypes were also present within lymphoid cells. Functional characterization of the most commonly detected variants (Guanine-1896-Adenine and Adenine-1762-Thymine/Guanine-1764-Adenine) were evaluated in vitro. Compared to wild-type, these mutants showed reduced viral HBeAg, modulated cytokine/chemokine expression, decreased APOBEC3G protein expression. The A1762T/G1764A mutant had more robust HBV replication than the G1896A variant. Overall, the findings in this thesis contributes to the literature on the epidemiological association of occult HBV, specific HBV SNPs, and integrated virus in hepatic and extrahepatic reservoirs. Persistent carcinogenic HBV poses continual risks of HCC recurrence and viral reactivation thus advocating for long-term HBV prophylaxis use post-transplant. Pro-oncogenic HBV within lymphoid cells may contribute towards oncogenesis of extrahepatic malignancies such as DCS. HCC-associated variants show functional differences in viral replicative fitness and host immune responses. Taken together, this thesis is significant for advancing the currently limited understanding of HBV molecular virology and pathogenesis of HBV-related carcinogenesis within the hepatic and extrahepatic reservoirs.