Occult Hepatitis B Infection in South African HIV Patients

描述（由申请人提供）：全球有3.5亿人慢性感染B型肝炎病毒（HBV）-世界上导致肝硬化和肝细胞癌（HCC）的主要原因。慢性HBV感染的特征在于血清中存在肝炎B表面抗原（HBsAg）。相反，隐匿性HBV感染（O-HBV）被定义为在缺乏可检测的循环HBsAg的情况下的低水平HBV复制。O-HBV的传播性和随后的慢性HBV感染的建立在人类和灵长类动物中有充分的记录。此外，O-HBV与晚期肝纤维化、对干扰素治疗的反应降低、HCC的发展和肝酶水平升高相关。 在HIV阳性队列中，O-HBV感染的患病率显著升高。在南非，HIV和HBV都是地方病，HIV合并感染是O-HBV感染的主要危险因素。此外，HBV聚合酶（P）基因中的治疗抗性突变-与表面（S）基因重叠-在南非很常见-即使在未经治疗的个体中-也可能影响HBsAg表达。只有少数研究评价了这种缺乏体外HBsAg检测的潜在机制。表征O-HBV感染的主要局限性包括1）缺乏HBV DNA的灵敏定量测定，和2）在全长、可复制基因组的背景下识别和表征与O-HBV相关的突变的能力有限。幸运的是，用于HBV DNA定量的高灵敏度，成本效益高的实时PCR检测-如我们实验室开发的-现在可用。此外，已经开发了一种用于有效扩增整个HBV基因组的新方法，该方法还允许快速功能分析。 本申请的目的是使用全长复制型HBV表达载体确定与O-HBV感染相关的S和P基因突变对肝细胞中HBsAg合成/保留/分泌和HBV复制的影响。在体内鉴定和表征使用当前HBV筛查测定法未检测到的O-HBV突变，以及开发体外测定法以评价缺乏HBsAg检测的潜在机制，将提高未来O-HBV感染的诊断灵敏度，限制HBV的二次传播，提供关于O-HBV治疗选择的关键信息，并提高我们对HBV复制如何促进HCC发展的理解。 公共卫生相关性：慢性肝病是HIV阳性个体发病和死亡的主要原因。在南非，HBV和HIV都是地方病，HIV是隐匿性HBV的重要危险因素-定义为在血清HBV表面抗原检测缺失的情况下可检测到HBV DNA。拟议的研究将检查流行病学特征和病毒学机制，这种缺乏表面抗原检测在这种地方性环境中，并提供一个框架，为未来的体内和体外研究隐匿性HBV感染，最终可能导致提高诊断敏感性HBV感染和限制继发感染。

DESCRIPTION (provided by applicant): Globally, 350 million people are chronically infected with hepatitis B virus (HBV) - the world's leading cause of cirrhosis and hepatocellular carcinoma (HCC). Chronic HBV infection is characterized by the presence of hepatitis B surface antigen (HBsAg) in the serum. In contrast, occult HBV infection (O-HBV) is defined as low level HBV replication in the absence of detectable circulating HBsAg. The transmissibility of O-HBV and the subsequent establishment of chronic HBV infection are well documented in humans and in primates. Moreover, O-HBV is associated with advanced liver fibrosis, reduced response to interferon therapy, the development of HCC, and increased liver enzyme levels. In HIV-positive cohorts, the prevalence of O-HBV infection is significantly elevated. In South Africa, both HIV and HBV are endemic, and HIV co-infection is a major risk factor for O-HBV infection. Moreover, treatment resistance mutations in the HBV Polymerase (P) gene - which overlaps with the Surface (S) gene - are common in South Africa - even among treatment-naove individuals - and may also impact HBsAg expression. Only a small number of studies evaluated the potential mechanism(s) for this lack of HBsAg detection in vitro. Major limitations to characterizing O-HBV infection include 1) the lack of sensitive quantitative assays for HBV DNA, and 2) the limited ability to identify and characterize mutations that are associated with O-HBV in the context of full-length, replication-competent genomes. Fortunately, highly sensitive, cost effective real-time PCR assays for HBV DNA quantification - such as that developed within our lab - are now available. Moreover, a novel method for efficient amplification of whole HBV genomes that also permits rapid functional analysis has been developed. The aims of this application are to determine the effects of S and P gene mutations associated with O-HBV infection on HBsAg synthesis/retention/secretion and HBV replication in hepatocytes using full-length, replication-competent HBV expression vectors. The identification and characterization of O-HBV mutations in vivo that are not detected using current HBV screening assays and the development of in vitro assays to evaluate the mechanism(s) underlying the lack of HBsAg detection would improve future diagnostic sensitivity for O-HBV infection, limit secondary transmission of HBV, provide critical information on treatment options for O-HBV, and improve our understanding of how HBV replication contributes to the development of HCC. PUBLIC HEALTH RELEVANCE: Chronic liver disease is a major cause of morbidity and mortality in HIV-positive individuals. In South Africa, where both HBV and HIV are endemic, HIV is a significant risk factor for occult HBV - defined as detectable HBV DNA in the absence of serum HBV surface antigen detection. The proposed studies will examine the epidemiologic characteristics and virologic mechanisms for this lack of surface antigen detection in this endemic setting and provide a framework for future in vivo and in vitro studies of occult HBV infection that could ultimately lead to improved diagnostic sensitivity for HBV infection and limit secondary infections.