Protective CD8+ T cell responses and role of viral escape in HBV infection

病毒特异性CD 8 + T细胞在HBV控制中发挥核心作用。然而，在慢性HBV感染中，病毒特异性CD 8 + T细胞已被证明功能受损。尽管有这些被广泛接受的发现，HBV免疫生物学的核心问题尚未得到解决。具体而言，CD 8 + T细胞表位，可能是HBV感染的结果保护尚未确定和病毒逃逸的HBV持久性的作用仍然存在争议。事实上，只有少数HBV特异性CD 8 + T细胞表位，主要是由HLA-A2限制，已被确定。分析这些HLA-A2表位的研究表明，病毒逃逸在HBV特异性T细胞衰竭中不起主要作用。然而，针对人类病毒如HIV和HCV的保护性CD 8 + T细胞应答通常受到除了A2以外的HLA等位基因（例如B27、B57、A3）的限制，这些等位基因对病毒施加最强的选择压力。我们先前已经鉴定了第一个HLA-B27限制性HBV特异性CD 8 + T细胞表位，并获得了HLA-B27驱动病毒逃逸的证据。这些结果表明，HLA-B27可能在HBV感染中具有主导和保护作用，并且病毒逃逸确实是HBV特异性T细胞衰竭的中心机制，从而质疑了该领域目前的概念，即病毒逃逸在HBV感染中不起主要作用。我们的目标是鉴定额外的显性HBV特异性CD 8 + T细胞表位，其受可能的保护性HLA等位基因如HLA-B27、B57和A3限制。这些研究将在急性、消退或慢性HBV感染的大型患者队列中进行。这些结果将克服目前对HBV免疫发病机制的有限理解，即仅限于HLA-A2背景。通过分析新发现的CD 8 + T细胞显性表位对应的病毒序列，我们将阐明病毒逃逸在持续HBV感染中的作用。在一个大的患者队列中进行全基因组HBV序列分析将允许在已确定的表位之外鉴定HLA相关的序列多态性。由于功能限制（例如重叠的阅读框）被认为会强烈限制病毒逃逸，因此我们将分析已鉴定的病毒逃逸突变（例如针对HLA-B27鉴定的突变）对细胞培养模型中HBV复制的影响。建立表达HLA-B27的细胞培养系统将允许分析病毒逃逸对病毒特异性CD 8 + T细胞控制HBV的影响。最后，由于病毒逃逸在HIV和HBV感染中对CD 8 + T细胞的表型和功能有重要影响，我们将分析HBV特异性CD 8 + T细胞针对野生型或突变表位的表型和功能。总之，我们的结果将有助于更好地定义HBV特异性CD 8 + T细胞，阐明病毒逃逸在HBV持续存在中的作用，并可能改变目前公认的HBV免疫生物学概念。

Virus-specific CD8+ T cells play a central role in HBV control. In chronic HBV infection, however, virusspecific CD8+ T cells have been shown to be functionally impaired. Despite these well accepted findings, central questions in HBV immunobiology have not been addressed. Specifically, CD8+ T cell epitopes that might be protective in outcome of HBV infection have not been defined and the role of viral escape in HBV persistence remains controversial. Indeed, only few HBV-specific CD8+ T cell epitopes, mostly restricted by HLA-A2, have been identified. Studies analyzing these HLA-A2 epitopes have suggested that viral escape does not play a major role in HBV-specific T cell failure. However, protective CD8+ T cell responses against human viruses such as HIV and HCV are typically restricted by HLA alleles other than A2 (e.g. B27, B57, A3) that exert the strongest selective pressure on the virus. We have previously identified the first HLA-B27 restricted HBV-specific CD8+ T cell epitopes and obtained evidence for HLA-B27 driven viral escape. These results indicate that HLA-B27 may have a dominant and protective role in HBV infection and that viral escape is indeed a central mechanism of HBV-specific T cell failure, thus questioning the current concept in the field that viral escape does not play a major role in HBV infection.To extend these preliminary findings and to confirm them on a broader scale, we aim to identify additional dominant HBV-specific CD8+ T cell epitopes restricted by likely protective HLA alleles such as HLA-B27, B57, and A3. These studies will be performed in a large cohort of patients with acute, resolved, or chronic HBV infection. The results will overcome the currently limited understanding of HBV immunopathogenesis that is restricted to the HLA-A2 background. By analyzing viral sequences corresponding to newly identified dominant CD8+ T cell epitopes, we will clarify the role of viral escape in persistent HBV infection. A fullgenome HBV sequence analysis in a large patient cohort will allow the identification of HLA-associated sequence polymorphisms outside of identified epitopes. Since functional constraints, e.g. overlapping reading frames, are thought to strongly limit viral escape, we will analyze the impact of identified viral escape mutations (e.g. those identified for HLA-B27) on HBV replication in a cell culture model. Establishment of an HLA-B27 expressing cell culture system will allow the analysis of the effect of viral escape on HBV control by virus-specific CD8+ T cells. Finally, since viral escape has been described to have an important impact on CD8+ T cell phenotype and function in HIV and HBV infection, we will analyze the phenotype and function of HBV-specific CD8+ T cells targeting wild-type or mutated epitopes.In sum, our results will contribute to a better definition of protective HBV-specific CD8+ T cells, clarify the role of viral escape in HBV persistence, and may change currently accepted concepts of HBV immunobiology.