慢性丙型肝炎患者中丙型肝炎病毒准种变异研究进展

丙型肝炎病毒（HCV）具有较高的变异性,通常以准种的形式分布在感染者的体内,病毒容易逃离机体的免疫监控,因而无法被有效地清除,导致机体很难控制其感染的发展,故易转变成慢性肝炎。HCV准种变异在宿主体内的持续存在对病毒感染的控制、抗病毒药物和疫苗的发展都是一个巨大的挑战。,我们重点阐述近年来关于HCV准种变异及其与慢性丙型肝炎患者的机体免疫、疾病进展、治疗效果之间关系的研究进展。     

丙型肝炎病毒准种在NS2区的变异状况初探

探讨HCV准种在NS2区的基因结构特征及变异状况。利用逆转录－巢式PCR从1份HCV慢性携带者的阳性血清及1份丙肝患者的血清中获得HCV NS2全长cDNA,将其克隆于T载体,各随机挑取5个阳性克隆进行序列测定,结果显示克隆到HCV NS2全长基因,所测克隆在核苷酸水平和氨基酸水平互不相同。该慢性携带者HCV NS2区序列以完整读码框架（ORF）为主,一个于HCV多聚蛋白第835位氨基酸的位置出现终止信号,而该丙型肝炎患者以NS2N端发现终止信号的序列为主,其中三个于第835位氨基酸的位置出现终止信号,一个于第887位氨基酸的位置出现终止信号,仅一个克隆的序列为完整ORF。对ORF完整的序列进行比较,发现丙型肝炎患者氨基酸变异主要集中于N端,蛋白二级结构模拟显示丙肝患者NS2与慢性携带者的优势二级结构类似,研究表明从我们选择的两种感染者的HCV NS2序列看,不同临床类型的HCV病人体内的HCV准种在NS2区存在差异,这种差异可能与病毒存在于机体的状态一定的一致性。     

丙型肝炎病毒准种在NS2区的变异状况初探

探讨HCV准种在NS2区的基因结构特征及变异状况.利用逆转录-巢式PCR从1份HCV慢性携带者的阳性血清及1份丙肝患者的血清中获得HCVNS2全长cDNA,将其克隆于T载体,各随机挑取5个阳性克隆进行序列测定.结果显示克隆到HCVNS2全长基因,所测克隆在核苷酸水平和氨基酸水平互不相同.该慢性携带者HCVNS2区序列以完整读码框架(ORF)为主,一个于HCV多聚蛋白第835位氨基酸的位置出现终止信号,而该丙型肝炎患者以NS2N端发现终止信号的序列为主,其中三个于第835位氨基酸的位置出现终止信号,一个于第887位氨基酸的位置出现终止信号,仅一个克隆的序列为完整ORF.对ORF完整的序列进行比较,发现丙型肝炎患者氨基酸变异主要集中于N端,蛋白二级结构模拟显示丙肝患者NS2与慢性携带者的优势二级结构类似.研究表明从我们选择的两例感染者的HCVNS2序列看,不同临床类型的HCV病人体内的HCV准种在NS2区存在差异,这种差异可能与病毒存在于机体的状态有一定的一致性.     

丙型肝炎病毒准种血清学检测技术的建立

目的:建立一种以血清学为基础的丙型肝炎病毒(HCV)准种检测技术。方法:自20份HCV血清中各挑选30个克隆进行测序比较,分析HCV准种的复杂程度;以HCV准种代表性抗原组合制备免疫芯片,用血清学检测技术分析上述20份HCV血清中的准种变异程度;比较两种方法之间的检出灵敏度和相关性。结果:测序法检出灵敏度为70.0%,血清学检测法检出灵敏度为95.0%,后者显著高于前者(P0.05);两种方法检测结果的相关性为74.7%(P0.01)。结论:血清学检测技术操作简单,且能够反映丙型肝炎患者的HCV准种变异程度,适于临床推广。     

乙型肝炎病毒逆转录酶区基因序列准种与变异特点

乙型肝炎病毒(Hepatitis B Virus,HBV)P基因编码产物从功能上分为末端蛋白(1～178aa)、间隔区(179～336aa)、逆转录酶区(337～682aa)和RNA酶H区(683～816aa),各区有相应的生物学功能;逆转录酶区包含S基因主蛋白编码区.近年来的研究提出HBV感染者体内存在有准种[1,2]的假说.我们以逆转录酶区序列为研究靶区域,应用聚合酶链反应(PCR)技术扩增慢性乙型肝炎患者血清中的靶基因序列,随机选择克隆测序,比较其结果,证明了HBV准种特点的存在,并发现多种基因突变形式.     

免疫活性细胞回输造成丙型肝炎病毒准种构成一过性改变

观察持续性感染者外周血HCV准种构成及其在增强的免疫压力下的变化规律。应用基因扩增、分子克隆和测序的方法,对4例接受自体免疫活性细胞回输的丙型肝炎患者系列血清中的HCVC区基因片段,进行了序列分析及遗传进化关系比较。HCV病毒池中均以遗传密切相关的优势准种群为主,当机体免疫状态发生变化时,4例中有3名患者血清HCV准种构成发生了一过性改变,优势准群被弱势准群替代。随后其中两例的准种构成又回复到细胞回输前的状态,另一例则形成了新的优势毒株群,第四例患者在全部随访期内准种构成没有明显规律性变化。持续性感染的HCV准种构成是处于与机体免疫压力平衡的较稳定状态,且多以一个遗传密切相关的准种群为优势群体,在受到增强的免疫压力时,这种构成的平衡被打破,HCV的准种构成变化有不同的表现形式,主导毒株的规律性变化是主要的形式之一;但随时间推移,初始状态的准种构成还可回复。     

免疫活性细胞回输造成丙型肝炎病毒准种构成-过性改变

观察持续性感染者外周血HCV准种构成及其在增强的免疫压力下的变化规律。应用基因扩增、分子克隆和测序的方法,对4例接受自体免疫活性细胞回输的丙型肝炎患者系列血清中的HCV V区基因片段,进行了序列分析及遗传进化关系比较。HCV病毒池中均以遗传密切相关的优势准种群为主,当机体免疫状态发生变化时,4例中有3名患者血清HCV准种构成发生了一过性改变。优势准群被弱势准群替代。随后其中两例的准种构成又回复到细胞回输前的状态,另一例则形成了新的优势毒株群。第四例患者在全部随访期内准种构成没有明显规律性变化。持续性感染的HCV准种构成是处于与机体免疫压力平衡的较稳定状态,且多以一个遗传密切相关的准种群为优势群体,在受到增强的免疫压力时,这种构成的平衡被打破,HCV的准种构成变化有不同的表现形式,主导毒株的规律性变化是主要的形式之一;但随时间推移,初始状态的准种构成还可回复。     

丙型肝炎病毒基因组多样性的分子基础及临床意义

丙型肝炎病毒(HCV)是一种有包膜的单股正链RNA病毒,其编码的前体多聚大蛋白可加工成具有不同功能的结构蛋白和非结构蛋白。研究结果表明,HCV核酸序列的变异很大,因此存在许多不同的基因型和亚型。了解HCV基因组多样性的分子基础,对HCV的病原学、流行病学、诊断和治疗都具有重要的指导意义。     

猪戊肝病毒存在准种现象

为研究猪戊肝病毒准种存在情况,采用逆转录-巢式聚合酶链反应法(RT-nested-PCR)对四株猪戊肝病毒(Hepatitis E virus)第2可读框(ORF2)部分序列进行PCR扩增,将产物克隆后,每个毒株分别随机挑取20个阳性克隆测序,进行DNA序列分析。结果显示4株HEV不同克隆间的ORF2核苷酸序列同源性分别为96.8%~99.7%、98.8%~99.7%、98.8%~99.7%和100%,有变异的克隆核苷酸序列与上海株(SAAS-JDY5)同源性为96.8%~100%。由此证实感染戊肝病毒的猪个体内存在HEV准种。     

用RFLP和PCR—RFLP技术研究东北虎和华南虎线粒体DNA多态性

采用ｍｔＤＮＡＲＦＬＰ和ＰＣＲＲＦＬＰ技术研究了东北虎和华南虎的ｍｔＤＮＡ的多态性。在ｍｔＤＮＡＲＦＬＰ研究中,分离纯化了东北虎和华南虎肝、肾和心脏组织的ｍｔＤＮＡ,用２０种识别６碱基对的限制性内切酶消化,结果只有１种限制性内切酶（ＸｂａⅠ）检测到多态性片段,其余１９种限制性内切酶消化产生的限制性格局在东北虎和华南虎完全一致。在ＰＣＲＲＦＬＰ研究中,用ＰＣＲ技术分别扩增了东北虎和华南虎ｍｔＤＮＡ的控制区（ｃｏｎｔｒｏｌｒｅｇｉｏｎ）,用８种识别４碱基对的限制性内切酶分别对扩增产物进行消化,结果只有１种限制性内切酶（ＲｓａⅠ）检测到多态性片段。ｍｔＤＮＡＲＦＬＰ及ＰＣＲＲＦＬＰ的结果均提示东北虎和华南虎之间的遗传距离极小。这可能与下列因素有关：两者分布区间无天然隔离屏障;具有强扩散能力;近几百年才被相互隔离。     

Influence of increased CD4 cell counts on the genetic variability of hepatitis C virus in patients co-infected with human immunodeficiency virus I.

In order to study the effect of increased CD4 cell counts on the biology of hepatitis C virus (HCV), we analyzed the genetic variability of HCV generated over 8 y in eight human immunodeficiency virus-1 (HIV-1) and HCV co-infected patients. This was a retrospective study in which HIV patients were selected who had profound immune impairment evident over four years and were co-infected with HCV genotype 1 and who then went on highly active antiretroviral therapy (HAART). These patients achieved different degrees of immune reconstitution, measured as increased CD4 cell counts during a 4- to 8-y period, following initiation of HAART. HCV genetic variability was determined by measuring the genetic diversity (Hamming distance, HD), and complexity (number of viral variants) in plasma samples collected at yearly intervals just before and after the initiation of HAART. The parameters were assessed by molecular cloning and sequencing of a 575-bp fragment including the HCV envelope 1 and envelope 2 genes (E1/E2), containing the hypervariable region 1 (HVR1). significantly increased HVR1 genetic diversity was observed in analyzed samples where the patients' CD4 cell counts were > or =100 compared with CD4 cell counts <100. A significant increase in genetic diversity in HVR1 was detected in co-infected patients whose CD4 cell counts increased from <100 to >400 over a period of more than 4 y of HAART therapy. This was in contrast to a minimal increase in HCV genetic diversity of HVR1 occurring in patients whose CD4 cell counts failed to rise much over 200 over 7 y of follow up. Insertion and deletion of HCV genomic fragments in the E1/E2 region was documented in one patient who developed fulminant hepatitis C.     

Human immunodeficiency virus seroconversion and evolution of the hepatitis C virus quasispecies

When chronic hepatitis C virus (HCV) infections are complicated by acquisition of human immunodeficiency virus (HIV), liver disease appears to accelerate and serum levels of HCV RNA may rise. We hypothesized that HIV might affect the HCV quasispecies by decreasing both complexity (if HIV-induced immunosuppression lessens pressure for selecting HCV substitutions) and the ratio of nonsynonymous (d(N)) to synonymous (d(S)) substitutions, because d(N) may be lower (if there is less selective pressure). To test this hypothesis, we studied the evolution of HCV sequences in 10 persons with chronic HCV infection who seroconverted to HIV and, over the next 3 years, had slow or rapid progression of HIV-associated disease. From each subject, four serum specimens were selected with reference to HIV seroconversion: (i) more than 2 years prior, (ii) less than 2 years prior, (iii) less than 2 years after, and (iv) more than 2 years after. The HCV quasispecies in these specimens was characterized by generating clones containing 1 kb of cDNA that spanned the E1 gene and the E2 hypervariable region 1 (HVR1), followed by analysis of clonal frequencies (via electrophoretic migration) and nucleotide sequences. We examined 1,320 cDNA clones (33 per time point) and 287 sequences (median of 7 per time point). We observed a trend toward lower d(N)/d(S) after HIV seroconversion in 7 of 10 subjects and lower d(N)/d(S) in those with rapid HIV disease progression. However, the magnitude of these differences was small. These results are consistent with the hypothesis that HIV infection alters the HCV quasispecies, but the number of subjects and observation time may be too low to characterize the full effect.     

Structural basis for broad neutralization of hepatitis C virus quasispecies

Monoclonal antibodies directed against hepatitis C virus (HCV) E2 protein can neutralize cell-cultured HCV and pseudoparticles expressing envelopes derived from multiple HCV subtypes. For example, based on antibody blocking experiments and alanine scanning mutagenesis, it was proposed that the AR3B monoclonal antibody recognized a discontinuous conformational epitope comprised of amino acid residues 396–424, 436–447, and 523–540 of HCV E2 envelope protein. Intriguingly, one of these segments (436–447) overlapped with hypervariable region 3 (HVR3), a domain that exhibited significant intrahost and interhost genetic diversity. To reconcile these observations, amino-acid sequence variability was examined and homology-based structural modelling of E2 based on tick-borne encephalitis virus (TBEV) E protein was performed based on 413 HCV sequences derived from 18 subjects with chronic hepatitis C. Here we report that despite a high degree of amino-acid sequence variability, the three-dimensional structure of E2 is remarkably conserved, suggesting broad recognition of structural determinants rather than specific residues. Regions 396–424 and 523–540 were largely exposed and in close spatial proximity at the surface of E2. In contrast, region 436–447, which overlaps with HVR3, was >35 Å away, and estimates of buried surface were inconsistent with HVR3 being part of the AR3B binding interface. High-throughput structural analysis of HCV quasispecies could facilitate the development of novel vaccines that target conserved structural features of HCV envelope and elicit neutralizing antibody responses that are less vulnerable to viral escape.     

Broadly neutralizing antibodies protect against hepatitis C virus quasispecies challenge

A major problem in hepatitis C virus (HCV) immunotherapy or vaccine design is the extreme variability of the virus. We identified human monoclonal antibodies (mAbs) that neutralize genetically diverse HCV isolates and protect against heterologous HCV quasispecies challenge in a human liver-chimeric mouse model. The results provide evidence that broadly neutralizing antibodies to HCV protect against heterologous viral infection and suggest that a prophylactic vaccine against HCV may be achievable.     

The remarkable history of the hepatitis C virus

The infection with the hepatitis C virus (HCV) is an example of the translational research success. The reciprocal interactions between clinicians and scientists have allowed in 30 years the initiation of empirical treatments by interferon, the discovery of the virus, the development of serological and virological tools for diagnosis but also for prognosis (the non-invasive biochemical or morphological fibrosis tests, the predictors of the specific immune response including genetic IL28B polymorphisms). Finally, well-tolerated and effective treatments with oral antivirals inhibiting HCV non-structural viral proteins involved in viral replication have been marketed this last decade, allowing the cure of all infected subjects. HCV chronic infection, which is a public health issue, is a hepatic disease which may lead to a cirrhosis and an hepatocellular carcinoma (HCC) but also a systemic disease with extra-hepatic manifestations either associated with a cryoglobulinemic vasculitis or chronic inflammation. The HCV infection is the only chronic viral infection which may be cured: the so-called sustained virologic response, defined by undetectable HCV RNA 12 weeks after the end of the treatment, significantly reduces the risk of morbidity and mortality associated with hepatic and extra-hepatic manifestations which are mainly reversible.The history of HCV ends with the pangenotypic efficacy of the multiple combinations, easy to use for 8–12 weeks with one to three pills per day and little problems of tolerance. This explains the short 30 years from the virus discovery to the viral hepatitis elimination policy proposed by the World Health Organization (WHO) in 2016.     

Functional hepatitis C virus envelope glycoproteins

Hepatitis C virus (HCV) encodes two envelope glycoproteins, E1 and E2, that are released from HCV polyprotein by signal peptidase cleavage. These proteins assemble as a noncovalent heterodimer that is retained in the endoplasmic reticulum. The transmembrane domains of E1 and E2 are multifunctional and play a major role in the biogenesis of E1E2 heterodimer. Because HCV does not replicate efficiently in cell culture, surrogate models have been developed to study some steps of its life cycle. Recently, infectious pseudotype particles (HCVpp) harboring unmodified E1E2 glycoproteins onto retroviral core particles have successfully been generated. They mimic the function of native HCV particles, thus representing a model to study the early steps of its lifecycle. The noncovalent E1E2 heterodimers present at the surface of the HCVpp, which contain complex-type glycans indicating modification by Golgi enzymes, are likely to mediate virus entry. The CD81 tetraspanin and the scavenger receptor SR-BI, two cellular molecules shown to interact with E2, are essential for HCVpp entry. However, these two proteins are not sufficient to provide entry functions in non permissive cells, suggesting that additional unidentified cellular factor(s) are necessary for HCVpp entry. Potential structural homology with other fusion proteins from closely related viruses suggest that HCV envelope glycoproteins belong to class II fusion proteins, but contrary to what is observed for other viral envelope proteins of this class, they are highly glycosylated and are not matured by a cellular endoprotease cleavage.