HCV-Specific Cellular Immunity in Acute Hepatitis C

我们最近证明，黑猩猩急性丙型肝炎的成功解决引发了保护性记忆T细胞反应。再次感染前即刻用亚群特异性抗体耗尽记忆性CD8+ T细胞导致长期病毒血症。如果CD4+ T细胞耗尽，则感染从未消退。事实上，在没有辅助活性的情况下，记忆CD8+ T细胞被选择用于逃避病毒的MHC I类限制性表位中的突变。这些结果表明两种T细胞亚群在控制HCV复制中起着重要作用，但它们通常失败的原因尚不清楚。T细胞应答似乎集中在有限的一组MHC I类和II类表位上，在感染消退时，随后扩大到包括亚显性表位。因此，虽然反应似乎是多特异性的，但当病毒复制（以及RNA聚合酶的错误）处于峰值时，它有效地靶向有限的一组显性表位。具体目标1是确定这是否导致显性MHC II类表位的突变逃逸。 突变逃逸将与CD4+ T细胞沉默的其他潜在机制进行比较，包括抗原活化后无法扩增、获得功能或遵循正常分化程序。适用于黑猩猩的MHC II类四聚体技术将有助于分析。具体目标2是确定急性丙型肝炎期间CD8+ T细胞的缺陷，并确定它们是否与CD4+ T细胞损失同时发生。最后，具体目标3将通过用病毒变体重新攻击免疫动物来测试T细胞保护抵抗持久性的极限， 在主要的MHC I类和II类表位中含有适应性突变。我们的三个具体目标是：具体目标1。比较MHCII类表位的突变逃逸与CD4+ T细胞的功能缺陷如何导致HCV的持续存在。具体目标2。确定在急性丙型肝炎期间HCV特异性CD8+ T细胞是如何失活的，以及这些缺陷是否是由持续感染的特征性CD4+ T细胞帮助的突然丧失引起的。具体目标3。确定在主要的MHC I类或II类表位中含有逃逸突变的HCV变体的传播是否可以破坏免疫黑猩猩中的保护性记忆T细胞应答。

We recently demonstrated that successful resolution of acute hepatitis C in chimpanzees primes a protective memory T cell response. Depletion of memory CD8+ T cells with subset-specific antibodies immediately before re-infection resulted in prolonged viremia. Infections never resolved if CD4+ T cells were depleted. Indeed, without helper activity memory CD8+ T cells selected for escape mutations in MHC class I restricted epitopes of the virus. These results indicate an essential role for both T cell subsets in control of HCV replication but why they usually fail is not known. T cell responses appear to focus on a limited set of MHC class I and II epitopes at the point infection resolves and later broaden to include sub-dominant epitopes. Thus, while the response appears multi-specific, it effectively targets a limited set of dominant epitopes when virus replication (and errors by the RNA polymerase) are at a peak. Specific aim 1 is to determine if this causes mutational escape of dominant MHC class II epitopes. Mutational escape will be compared with other potential mechanisms of CD4+ T cell silencing including failure to expand, acquire function, or follow a normal differentiation program after antigen activation. MHC class II tetramer technology adapted to chimpanzees will facilitate the analysis. Specific aim 2 is to identify defects in CD8+ T cells during acute hepatitis C and to determine if they occur coincident with CD4+ T cell loss. Finally, specific aim 3 will test the limits of T cell protection against persistence by rechallenging immune animals with virus variants that contain adaptive mutations in dominant MHC class I and II epitopes. Our three specific aims are to: Specific Aim 1. Compare how mutational escape in MHC class II epitopes versus functional defects in CD4+ T cells contribute to persistence of HCV. Specific Aim 2. Determine how HCV-specific CD8+ T cells are inactivated during acute hepatitis C and whether these defects are precipitated by the sudden loss of CD4+ T cell help that is characteristic of infections that persist. Specific Aim 3. Determine if transmission of HCV variants containing escape mutations in dominant MHC class I or II epitopes can subvert protective memory T cell responses in immune chimpanzees.