HCV-Specific Cellular Immunity in Acute Hepatitis C

我们最近证明，在黑猩猩中成功解决急性丙型肝炎启动了一种保护性记忆T细胞反应。在再次感染前立即用亚群特异性抗体耗尽记忆中的CD8+T细胞会导致长期的病毒血症。如果CD4+T细胞耗尽，感染永远不会得到解决。事实上，没有辅助记忆活性的CD8+T细胞被选为MHC I类限制病毒表位中逃逸突变的细胞。这些结果表明，这两个T细胞亚群在控制丙型肝炎病毒复制方面发挥了重要作用，但它们通常失败的原因尚不清楚。T细胞反应似乎集中在感染解决点的一组有限的MHC I类和II类表位上，后来又扩大到包括亚显性表位。因此，尽管这种反应看起来是多特异性的，但当病毒复制(以及RNA聚合酶的错误)达到顶峰时，它有效地针对有限的优势表位。具体目的1是确定这是否会导致主要的MHC II类表位的突变逃逸。 突变逃逸将与其他可能的CD4+T细胞沉默机制进行比较，包括在抗原激活后未能扩大、获得功能或遵循正常的分化程序。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细胞丢失同时发生。最后，特殊目标3将通过用病毒变体重新攻击免疫动物来测试T细胞保护免受持久性的限制 在主要的MHC I类和II类表位中包含适应性突变。我们的三个具体目标是：特定目标1.比较MHC II类表位的突变逃逸与CD4+T细胞的功能缺陷如何促进丙型肝炎病毒的持久性。具体目标2.确定丙型肝炎病毒特异性CD8+T细胞在急性丙型肝炎期间是如何失活的，以及这些缺陷是否是由于CD4+T细胞突然丧失所致，这是持续感染的特征。具体目的3.确定丙型肝炎病毒变异体的传播是否可以颠覆免疫黑猩猩的保护性记忆T细胞反应。

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.