Uebelhoer Luke, Han Jin-Hwan, Callendret Benoit, Mateu Guaniri, Shoukry Naglaa H, Hanson Holly L, Rice Charles M, Walker Christopher M, Grakoui Arash
Department of Medicine, Division of Infectious Diseases, Microbiology and Immunology, Emory Vaccine Center, Emory University School of Medicine, Atlanta, Georgia, United States of America.
PLoS Pathog. 2008 Sep 5;4(9):e1000143. doi: 10.1371/journal.ppat.1000143.
Mechanisms by which hepatitis C virus (HCV) evades cellular immunity to establish persistence in chronically infected individuals are not clear. Mutations in human leukocyte antigen (HLA) class I-restricted epitopes targeted by CD8(+) T cells are associated with persistence, but the extent to which these mutations affect viral fitness is not fully understood. Previous work showed that the HCV quasispecies in a persistently infected chimpanzee accumulated multiple mutations in numerous class I epitopes over a period of 7 years. During the acute phase of infection, one representative epitope in the C-terminal region of the NS3/4A helicase, NS3(1629-1637), displayed multiple serial amino acid substitutions in major histocompatibility complex (MHC) anchor and T cell receptor (TCR) contact residues. Only one of these amino acid substitutions at position 9 (P9) of the epitope was stable in the quasispecies. We therefore assessed the effect of each mutation observed during in vivo infection on viral fitness and T cell responses using an HCV subgenomic replicon system and a recently developed in vitro infectious virus cell culture model. Mutation of a position 7 (P7) TCR-contact residue, I1635T, expectedly ablated the T cell response without affecting viral RNA replication or virion production. In contrast, two mutations at the P9 MHC-anchor residue abrogated antigen-specific T cell responses, but additionally decreased viral RNA replication and virion production. The first escape mutation, L1637P, detected in vivo only transiently at 3 mo after infection, decreased viral production, and reverted to the parental sequence in vitro. The second P9 variant, L1637S, which was stable in vivo through 7 years of follow-up, evaded the antigen-specific T cell response and did not revert in vitro despite being less optimal in virion production compared to the parental virus. These studies suggest that HCV escape mutants emerging early in infection are not necessarily stable, but are eventually replaced with variants that achieve a balance between immune evasion and fitness for replication.
丙型肝炎病毒（HCV）在慢性感染个体中逃避细胞免疫以建立持续感染的机制尚不清楚。CD8(+) T细胞靶向的人类白细胞抗原（HLA）I类限制性表位中的突变与持续感染有关，但这些突变对病毒适应性的影响程度尚未完全了解。先前的研究表明，一只持续感染的黑猩猩体内的HCV准种在7年时间里在众多I类表位中积累了多个突变。在感染急性期，NS3/4A解旋酶C末端区域的一个代表性表位NS3(1629 - 1637)在主要组织相容性复合体（MHC）锚定残基和T细胞受体（TCR）接触残基中出现了多个连续的氨基酸替换。在准种中，该表位第9位（P9）的这些氨基酸替换中只有一个是稳定的。因此，我们使用HCV亚基因组复制子系统和最近开发的体外感染性病毒细胞培养模型，评估了在体内感染期间观察到的每个突变对病毒适应性和T细胞反应的影响。预期位于第7位（P7）的TCR接触残基I1635T发生突变会消除T细胞反应，而不影响病毒RNA复制或病毒粒子产生。相比之下，P9 MHC锚定残基处的两个突变消除了抗原特异性T细胞反应，但还降低了病毒RNA复制和病毒粒子产生。在感染后3个月在体内仅短暂检测到的第一个逃逸突变L1637P降低了病毒产生，并在体外回复到亲本序列。第二个P9变体L1637S在长达7年的随访中在体内是稳定的，它逃避了抗原特异性T细胞反应，并且尽管与亲本病毒相比在病毒粒子产生方面不太理想，但在体外并未回复。这些研究表明，感染早期出现的HCV逃逸突变体不一定稳定，但最终会被在免疫逃逸和复制适应性之间取得平衡的变体所取代。
