Heteroclitic and modified T cell epitopes in coronavirus encephalomyelitis

描述（由申请人提供）：小鼠感染嗜神经型小鼠冠状病毒，小鼠肝炎病毒（JHMV）的JHM株，会发生急性和慢性脱髓鞘疾病，这是人类疾病多发性硬化症的有用模型。其中一种方法是，在哺乳期的C57Bl/6 （B6）小鼠感染JHMV后，通过JHMV免疫坝的护理保护其不患急性脑炎。感染后3-8周发生脱髓鞘性脑脊髓炎的小鼠比例不等；这种感染的特征是在B6小鼠中识别的免疫显性CD8 T细胞表位（S510）发生突变。这些突变取消了s510特异性CD8 T细胞的识别（细胞毒性淋巴细胞逃逸，CTL逃逸）。第二个表位（S598）在这些小鼠中也被识别，但对该表位的免疫反应并不阻止CTL逃逸。然而，对S598肽进行修饰，使其更好地与MHC I类抗原结合，从而导致CD8 T细胞反应具有更高的功能亲和力。值得注意的是，与原始表位诱导的细胞相比，这种修饰表位免疫现在选择CD8 T细胞更有效地识别原生S598表位，从而表现出异位效应。修饰表位免疫可防止CTL逃逸。本提案的主要目的是探讨为什么表位是异位的。第一个特定目的是评估由先前鉴定的异位S598表位诱导的CD8 T细胞应答在减少JHMV减毒株感染后脱髓鞘的功效。第二个具体目标将确定S598的其他异斜变异体，并开始确定有助于预测此类异斜肽的特征；现在，异质表位是经验鉴定。第三个目标将进行S598特异性T细胞受体（TCRs）与MHCI （H-2Kb）结合的天然或异位S598肽复合物的结构和生物物理研究。最终目的是了解高亲和力tcr与异位表位/MHC I类抗原之间相互作用的分子基础。通过了解这些相互作用，将有可能设计出诱导CD8 T细胞具有高功能亲和力的变异表位，这些表位可以与天然表位发生有效的交叉反应，但不会诱导大部分具有不需要的特异性的细胞。这种方法将有助于设计旨在增强病原体特异性CD8 T细胞反应的疫苗。

DESCRIPTION (provided by applicant): Mice infected with the neurotropic JHM strain of the murine coronavirus, mouse hepatitis virus, (JHMV) develop acute and chronic demyelinating disease, which are useful models for the human disease, multiple sclerosis. In one version, suckling C57Bl/6 (B6) mice are infected with JHMV and are protected from developing acute encephalitis by nursing by JHMV-immune dams. A variable percentage of mice develop demyelinating encephalomyelitis 3-8 weeks after infection; this infection is characterized by mutations in the immunodominant CD8 T cell epitope (S510) recognized in B6 mice. These mutations abrogate recognition by S510-specific CD8 T cells (cytotoxic lymphocyte escape, CTL escape). A second epitope (S598) is also recognized in these mice, but the immune response to this epitope does not prevent CTL escape. However, modification of the S598 peptide that result in better binding to MHC class I antigen results in a CD8 T cell response with higher functional avidity. Remarkably, immunization with this modified epitope now selects for CD8 T cells that more potently recognize the native S598 epitope than do cells elicited by the original epitope, thereby exhibiting a heteroclitic effect. Immunization with the modified epitope protects against CTL escape. The main goal of this proposal is to probe why an epitope is heteroclitic. The first specific aim will evaluate the efficacy of the CD8 T cell response induced by the previously identified heteroclitic S598 epitope in diminishing demyelination after infection with an attenuated strain of JHMV. The second specific aim will identify other heteroclitic variants of S598 and to begin to identify features that facilitate prediction of such heteroclitic peptides; now heteroclitic epitopes are identified empirically. The third aim will perform structural and biophysical studies of S598-specific T cell receptors (TCRs) in complex with the native or heteroclitic S598 peptide bound to MHCI (H-2Kb). The ultimate goal is to understand the molecular basis of interactions between high affinity TCRs and heteroclitic epitope/MHC class I antigen. By understanding these interactions, it will be possible to design variant epitopes that induce CD8 T cells with high functional avidity that potently cross-react with the native epitope, but do not induce a large fraction of cells with unwanted specificity. This approach will be useful in design of vaccines that are directed at enhancing pathogen-specific CD8 T cell responses.