Heteroclitic and modified T cell epitopes in coronavirus encephalomyelitis

描述(申请人提供)：小鼠感染嗜神经性的小鼠冠状病毒JHM株，小鼠肝炎病毒(JHMV)发展成急性和慢性脱髓鞘疾病，这是有用的人类疾病多发性硬化症的模型。在一个版本中，哺乳的C57BL/6(B6)小鼠感染了JHMV，并通过JHMV免疫堤坝的护理保护其免受急性脑炎的侵袭。有不同比例的小鼠在感染后3-8周发展为脱髓鞘脑脊髓炎；这种感染的特征是B6小鼠识别的免疫优势CD8T细胞表位(S510)发生突变。这些突变破坏了S510特异性CD8 T细胞的识别(细胞毒性淋巴细胞逃逸，CTL逃逸)。在这些小鼠中也识别了第二个表位(S598)，但对该表位的免疫反应并不能阻止CTL逃逸。然而，S598肽的修饰可以更好地与MHC I类抗原结合，从而产生具有更高功能亲和力的CD8T细胞反应。值得注意的是，现在用这种修饰的表位免疫CD8T细胞，与由原始表位诱导的细胞相比，CD8T细胞对天然S598表位的识别能力更强，从而表现出异源融合效应。用修饰后的表位免疫可防止CTL逃逸。这项提议的主要目标是探索为什么表位是异位的。第一个特定目的是评估先前发现的异型S598表位诱导的CD8T细胞反应在减少JHMV减毒株感染后脱髓鞘的效果。第二个具体目标将确定S598的其他异位变异，并开始识别有助于预测这种异位多肽的特征；现在，异位表位的识别是经验上的。第三个目标将对S598特异性T细胞受体(TCR)与MHCI(H-2kb)结合的天然或异源S598多肽的复合体进行结构和生物物理研究。最终目的是了解高亲和力TCR与异源表位/MHC-I类抗原相互作用的分子基础。通过了解这些相互作用，将有可能设计不同的表位，诱导具有高功能亲和力的CD8T细胞，有效地与天然表位发生交叉反应，但不会诱导大量具有不必要的特异性的细胞。这一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。 与公共卫生相关：该项目探索了观察到的基础，即对病毒特异性CD8 T细胞表位的弱反应可以通过异源多肽(对天然表位的反应比表位本身更强的多肽)免疫来增强。异源多肽可能为提高T细胞疫苗的效力提供了一种普遍有用的方法。

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. PUBLIC HEALTH RELEVANCE: This project probes the basis of the observation that a weak response to a virus-specific CD8 T cell epitope can be enhanced by immunization with a heteroclitic peptide (peptide that induces a stronger response to the native epitope than does the epitope itself). Heteroclitic peptides may provide a generally useful way to enhance T cell vaccine efficacy.