Novel Mouse Xenograft Models Reveal a Critical Role of CD4+ T Cells in the Proliferation of EBV-Infected T and NK Cells

Epstein-Barr virus (EBV), a ubiquitous B-lymphotropic herpesvirus, ectopically infects T or NK cells to cause severe diseases of unknown pathogenesis, including chronic active EBV infection (CAEBV) and EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH). We developed xenograft models of CAEBV and EBV-HLH by transplanting patients' PBMC to immunodeficient mice of the NOD/Shi-scid/IL-2Rγnull strain. In these models, EBV-infected T, NK, or B cells proliferated systemically and reproduced histological characteristics of the two diseases. Analysis of the TCR repertoire expression revealed that identical predominant EBV-infected T-cell clones proliferated in patients and corresponding mice transplanted with their PBMC. Expression of the EBV nuclear antigen 1 (EBNA1), the latent membrane protein 1 (LMP1), and LMP2, but not EBNA2, in the engrafted cells is consistent with the latency II program of EBV gene expression known in CAEBV. High levels of human cytokines, including IL-8, IFN-γ, and RANTES, were detected in the peripheral blood of the model mice, mirroring hypercytokinemia characteristic to both CAEBV and EBV-HLH. Transplantation of individual immunophenotypic subsets isolated from patients' PBMC as well as that of various combinations of these subsets revealed a critical role of CD4+ T cells in the engraftment of EBV-infected T and NK cells. In accordance with this finding, in vivo depletion of CD4+ T cells by the administration of the OKT4 antibody following transplantation of PBMC prevented the engraftment of EBV-infected T and NK cells. This is the first report of animal models of CAEBV and EBV-HLH that are expected to be useful tools in the development of novel therapeutic strategies for the treatment of the diseases.

爱泼斯坦-巴尔病毒（Epstein-Barr virus, EBV）是一种广泛分布的嗜B淋巴细胞疱疹病毒，可异位感染T细胞或自然杀伤细胞（natural killer cell, NK），引发发病机制尚未阐明的重症疾病，包括慢性活动性EB病毒感染（chronic active EBV infection, CAEBV）与EB病毒相关噬血细胞性淋巴组织细胞增生症（EBV-associated hemophagocytic lymphohistiocytosis, EBV-HLH）。本研究通过将患者外周血单个核细胞（peripheral blood mononuclear cell, PBMC）移植至NOD/Shi-scid/IL-2Rγnull品系的免疫缺陷小鼠体内，构建了CAEBV与EBV-HLH的异种移植模型。在该模型中，EB病毒感染的T细胞、NK细胞或B细胞可发生全身性增殖，并重现两种疾病的组织病理学特征。对T细胞受体（T cell receptor, TCR）库的表达分析显示，患者及其PBMC移植受体小鼠体内，均存在优势扩增的同一群EB病毒感染性T细胞克隆。移植细胞中爱泼斯坦-巴尔病毒核抗原1（EBV nuclear antigen 1, EBNA1）、潜伏膜蛋白1（latent membrane protein 1, LMP1）与LMP2的表达（而非EBNA2），与CAEBV中已知的EB病毒潜伏II型基因表达程序相符。模型小鼠外周血中可检测到包括白细胞介素8（interleukin 8, IL-8）、干扰素γ（interferon γ, IFN-γ）及RANTES（regulated on activation, normal T cell expressed and secreted）在内的高水平人源细胞因子，重现了CAEBV与EBV-HLH特征性的高细胞因子血症表型。对从患者PBMC中分离得到的单一免疫表型亚群及其不同组合进行移植实验，结果揭示CD4+ T细胞在EB病毒感染的T细胞与NK细胞的移植定植中发挥关键作用。基于该发现，在PBMC移植后通过注射OKT4抗体体内耗竭CD4+ T细胞，可阻断EB病毒感染的T细胞与NK细胞的移植定植。本研究首次构建了CAEBV与EBV-HLH的动物模型，该模型有望成为开发该类疾病新型治疗策略的实用工具。