TOWARDS A MOUSE MODEL OF CLASSICAL HODGKIN'S DISEASE

描述（由申请人提供）：经典霍奇金病（HD）是西方世界最常见的淋巴瘤。HD的恶性细胞是所谓的霍奇金和里德-斯滕伯格（HRS）细胞，它们只占淋巴瘤组织的百分之几或更少。在大约一半的患者中，HRS细胞感染了eb病毒（EBV）并表达EBV编码的膜蛋白LMP1和LMP2A。这些蛋白具有组成性活性，在B细胞中分别部分模拟CD40共受体和抗原受体（BCR）的信号。基于这些情况和我们自己对微操作HRS细胞中Ig基因重排的分子分析，我们已经开发了HD发病机制的场景。在这种情况下，HRS细胞在大多数情况下来源于凋亡前生发中心（GC） B细胞，这些细胞被一些转化事件拯救。在EBV+ HD中，LMP1和LMP2A可能参与这一初始拯救。本建议的目的是通过条件基因靶向技术在小鼠中重建这种情况。我们已经开发了一种小鼠突变体，其中Cre重组酶在GC中有效表达，而不是在幼稚B细胞中表达。这将用于在体内靶向LMP2A和/或LMP1在GC B细胞中的表达。研究病毒蛋白对GC反应的干扰。考虑到已知的LMP1的致癌特性，可能会观察到由于体细胞超突变而失去BCR表达的凋亡前GC B细胞的拯救，以及淋巴瘤的发生。这些实验将通过尝试将HRS细胞的另一种潜在肿瘤决定因素靶向到GC B细胞，即激活形式的Notch1来补充。该分子最近被证明在HRS细胞中以高水平和活化的形式表达。Notch1在这种情况下特别有吸引力，因为它参与淋巴细胞祖细胞的谱系决定，促进T细胞的发育。奇怪的是，HRS细胞下调了许多B细胞特异性基因，并表达其他造血谱系的分子标记，包括T细胞。Notch1，如果异位表达，也是一个有效的致癌基因，因此可能有助于这种奇怪的表型以及HRS细胞转化。通过条件基因靶向结合LMP2A、LMP1和Notch1在GC B细胞中的表达，可能导致小鼠HD模型的建立。除了淋巴瘤发生外，拟议的实验还应该为EBV感染背景下的GC反应的生物学提供新的见解。

DESCRIPTION (provided by applicant): Classical Hodgkin's disease (HD) is the most common lymphoma in the Western World. The malignant cells in HD are the so-called Hodgkin and Reed-Sternberg (HRS) cells, which comprise only a few percent or less of the lymphoma tissue. In roughly half of the patients, the HRS cells are infected with Epstein-Barr-Virus (EBV) and express the EBV-encoded membrane proteins LMP1 and LMP2A. These proteins are constitutively active and in B cells partially mimic signals of the CD40 co-receptor and the antigen receptor (BCR), respectively. Based on these circumstances and on our own molecular analysis of Ig gene rearrangements in micro manipulated HRS cells we have developed a scenario of HD pathogenesis. In this scenario, HRS cells derive in most instances from pre-apoptotic germinal center (GC) B cells rescued by some transforming event(s). In EBV+ HD, LMP1 and LMP2A may participate in this initial rescue. The aim of this proposal is to reconstruct this scenario in the mouse by conditional gene targeting techniques. We have developed a mouse mutant in which Cre recombinase is efficiently expressed in GC but not naive B cells. This will be used to target expression of LMP2A and/or LMP1 to GC B cells in vivo. The interference of the viral proteins with the GC reaction will be investigated. Rescue of pre-apoptotic GC B cells that have lost BCR expression because of somatic hypermutation might be observed, as well as lymphomagenesis, given the known oncogenic properties of LMP1. These experiments will be complemented by an attempt to target another potential tumor determinant of HRS cells into GC B cells, namely the activated form of Notch1. This molecule has recently been shown to be expressed in HRS cells at high levels and in an activated form. Notch1 is particularly attractive in this context, because it is involved in lineage decisions in lymphocyte progenitors, promoting T cell development. Curiously, HRS cells have down regulated many B cell-specific genes and express molecular markers of other hematopoietic lineages, including T cells. Notch1, which is also a potent oncogene if ectopically expressed, might thus contribute to this curious phenotype as well as to HRS cell transformation. Combining LMP2A, LMP1 and Notch1 expression in GC B cells by conditional gene targeting might lead to a mouse model of HD. Apart from lymphomagenesis, the proposed experiments should also lead to new insights into the biology of the GC reaction in the context of EBV infection.