(PQB3) CD4 T cell response to BCR-ABL-positive Leukemia

描述（由申请人提供）：9号和22号染色体之间的易位导致新型融合蛋白的产生，该融合蛋白是慢性髓细胞性白血病（CML）和B细胞急性淋巴细胞白血病（B-ALL）中的关键癌基因。使用酪氨酸激酶抑制剂（TKI），如靶向BCR-ABL融合蛋白的伊马替尼，已被证明在CML患者中非常成功。相比之下，TKI在治疗B-ALL患者方面并不十分有效，这主要是由于获得了使抑制剂失去功能的耐药突变。由于BCR-ABL融合产生了一种可以被免疫系统看到的外源抗原，因此治疗BCR-ABL+ ALL的替代方法包括免疫疗法。这种方法的潜在疗效是由极低水平的微小残留病（MRD）的BCR-ABL+ B-ALL患者亚组提出的。低MRD与具有产生干扰素-γ的BCR-ABL特异性T细胞的患者相关;这些T细胞的损失与MRD增加和患者预后不良相关。同样，在BCR-ABL+ B-ALL的小鼠模型中，我们观察到T细胞存在，可以对BCR-ABL融合肽产生强烈的免疫应答。一个关键的问题是，为什么小鼠和人类中的这种T细胞通常不能消除BCR-ABL+白血病细胞。这是一个很难回答的问题，因为以前的研究还没有能够检查内源性T细胞对BCR-ABL肽的反应。为了解决这一问题，本项目将使用MHC II类：肽四聚体跟踪CD 4 + T细胞对BCR-ABL诱导的B-ALL的应答。这些四聚体由跨越e1 a2 BCR-ABL断裂点的13个氨基酸肽组成，与I-Ab（BAp：I-Ab）结合，I-Ab是C57 BL/6小鼠中的MHCII分子。这种新型试剂将使我们能够确定幼稚小鼠中BAp：I-Ab特异性T细胞的数量，并确定这些细胞在用BAp肽强烈免疫后或在BCR-ABL+白血病引发后的扩增程度。这种方法将允许我们确定BA p：I-Ab特异性T细胞消除BCR-ABL+细胞的失败是否是由于抗原呈递缺陷、无反应性诱导、BA p：I-Ab特异性细胞缺失或免疫偏离（即，分化成Treg、TFH或TH 2细胞谱系）。基于这些发现，我们将采取各种策略来增强BAp：I-Ab特异性免疫应答。我们的假设是，产生具有细胞溶解活性的CD 4 + T细胞对于诱导针对BCR的有效T细胞免疫至关重要 ABL+ B-ALL。最后，为了增强我的发现的翻译潜力，我们将产生BAp：DR 4四聚体，这将使我们能够在表达人DR 4的小鼠（B6.DR4小鼠）中追踪类似的抗白血病反应。这些研究的结果可以直接应用于人类患者，因为BAp：DR 4四聚体可以用于追踪DR 4+或接受DR 4+骨髓移植的BCR-ABL患者中的BAp特异性T细胞。

DESCRIPTION (provided by applicant): Translocations between chromosomes 9 and 22 result in the generation of the novel fusion protein that is a critical oncogene in both chronic myelogenous leukemia (CML) and B cell acute lymphoblastic leukemia (B-ALL). The use of tyrosine kinase inhibitors (TKIs), such as imatinib that targets the BCR-ABL fusion protein, has proven to be extremely successful in patients with CML. In contrast, TKIs have not been very effective in treating patients with B-ALL, largely due to the acquisition of resistance mutations that render the inhibitors non-functional. Since the BCR-ABL fusion generates a foreign antigen that can be seen by the immune system, an alternative approach to treating BCR-ABL+ ALL involves immunotherapy. The potential efficacy of such an approach is suggested by a subset of BCR-ABL+ B-ALL patients with very low levels of minimal residual disease (MRD). Low MRD is associated with patients that have BCR-ABL-specific T cells that make interferon-gamma; loss of these T cells correlates with an increase in MRD and poor patient outcome. Likewise, in a mouse model of BCR-ABL+ B-ALL, we have observed that T cells exist that can mount robust immune responses to the BCR-ABL fusion peptide. A key question is why such T cells in both mice and humans typically do not eliminate BCR-ABL+ leukemic cells. This has been a difficult question to answer because previous studies have not been able to examine the endogenous T cell response to the BCR-ABL peptide. To address this issue this project will track the CD4+ T cell response to BCR-ABL-induced B-ALL using MHC Class II: peptide tetramers. These tetramers are composed of a 13 amino acid peptide that spans the e1a2 BCR-ABL breakpoint bound to I-Ab (BAp:I-Ab), which is the MHCII molecule in C57BL/6 mice. This novel reagent will allow us to determine the number of BAp:I-Ab-specific T cells in a naive mouse and establish how well these cells expand following strong immunization with the BAp peptide or following initiation of BCR- ABL+ leukemia. This approach will allow us to determine whether the failure of BAp:I-Ab specific T cells to eliminate BCR-ABL+ cells is due to a defect in antigen presentation, induction of anergy, deletion of BAp:I-Ab- specific cells or immune deviation (i.e., differentiatio into Treg, TFH or TH2 cell lineages). Based on these findings we will then pursue a variety of strategies to enhance BAp:I-Ab-specific immune responses. Our hypothesis is that generating CD4+ T cells with cytolytic activity will be critical for inducing effective T cell immunity to BCR ABL+ B-ALL. Finally, to enhance the translational potential of my findings we will generate BAp:DR4 tetramers that will allow us to track similar anti-leukemia responses in mice expressing human DR4 (B6.DR4 mice). The results of these studies could then be directly applied to human patients as the BAp:DR4 tetramer could be used to track BAp-specific T cell in patients with BCR-ABL that are DR4+ or that receive a DR4+ bone marrow transplant.