(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的融合蛋白的产生，该融合蛋白是慢性髓性白血病（CML）和B细胞急性淋巴细胞白血病（B- all）的关键致癌基因。使用酪氨酸激酶抑制剂（TKIs），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，TKIs在治疗B-ALL患者方面并不是很有效，这主要是由于获得耐药突变使抑制剂失去功能。由于BCR-ABL融合产生一种可以被免疫系统识别的外来抗原，治疗BCR-ABL+ ALL的另一种方法包括免疫治疗。BCR-ABL+ B-ALL患者的极小残留病（MRD）水平非常低，表明了这种方法的潜在疗效。低MRD与bcr - abl特异性T细胞产生干扰素γ相关；这些T细胞的缺失与MRD的增加和患者预后不良相关。同样，在BCR-ABL+ B-ALL小鼠模型中，我们观察到T细胞可以对BCR-ABL融合肽产生强大的免疫反应。一个关键的问题是，为什么这种T细胞在小鼠和人类中通常都不能消除BCR-ABL+白血病细胞。这是一个很难回答的问题，因为以前的研究无法检测内源性T细胞对BCR-ABL肽的反应。为了解决这个问题，本项目将使用MHC II类肽四聚体追踪CD4+ T细胞对bcr - abl诱导的B-ALL的反应。这些四聚体由一个13个氨基酸的肽组成，该肽跨越e1a2 BCR-ABL与I-Ab结合的断点（BAp:I-Ab），这是C57BL/6小鼠的MHCII分子。这种新型试剂将使我们能够确定初始小鼠中BAp: i - ab特异性T细胞的数量，并确定这些细胞在BAp肽强免疫或BCR- ABL+白血病启动后的扩增情况。这种方法将使我们能够确定BAp:I-Ab特异性T细胞消灭BCR-ABL+细胞的失败是由于抗原呈递缺陷、能量诱导、BAp:I-Ab特异性细胞的缺失还是免疫偏差（即分化为Treg、TFH或TH2细胞系）。基于这些发现，我们将寻求多种策略来增强BAp: i - ab特异性免疫反应。我们的假设是，产生具有细胞溶解活性的CD4+ T细胞对于诱导有效的T细胞免疫BCR至关重要

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.