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

描述(申请人提供)：9号和22号染色体之间的易位导致了新的融合蛋白的产生，这是慢性粒细胞白血病(CML)和B细胞急性淋巴细胞白血病(B-ALL)的关键癌基因。酪氨酸激酶抑制剂(TKI)的使用，如针对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患者方面并不是非常有效，这主要是由于获得了使抑制剂无效的耐药性突变。由于bcr-abl融合产生了一种免疫系统可以看到的外来抗原，治疗bcr-abl的另一种方法都涉及免疫治疗。这种方法的潜在疗效是由BCR-ABL B-ALL患者的一个子集提出的，这些患者的微小残留病(MRD)水平都很低。低MRD与具有BCR-ABL特异性T细胞产生干扰素-伽马的患者有关；这些T细胞的丢失与MRD增加和患者预后差相关。同样，在BCR-ABL B-ALL小鼠模型中，我们观察到存在能够对BCR-ABL融合肽产生强大免疫反应的T细胞。一个关键的问题是，为什么老鼠和人类体内的这种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，因为以前的研究还不能检测内源性T细胞对BCR-ABL多肽的反应。为了解决这个问题，该项目将使用MHC第二类：多肽四聚体跟踪CD4T细胞对BCR-ABL诱导的B-ALL的反应。这些四聚体由13个氨基酸组成，横跨与I-Ab(BaP：I-Ab)结合的e1a2 BCR-ABL断裂点，I-Ab是C57BL/6小鼠的MHCII分子。这种新的试剂将使我们能够确定幼鼠体内BaP：I-Ab特异性T细胞的数量，并确定这些细胞在BaP多肽强烈免疫后或在BCR-ABL白血病启动后的扩张情况。这一方法将使我们能够确定Bap：I-Ab特异性T细胞未能消除BCR-ABL细胞是由于抗原提呈缺陷、诱导无能、Bap：I-Ab特异性细胞缺失还是免疫偏离(即分化为Treg、TFH或TH2细胞系)。基于这些发现，我们将寻求各种策略来增强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CD4T细胞将是诱导对BCR的有效T细胞免疫的关键 ABL B-ALL。最后，为了增强我的发现的翻译潜力，我们将产生BaP：DR4四聚体，使我们能够在表达人DR4的小鼠(B6.DR4小鼠)中跟踪类似的抗白血病反应。这些研究的结果随后可以直接应用于人类患者，因为BaP：DR4四聚体可以用于跟踪患有DR4或接受DR4骨髓移植的BCR-ABL患者的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.