(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产生新型融合蛋白，该蛋白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) 中的关键癌基因。酪氨酸激酶抑制剂 (TKI)（例如针对 BCR-ABL 融合蛋白的伊马替尼）的使用已被证明在 CML 患者中非常成功。相比之下，TKI 在治疗 B-ALL 患者方面并不是非常有效，这主要是由于耐药突变的获得导致抑制剂失去功能。由于 BCR-ABL 融合会产生免疫系统可以识别的外源抗原，因此治疗 BCR-ABL ALL 的另一种方法是免疫疗法。微小残留病 (MRD) 水平非常低的 BCR-ABL B-ALL 患者亚群表明了这种方法的潜在功效。低 MRD 与具有产生干扰素 γ 的 BCR-ABL 特异性 T 细胞的患者有关；这些 T 细胞的损失与 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 细胞的存在可以对 BCR-ABL 融合肽产生强大的免疫反应。一个关键问题是为什么小鼠和人类中的此类 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，因为之前的研究无法检查内源性 T 细胞对 BCR-ABL 肽的反应。为了解决这个问题，该项目将使用 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 13 个氨基酸的肽组成，该肽跨越与 I-Ab (BAp:I-Ab) 结合的 e1a2 BCR-ABL 断点，I-Ab 是 C57BL/6 小鼠中的 MHCII 分子。这种新型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，并确定这些细胞在使用 BAp 肽进行强力免疫后或在 BCR-ABL 白血病开始后的扩增情况。这种方法将使我们能够确定 BAp:I-Ab 特异性 T 细胞未能消除 BCR-ABL 细胞是否是由于抗原呈递缺陷、无反应性诱导、BAp:I-Ab 特异性细胞缺失或免疫偏差（即分化为 Treg、TFH 或 TH2 细胞谱系）所致。基于这些发现，我们将采取多种策略来增强 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转化潜力，我们将生成 BAp:DR4 四聚体，这将使我们能够追踪表达人类 DR4 的小鼠（B6.DR4 小鼠）中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:DR4 四聚体可用于追踪 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.