Modulation of T cell Homeostasis in Myelodysplastic Syndrome (MDS)

描述（由申请人提供）：骨髓增生异常综合征（MDS）的特征是造血功能不全，导致单系或多系外周血细胞减少，约30-40%的病例发生急性髓性白血病（AML）。MDS的病因尚不清楚，导致AML进展的因素也没有得到很好的表征。与其他癌症患者相似，MDS患者在近端T细胞受体信号传导途径中存在缺陷，并改变了T细胞稳态。一类新的有趣的治疗药物（IMiD），衍生自母体化合物沙利度胺，已显示出在各种炎症，自身免疫性和肿瘤性疾病，包括MDS的活性，其中观察到临床反应，并在选定的患者中获得FDA批准。来那度胺以及其他IMiD具有独特的增强T细胞功能的能力，通过涉及CD 28受体活化的未知机制取代不充分的二级抗原非依赖性共刺激信号。来那度胺能够逆转MDS患者的外周T细胞无反应性，增强TH 1型细胞因子应答，并改变T细胞稳态。尽管已经使用了激活T细胞信号传导和扩增的治疗，但激活通常不改变T细胞亚群分布或优先激活抗原特异性T细胞。重要的是，IMiD与癌症疫苗组合的动物模型表明，这些药物选择性地增强抗肿瘤特异性T细胞应答。因此，我们假设来那度胺沿着与内源性肿瘤抗原交叉反应的细胞疫苗逆转T细胞信号传导缺陷和改善T细胞稳态应导致有效的治疗性治疗，其将预防MDS中的白血病进展。为了检验所提出的假设，我们将执行三个具体目标。在目的1中，将在体外研究来那度胺诱导的近端T细胞受体信号传导事件的分子机制。我们发现来那度胺作为PP 2A磷酸酶活性的抑制剂。已知PP 2A结合并可能抑制CD 28受体胞内结构域中的YXXM PI 3 K结合基序，该基序在T细胞/CD 28途径水平募集和/或激活近端信号传导中间体。为了确定YXXM区域中PP 2A抑制的抑制是否是来那度胺共刺激功能的原因，将进行体外结合试验、蛋白酪氨酸激酶活化试验、磷酸酶功能、原代细胞中信号传导组分的遗传操作以及YXXM区域中携带基因突变的CD 28受体的过表达。在目的2中，设计研究以鉴定在MDS患者用来那度胺疗法在体内治疗后响应于白血病相关抗原的T细胞群体动力学变化的机制。作为我们假设的最终检验，我们计划在高危MDS患者中进行K562“旁观者”细胞疫苗的I期剂量递增试验，该细胞疫苗转导有GM-CSF和CD 40 L基因，并与FDA批准剂量的来那度胺联合使用。目的3的目标是确定这种疫苗/来那度胺治疗是否调节针对MDS患者骨髓中存在的内源性白血病相关抗原的抗原特异性T细胞应答。公共卫生相关性：骨髓增生异常综合征（MDS）的特征在于有缺陷的血液形成和白血病发展的高风险，并且主要发生在65岁以上的个体中。随着美国人口老龄化，需要新的治疗策略来治疗年龄相关疾病，如MDS。对于在MDS和癌症患者中产生临床应答的肿瘤疫苗疗法，适当的抗原选择、完整的抗原呈递和T细胞功能都是至关重要的。我们提出了一种新的联合疗法，其中一种新的细胞疫苗将与一种新的药物相结合，以解决这个问题的各个方面。我们认为，这种新的治疗策略最好在高危MDS患者中进行测试，这些患者通常生存率低，治疗选择有限，并且可能对单独的药物有临床反应。机制研究将有助于我们理解T细胞免疫，并提高我们利用这种形式的免疫疗法和其他形式治疗癌症的能力。

DESCRIPTION (provided by applicant): Myelodysplastic syndromes (MDS) are characterized by incompetent hematopoiesis that leads to single or multi-lineage peripheral cytopenias with the development of acute myeloid leukemia (AML) in approximately 30-40% of cases. The etiology of MDS is unknown and the factors leading to AML progression are not well characterized. With similarity to other cancer patients, MDS patients have defects in proximal T-cell receptor signaling pathways and altered T-cell homeostasis. A new class of interesting therapeutic drugs (IMiDs), derived from the parent compound thalidomide, has shown activity in a variety of inflammatory, autoimmune, and neoplastic diseases including MDS where clinical responses were observed and the drug was awarded FDA approval in select patients. Lenalidomide, as well as other IMiDs, possess a unique ability to augment T-cell function by substituting for inadequate secondary antigen-independent co-stimulatory signals through an unknown mechanism that involves activation of the CD28 receptor. Lenalidomide was able to reverse peripheral T-cell anergy, enhance TH1-type cytokine responses, and change T-cell homeostasis in patients with MDS. Although treatments to activate T-cell signaling and expansion have been used, activation in general does not alter T-cell subset distribution or preferentially activate antigen-specific T-cells. Importantly, animal models of IMiDs combined with cancer vaccines suggest that these drugs selectively enhance anti-tumor specific T-cell responses. Therefore, we hypothesize that reversal of the T-cell signaling defects and improved T-cell homeostasis with lenalidomide along with a cellular vaccine that is cross-reactive to endogenous tumor antigens should result in an effective therapeutic treatment that will prevent leukemia progression in MDS. To examine the proposed hypothesis, we will perform three specific aims. In Aim 1, the molecular mechanism of lenalidomide-induced proximal T-cell receptor signaling events will be investigated in vitro. We found that lenalidomide acts as an inhibitor of PP2A phosphatase activity. PP2A is known to bind and possibly repress the YXXM PI3K binding motif in the CD28 receptor intracellular domain that recruits and/or activates proximal signaling intermediates at the level of the T-cell/CD28 pathway. To determine whether inhibition of PP2A repression in the YXXM region is responsible for the co-stimulatory function of lenalidomide, in vitro binding assays, protein tyrosine kinase activation assays, phosphatase function, genetic manipulation of signaling components in primary cells, and overexpression of the CD28 receptor carrying genetic mutations in the YXXM region will be performed. In Aim 2, studies are designed to identify the mechanisms responsible for changes in T-cell population dynamics in response to leukemia-associated antigens after MDS patients are treated in vivo with lenalidomide therapy. As an ultimate test of our hypothesis, we plan to perform a Phase I dose-escalation trial of the K562 "bystander" cellular vaccine that is transduced with the genes for GM-CSF and CD40L in combination with the FDA-approved dose of lenalidomide in high-risk MDS patients. The goal of Aim 3 is to determine whether this vaccine/lenalidomide therapy modulates antigen-specific T-cell response against endogenous leukemia-associated antigens present in the bone marrow of MDS patients. PUBLIC HEALTH RELEVANCE: Myelodysplastic syndromes (MDS) are characterized by defective blood formation and high risk for leukemia development and primarily occur in individuals over the age of 65 years old. New strategies of treatment are needed for age-related diseases such as MDS as the US population ages. For tumor vaccine therapies to produce clinical responses in MDS and in cancer patients, appropriate antigen selection, intact antigen presentation, and T-cell function are all critical. We propose a new combination therapy in which a novel cellular vaccine will be combined with a new drug to attack all aspects of this problem. We believe that this new treatment strategy is best tested in the setting of high-risk MDS that generally have poor survival, limited treatment options, and who may have a clinical response to the drug alone. Mechanistic studies will aide our understanding of T-cell immunity and improve our ability to utilize this form of immunotherapy and other forms for the treatment of cancer in general.