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）的特点是造血功能不全，导致单系或多系外周细胞减少，约30-40%的病例发展为急性髓性白血病（AML）。MDS的病因尚不清楚，导致AML进展的因素也不清楚。与其他癌症患者相似，MDS患者近端t细胞受体信号通路存在缺陷，t细胞稳态改变。一类新的有趣的治疗药物（IMiDs），衍生自母体化合物沙利度胺，在多种炎症、自身免疫和肿瘤疾病（包括MDS）中显示出活性，在这些疾病中观察到临床反应，并且该药物在选定的患者中获得了FDA的批准。来那度胺和其他IMiDs具有独特的增强t细胞功能的能力，通过一种未知的机制，包括CD28受体的激活，取代不充分的次级抗原非依赖性共刺激信号。来那度胺能够逆转MDS患者外周血t细胞能量，增强th1型细胞因子反应，改变t细胞稳态。虽然已经使用了激活t细胞信号传导和扩增的治疗方法，但激活通常不会改变t细胞亚群分布或优先激活抗原特异性t细胞。重要的是，IMiDs联合癌症疫苗的动物模型表明，这些药物选择性地增强了抗肿瘤特异性t细胞反应。因此，我们假设，来那度胺和对内源性肿瘤抗原有交叉反应的细胞疫苗可以逆转t细胞信号缺陷和改善t细胞稳态，从而有效地预防MDS患者白血病的进展。为了检验提出的假设，我们将执行三个具体目标。在Aim 1中，来那度胺诱导近端t细胞受体信号事件的分子机制将在体外进行研究。我们发现来那度胺作为PP2A磷酸酶活性的抑制剂。已知PP2A结合并可能抑制CD28受体胞内域的YXXM PI3K结合基序，该基序在t细胞/CD28通路水平上招募和/或激活近端信号中间体。为了确定来那度胺对YXXM区PP2A抑制的抑制是否与来那度胺的共刺激功能有关，将进行体外结合试验、蛋白酪氨酸激酶激活试验、磷酸酶功能、原代细胞中信号传导成分的遗传操作以及携带基因突变的CD28受体在YXXM区过表达。在Aim 2中，研究旨在确定在MDS患者体内接受来那度胺治疗后，t细胞群体对白血病相关抗原的反应动态变化的机制。作为我们假设的最终测试，我们计划在高风险MDS患者中进行K562“旁观者”细胞疫苗的I期剂量递增试验，该疫苗由GM-CSF和CD40L基因转导，与fda批准的来那度胺剂量联合使用。Aim 3的目的是确定这种疫苗/来那度胺疗法是否调节针对MDS患者骨髓中内源性白血病相关抗原的抗原特异性t细胞反应。公共卫生相关性：骨髓增生异常综合征（MDS）的特点是血液形成缺陷和白血病发展的高风险，主要发生在65岁以上的个体中。随着美国人口的老龄化，需要新的治疗策略来治疗与年龄相关的疾病，如MDS。为了使肿瘤疫苗疗法在MDS和癌症患者中产生临床反应，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，一种新的细胞疫苗将与一种新药相结合，以解决这个问题的各个方面。我们认为，这种新的治疗策略在高风险MDS患者中得到最好的测试，这些患者通常生存率低，治疗选择有限，并且可能对单独使用该药物有临床反应。机制研究将有助于我们了解t细胞免疫，并提高我们利用这种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.