Modulation of T cell Homeostasis in Myelodysplastic Syndrome (MDS)

描述(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，并发展为急性髓系白血病(AML)，约占30%-40%。MDS的病因尚不清楚，导致AML进展的因素也没有很好的描述。与其他癌症患者相似，MDS患者存在近端T细胞受体信号通路缺陷和T细胞稳态改变。一类新的有趣的治疗药物(IMids)源自母体化合物沙利度胺，已在包括MDS在内的各种炎症性、自身免疫性和肿瘤性疾病中显示出活性，临床反应被观察到，该药物在特定患者中获得FDA批准。来那度胺和其他IMIDS一样，具有独特的增强T细胞功能的能力，通过一种涉及CD28受体激活的未知机制来替代不充分的次级抗原非依赖性共刺激信号。来那度胺能逆转MDS患者外周T细胞无能，增强TH1型细胞因子应答，改变T细胞稳态。虽然已经使用了激活T细胞信号和扩增的治疗方法，但激活通常不会改变T细胞亚群的分布，也不会优先激活抗原特异性T细胞。重要的是，IMiDS与癌症疫苗相结合的动物模型表明，这些药物选择性地增强了抗肿瘤特异性T细胞反应。因此，我们推测，来那度胺逆转T细胞信号缺陷和改善T细胞稳态，加上对内源性肿瘤抗原有交叉反应的细胞疫苗，应该会导致一种有效的治疗方法，防止MDS中的白血病进展。为了检验提出的假设，我们将实现三个具体目标。目的1研究来那度胺诱导的近端T细胞受体信号转导的分子机制。我们发现来那度胺对PP2A磷酸酶活性有抑制作用。已知PP2A结合并可能抑制CD28受体胞内结构域中的YXXM PI3K结合基序，该基序在T细胞/CD28途径水平上招募和/或激活近端信号中间产物。为了确定抑制PP2A在YXXM区域的协同刺激作用是否与来那度胺的协同刺激作用有关，将进行体外结合分析、蛋白酪氨酸激酶激活分析、磷酸酶功能、原代细胞中信号成分的遗传操作以及携带YXXM区域基因突变的CD28受体的过表达。在目的2中，研究旨在确定在体内用来那度胺治疗MDS患者后，T细胞群动态变化对白血病相关抗原反应的机制。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，该疫苗转导GM-CSF和CD40L基因，结合FDA批准的来那度胺剂量。目标3的目的是确定这种疫苗/来那度胺疗法是否调节针对MDS患者骨髓中存在的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)的特点是有缺陷的血液形成和发展成白血病的高风险，主要发生在65岁以上的人。随着美国人口老龄化，需要为MDS等与年龄相关的疾病制定新的治疗策略。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，在这种疗法中，一种新的细胞疫苗将与一种新药相结合，以解决这个问题的所有方面。我们认为，这种新的治疗策略最好在高风险MDS的背景下进行测试，这些MDS通常存活率较低，治疗选择有限，而且可能只对药物有临床反应。机械论研究将有助于我们对T细胞免疫的理解，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.