HIV-Induced CD4 T-Cell Depletion: An Innate Host Defense Gone Awry?

描述（由申请人提供）：CD4 T细胞的进行性耗竭是未经治疗的获得性免疫缺陷综合征（AIDS）的标志，然而CD4 T细胞在HIV感染期间死亡的机制仍然知之甚少。HIV可以直接感染并杀死CD4 T细胞，但体内存在的有效感染细胞太少，无法解释发生的大量CD4 T细胞损失。利用扁桃体或脾脏组织形成的原代人淋巴细胞聚集体培养（HLAC），我们探索了CD4 T细胞在淋巴组织中HIV感染期间死亡的机制。我们的研究揭示了一些令人惊讶的发现，包括：(1)静止的“旁观者”CD4 T细胞，不允许X4-tropic HIV-1产生性感染，由于病毒感染失败并伴随着细胞质中不完整病毒DNA转录物的积累而大量死亡；(2)死亡不是由这些DNA或其他病毒产物的毒性作用引起的；相反，CD4 T细胞的死亡是针对病毒DNA的强大先天免疫反应的结果，导致干扰素的产生和caspase-3和caspase-1的激活；(3)最终，这种反应导致炎性小体组装和caspase-1激活，触发生物活性IL-1的释放，并诱导焦亡，这是一种强烈炎症形式的程序性细胞死亡。这些事件可以建立一个恶性循环，死亡的CD4 T细胞释放炎症介质，吸引更多的细胞进行新一轮的流产感染和死亡；4)令人惊讶的是，hiv介导的CD4 T细胞凋亡可以被fda批准的用于治疗II型糖尿病的特定类别的口服磺脲类药物完全阻断。我们现在提出一系列关键的新研究。在Specific Aim 1中，我们将测试CD4 T细胞耗竭的这种机制是否也延伸到表达ccr5的CD4 T细胞，这些细胞通常表现出更高的细胞激活状态，因此可能不太容易受到流产感染。在特异性目标2中，我们建议鉴定检测病毒DNA的细胞质传感器。多个传感器可能激活干扰素反应和炎性小体内caspase-1的激活。在Specific Aim 3中，我们提出确定募集caspase-1来加工和释放IL-1并诱导焦亡的炎性体。总之，这些研究将对HIV诱导CD4 T细胞耗竭的机制——艾滋病的根本问题——产生新的见解。这一新的认识可能会导致一种全新的艾滋病治疗方法，包括阻断促进CD4 T细胞死亡和炎症的宿主先天免疫反应。这种方法可以成为传统抗病毒治疗的有力补充，对表现出广泛耐药性或疾病快速进展的患者可能特别有益。

DESCRIPTION (provided by applicant): Progressive depletion of CD4 T cells is a halmark of untreated acquired immune deficiency syndrome (AIDS), yet the mechanism by which CD4 T cells die during HIV infection remains poorly understood. HIV can directly infect and kill CD4 T cels however too few productively infected cells are present in vivo to explain the masive CD4 T-cell losses that occur. Using primary human lymphoid aggregate cultures (HLAC) formed with tonsil or spleen tissue, we have explored how CD4 T cells die during HIV infection in lymphoid tissues. Our studies have revealed several surprises including: (1) Quiescent "bystander" CD4 T cells, which are not permissive to productive infection by X4-tropic HIV-1, die in huge numbers as a result of abortive viral infection accompanied by the the accumulation of incomplete viral DNA transcripts in the cytoplasm; (2) Death is not cause by a toxic effect of these DNA or other viral products; rather the CD4 T cells die as a result of a powerful innate immune response launched against the viral DNA, resulting in the production of interferon-¿ and activation of caspase-3 and caspase-1; (3) Ultimately, this response leads to inflammasome assembly and caspase-1 activation triggering the release of bioactive IL-1¿ and induction of pyroptosis, an intensely inflammatory form of programmed cell death. These events can establish a vicious cycle, whereby dying CD4 T cells release inflammatory mediators that attract additional cells for new rounds of abortive infection and death; 4) Surprisingly, HIV-mediated CD4 T cell depletion by pyroptosis can be completely blocked by specific class of FDA-approved oral sulfonylurea drugs currently used to treat type II diabetes. We now propose a set of pivotal new studies. In Specific Aim 1, we will test whether this mechanism of CD4 T cell depletion also extends to CCR5-expressing CD4 T cells that often display a higher state of cellular activation and thus might be less susceptible to abortive infection. In Specific Aim 2, we propose to identify the cytoplasmic sensor(s) that detects the viral DNA. Multiple sensors may activate the interferon response and the activation of caspase-1 within inflammasomes. In Specific Aim 3, we propose to identify the inflammasome that recruits caspase-1 to process and release IL-1¿ and to induce pyroptosis. Together, these studies will yield new insights into the mechanism(s) underlying HIV- induced depletion of CD4 T cells-the fundamental problem in AIDS. This new understanding could lead to an entirely new therapeutic approach to AIDS involving interdiction of the host innate immune response that promotes both CD4 T cell death and inflammation. This approach could form a strong adjunct to traditional antiviral therapy and might be particularly beneficial for patients exhibiting broad drug resistance or rapid progression of disease.