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）的一个标志，但对HIV感染期间CD4 T细胞死亡的机制仍知之甚少。HIV可以直接感染和杀死CD4 T细胞，但是体内很少有有效感染的细胞，无法解释发生的大量CD4 T细胞损失。利用扁桃体或脾组织形成的原代人淋巴聚集体培养物（HLAC），我们探索了淋巴组织中HIV感染期间CD4 T细胞是如何死亡的。我们的研究已经揭示了几个令人惊讶的结果，包括：（1）静止的"旁观者" CD4 T细胞，其不允许嗜X4的HIV-1的生产性感染，由于伴随着不完整的病毒DNA转录物在细胞质中的积累的失败的病毒感染而大量死亡;（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细胞由于针对病毒DNA发起的强大的先天免疫应答而死亡，导致干扰素的产生以及半胱天冬酶-3和半胱天冬酶-1的激活;（3）最终，这种应答导致炎性小体组装和半胱天冬酶-1激活，触发生物活性IL-1的释放。以及诱导焦亡，一种强烈的炎症形式的程序性细胞死亡。这些事件可以建立恶性循环，由此垂死的CD4 T细胞释放炎性介质，吸引额外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细胞耗竭通过焦亡可以被目前用于治疗II型糖尿病的特定类别的FDA批准的口服磺酰脲类药物完全阻断。我们现在提出一系列关键的新研究。在特定目标1中，我们将测试这种CD4 T细胞耗竭机制是否也延伸到CCR5表达的CD4 T细胞，这些细胞通常表现出更高的细胞活化状态，因此可能对流产感染不太敏感。在具体目标2中，我们提出鉴定检测病毒DNA的细胞质传感器。多个传感器可以激活干扰素反应和炎症小体内的半胱天冬酶-1的激活。在具体目标3中，我们提出鉴定招募caspase-1以加工和释放IL-1并诱导细胞凋亡的炎性小体。总之，这些研究将对HIV诱导的CD4 T细胞耗竭的潜在机制产生新的见解，这是AIDS的基本问题。这种新的理解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辅助手段，对于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.