绝大多数HIV感染者在缺乏抗逆转录病毒治疗（antiretroviral therapy，ART）的情况下，表现为病毒快速复制和CD4⁺ T细胞逐渐减少的疾病进程。然而，存在一小部分HIV感染群体能有效地控制病毒复制，即能自发控制病毒复制的精英控制者（elite controllers，ECs）或经抗逆转录病毒治疗（ART）实现停药后病毒持久性控制的治疗后控制者（posttreatment controllers，PTCs）。ECs和PTCs是阐明HIV病毒控制机制和研究HIV缓解或治愈的关键模型。近年来，大量研究表明免疫检查点（immune checkpoints，ICs）通过调控HIV潜伏库的持续存在和T细胞功能影响HIV感染的疾病进展。然而，免疫检查点是否参与ECs和PTCs的形成尚不明确。因此，本课题利用ECs和PTCs恒河猴模型，通过进展猴与EC猴、停药后反弹猴与PTC猴比较，开展系统地纵向研究，探寻免疫检查点在病毒持久性控制中的作用机制以及HIV精英控制的形成机制，有助于实现长期病毒缓解的HIV新型治疗策略的研发和优化。

第一部分 免疫检查点表达对强效HIV膜融合抑制剂治疗SHIV_SF162P3感染恒河猴实现停药后病毒持久控制的影响

    HIV潜伏库和宿主免疫应答是影响PTCs形成的两大关键因素，较小的HIV潜伏库和较强的病毒特异性免疫应答有利于PTCs对病毒的持久控制。免疫检查点分子（ICs）在T细胞上的表达被证明与HIV病毒潜伏及HIV特异性T细胞免疫功能密切相关，然而其发挥的免疫学功能是否参与PTCs的形成尚不清楚。本研究通过对强效HIV膜融合抑制剂（lipopeptide, LP-98）治疗停药后的SHIV_SF162P3-稳定的病毒控制猴（stable virologic control, SVC）和SHIV_SF162P3-稳定的病毒反弹猴（stable virologic rebound，SVR）进行ICs表达及免疫学功能的分析，探究ICs对PTCs形成的影响。我们发现与SVR猴相比，表达TIGIT（T cell immunoglobulin and ITIM domain，T细胞免疫球蛋白和ITIM结构域）和BTLA（B and T lymphocyte attenuator，B和T淋巴细胞衰减子）的CD4⁺ T细胞、静息CD4⁺ T细胞和静息中央记忆CD4⁺ T细胞（central memory CD4⁺ T cell，CD4⁺ TCM）频率分别在SVC猴浅表和深部淋巴结中显著性降低，而且，TIGIT在SVC猴外周血和淋巴结的CD8⁺ T细胞上的表达降低诱导了更强的SIV特异性CD8⁺ T细胞功能。此外，RNA-Seq转录组测序结果显示浅表淋巴结单个核细胞（lymph node mononuclear cells，LNMCs）中主要以TIGIT来调控免疫系统对病毒的控制，而深部LNMCs中则以BTLA促进病毒的深潜伏以此形成对病毒的有效控制。

第二部分 免疫检查点表达对SHIV_SF162P3感染恒河猴实现病毒自发控制的影响

    精英控制者的研究有利于揭示实现自发HIV控制的病毒学和免疫学机制，其中宿主遗传因素、免疫反应因素和病毒因素与ECs的表型紧密相关，这能为开发HIV功能性治愈疗法提供潜在的理论依据。近年来，很多研究表明免疫检查点分子可通过富集病毒潜伏库并抑制T细胞反应来影响HIV感染疾病进展，但其在ECs形成中的作用机制尚不明确。本研究中，我们选取8只黏膜途径感染SHIV_SF162P3的恒河猴模型，根据病毒载量将其分为疾病进展组（progressors，PGs）和精英控制组（ECs），对其ICs的表达量、原病毒水平及SIV特异性CD8⁺ T细胞功能进行检测并分析，从而探究ICs是否调控病毒潜伏及T细胞免疫反应来促进ECs体内的病毒控制。我们发现在感染病毒前，EC猴外周血中总ICs⁺ CD4⁺和CD8⁺ T细胞频率明显低于PG猴。此外，在SHIV_SF162P3感染后，与PG猴相比，EC猴外周血表达BTLA的静息CD4⁺ T细胞频率和浅表/深部淋巴结中表达BTLA和TIGIT的静息CD4⁺ T细胞频率均显著降低，且其频率均与原病毒水平呈正相关。EC猴CD8⁺ T细胞表达较低水平的TIGIT并表现出更强的病毒特异性免疫反应。同时，RNA-Seq转录组测序结果表明外周血单个核细胞（peripheral blood mononuclear cells，PBMCs）中BTLA和TIGIT主要通过与免疫调节信号通路相互作用来实现病毒的有效控制。

    综上，本课题利用PTCs和ECs动物模型模拟了HIV感染控制者，探讨了ICs在HIV持久性控制中的作用及分子机制，提示了BTLA和TIGIT可能是潜在的HIV治疗靶点，推测联合阻断BTLA和TIGIT有利于减少HIV潜伏库并提高CD8⁺ T细胞免疫反应，有望实现对HIV的持久控制，为提出HIV治疗新策略奠定理论基础。

    The vast majority of HIV-infected individuals generally show the characteristics of HIV progression, such as rapid viral replication and loss of CD4⁺ T cells in the absence of antiretroviral therapy (antiretroviral therapy, ART). However, there are a small subset of HIV-infected people who can effectively control viral infection, that is, elite controllers (elite controllers, ECs) who can spontaneously control viral replication, and posttreatment controllers (posttreatment controllers, PTCs) who can control viral replication post ART. ECs and PTCs can be considered as research models for HIV remission or HIV cure to clarify the mechanism of HIV control. In recent years, various studies have shown that immune checkpoints (immune checkpoints, ICs) can regulate the HIV latency and T cell function to affect the progress of HIV infection. However, it is still unknown whether immune checkpoints pose vital role on the formation of ECs and PTCs. Therefore, we exploit the rhesus monkey models of ECs and PTCs to explore the role and mechanism of ICs in the durable control of virus. Clarifying the specific mechanism of the HIV control is conducive to the development and optimization of HIV treatment strategies to achieve long-term virus remission.

Part I: Lower expression of BTLA and TIGIT on T lymphocytes determines the durable control of SHIV_SF162P3 infection in rhesus macaques treated with LP-98

    HIV reservoir and immune response are two key factors affecting the formation of PTCs. Small HIV reservoir and robust immune response promote the effective HIV control of PTCs. The expression of immune checkpoint (ICs) on T cells has been proved to be closely related to HIV latency and HIV-specific T cell immune function. However, it is not clear whether they play an immunological role in the formation of PTCs. In this study, we have analyzed the expression and immunological effects of ICs in SHIV_SF162P3 infected monkeys with stable virological control (stable virologic control, SVC) and stable virological rebound (stable virologic rebound, SVR) treated with a powerful HIV fusion-inhibitory lipopeptide LP-98 to explore the effect of ICs on durable control SHIV_SF162P3 for PTCs. We have found that the frequencies of CD4⁺ T cells, resting CD4⁺ T cells and resting central memory CD4⁺ T cells (central memory CD4⁺ T cell, CD4⁺ TCM) expressing TIGIT and BTLA are significantly reduced in superficial or deep lymph nodes of SVC monkeys respectively when compared with SVR monkeys. Simultaneously, the decreased expression of TIGIT on CD8⁺ T cells in peripheral blood and lymph nodes of SVC monkeys is accompanied by the stronger SIV specific CD8⁺ T cell function. In addition, RNA sequencing also reveals that TIGIT mainly regulates the antiviral immune system in superficial lymph node mononuclear cells (lymph node mononuclear cells, LNMCs), while BTLA promote the deep virus latency in deep LNMCs, facilitating to drive effective control of virus.

Part II: Lower expression of BTLA and TIGIT on T lymphocytes contributes to the durable control of SHIV_SF162P3 infection in elite control rhesus macaques

    The researches that focus on elite controllers have revealed the virological and immunological mechanisms to achieve spontaneous control of HIV, in which host genetic factors, immune response factors and viral factors are closely related to the phenotype of ECs, providing a potential theoretical basis for the development of HIV functional cure therapy. Recently, a growing number of studies have shown that immune checkpoints (ICs) participate in affecting the progress of HIV infection by enriching virus latency and inhibiting T cell response, where the role and molecular mechanism of ICs in the formation of ECs are unclear and need to be studied. In this study, we have selected 8 rhesus monkey models infected with SHIV_SF162P3 via mucosal route, and divide them into progressive group (progressors, PGs) and elite control group (ECs) according to the plasma viral load. The ICs expression, provirus level and SIV-specific CD8⁺ T cell function are detected and analyzed to explore whether ICs regulate virus latency and T cell immune response to determine the control of virus in ECs. We have found that the frequencies of total ICs⁺ CD4⁺ and CD8⁺ T cells in peripheral bloods of EC monkeys are significantly lower than those of PG monkeys before virus challenge. In addition, compared with PG monkeys, the frequencies of resting CD4⁺ T cells expressing BTLA in peripheral bloods and BTLA/TIGIT in superficial and deep lymph nodes of EC monkeys decrease significantly post virus challenge, which are positively correlated with the level of provirus. EC monkeys elicit stronger virus-specific CD8⁺ T cell responses accompanied by the attenuation of TIGIT expression. In additional, RNA sequencing results show that BTLA and TIGIT mainly manage effective virus control by interacting with immune regulatory signal pathways in peripheral blood mononuclear cells (peripheral blood mononuclear cells, PBMCs).

    In conclusion, this study exploits PTCs and ECs animal models to investigate the role and related mechanisms of ICs in the formation of HIV controllers. Our findings demonstrate that BTLA and TIGIT are potential targets for HIV treatment, proposing that the combined blocking of BTLA and TIGIT is conducive to reducing the HIV latency and improving the T cell immune responses, and achieving durable control of HIV and provide a novel strategy for HIV treatment.