Delineating CD4 dependency of HIV-1: Adaptation to infect low level CD4 expressing target cells widens cellular tropism but severely impacts on envelope functionality.
Delineating CD4 dependency of HIV-1: Adaptation to infect low level CD4 expressing target cells widens cellular tropism but severely impacts on envelope functionality.
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DOI：
10.1371/journal.ppat.1006255
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发表时间：
2017-03
期刊：
影响因子：
6.7
通讯作者：
Trkola A
中科院分区：
文献类型：
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作者：
Beauparlant D;Rusert P;Magnus C;Kadelka C;Weber J;Uhr T;Zagordi O;Oberle C;Duenas-Decamp MJ;Clapham PR;Metzner KJ;Günthard HF;Trkola A
HIV-1感染的一个标志是病毒主要靶细胞（活化的CD 4 + T细胞）的数量持续下降。随着CD 4 + T细胞水平的降低，利用替代细胞类型和受体的能力，包括表达低CD 4受体水平的细胞，如巨噬细胞，因此变得至关重要。为了探索HIV-1通过感染具有较低CD 4水平的细胞而获得更广泛宿主细胞范围的进化路径，我们使用原型亚型B，R5嗜性毒株，在模拟CD 4高靶细胞下降的体外培养条件下，剖析了HIV-1与CD 4相互作用的进化。对CD 4low靶标的适应被证明严重改变了包膜功能，包括三聚体开放，如对CD 4的更高亲和力和对中和抗体的屏蔽损失所示。我们观察到对CD 4 high靶细胞的感染性显著降低，但对CD 4low靶细胞（包括巨噬细胞）的感染性持续存在。有趣的是，对CD 4low靶点的适应改变了进入过程的动力学，导致进入过程中CD 4的快速接合和CD 4与CCR 5结合之间的过渡时间延长。在某些中枢神经系统（CNS）衍生的嗜巨噬细胞病毒中也观察到这种表型，这突出表明我们定义的体外适应CD 4low靶点的功能扰动发生在体内。总的来说，我们的研究结果表明，CD 4low适应信封可能表现出严重的缺陷，在进入健身和屏蔽早期在其演变。考虑到这一点，对CD 4low靶点的适应可能优先发生在庇护和免疫豁免的环境中，如CNS，以允许发生适应性恢复补偿突变。未经治疗的HIV-1感染导致CD 4 + T细胞的逐渐耗尽，迫使病毒不断适应不断减少的合适靶细胞数量。我们的数据基于在高度受控的体外环境中的实验，描述了包膜适应的一种途径，该途径允许病毒感染表达少量CD 4的靶细胞，如巨噬细胞。与病毒感染表达低水平CD 4的靶细胞的适应相关的功能性包膜表型的分析突出了病毒的改变的进入动力学。这些改变导致CD 4诱导的中和敏感表位的暴露延长，以及对靶向CD 4结合位点和V3环的中和抗体的敏感性增加。有趣的是，从感染个体的中枢神经系统（CNS）中分离的嗜巨噬细胞HIV-1分离株也观察到了类似的表型，这增加了免疫豁免的CNS可能有利于利用包膜变体发展嗜巨噬细胞/低CD 4水平的可能性。
A hallmark of HIV-1 infection is the continuously declining number of the virus’ predominant target cells, activated CD4+ T cells. With diminishing CD4+ T cell levels, the capacity to utilize alternate cell types and receptors, including cells that express low CD4 receptor levels such as macrophages, thus becomes crucial. To explore evolutionary paths that allow HIV-1 to acquire a wider host cell range by infecting cells with lower CD4 levels, we dissected the evolution of the envelope-CD4 interaction under in vitro culture conditions that mimicked the decline of CD4high target cells, using a prototypic subtype B, R5-tropic strain. Adaptation to CD4low targets proved to severely alter envelope functions including trimer opening as indicated by a higher affinity to CD4 and loss in shielding against neutralizing antibodies. We observed a strikingly decreased infectivity on CD4high target cells, but sustained infectivity on CD4low targets, including macrophages. Intriguingly, the adaptation to CD4low targets altered the kinetic of the entry process, leading to rapid CD4 engagement and an extended transition time between CD4 and CCR5 binding during entry. This phenotype was also observed for certain central nervous system (CNS) derived macrophage-tropic viruses, highlighting that the functional perturbation we defined upon in vitro adaptation to CD4low targets occurs in vivo. Collectively, our findings suggest that CD4low adapted envelopes may exhibit severe deficiencies in entry fitness and shielding early in their evolution. Considering this, adaptation to CD4low targets may preferentially occur in a sheltered and immune-privileged environment such as the CNS to allow fitness restoring compensatory mutations to occur. Untreated HIV-1 infection leads to a gradual depletion of CD4+ T cells forcing the virus to continuously adapt to an ever-decreasing number of suitable target cells. Our data based on experiments in a highly controlled in vitro setting describe one avenue of envelope adaptation that allows the virus to infect target cells expressing low amounts of CD4 such as macrophages. Analysis of the functional envelope phenotypes associated with adaptation of the virus to infect target cells expressing low levels of CD4 highlighted altered entry kinetics of the virus. These alterations resulted in extended exposure of CD4-induced neutralization sensitive epitopes in combination with an increased sensitivity to neutralizing antibodies targeting the CD4 binding site and the V3 loop. Interestingly, a similar phenotype was observed for macrophage-tropic HIV-1 isolates derived from the central nervous system (CNS) of infected individuals raising the possibility that the immune-privileged CNS may favor the development of macrophage-tropic / low CD4 level utilizing envelope variants.