Non-CD4 tropic SIV: Enhancing CD4 T-cell help in antiviral immune responses

描述(由申请人提供)：HIV和SIV致病机制的一个不变特征是CD4趋向性，由包膜糖蛋白上高度保守的CD4结合位点介导。通过将感染集中在为获得性免疫提供帮助的T细胞亚群(如Th1、Th17、Tfh)上，CD4的趋向性很可能对抗病毒免疫反应产生深远影响，最终不足以遏制病毒复制和疾病进展。Gp120与CD_4的结合也可能破坏CD_4‘S与抗原提呈细胞上的HLAII类的生理相互作用，这是T细胞免疫辅助功能的基础。我们正在探索一种高度创新的假说，即慢病毒被设计成在缺乏CD4结合位点和CD4趋向性的情况下保持感染性，将在其发病机制中发生根本改变，使其能够产生更强大的辅助T细胞功能，这在嗜CD4感染的情况下通常是不允许的。了解在这方面可能扩大的抗病毒免疫反应范围可能会对艾滋病毒疫苗领域有所帮助。我们已经获得了一种高度不依赖于CD4的SIVmac239变体，并表明即使在其CD4结合部位被去除后，它在体外和体内对猕猴也是有感染力的。这种病毒被称为“iMac-？d”，在血浆中复制到一个较高的急性高峰，然后被控制在精英水平；感染巨噬细胞和其他非T细胞类型；不消耗CD4+T细胞；保留结节中的皮质T细胞区域；并在血浆病毒血症清除很长时间后产生高水平和持续的中和抗体。这种第一种非嗜CD4的灵长类慢病毒将以4个具体目标进行评估：1)在体内确定和表征其致病性、嗜性，以及与嗜CD4的SIVmac239感染相比在宿主体液和细胞抗病毒免疫反应中的定性和/或定量差异；2)识别负责iMac-？D控制的宿主适应性免疫反应的成分，并确定它们是否能够保护动物免受致病的异源SIV的攻击；3)通过评估该病毒保留其CD4结合部位时的致病性和感染的免疫学参数，进一步检查CD4相互作用的影响；以及4)将这种方法扩展到HIV-1包膜糖蛋白，方法是在体外和体内创建并鉴定一种非嗜CD4的猿猴/人类免疫缺陷病毒(SHIV)，该病毒与iMac-D一样，可以在恒河猴PBMC和猕猴中复制，但缺乏CD4结合位点。这种非CD4嗜性的SIV将为进一步的研究提供一座桥梁，该研究将在CD4+辅助T细胞备用的情况下与抗HIV-1免疫反应相关。这些独特的病毒和这种新的模型将使我们能够解决艾滋病毒和SIV发病机制和疫苗设计的新的和潜在的范式转变主题。

DESCRIPTION (provided by applicant): An invariant feature of HIV and SIV pathogenesis is CD4 tropism, mediated by a highly conserved CD4 binding site on the envelope glycoprotein. By focusing infection onto T-cell subsets that provide help for adaptive immunity (e.g. Th1, Th17, Tfh), it is likely that CD4 tropism has profound effects on antiviral immune responses, which are ultimately inadequate to contain viral replication and disease progression. Binding of gp120 to CD4 also has the potential to disrupt CD4's physiologic interaction with HLA class-II on antigen presenting cells, which underlies T-cell immunologic helper functions. We are exploring a highly innovative hypothesis that lentiviruses engineered to retain infectivity while lacking a CD4 binding site and CD4 tropism would be fundamentally altered in their pathogenesis, enabling more potent helper T-cell functions to be generated that are typically not permitted in the context of CD4-tropic infection. An understanding of the possible expansion in the repertoire of antiviral immune responses in this context could be informative for the HIV vaccine field. We have derived a highly CD4-independent variant of SIVmac239 and shown that it is infectious in vitro and in vivo in rhesus macaques even after its CD4 binding site has been ablated. This virus, termed "iMac-?D," replicates to a high acute peak in plasma and is then controlled to elite levels; infects macrophages and other non-T-cell types; does not deplete CD4+ T-cells; spares cortical T-cell regions in nodes; and generates high and sustained levels of neutralizing antibodies long after plasma viremia is cleared. This first non-CD4 tropic primate lentivirus will be evaluated with 4 specific aims: 1) To define and characterize in vivo its pathogenicity, tropism, and qualitative and/or quantitative differences in host humoral and cellular antiviral immune responses compared to CD4-tropic SIVmac239 infection; 2) To identify components of the host adaptive immune response responsible for iMac-?D's control and to determine if they can protect animals from a pathogenic heterologous SIV challenge; 3) To further examine the effects of CD4 interactions by evaluating pathogenicity and immunological parameters of infection when this virus retains its CD4 binding site; and 4) To extend this approach to an HIV-1 envelope glycoprotein by creating and characterizing in vitro and in vivo a non-CD4 tropic, simian/human immunodeficiency virus (SHIV) that, like iMac- D, can replicate in rhesus PBMCs and macaques while lacking a CD4 binding site. This non-CD4 tropic SHIV will provide a bridge to further studies that will be relevant to anti-HIV-1 immune responses in the setting of CD4+ helper T-cell sparing. These unique viruses and this novel model will enable us to address new and potentially paradigm-shifting themes of HIV and SIV pathogenesis and vaccine design.