The role of antibody and the Fc neonatal receptor in transmitted/founder strain selection

 描述(由申请人提供)：在体外，环境特异性免疫球蛋白显著增强HIV-1和SIV跨生殖器和肠道上皮细胞的细胞转运。这种增强的跨细胞作用是由Fc新生儿受体(FcRN)介导的，FcRN在低pH时与含有LGG的免疫复合体(IC)结合，穿梭于上皮细胞，并在中性pH下释放它们。我们发现，在四种不同的疫苗方案下，免疫猕猴在反复低剂量SIVmac251直肠攻击后，FcRN介导的血清转胞活性与感染动物的T/F变异体的数量密切相关。此外，使用基于ALVAC的疫苗方案提供高达40%的保护，具有高疫苗诱导的血清FcRN介导的细胞转运活性的动物比那些低活性的动物感染的挑战更少，而保持未感染的动物总是具有非常低的活性。因此，疫苗同时保护了一些动物，同时导致了感染，并在其他动物中产生了更多的T/F菌株。我们解决了这个难题，并试图通过检验以下假设来理解有益抗体和有害抗体之间的关系：1)疫苗诱导的抗病毒抗体和增强抗体的相对水平是T/F变种选择和感染获得的关键决定因素。我们还将探索为什么FcRN介导的跨细胞作用从机制上对感染有如此强烈的影响。FcRN只有在低pH值(=~6.5)时才能很好地与Ig G或Ics结合，我们的初步数据表明猕猴直肠分泌物很少是酸性的。然而，在中性pH条件下与IC结合的Fc受体(FcγRs，FcγR)与FcRN一起在猕猴直肠上皮细胞中表达。鉴于这些和其他观察结果，我们提出了一个新的假设：2)感染IC通过Fcγ受体进入直肠上皮细胞，进入通常是pH中性的直肠黏膜，然后依赖FcRN递送到发生感染的上皮下组织。为了验证这些假说，我们将实现以下目标：1.描述ALVAC-SIV/gp120疫苗接种后抗病毒抗体、增强抗体、T/F株选择和感染结果之间的关系。我们将测量疫苗诱导的中和抗体、ADCC抗体、病毒捕获抗体和FcRN介导的直肠免疫球蛋白抗体对一组在反复低剂量SIVmac251直肠攻击后确定感染的T/F菌株的广度和效力。我们还将用一种新的方法在体外模拟T/F选择。具体目的2.确定FcRN介导的细胞转运和感染结局之间的联系的潜在机制。利用工程细胞和直肠组织外植体，我们将确定在依赖FcRN的上皮细胞穿梭之前，SIV或HIV-1-IC是否通过Fcγ受体内化。我们发现了一种独特的抗体活性，它与疫苗接种后的感染结果密切相关。确定这一活动的含义和机制可能会导致对对立抗体功能如何相互作用的新见解，杀微生物剂的新靶点，以及以最小有害影响产生最大抗病毒反应的疫苗策略。

 DESCRIPTION (provided by applicant): Env-specific IgG markedly enhances HIV-1 and SIV transcytosis across genital and gut epithelial cells in vitro. The enhanced transcytosis is mediated by the Fc neonatal receptor (FcRn), which binds lgG-containing immune complexes (ICs) at low pH, shuttles them through epithelial cells, and releases them at neutral pH. We found that with four different vaccine regimens, FcRn-mediated transcytosis activity in serum of vaccinated macaques strongly correlated with the number of T/F variants infecting the animals after repeated low-dose SIVmac251 rectal challenges. Moreover, with ALVAC-based vaccine regimens that provided up to 40% protection, animals with high vaccine-induced serum FcRn-mediated transcytosis activity became infected with fewer challenges than those with low activity, and animals that remained uninfected always had very low activity. Thus, vaccines simultaneously protected some animals while driving infection and more T/F strains in others. We address this conundrum and so seek to understand relationships between beneficial and deleterious antibodies by testing the following hypothesis: 1) relative levels of vaccine-induced antiviral and enhancing antibodies are key determinants of T/F variant selection and infection acquisition. We will also explore why, mechanistically, FcRn-mediated transcytosis so strongly impacts infection. FcRn only binds well to IgG or ICs at low pH (=~6.5), and our preliminary data indicate that macaque rectal secretions are infrequently acidic. However, Fcγ receptors (FcγRs), which bind ICs at neutral pH, are expressed along with FcRn in macaque rectal epithelial cells. In view of these and other observations, we propose a novel hypothesis: 2) infectious ICs enter rectal epithelial cells via FcγRs at the usually pH-neutral rectal mucosa, followed by FcRn-dependent delivery to subepithelial tissue where infection occurs. To test these hypotheses we will accomplish the following: Specific Aim 1. Delineate relationships between antiviral antibodies, enhancing antibodies, T/F strain selection, and infection outcome following ALVAC-SIV/gp120 vaccination. We will measure the breadth and potency of vaccine-induced neutralizing, ADCC, virus-capturing, and FcRn-mediated enhancing antibodies in serum and rectal IgG against a panel of T/F strains that established infection after repeated low dose SIVmac251 rectal challenge. We will also model T/F selection in vitro with a novel approach. Specific Aim 2. Determine the mechanisms underlying the association between FcRn-mediated transcytosis and infection outcomes. Using engineered cells and rectal tissue explants, we will determine if SIV- or HIV-1-ICs are internalized via FcγRs prior to FcRn-dependent shuttling across the epithelium. We have uncovered a unique antibody activity that is strongly associated with infection outcome following vaccination. Defining the implications and mechanisms of this activity could lead to new insights into how opposing antibody functions interact with each other, to novel targets for microbicides, and to vaccine strategies that elicit maximal antiviral responses with minimal deleterious effects.