Development of prime-boost immunization schemes to elicit VRC01-class bNAbs in polyclonal human BCR backgrounds

摘要 VRC01类广谱中和抗体(BNAbs)识别CD4- HIV-1包膜蛋白的结合位点。它们是已知的最有效的bNAb之一，可以保护动物免受 实验性S/艾滋病病毒感染，使其成为一种极具吸引力的抗体类型，可通过接种疫苗诱导产生。他们 从多个HIV-1感染者中分离出来，但都来自相同的VH1-2等位基因(*02) 以及少量轻链，它们都表达5个氨基酸的CDRL3。与成熟的、完全的 VRC01类抗体的突变形式，其推断的种系形式不识别环境病毒，也不 中和HIV-1病毒。这导致了一种假设，即以前的重组Env免疫原在 激活表达胚系VRC01-类B细胞受体(BCR)的幼稚B细胞，这可能在一定程度上解释了 为什么这些免疫原在疫苗研究中没有引起类似VRC01的抗体反应。我们报道了 一种C分支衍生的包膜蛋白(426c核心)的设计 在体内启动表达相应BCR的幼稚B细胞的扩张，但不足以诱导 这些BCR向它们的中和形式成熟。一个需要克服的主要障碍，以吸引任何 通过免疫的bNAbs是由于保守分子中存在的多糖施加的空间限制。 Env.D环的糖基化位点N276。这些糖链限制了对生殖系识别的表位的访问 VRC01类抗体，但由于抗体经历了体细胞超突变和基于亲和力的选择 他们“学习”如何绕过这一“立体障碍”。我们的免疫策略成功地引发了VRC01级 因此，bNAbs将取决于我们引导胚系VRC01类抗体进化的能力 特殊的成熟途径，绕过N276糖施加的限制。在本项目中，我们建议 使用以前没有测试过的概念和试剂，努力克服这些主要障碍，防止 通过免疫产生VRC01类抗体。具体来说，我们建议使用反独特型 针对生殖系VRC01类抗体的单抗(AiMAbs)可特异性增加 种系结合‘426c核心蛋白免疫前表达VRC01的B细胞的频率 免疫基因，然后用基于环境的试剂加强免疫，选择VRC01-B类细胞 这可以绕过N276葡聚糖施加的限制。我们的研究将在迭代中进行 表达VRC01类BCR的不同动物模型中的时尚，包括被设计为表达 多克隆人bcr谱系。

ABSTRACT VRC01-class broadly neutralizing antibodies (bNAbs) recognize a conserved epitope within the CD4- binding site of HIV-1 Env. They are among the most potent bNAbs known and protect animals from experimental S/HIV infection, making them a highly attractive type of antibody to elicit by vaccination. They have been isolated from multiple HIV-1-infected subjects, but are all derived from the same VH1-2 allele (*02) and a small number of light chains, all of which express a 5 amino-acid CDRL3. In contrast to the mature, fully mutated forms of VRC01-class antibodies, their inferred germline forms do not recognize Env and do not neutralize HIV-1. This led to the hypothesis that previous recombinant Env immunogens were ineffective in activating naïve B cells expressing germline VRC01-class B cell receptors (BCRs), which may, in part, explain why such immunogens have not elicited VRC01-like antibody responses in vaccine studies. We reported on the design of a clade C-derived Env protein (426c Core) that binds germline VRC01-class antibodies and initiates the expansion of naïve B cells expressing the corresponding BCRs in vivo, but is insufficient to induce the maturation of these BCRs towards their neutralizing forms. A major hurdle to overcome in order to elicit any bNAbs through immunization is due to steric restrictions imposed by glycans present at the conserved glycosylation site N276 in Loop D of Env. These glycans limit access to the epitope recognized by germline VRC01-class antibodies, but as the antibodies undergo somatic hypermutation and affinity-based selection they ‘learn’ how to bypass this steric block. The success of our immunization strategies to elicit VRC01-class bNAbs will therefore depend on our ability to guide the evolution of germline VRC01-class antibodies along particular maturation pathways to bypass the N276 glycan-imposed restrictions. In this Project we propose to use concepts and reagents, not tested previously, in an effort to overcome these major obstacles preventing the generation of VRC01-class antibodies by immunization. Specifically, we propose to use anti-idiotypic monoclonal antibodies (aiMAbs) against the germline VRC01-class antibodies to specifically increase the frequency of VRC01-expressing B cells prior to immunization with the germline-binding’ 426c Core immunogen, followed by booster immunizations with Env-based reagents that select for VRC01-class B cells that can bypass the restrictions imposed by the N276 glycans. Our studies will be performed in an iterative fashion in diverse animal models that express VRC01-class BCRs, including mice engineered to express a polyclonal human BCR repertoire.