Guiding the humoral response against HIV-1 toward a MPER proximal region by immunization with a VLP-formulated antibody-selected envelope variant. Human immunodeficiency virus 1

Preventive HIV-1 vaccine strategies rely on the elicitation of broadly neutralizingantibody (bNAb) responses, but their induction in vivo by vaccination remainschallenging. Considering that the ability of an epitope to elicit effective humoralimmunity depends on its exposure on the virion, we have used a reverse geneticsapproach to select variants from an HIV-1 AC10_29 randomly mutated envelope librarythat showed increased affinity for a selected bNAb (4E10 bNAb targeting the HIV-1MPER region). Isolated envelope sequences were analyzed by deep-sequencingshowing a small number of dominant changes, including the loss of four potential Nlinkedglycosylation sites and disruption of the V1/V2 loop. Accordingly, the dominantvariant (LR1-C1), showed not only increased affinity for MPER bNAbs 4E10 and 2F5,but also higher affinity for an additional antibody targeting the V3 loop (447-52D) thatcould be a consequence of an open conformation tier 1-like. Furthermore, the aminoacids specific for the selected variant are associated with an increased sensitivity for4E10 and 2F5 antibodies. In vivo studies showed that sera from mice immunized withLR1-C1 viruses possessed an improved neutralizing activity compared to the wild-typeAC10_29 env. While Virus Like Particles (VLPs) carrying this envelope were unable toinduce detectable neutralizing activity in immunized rabbits, one animal showedantibody response to the 4E10-proximal region. Our data establish a novel approachthat has the potential to yield HIV envelope immunogen sequences that direct antibodyresponses to specific envelope regions.

预防性HIV-1疫苗策略依赖于广谱中和抗体（broadly neutralizing antibody，bNAb）应答的诱导，但通过疫苗接种在体内诱导此类应答仍极具挑战。鉴于表位诱导有效体液免疫的能力取决于其在病毒粒子表面的暴露情况，我们采用反向遗传学策略，从经随机诱变的HIV-1 AC10_29包膜文库中筛选出对选定bNAb（靶向HIV-1膜近端外区（membrane-proximal external region，MPER）的4E10 bNAb）亲和力提升的变异株。通过深度测序对分离得到的包膜序列进行分析，结果显示存在少量显性突变，包括4个潜在N-连接糖基化位点的丢失以及V1/V2环的破坏。相应地，优势变异株（LR1-C1）不仅对MPER靶向的bNAbs 4E10和2F5的亲和力有所提升，对另一株靶向V3环的抗体（447-52D）的亲和力也更高，这一现象可能源于其开放构象的类1型特征。此外，该筛选得到的变异株所特有的氨基酸残基，使其对4E10和2F5抗体的敏感性提升。体内研究表明，与野生型AC10_29 env免疫的小鼠血清相比，接种LR1-C1病毒的小鼠血清所具有的中和活性得到了提升。尽管携带该包膜的病毒样颗粒（Virus Like Particles，VLPs）无法在免疫兔中诱导出可检测到的中和活性，但其中一只兔子产生了针对4E10表位邻近区的抗体应答。本研究建立了一种全新的策略，有望获得能够引导抗体应答靶向包膜特定区域的HIV包膜免疫原序列。