Department of Immunology and Microbiology, The Scripps Research Institute, La Jolla, California, USA.
J Virol. 2021 Jun 10;95(13):e0000521. doi: 10.1128/JVI.00005-21.
A major goal of HIV vaccine design is to elicit broadly neutralizing antibodies (bNAbs). Such bNAbs target HIV's trimeric, membrane-embedded envelope glycoprotein spikes (mEnv). Soluble Env (sEnv) trimers have been used as vaccines, but engineering sEnvs for stability, multivalency, and desired antigenicity is problematic and deletes key neutralizing epitopes on glycoprotein 41 (gp41) while creating neoepitopes that elicit unwanted antibodies. Meanwhile, multivalent mEnv vaccines are challenging to develop due to trimer instability and low mEnv copy number amid other extraneous proteins on virus-like particles. Here, we describe a multivalent mEnv vaccine platform that does not require protein engineering or extraneous proteins. mEnv trimers were fixed, purified, and combined with naked liposomes in mild detergent. On removal of detergent, mEnv spikes were observed embedded in liposome particles (mean diameter, 133 nm) in correct orientation. These particles were recognized by HIV bNAbs and not non-NAbs and are designated nv iposomes (MELs). Following a sequential immunization scheme in rabbits, MELs elicited antibodies that neutralized tier 2 HIV isolates. Analysis of serum antibody specificities, including those to epitopes involving a missing conserved N-glycosylation site at position 197 near the CD4 binding site on two of the immunogens, provides clues on how NAb responses can be improved with modified immunogens. In sum, MELs are a biochemically defined platform that enables rational immunization strategies to elicit HIV bNAbs using multimerized mEnv. A vaccine that induced broadly neutralizing antibodies against HIV would likely end the AIDS pandemic. Such antibodies target embrane-embedded elope glycoprotein spikes (mEnv) that HIV uses to enter cells. Due to HIV Env's low expression and instability, soluble stabilized Env trimers have been used as vaccine candidates, but these have an altered base that disrupts targets of HIV broadly neutralizing antibodies that bind near the membrane and are not available for all HIV isolates. Here, we describe membrane Env liposomes (MELs) that display a multivalent array of stable mEnvs on liposome particles. MELs showed the expected antibody recognition properties, including targeting parts of mEnv missing on soluble Envs. Immunization with MELs elicited antibodies that neutralized diverse HIV isolates. The MEL platform facilitates vaccine development with potentially any HIV Env at high valency, and a similar approach may be useful for eliciting antibodies to membrane-embedded targets of therapeutic interest.
HIV 疫苗设计的一个主要目标是引发广泛中和抗体 (bNAb)。此类 bNAb 靶向 HIV 的三聚体、膜嵌入包膜糖蛋白刺突（mEnv）。可溶性包膜 (sEnv) 三聚体已被用作疫苗，但为了稳定性、多价性和所需抗原性而对 sEnv 进行工程改造存在问题，并且在删除糖蛋白 41 (gp41) 上的关键中和表位的同时会产生引发不需要抗体的新表位。同时，由于三聚体不稳定以及病毒样颗粒中存在其他额外蛋白质，多价 mEnv 疫苗的开发具有挑战性。在这里，我们描述了一种不需要蛋白质工程或额外蛋白质的多价 mEnv 疫苗平台。mEnv 三聚体被固定、纯化并与裸脂质体在温和去污剂中结合。在去除去污剂后，观察到 mEnv 刺突以正确的方向嵌入脂质体颗粒（平均直径 133nm）中。这些颗粒被 HIV bNAb 识别，而非非 bNAb 识别，并且被指定为 nv 脂质体（MEL）。在兔子中进行序贯免疫方案后，MEL 引发的抗体可中和第 2 层 HIV 分离株。对血清抗体特异性的分析，包括针对两种免疫原上靠近 CD4 结合位点的位置 197 处缺失保守 N-糖基化位点的表位的抗体特异性的分析，为如何通过修饰免疫原来改善 NAb 反应提供了线索。总之，MEL 是一种生化定义的平台，可使用多聚化 mEnv 来实现引发 HIV bNAb 的合理免疫策略。 诱导针对 HIV 的广泛中和抗体的疫苗可能会终结艾滋病大流行。此类抗体靶向 HIV 用于进入细胞的膜嵌入 elope 糖蛋白刺突（mEnv）。由于 HIVEnv 的低表达和不稳定性，已使用可溶性稳定化 Env 三聚体作为候选疫苗，但这些三聚体具有改变的基础，破坏了与膜结合的 HIV 广泛中和抗体的靶标，并且不适用于所有 HIV 分离株。在这里，我们描述了显示在脂质体颗粒上的稳定 mEnv 的多价阵列的膜 Env 脂质体（MEL）。MEL 显示出预期的抗体识别特性，包括针对可溶性 Env 上缺失的 mEnv 部分的靶向。用 MEL 免疫引发的抗体可中和多种 HIV 分离株。MEL 平台可促进具有高效价的任何 HIVEnv 的疫苗开发，类似的方法可能对引发针对治疗相关膜嵌入靶标的抗体有用。
