Boosting of HIV envelope CD4 binding site antibodies with long variable heavy third complementarity determining region in the randomized double blind RV305 HIV-1 vaccine trial

The canary pox vector and gp120 vaccine (ALVAC-HIV and AIDSVAX B/E gp120) in the RV144 HIV-1 vaccine trial conferred an estimated 31% vaccine efficacy. Although the vaccine Env AE.A244 gp120 is antigenic for the unmutated common ancestor of V1V2 broadly neutralizing antibody (bnAbs), no plasma bnAb activity was induced. The RV305 (NCT01435135) HIV-1 clinical trial was a placebo-controlled randomized double-blinded study that assessed the safety and efficacy of vaccine boosting on B cell repertoires. HIV-1-uninfected RV144 vaccine recipients were reimmunized 6–8 years later with AIDSVAX B/E gp120 alone, ALVAC-HIV alone, or a combination of ALVAC-HIV and AIDSVAX B/E gp120 in the RV305 trial. Env-specific post-RV144 and RV305 boost memory B cell VH mutation frequencies increased from 2.9% post-RV144 to 6.7% post-RV305. The vaccine was well tolerated with no adverse events reports. While post-boost plasma did not have bnAb activity, the vaccine boosts expanded a pool of envelope CD4 binding site (bs)-reactive memory B cells with long third heavy chain complementarity determining regions (HCDR3) whose germline precursors and affinity matured B cell clonal lineage members neutralized the HIV-1 CRF01 AE tier 2 (difficult to neutralize) primary isolate, CNE8. Electron microscopy of two of these antibodies bound with near-native gp140 trimers showed that they recognized an open conformation of the Env trimer. Although late boosting of RV144 vaccinees expanded a novel pool of neutralizing B cell clonal lineages, we hypothesize that boosts with stably closed trimers would be necessary to elicit antibodies with greater breadth of tier 2 HIV-1 strains.Trial Registration: ClinicalTrials.gov NCT01435135在RV144 HIV-1疫苗临床试验中，金丝雀痘载体（canary pox vector）与gp120疫苗（ALVAC-HIV及AIDSVAX B/E gp120）联合使用的疫苗，经评估其疫苗效力约为31%。尽管该疫苗所使用的包膜糖蛋白（Env）AE.A244 gp120可针对V1V2广谱中和抗体（broadly neutralizing antibody, bnAbs）的未突变共同祖先发挥抗原性，但并未诱导出血浆广谱中和抗体活性。 RV305（临床试验编号NCT01435135）HIV-1临床试验为一项安慰剂对照随机双盲研究，旨在评估加强免疫对B细胞库（B cell repertoires）的安全性与有效性。RV144疫苗接种者中未感染HIV-1的受试者，在完成基础免疫6~8年后接受加强免疫，加强免疫方案分别为单独接种AIDSVAX B/E gp120、单独接种ALVAC-HIV，或ALVAC-HIV与AIDSVAX B/E gp120联合接种。RV144基础免疫后及RV305加强免疫后的Env特异性记忆B细胞VH突变频率，从RV144免疫后的2.9%提升至RV305加强免疫后的6.7%。该疫苗耐受性良好，未报告任何不良事件。 尽管加强免疫后的血浆未检测到广谱中和抗体活性，但该加强免疫策略扩增了一群携带较长重链第三互补决定区（heavy chain complementarity determining region 3, HCDR3）的包膜CD4结合位点（CD4 binding site, bs）反应性记忆B细胞；其种系前体及亲和力成熟的B细胞克隆谱系成员，可中和HIV-1 CRF01_AE 2级（难以中和）原代分离株CNE8。对其中两株与近天然构象gp140三聚体（gp140 trimers）结合的抗体进行电子显微镜（electron microscopy）观察发现，它们识别Env三聚体的开放构象。 尽管对RV144疫苗接种者实施晚期加强免疫，可扩增出一群新型的中和性B细胞克隆谱系，但我们推测，使用稳定闭合构象的三聚体进行加强免疫，才有可能诱导出对2级HIV-1毒株具有更广中和广度的抗体。 试验注册：ClinicalTrials.gov 编号NCT01435135