Development of a Vaccine for HIVAIDS: Humoral Immunity

我们已经证明，活的、复制能力强的Ad-HIV或Ad-SIV包膜重组疫苗的免疫不仅能引起细胞免疫，还能激发强烈的抗体反应，这些抗体反应是在用包膜蛋白加强免疫后产生的。这些抗体表现出多种功能活性。艾滋病毒/艾滋病疫苗最可取的是中和活性，能够防止接触病毒后的感染。我们的临床前研究表明，我们的主要/增强疫苗方法产生了中和抗体，在用HIV/SIV嵌合Shiv病毒攻击恒河猴后，这些抗体可以提供明显的灭菌免疫。HIV/SIV感染最初表现为感染细胞的小病灶。在2至6天内，病毒从这些病灶扩散到引流淋巴结，随后导致全身感染。除了中和外，我们的疫苗方法还会诱导具有其他功能活性的抗体，这些抗体虽然不能阻止感染，但可能有助于通过限制病毒从这些感染源传播来控制最初的病毒负担。这些活性包括抗体依赖的细胞毒性(ADCC)和抗体依赖的细胞介导的病毒抑制(ADCVI)。我们最近的研究，同样是在恒河猴模型中，证明了这些非中和抗体活性与较低的病毒负荷相关。由于HIV主要在直肠/生殖器粘膜部位传播，因此HIV疫苗开发的一个关键目标是诱导粘膜免疫。重组腺病毒载体/蛋白增强策略在粘膜分泌物中诱导抗体，我们已经证明这种抗体可以抑制SIV跨越上皮细胞屏障的跨细胞作用，这表明另一种机制可能有助于保护SIV。事实上，我们最近已经证明，这种疫苗诱导的粘膜抗体抑制跨细胞反应也与攻击后慢性病毒血症的减少有关，这表明这种活性可能有助于防止病毒在细胞之间的传播。在旨在充分表征疫苗诱导抗体的全面研究中，我们检查了它们的亲和力，以确定这一特征是否在保护效力中发挥作用。我们发现抗体亲和力与功能性抗体活性相关，表明抗体成熟是疫苗诱导抗体的重要特性。此外，我们还开发了研究记忆B细胞的方法。如果免疫要提供持久的、可能是终身的保护，疫苗诱导长期记忆B细胞的能力是一个关键属性。我们已经证明，我们的复制能力的重组腺病毒载体/包膜增强方法可以激发记忆B细胞，不仅与抗体依赖的细胞毒性、抗体依赖的细胞介导的病毒抑制和跨细胞抑制相关，而且还与更好的保护相关。8年多前首次接种疫苗的精英控制者猕猴被证明通过强大的多功能抗病毒反应和细胞免疫将血浆病毒血症控制到无法检测的水平。通过微阵列分析证实了体液免疫在这一精英对照中的作用，该微阵列分析显示在异源病毒攻击后免疫球蛋白基因在肠道中表达。总体而言，我们最近的研究继续表明，我们的疫苗策略诱导了在血清和粘膜分泌物中具有一系列活性的持久、高滴度抗体，这些抗体共同有助于在非人类灵长类动物模型中针对病毒挑战提供强大的保护。这些发现推进了I期临床试验的方法。

We have shown that immunization with live, replication-competent Ad-HIV or Ad-SIV envelope recombinant vaccines not only elicits cellular immunity, but also primes strong antibody responses that develop following administration of booster immunizations with envelope protein. These antibodies display a variety of functional activities. The most desirable for an HIV/AIDS vaccine is neutralizing activity that is able to prevent infection following exposure to the virus. We have shown in pre-clinical studies that our prime/boost vaccine approach results in neutralizing antibodies that can confer apparent sterilizing immunity following challenge of rhesus macaques with an HIV/SIV chimeric SHIV virus. HIV/SIV infection is initially manifested as small foci of infected cells. Within 2 to 6 days, virus spreads from these foci to draining lymph nodes, subsequently leading to systemic infection. In addition to neutralization, our vaccine approach elicits antibodies that possess other functional activities that although not able to block infection, may contribute to control of the initial viral burden by limiting the spread of virus from these foci of infection. Such activities include antibody dependent cellular cytotoxicity (ADCC), and antibody dependent cell-mediated viral inhibition (ADCVI). Our recent studies, again in the rhesus macaque model, demonstrate that these non-neutralizing antibody activities are correlated with lower viral burdens. Since HIV is transmitted mainly at rectal/genital mucosal sites, a key goal of HIV vaccine development is to elicit mucosal immunity. The Ad-recombinant prime/protein boost strategy induces antibodies in mucosal secretions which we have shown can inhibit transcytosis of SIV across an epithelial cell barrier, suggesting another mechanism which may contribute to protection. In fact, we have recently shown that transcytosis inhibition by such vaccine-induced mucosal antibodies is also correlated with reduced chronic viremia following challenge, suggesting this activity may help prevent cell-to-cell spread of the virus. In comprehensive studies aimed at fully characterizing vaccine-elicited antibodies, we have examined their avidity to determine whether this characteristic plays a role in protective efficacy. We have discovered that antibody avidity is correlated with functional antibody activities, indicating that antibody maturation is an important property of vaccine-elicited antibodies. Further, we have developed methodology to investigate memory B cells. The ability of vaccines to elicit long lasting memory B cells is a critical property if immunization is to provide long-lasting, and potentially life-long protection. We have shown that our repliction-competent Ad-recombinant prime/envelope boost approach elicits memory B cells, correlated not only with antibody-dependent cellular cytotoxicity, antibody-dependent cell-mediated viral inhibition, and transcytosis inhibition, but also with better protection. Elite-controller macaques initially vaccinated more than 8 years ago, were shown to control plasma viremia to undetectable levels by potent, multifunctional antibydy responses, as well as cellular immunity. The role of humoral immunity in this elite control was substantiated by microarray analysis showing expression of immunoglobulin genes in the intestine following a heterologous viral challenge. Overall, our recent studies continue to demonstrate that our vaccine strategy induces long-lasting, high-titered antibodies with a spectrum of activities both in serum and mucosal secretions, which together contribute to strong protection against viral challenge in non-human primate models. These findings have advanced the approach toward phase I clinical trials.