Designing Improved HIV-1 Envelope Proteins as Vaccine Candidates

描述(申请人提供)：艾滋病毒-1疫情在2007年造成约270万人新感染，总共约3300万艾滋病毒/艾滋病患者。临床试验表明，用病毒包膜蛋白的单体重组形式免疫不能预防HIV-1感染。然而，很明显，HIV-1Env含有能够诱导中和抗体的表位，而且这种抗体可以保护灵长类动物免受感染。 在以前的动物和人类研究中，单体gp120在诱导中和抗体方面无效的原因有几个。表面暴露的可变序列围绕着CD4结合位点，可能会限制B细胞对该表位的访问。Gp120蛋白携带V3环等表位，这些表位具有免疫原性，但不暴露于天然病毒包膜结构中的抗体。 HIV-1疫苗免疫原的设计有两个主要假设。第一个假设集中在由单抗定义的广泛中和表位上。据推测，合适的免疫原将暴露这些表位并诱导多克隆抗体，其中和特异性与单克隆抗体相当。第二个假设表明，单一的广泛交叉反应的中和特异性是不容易诱导的，必须识别多个表位来抑制病毒的感染性。 这两种假说都可以通过设计和创造基于环境的免疫原来检验，这些免疫原缺乏可变序列，这些可变序列可能是免疫显性的，而且在任何情况下都不能诱导广泛的中和活性。在保留CD4结合活性的同时去除可变区可能会暴露这一重要的表位以及位于Env相对保守区域的其他表位。这种方法代表了递归过程的第一步，以建立一个免疫原应该具有哪些特征的概念或设计。 然而，单个原型序列的实验测试不允许对概念进行稳健的评估。本提案中使用的另一种方法是为给定的疫苗概念创建序列变体，并测试这些变体中的一些。通过这种方式，可以获得更大和更重要的数据集，从中可以得出关于免疫原设计价值的结论。在这项提案中，我们将试图克服gp120作为免疫原的一些局限性。我们认识到，有效的基于环境的疫苗最终可能需要一种免疫原形式，如模拟的可溶性三聚体或携带gp120的病毒样颗粒。 本建议的具体目的如下：(1)将修饰引入gp120并评估其对配体结合特性的影响；(2)建立gp120变异体的组合库并鉴定具有c4结合活性的变异体；(3)用选定的gp120变异体免疫兔子并评价其中和活性。 如果gp120变异体能够诱导中和抗体，那么额外的研究将形成第二阶段SBIR提案的基础。 与公共卫生有关：2007年，艾滋病毒/艾滋病疫情已导致200万人死亡和270万新感染者，总共有近3300万艾滋病毒/艾滋病患者。疫苗的开发被认为是减缓疫情所需的公共卫生措施的重要组成部分。这项研究计划旨在创造一种疫苗，可以诱导能够预防艾滋病毒感染的抗体。

DESCRIPTION (provided by applicant): The HIV-1 epidemic has resulted in ~2.7 million new infections in 2007 for a total of ~33 million people living with HIV/AIDS. Clinical trials have shown that HIV-1 infection cannot be prevented by immunization with monomeric recombinant forms of viral envelope (Env) proteins. However, it is clear that the HIV-1 Env contains epitopes that can induce neutralizing antibodies and that such antibodies can protect primates from infection. There are several reasons why monomeric gp120 has been ineffective at inducing neutralizing antibodies in previous animal and human studies. The surface-exposed variable sequences surround the CD4 binding site and might restrict B-cell access to this epitope. The gp120 protein carries epitopes such as the V3 loop that are immunogenic but not exposed to antibodies in the native virus Env structure. Two main hypotheses inform the design of immunogens for HIV-1 vaccines. The first hypothesis focuses on broadly neutralizing epitopes defined by monoclonal antibodies. It is hypothesized that suitable immunogens will expose these epitopes and induce polyclonal antibodies with neutralizing specificities comparable to those of the monoclonals. The second hypothesis suggests that a single broadly cross-reactive neutralizing specificity is not be readily induced and that multiple epitopes must be recognized to inhibit virus infectivity. Both hypotheses can be tested by the design and creation of Env-based immunogens lacking variable sequences that might be immunodominant and in any case cannot induce broad neutralizing activity. Removal of variable regions while retaining CD4 binding activity might expose this important epitope as well as others that reside in the relative conserved regions of Env. This approach represents an initial step in a recursive process to build upon a concept, or design, of what features an immunogen should possess. However, experimental testing of a single prototype sequence does not allow a robust evaluation of the concept. An alternative approach, used in this Proposal, is to create sequence variants for a given vaccine concept and to test a number of those variants. In this way, a larger and more significant dataset can be obtained from which to draw conclusions regarding the value of the immunogen design. In this Proposal, we will attempt to overcome some of the limitations of gp120 as an immunogen. We recognize that an immunogen format such as a soluble trimer mimic or a virus-like particle carrying gp120 might ultimately be required for an effective Env-based vaccine. The specific aims of this Proposal are as follows: (1) incorporate modifications into gp120 and evaluate their effect on ligand binding properties; (2) create combinatorial libraries of gp120 variants and identify those with CD4 binding activity; (3) immunize rabbits with selected gp120 variants and evaluate the neutralizing activity If the gp120 variants are able to induce neutralizing antibodies, then additional studies will form the basis of a Phase II SBIR proposal. PUBLIC HEALTH RELEVANCE: The HIV/AIDS epidemic has resulted in 2 million deaths and 2.7 million new infections in 2007, for a total of nearly 33 million people living with HIV/AIDS. Development of a vaccine is considered to be an essential component of the public health measures needed to slow the epidemic. This research proposal is designed to create a vaccine that can induce antibodies capable of preventing infection by the HIV virus.