Multivalent chimeric subunit malaria vaccines

 描述（由申请人提供）：尽管最近在许多流行地区的各种蚊媒控制和抗疟药物项目取得了成功，但由恶性疟原虫和间日疟原虫引起的疟疾仍然是一个主要的全球公共卫生问题。开发有效的疫苗可以大大加强减少疟疾负担的努力。然而，一些临床试验的结果，包括目前的III期试验， 红细胞前期疫苗RTS、S的效果并不令人鼓舞。虽然有若干挑战必须解决，但两个关键问题一再出现。首先，必须提高亚单位疫苗的免疫原性。其次，没有迹象表明对这些复杂的、多阶段的疟原虫的免疫是针对单一的保护性抗原的。疫苗候选抗原需要组合配制，而不会降低单个组分的免疫原性。该项目的重点是疫苗靶点，其中抗体依赖性免疫机制是必不可少的，但中和B细胞表位的免疫原性不是最佳的。在概念验证研究中，我们通过工程化一种高度保守的、高免疫原性的恶性疟原虫特异性载体蛋白克服了与基于重组抗原的疫苗的生产和次优免疫原性相关的障碍，该载体蛋白诱导有效的CD4 + T细胞帮助产生中和抗体。恶性疟原虫的中和B细胞表位与寄生虫特异性载体蛋白的遗传融合也将允许同时加强疫苗引发的B细胞， 疫苗致敏的CD4 + T细胞通过自然恶性疟原虫感染。在这个项目中，我们将系统地评估4种领先的候选疫苗，以确定高效的多抗原制剂，并将抗体特异性和同种型与寄生虫中和的功能测定联系起来。我们将表达和纯化重组裂殖子表面蛋白2、网织红细胞结合蛋白同源物5和恶性疟原虫25 kDa性期抗原，每种抗原均作为单一抗原，并作为与rPfMSP 8（Δ Asn/Asp）载体的嵌合融合蛋白。我们将在功能测定中比较用Th1/Th2偏向性佐剂配制的单一抗原疫苗与嵌合抗原疫苗在抗体滴度、同种型和活性方面的免疫原性 寄生虫中和在小鼠和非人灵长类动物中，我们将测试三种具有高免疫原性的重组疫苗与rPfMSP 1/8的组合制剂，rPfMSP 1/8是一种基于嵌合MSP的疫苗，可引发高滴度的生长抑制抗体。这一努力的成功将1）代表朝着生产血液阶段/性阶段组合疟疾疫苗的目标迈出了重要一步，以同时降低临床疾病的严重程度并阻断传播，以及2）为随后在人类受试者中进行安全性和免疫原性测试提供坚实的基础。1

 DESCRIPTION (provided by applicant): Despite recent successes of various mosquito vector control and antimalarial drug programs in many endemic areas, malaria due to Plasmodium falciparum and Plasmodium vivax remains a major global public health problem. The development of an efficacious vaccine could greatly enhance efforts to reduce the malaria burden. However, results from a number of clinical trials, including the current phase III trial of the pre- erythrocytic stage vaccine, RTS,S have not been encouraging. While there are several challenges that must be addressed, two key issues have repeatedly emerged. First, the immunogenicity of subunit vaccines must be improved. Second, there is no indication that immunity to these complex, multi-stage plasmodial parasites is directed toward a single protective antigen. Vaccine candidate antigens will need to be formulated in combination, without any reduction in the immunogenicity of individual components. This project focuses on vaccine targets where antibody-dependent mechanisms of immunity are essential, but where immunogenicity of neutralizing B cell epitopes has not been optimal. In proof-of-concept studies, we overcome obstacles related to both production and suboptimal immunogenicity of recombinant antigen based vaccines by engineering a well-conserved, highly immunogenic, P. falciparum specific carrier protein that induces potent CD4+ T cell help for the production of neutralizing antibodies. Genetic fusion of neutralizing B cell epitopes of P. falciparum to a parasite specific carrier protein will also allow concurrent boosting of vaccine-primed B cells and vaccine-primed CD4+ T cells by natural P. falciparum infection. In this project, we will systematically evaluate 4 leading vaccine candidates to define highly efficacious, multi-antigen formulations and link antibody specificity and isotype with functional assays of parasite neutralization. We will express and purify recombinant merozoite surface protein 2, reticulocyte-binding protein homologue 5 and the 25 kDa sexual stage antigen of P. falciparum, each as a single antigen and as a chimeric fusion protein with the rPfMSP8 (ΔAsn/Asp) carrier. We will compare the immunogenicity of single versus chimeric antigen vaccines formulated with Th1/Th2 biasing adjuvants with respect to antibody titer, isotype and activity in functional assays of parasite neutralization. In mice and non-human primates, we will test three, highly immunogenic recombinant vaccines in combined formulations with rPfMSP1/8, a chimeric MSP-based vaccine shown to elicit high titers of growth inhibitory antibodies. Success in this effort would 1) represent a major step toward the goal of producing a combined blood-stage/sexual stage malaria vaccine to concurrently reduce the severity of clinical disease and block transmission and 2) provide a solid foundation for subsequent safety and immunogenicity testing in human subjects. 1