Immunizing Against Malaria by Inducing Both Protective Antibodies and CD8 T Cells

描述（由申请人提供）：疟疾每年至少造成2.5亿例病例和近100万人死亡。GSK的疟疾疫苗RTS， S/AS01正在三期临床试验中进行测试，如果安全有效，可能会获准用于发展中国家的儿童。该疫苗完全基于恶性疟原虫（Pf）环孢子子蛋白（CSP）的重复区和羧基端。它与佐剂AS01一起使用，其中包括脂质体、单磷酰脂质A和纯化植物提取物QS21，但最初是用油基水基佐剂开发的。通过在小鼠和非人灵长类动物（NHPs）中进行的一系列反复研究，降低了临床试验佐剂的选择。在其最终配方中，该疫苗在最后一次剂量后2周内可保护50%的志愿者免受Pf的实验性攻击，22%的志愿者可保护6个月。保护被认为主要是由针对PfCSP重复区的抗体介导的，也可能是针对PfCSP C端的CD4+ T细胞应答。该疫苗不能诱导有意义的CD8+ T细胞反应。然而，许多疟疾学家认为，长期保护将依赖于诱导pf特异性CD8+ T细胞免疫，正如在用辐照孢子子免疫的小鼠和NHPs中观察到的那样。RTS， S/AS01不考虑用于非免疫旅行者和军事人员，因为其保护功效太低。针对这一人群的疫苗需要在至少6个月内提供80%的保护性免疫力，才能有可观的市场。我们假设，通过在针对PfCSP的抗体应答中加入高功能的保护性CD8+ T细胞应答，可以实现这种保护性免疫。表达PfCSP等蛋白的重组腺病毒（Ad）是目前在人体内诱导CD8+ T细胞反应的一种流行方法。然而，尽管诱导抗原特异性CD8+ T细胞的反应非常大，但这种基于ad的疫苗在人类中并没有高度保护作用，特别是对疟疾。最近，研究表明，在小鼠中，重组减毒单核增生李斯特菌（Lm）诱导的CD8+ T细胞反应比重组Ad5高得多。我们将使用一种异种的启动-增强方案，结合佐剂重组PfCSP蛋白（rPfCSP）和表达PfCSP的Lm （Lm-PfCSP）。该策略的目标是诱导PfCSP特异性保护性抗体和保护性CD8+和CD4+ T细胞反应，提供至少持续6个月的80%的保护。在I期，我们将鉴定rPfCSP、佐剂和Lm- PfCSP的组合，它们在小鼠中诱导高水平抗体和CD8+和CD4+ T细胞反应。在II期，我们将采用GSK使用的方法，并利用NHPs的免疫原性来选择疫苗的临床试验组合，该疫苗的有效性足以防止80%的疫苗接种者发生Pf寄生虫病；一种疫苗，适用于潜在的数十亿美元的非免疫旅行者、商业和军事市场，并适用于在发展中国家以地理为重点的运动中消除Pf。

DESCRIPTION (provided by applicant): Malaria causes at least 250 million cases and nearly 1 million deaths per year. GSK's malaria vaccine, RTS, S/AS01 is being tested in a Phase 3 clinical trial, and is likely to be licensed for use in children in the developing world, if safe ad effective. This vaccine is based entirely on the repeat region and carboxy terminus of the Plasmodium falciparum (Pf) circumsporozoite protein (CSP). It is administered with an adjuvant AS01, which includes liposomes, monophosphoryl lipid A, and a purified plant extract, QS21, but was initially developed with an oil in water-based adjuvant. Downselection of adjuvants for clinical trials was done through a series of iterative studies in mice and non-human primates (NHPs). In its final formulation this vacccine protects 50% of volunteers against experimental challenge with Pf for 2 weeks after last dose, and 22% of volunteers for 6 months. Protection is thought to be primarily mediated by antibodies against the repeat region of PfCSP and possibly CD4+ T cell responses against the C' terminus of the PfCSP. The vaccine does not induce meaningful CD8+ T cell responses. However, many malariologists believe that long- term protection will be dependent on induction of Pf-specific CD8+ T cell immunity, as has been obseved in mice and NHPs immunized with irradiated sporozoites. RTS, S/AS01 is not being considered for non-immune travelers and military personnel, because its protective efficacy is too low. A vaccine for this population needs to provide >80% protective immunity for at least 6 months to have a substantial market. We hypothesize that by adding highly functional, protective CD8+ T cell responses to antibody responses against the PfCSP, such protective immunity can be achieved. Recombinant adenovirus (Ad) expressing proteins like the PfCSP is currently a popular method for inducing CD8+ T cell responses in humans. However, despite the induction of antigen-specific CD8+ T cell responses of very high magnitude such Ad-based vaccines have not been highly protective in humans, especially against malaria. Recently, it was shown in mice that recombinant attenuated Listeria monocytogenes (Lm) induced much higher quality (functional) CD8+ T cell responses than did recombinant Ad5. We will use a heterologous prime-boost regimen combining an adjuvanted recombinant PfCSP protein (rPfCSP) and Lm expressing PfCSP (Lm-PfCSP). The goal of this strategy is to induce PfCSP- specific protective antibodies and protective CD8+ and CD4+ T cell responses that provide >80% protection that is sustained for at least 6 months. In Phase I we will identify combinations of rPfCSP, adjuvant and Lm- PfCSP that induce high level antibodies, and CD8+ and CD4+ T cell responses in mice. In Phase II we will take the approach used by GSK, and use immunogenicity in NHPs to downselect combinations for clinical trials of a vaccine that is intended to have efficacy adequate to prevent >80% of vaccinees from developing Pf parasitemia; a vaccine suitable for the potential multi-billion dollar non-immune traveler, business, and military markets, and for eliminating Pf in geographically focused campaigns in the developing world. PUBLIC HEALTH RELEVANCE: Malaria causes 400-500 million clinical cases and >1 million deaths annually, is responsible for >1% loss of GDP in Africa annually and is a serious concern for travelers and military personnel. Protein Potential's goal is to develop and commercialize a >90% protective malaria vaccine for primary markets with a potential for >$1 billion annual revenues; 1) travelers from the developed world, and 2) all populations in the developing world. Success in this project will significantly decrease the cost of development and time to market for this malaria vaccine.