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

描述(申请人提供)：疟疾每年造成至少2.5亿个病例和近100万人死亡。葛兰素史克的疟疾疫苗RTS，S/AS01正在进行3期临床试验，如果安全有效，很可能获得许可用于发展中国家的儿童。该疫苗完全基于恶性疟原虫(PF)环子孢子蛋白(CSP)的重复区域和羧基末端。它与佐剂AS01一起服用，其中包括脂质体、单磷脂A和纯化的植物提取物QS21，但最初是用水包油的佐剂开发的。通过在小鼠和非人灵长类动物(NHP)中进行一系列迭代研究，对临床试验中的佐剂进行了下调选择。在其最终配方中，该疫苗在最后一次接种后2周内保护50%的志愿者免受PF的实验性攻击，并在6个月内保护22%的志愿者免受PF的攻击。保护被认为主要是由针对PfCSP重复区的抗体和可能的针对PfCSP C‘端的CD4+T细胞反应介导的。该疫苗不会诱导有意义的CD8+T细胞反应。然而，许多疟疾专家认为，长期的保护将依赖于诱导PF特异性CD8+T细胞免疫，正如已经在小鼠和用辐照的子孢子免疫的NHP中观察到的那样。非免疫旅行者和军事人员不考虑使用S/AS01RTS，因为它的保护效果太低。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，才能拥有可观的市场。我们推测，通过将高功能的保护性CD8+T细胞反应添加到针对PfCSP的抗体反应中，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细胞应答的一种流行方法。然而，尽管诱导了非常高幅度的抗原特异性CD8+T细胞反应，但这种基于Ad的疫苗对人类并没有高度的保护作用，特别是对疟疾。最近，有研究表明，重组减毒单核细胞增生性李斯特菌(Lm)诱导的高质量(功能性)CD8+T细胞反应比重组Ad5高得多。我们将使用异源Prime-Boost方案，结合佐剂重组PfCSP蛋白(RPfCSP)和表达PfCSP的Lm(Lm-PfCSP)。这一策略的目标是诱导PfCSP特异性保护性抗体和保护性CD8+和CD4+T细胞反应，提供持续至少6个月的80%保护。在第一阶段，我们将确定rPfCSP、佐剂和LM-PfCSP的组合可以在小鼠中诱导高水平抗体以及CD8+和CD4+T细胞反应。在第二阶段，我们将采用葛兰素史克使用的方法，并利用NHP中的免疫原性来选择临床试验的疫苗组合，该疫苗旨在具有足够的效力来防止80%的受试者患上PF寄生虫血症；一种适合于潜在的数十亿美元的非免疫旅行者、商业和军事市场的疫苗，以及在发展中国家的地理重点活动中消除PF的疫苗。

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.