Structure guided design of a transmission-blocking malaria vaccine targeting Pfs48/45

疟疾是影响人类的最具破坏性的传染病之一。它导致大约50万人死亡，其中大多数是非洲的儿童。它还给世界大部分地区带来了巨大的疾病负担，导致数亿人严重感染。这不仅直接造成痛苦和死亡，还限制了全球大部分地区的发展，降低了生产力，维持了不平等。疟疾是由一种被称为疟原虫的微小单细胞寄生虫引起的。一个人被受感染的蚊子叮咬后感染疟疾。当蚊子进食时，寄生虫被注射到血液中。这些细胞首先在肝脏内发育和分裂而不会引起疾病。接下来，它们从肝脏中出现，感染红细胞，复制并增加数量，从而引发疟疾的症状。与此同时，血液中的一小部分寄生虫采取了不同的发育途径，采用了一种称为配子体的形式。当蚊子吸食感染者的血液时，它们很可能会摄入一些配子体。在蚊子的中肠内，它们发育成雄性和雌性配子，并融合在一起。这就完成了感染周期，寄生虫转移到蚊子的唾液腺，准备注射到另一个人类受害者身上。事实证明，开发一种预防疟疾的疫苗非常具有挑战性，未来的疫苗很可能同时针对寄生虫生命周期的多个阶段，阻断肝脏和血细胞的进入。这种疫苗的一个组成部分可能是针对寄生虫的配子并阻止它们融合。这被称为传播阻断疫苗成分，因为它将阻止寄生虫在蚊子体内的发展，从而阻止疾病通过这种吸血昆虫的作用在人与人之间传播。我们研究了一种叫做Pfs48/45的分子，它存在于疟原虫的配子细胞和配子表面。Pfs48/45对于雄性配子与雌性配子融合至关重要，如果动物的免疫系统接触到Pfs48/45，它会产生一种叫做抗体的分子，这种分子与Pfs48/45结合，阻止配子融合。这意味着，如果我们能在疫苗中加入Pfs48/45，它将触发人体产生抗体，防止疟疾传播给其他人。这将减少疟疾在社区的流行，并将有助于根除这种疾病。尽管前景光明，但Pfs48/45是一个具有挑战性的分子，难以以功能形式大量生产。此外，如果我们要制造同时含有多种成分的疫苗，重要的是每个成分都要尽可能小而集中，以便更容易和更便宜地生产和分发疫苗。因此，我们的目标是了解Pfs48/45的结构和形状，并了解防止配子融合抗体结合的位点的位置和性质。这些信息将使我们能够使用最新的计算工具来设计新的分子，这些分子只包含与抑制性抗体结合所需的Pfs48/45区域。然后，我们将给小鼠注射这些新的免疫原，并研究蚊子感染实验中产生的抗体。如果蚊子以含有疟疾寄生虫的人类血液为食，配子就会融合，导致蚊子肠壁形成囊肿。如果配子融合被阻止，囊肿就不再形成。因此，我们将研究由我们的新免疫原诱导的抗体防止囊肿形成的能力，揭示我们的设计在阻止配子融合和防止疟疾寄生虫传播方面最有效。这些新设计的分子将构成未来疟疾疫苗的一部分。

Malaria is one of the most devastating infectious diseases to affect humankind. It kills around half a million people, mostly young children in Africa. It also places a huge disease burden on large parts of the world, leading to hundreds of millions of serious infections. As well as directly causing suffering and death, this limits the development of large parts of the globe, reducing productivity and maintaining inequality.Malaria is caused by a tiny, single celled parasite, known as Plasmodium. An individual contracts malaria when bitten by an infected mosquito. The parasites are injected into the blood stream as the mosquito feeds. These first develop and divide within the liver without causing disease. They next emerge from the liver and infect red blood cells, replicating and increasing in number and driving the symptoms of malaria. At the same time, a fraction of the parasites within the blood take a different developmental route, adopting a form known as the gametocytes. When a mosquito takes a blood meal from an infected person, they are likely to ingest some of these gametocytes. Within the midgut of the mosquito these develop into male and female gametes, and fuse together. This completes the infection cycle and the parasites move to the salivary glands of the mosquito, ready to be injected into another human victim.Development of a vaccine to prevent malaria has proved very challenging and it is likely that the vaccines of the future will simultaneously target multiple stages of the parasite life cycle, blocking both liver and blood cell entry. One component of such a vaccine is likely to target the gametes of the parasite and to stop them from fusing. This is known as a transmission-blocking vaccine component as it will prevent the development of the parasite within the mosquito and will therefore stop the disease from being passed from person to person through the action of this blood-sucking insect. We study a molecule called Pfs48/45 that is found on the surface of the gametocytes and gametes of Plasmodium parasites. Pfs48/45 is essential for a male gamete to fuse with a female gamete and if the immune system of an animal is exposed to Pfs48/45, it produces molecules called antibodies that bind to Pfs48/45 and prevent gametes from fusing. This means that if we can include Pfs48/45 in a vaccine, it will trigger the human body to make antibodies that will prevent malaria from being transmitted to other people. This will reduce the prevalence of malaria in the community and will help to eradicate the disease.Despite this promise, Pfs48/45 is a challenging molecule to produce in a functional form and in large quantities. In addition, if we are to make vaccines that simultaneously contain multiple components, it will be important for each component to be as small and focused as possible, to make it easier and cheaper for them to be produced and distributed. For this reason we aim to understand the structure and shape of Pfs48/45 and also to understand the location and the nature of the sites where the gamete-fusion-preventing antibodies bind. This information will allow us to use the latest computational tools to design novel molecules which contain just the regions of Pfs48/45 that are needed to bind to inhibitory antibodies.We will then inject mice with these novel immunogens and study the antibodies that are produced in a mosquito-infection experiment. If mosquitoes are fed on human blood containing malaria parasites, gametes can fuse, leading to the formation of cysts in the gut wall of the mosquito. If gamete fusion is prevented, the cysts are no longer formed. We will therefore study the ability of the antibodies induced by our novel immunogens to prevent cyst formation revealing which of our designs is most effective at blocking gamete fusion and preventing transmission of the malaria parasite. These newly designed molecules will form part of the malaria vaccines of the future.