Identification of Novel Efficacious Anti-Malarial Transmission Blocking Antigens Targeting the Female Gametocyte

疟疾仍然是一项重大的全球卫生挑战，2020年估计有2.29亿新病例和40.9万人死亡。适当使用现有的抗疟疾保健工具大大减少了全球疾病负担，然而，最近进展停滞不前，发病率和死亡率仍然高得令人无法接受，特别是在5岁以下儿童中。人们普遍认为，新的创新工具对于在中长期内实现疟疾控制或消除至关重要。疟疾的病原体是疟原虫属的原生动物寄生虫，仅由按蚊传播。通过蚊子传播疟疾是维持疾病周期的链条中最薄弱的一环；在蚊子的发育阶段，寄生虫数量达到最低点，在这些阶段，遗传变异是有限的。这一瓶颈代表了在这一点上杀死寄生虫的干预措施合乎逻辑且经过验证，从而产生传播阻断效应。审查、制定和评估专门针对疟疾传播的干预措施是合乎逻辑和及时的。直接阻断寄生虫传播的一种潜在方法是使用传播阻断疫苗（TBVs）针对介导向蚊子传播的寄生性阶段靶向疟原虫。尽管在过去的几十年里，人们已经研究了多种寄生虫蛋白的TBV活性，但仍然只有五种免疫原能够毫无疑问地、可重复地赋予传播阻断免疫。令人惊讶的是，这些免疫原的发现很大程度上源于历史研究，迄今为止，大多数关于配子细胞生物学的研究（也许令人惊讶）都集中在雄性配子细胞上。相对而言，我们对雌性配子体的表面知之甚少。从我们最近的研究中，我们利用增强的方法专门分离雌性配子体并检查它们的生物学，我们已经表明，针对雌性配子体的抗疟疾药物可以强烈抑制寄生虫传播，证明它们作为抗疟疾靶点的可行性。在这里，我们建议扩大可用的抗雌性配子细胞TBV免疫原的范围，从而在实验室和现场产生有效的传播阻断效果。我们已经确定了23个新的和以前检测过的女性tbv候选靶点，并将在啮齿动物模型中测试它们作为疫苗接种时阻断疟疾传播的能力。该模型允许在廉价、可扩展和符合伦理的模型中对每种候选疫苗的免疫原性和效力进行有效的分类，然后再转化为成本更高、产量更低、在伦理上更具挑战性的人类疟疾寄生虫。然后，只有这些潜在疫苗中表现最好的5种将被转化并使用人类疟疾寄生虫进行检测，并通过直接膜喂养试验检测产生的抗体是否能够直接阻断疟疾流行环境中恶性疟原虫样本向蚊子传播。这些结果是在“仅限人类”的现场试验中获得的，将有助于未来转化为直接的人体试验。最后，与此同时，将在巴布亚新几内亚高传播环境和低传播环境中个人的蛋白质样本中评估对这些单个蛋白质的自然免疫反应水平，使我们能够了解对所检查的5种选定的TBV抗原中的每一种自然产生的抗体反应。我们预计，使用这种新颖的方法来帮助设计、评估和使用一种新型的、有效的抗疟疾TBV，可以为消除和控制工作做出重大贡献，同时产生试剂，以帮助我们在未来扩大我们对疟原虫传播过程的有限知识。

Malaria remains a major global health challenge with an estimated 229 million new cases and 409,000 deaths in 2020. Appropriate use of currently existing anti-malarial healthcare tools have substantially reduced the global burden of disease, however, progress has recently stalled and morbidity and mortality remain unacceptably high, particularly in children under 5. It is widely accepted that new, innovative tools will be essential to achieve malaria control or elimination within the medium to long term. The causative agent of malaria, the protozoan parasite of the genus Plasmodium, is transmitted exclusively by Anopheles mosquitoes. Transmission of malaria through the mosquito is the weakest link in the chain that maintains the disease cycle; parasite numbers reach their lowest ebb during their developmental stages in the mosquito, and genetic variation is limited at these stages. This bottleneck represents a logical and proven point for interventions that kill the parasite at this point, creating a transmission-blocking effect. Examination, development and assessment of interventions specifically targeting malarial transmission is logical and timely. A potential manner of interrupting parasitic transmission directly is by targeting Plasmodium using transmission blocking vaccines (TBVs) against the parasitic sexual stages that mediate transmission to mosquitoes. Although a wide range of parasite proteins have been examined for TBV activity over the previous decades, there are still only five immunogens that unquestionably and reproducibly confer transmission blocking immunity. Surprisingly, discovery of these immunogens stems largely from historic studies, and to date, the majority of studies on gametocyte biology have (perhaps surprisingly) focused on male gametocytes. Very little is comparatively known about the surface of the female gametocytes. From our recent studies, utilising enhanced methods to exclusively isolate female gametocytes and examine their biology, we have shown that anti-malarial agents targeting female gametocytes can strongly inhibit parasitic transmission, demonstrating their viability as an anti-malarial target. Here, we propose to expand the range of available anti-female gametocyte TBV immunogens that result in potent transmission-blocking efficacy in the lab and field. We have identified 23 novel and previously examined female-TBV candidate targets, and will test their ability to block malarial transmission when administered as a vaccine in a rodent model. This model allows the effective triage of immunogenicity and efficacy of each candidate vaccine, within a cheap, scalable and ethical model, prior to translation to more costly, lower throughput, and more ethically challenging human malaria parasites. Only the best performing five of these potential vaccines will then be translated and examined using human malaria parasites, with resulting antibodies examined for their ability to directly block transmission of P. falciparum samples to mosquitoes within a malaria-endemic setting by Direct Membrane Feeding Assay. These results, obtained in a field, "human-only" assay, will facilitate future translation to direct human trials. Finally, in parallel, the levels of naturally occurring immune responses to these individual proteins will be assessed in protein samples from individuals in high and low transmission settings in Papua New Guinea, allowing us to understand the naturally occurring antibody responses to each of the 5 selected TBV antigens examined. We anticipate that the use of this novel approach to aid the design, assessment and use of a novel, potent anti-malarial TBV, could significantly contribute towards elimination and control efforts, while generating reagents to aid the potential expansion of our sparse knowledge of the process of plasmodial transmission in the future.