Contribution of Pfs48/45 to Malaria Transmission-Blocking Immunity

描述（由申请人提供）：为了成功消除疟疾，疟疾仍然是造成5岁以下儿童死亡的8%的原因，需要新的疟疾控制策略，包括传播阻断（TxB）疫苗。为了实现这一目标，我们最近以准备用于GMP生产（GMZ 3）的形式生产了正确折叠的恶性疟原虫配子体表面蛋白P48/45（Pfs 48/45），并使用体外培养适应的寄生虫在标准膜饲料中诱导破坏寄生虫对蚊子的感染性的抗体。我们假设，抗GMZ 3抗体也将阻断天然寄生虫分离株感染蚊子的能力，并且天然获得的TxB免疫力将与识别GMZ 3的抗体的存在相关，这表明它是一种良好的疫苗候选物。为了测试这一点，我们建议AIM 1）评估在大鼠中产生的抗GMZ 3抗体阻断天然分离物对蚊子的感染性的能力。我们还将评估AIMS 2和3）自然寄生虫暴露是否诱导有助于传播阻断免疫的Pfs 48/45/GMZ 3抗体。Pfs 48/45是四种疟原虫蛋白（Pfs 48/45和P230、P25和P28）之一，它们是有效阻断疟疾Tx的单克隆抗体的靶标，并已被靶向作为候选疫苗。所有这些蛋白质都相对富含半胱氨酸，具有多个二硫键，导致依赖于三级结构而不是线性氨基酸序列的抗体表位。只有P25已经进入了Ia期临床试验，但由于免疫原性有限以及在自然疟疾感染期间缺乏加强，进一步的开发进展缓慢。Pfs 48/45和Pfs 230都在寄生虫在人类宿主中经历性分化为配子体时表达，并且在暴露于疟疾后发现了天然存在的抗Pfs 48/45抗体。这表明针对基于Pfs 48/45或Pfs 230的TxB疫苗的免疫应答可以在自然感染期间加强，从而增强疫苗的功效。本文提出的项目将直接评估GMZ 3作为针对天然分离株的候选疫苗的潜力。它通过直接比较传播阻断活性与配子体患病率、遗传变异和抗rPfs 48/45.10C抗体滴度来增强正在进行的流行病学和临床安全性研究，并将为指导进一步开发有效的传播阻断疫苗提供关键信息。

DESCRIPTION (provided by applicant): To successfully eliminate malaria, which continues to be responsible for 8% of all the deaths of children under five, new malaria control strategies are needed, including transmission blocking (TxB) vaccines. Toward this goal, we have recently produced correctly-folded P. falciparum gametocyte surface protein P48/45 (Pfs48/45) in a form that is ready for GMP production (GMZ3) and induces antibodies that disrupt parasite infectivity to mosquitoes in a standard membrane feed using in vitro culture-adapted parasites. We hypothesize that anti-GMZ3 antibodies will also block the ability of natural parasite isolates to infect mosquitoes and that naturally acquired TxB immunity will correlate with the presence of antibodies that recognize GMZ3 indicating that it is a good vaccine candidate. To test this we propose to AIM 1) evaluate the ability of anti-GMZ3 antibodies produced in rats to block the infectivity of natural isolates to mosquitoes. We will also evaluate AIMS 2 & 3) whether natural parasite exposure induces Pfs48/45/GMZ3 antibodies that contribute to transmission-blocking immunity. Pfs48/45 is one of four Plasmodium proteins (Pfs48/45 and P230, P25 and P28) that are the targets of monoclonal antibodies that effectively block malaria Tx and have been targeted as vaccine candidates. All these proteins are relatively cysteine-rich with multiple disulfide bonds resulting in antibody epitopes that are dependent on tertiary structure rather than linear amino acid sequence. Only P25 has advanced to a Phase Ia clinical trial, but further development has been slow due to limited immunogenicity and the lack of boosting during a natural malaria infection. Both Pfs48/45 and Pfs230 are expressed as the parasite undergoes sexual differentiation into gametocytes in the human host and naturally occurring anti-Pfs48/45 antibodies have been found after exposure to malaria. This suggests that the immune response against a Pfs48/45 or Pfs230-based TxB vaccine could be boosted during a natural infection enhancing the efficacy of the vaccine. The project proposed here will directly evaluate the potential of GMZ3 as a vaccine candidate against natural isolates. It augments ongoing epidemiologic and clinical safety studies by directly comparing transmission-blocking activity with gametocyte prevalence, genetic variation and anti-rPfs48/45.10C antibody titers and will provide critical information to direct the further development of an effective transmission-blocking vaccine.