National School of Tropical Medicine, Departments of Pediatrics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas, United States of America.
Texas Children's Hospital Center for Vaccine Development, Baylor College of Medicine, Houston, Texas, United States of America.
PLoS Negl Trop Dis. 2020 Feb 13;14(2):e0008057. doi: 10.1371/journal.pntd.0008057. eCollection 2020 Feb.
Ascaris lumbricoides is one of the three major soil-transmitted gastrointestinal helminths (STHs) that infect more than 440 million people in the world, ranking this neglected tropical disease among the most common afflictions of people living in poverty. Children infected with this roundworm suffer from malnutrition, growth stunting as well as cognitive and intellectual deficits. An effective vaccine is urgently needed to complement anthelmintic deworming as a better approach to control helminth infections. As37 is an immunodominant antigen of Ascaris suum, a pig roundworm closely related to the human A. lumbricoides parasite, recognized by protective immune sera from A. suum infected mice. In this study, the immunogenicity and vaccine efficacy of recombinant As37 were evaluated in a mouse model.
METHODOLOGY/PRINCIPAL FINDINGS: As37 was cloned and expressed as a soluble recombinant protein (rAs37) in Escherichia coli. The expressed rAs37 was highly recognized by protective immune sera from A. suum egg-infected mice. Balb/c mice immunized with 25 μg rAs37 formulated with AddaVax™ adjuvant showed significant larval worm reduction after challenge with A. suum infective eggs when compared with a PBS (49.7%) or adjuvant control (48.7%). Protection was associated with mixed Th1/2-type immune responses characterized by high titers of serological IgG1 and IgG2a and stimulation of the production of cytokines IL-4, IL-5, IL-10 and IL-13. In this experiment, the AddaVax™ adjuvant induced better protection than the Th1-type adjuvant MPLA (38.9%) and the Th2-type adjuvant Alhydrogel (40.7%). Sequence analysis revealed that As37 is a member of the immunoglobulin superfamily (IgSF) and highly conserved in other human STHs. Anti-As37 antibodies strongly recognized homologs in hookworms (Necator americanus, Ancylostoma ceylanicum, A. caninum) and in the whipworm Trichuris muris, but there was no cross-reaction with human spleen tissue extracts. These results suggest that the nematode-conserved As37 could serve as a pan-helminth vaccine antigen to prevent all STH infections without cross-reaction with human IgSF molecules.
CONCLUSIONS/SIGNIFICANCE: As37 is an A. suum expressed immunodominant antigen that elicited significant protective immunity in mice when formulated with AddaVax™. As37 is highly conserved in other STHs, but not in humans, suggesting it could be further developed as a pan-helminth vaccine against STH co-infections.
蛔虫是世界上感染超过 4.4 亿人的三种主要土壤传播性胃肠道蠕虫（STH）之一，这种被忽视的热带病是生活在贫困中的人们最常见的疾病之一。感染这种蛔虫的儿童会营养不良、生长迟缓以及认知和智力缺陷。迫切需要一种有效的疫苗来补充驱虫药物，作为控制蠕虫感染的更好方法。As37 是猪蛔虫的一种免疫显性抗原，猪蛔虫与人类寄生虫蛔虫密切相关，可被感染猪蛔虫的小鼠的保护性免疫血清识别。在这项研究中，重组 As37 在小鼠模型中的免疫原性和疫苗功效进行了评估。
方法/主要发现：As37 在大肠杆菌中被克隆并表达为可溶性重组蛋白（rAs37）。表达的 rAs37 被感染猪蛔虫卵的保护性免疫血清高度识别。与 PBS（49.7%）或佐剂对照（48.7%）相比，用 AddaVax™佐剂配制的 25μg rAs37 免疫的 Balb/c 小鼠在感染猪蛔虫感染性卵后，幼虫蠕虫减少显著。保护与混合 Th1/2 型免疫反应相关，其特征是血清 IgG1 和 IgG2a 的高滴度和细胞因子 IL-4、IL-5、IL-10 和 IL-13 的产生刺激。在这个实验中，AddaVax™佐剂诱导的保护作用优于 Th1 型佐剂 MPLA（38.9%）和 Th2 型佐剂 Alhydrogel（40.7%）。序列分析表明，As37 是免疫球蛋白超家族（IgSF）的成员，在其他人类 STH 中高度保守。抗 As37 抗体强烈识别钩虫（Necator americanus、Ancylostoma ceylanicum、A. caninum）和鞭虫 Trichuris muris 的同源物，但与人类脾脏组织提取物无交叉反应。这些结果表明，线虫保守的 As37 可以作为一种泛蠕虫疫苗抗原，预防所有 STH 感染，而不会与人类 IgSF 分子发生交叉反应。
结论/意义：As37 是一种表达于猪蛔虫的免疫显性抗原，当与 AddaVax™ 联合使用时，在小鼠中引起显著的保护性免疫。As37 在其他 STH 中高度保守，但在人类中没有保守，这表明它可以进一步开发为一种针对 STH 合并感染的泛蠕虫疫苗。
