Nielsen Morten A, Resende Mafalda, de Jongh Willem A, Ditlev Sisse B, Mordmüller Benjamin, Houard Sophie, Ndam Nicaise Tuikue, Agerbæk Mette Ø, Hamborg Mette, Massougbodji Achille, Issifou Saddou, Strøbæk Anette, Poulsen Lars, Leroy Odile, Kremsner Peter G, Chippaux Jean-Philippe, Luty Adrian J F, Deloron Philippe, Theander Thor G, Dyring Charlotte, Salanti Ali
Centre for Medical Parasitology at Department of Immunology and Microbiology, Faculty of Health and Medical Science, University of Copenhagen, and Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
ExpreS2ion Biotechnologies, SCION-DTU Science Park, Hørsholm, Denmark.
PLoS One. 2015 Sep 1;10(9):e0135406. doi: 10.1371/journal.pone.0135406. eCollection 2015.
The disease caused by Plasmodium falciparum (Pf) involves different clinical manifestations that, cumulatively, kill hundreds of thousands every year. Placental malaria (PM) is one such manifestation in which Pf infected erythrocytes (IE) bind to chondroitin sulphate A (CSA) through expression of VAR2CSA, a parasite-derived antigen. Protection against PM is mediated by antibodies that inhibit binding of IE in the placental intervillous space. VAR2CSA is a large antigen incompatible with large scale recombinant protein expression. Vaccines based on sub-units encompassing the functionally constrained receptor-binding domains may, theoretically, circumvent polymorphisms, reduce the risk of escape-mutants and induce cross-reactive antibodies. However, the sub-unit composition and small differences in the borders, may lead to exposure of novel immuno-dominant antibody epitopes that lead to non-functional antibodies, and furthermore influence the folding, stability and yield of expression. Candidate antigens from the pre-clinical development expressed in High-Five insect cells using the baculovirus expression vector system were transitioned into the Drosophila Schneider-2 cell (S2) expression-system compliant with clinical development. The functional capacity of antibodies against antigens expressed in High-Five cells or in S2 cells was equivalent. This enabled an extensive down-selection of S2 insect cell-expressed antigens primarily encompassing the minimal CSA-binding region of VAR2CSA. In general, we found differential potency of inhibitory antibodies against antigens with the same borders but of different var2csa sequences. Likewise, we found that subtle size differences in antigens of the same sequence gave varying levels of inhibitory antibodies. The study shows that induction of a functional response against recombinant subunits of the VAR2CSA antigen is unpredictable, demonstrating the need for large-scale screening in order to identify antigens that induce a broadly strain-transcending antibody response.
由恶性疟原虫（Pf）引起的疾病会表现出不同的临床症状，每年累计导致数十万人死亡。胎盘疟疾（PM）就是其中一种症状，在这种病症中，感染Pf的红细胞（IE）通过表达一种寄生虫衍生抗原VAR2CSA与硫酸软骨素A（CSA）结合。针对PM的保护作用是由抑制IE在胎盘绒毛间隙结合的抗体介导的。VAR2CSA是一种大型抗原，与大规模重组蛋白表达不兼容。理论上，基于包含功能受限的受体结合域的亚单位的疫苗可以规避多态性，降低逃逸突变体的风险，并诱导交叉反应抗体。然而，亚单位组成和边界处的微小差异可能会导致新的免疫显性抗体表位暴露，从而产生无功能的抗体，进而影响折叠、稳定性和表达产量。使用杆状病毒表达载体系统在High-Five昆虫细胞中表达的临床前开发候选抗原被转换到符合临床开发要求的果蝇Schneider-2细胞（S2）表达系统中。针对在High-Five细胞或S2细胞中表达的抗原的抗体功能能力相当。这使得能够对主要包含VAR2CSA最小CSA结合区域的S2昆虫细胞表达抗原进行广泛的筛选。一般来说，我们发现针对具有相同边界但var2csa序列不同的抗原的抑制性抗体效力存在差异。同样，我们发现相同序列抗原的细微大小差异会产生不同水平的抑制性抗体。该研究表明，针对VAR2CSA抗原重组亚单位诱导功能性反应是不可预测的，这表明需要进行大规模筛选以识别能诱导广泛的跨菌株抗体反应的抗原。
