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The genetic mutation of the coagulation factor VIII (fVIII) results in a defective or missing protein, leading to a malfunctioning blood coagulation. The resulting disease is called hemophilia A. Depending on the severity of the mutation, affected patients experience an increased risk of pathologic bleeding after minor trauma or even sudden bleeding events. Substitution therapies with extrinsic fVIII exist using plasmatic or recombinant fVIII products. Due to an insufficient immune tolerance towards substituted fVIII, about 30 % of patients develop allogenic neutralizing antibodies (inhibitors) against substituted fVIII products. The gold standard of treating inhibitors is the immune tolerance induction (ITI), where patients are given frequent, high doses of fVIII to induce an immune tolerance. ITI therapy fails in about 30 % of patients. Mechanisms of action of ITI are part of research, as insufficient knowledge about mechanisms and prognostic factors complicate treatment. For example, the development of anti-idiotypic antibodies, which occur naturally as a regulatory mechanism of the immune system, are being studied. Such anti-idiotypes have been detected in immunoglobuline preparations and in patients after successful ITI.
Inhibitors interfere with fVIII function in coagulation by binding functional epitopes within fVIII domains. Inhibitors against the A2 and C2 domain are predominantly found, however also the C1 domain has been shown to be highly immunogenic in some patients. The polyclonality of inhibitors aggravates the understanding and treatment of these. The present project therefore focusses on the selection of synthetic anti-idiotypic antibodies to target inhibitors in patients. The phage display method was applied to, for one, isolate anti-idiotypic single chain variable fragments (scFvs) specific against human polyclonal anti-fVIII antibodies and second against two C1 domain-specific inhibitory monoclonal antibodies (mAbs).
In the first project, anti-fVIII antibodies were purified from human plasma to serve as target molecules. A previous project showed that using full plasma as a target did not yield anti-idiotypic antibodies from phage display. For the purification, protein A chromatography and fVIII coupled Affi Gel® chromatography were applied. The isolated antibodies were next used as targets for the selection of anti-idiotypic scFvs. Analysis revealed that none of the selected phages solely bound the anti-fVIII antibody target. Consequently, the test protocol was modified, which resulted in a reduction of unspecific binders. Yet, no target-specific binders were isolated from phage pools. Reason for this may have been the high diversity of the polyclonal antibody target and the limited diversity of the phage libraries.
The aim of the second project, was the selection and characterization of scFvs, that target the paratopes of C1 domain-specific mAbs GMA8011 and LE2E9. From a therapeutic viewpoint, the preparation of an anti-idiotypic antibody pool, tailored to each patient’s inhibitor population, could help neutralize inhibitors in patients. Ultimately, one GMA8011-specific scFv-carrying phage clone (H2C1) and two specifics to LE2E9 (H3G7, H3F10) were isolated. In further experiments, only the GMA8011-specific scFv showed competitive behavior in presence of fVIII, pointing towards an anti-idiotypic binding to the inhibitor paratope. The LE2E9-specific scFvs did not prevent binding of the inhibitor to fVIII. Hence, no anti-idiotypic behavior could be determined. For further characterization, selected scFvs were genetically fused to Fc antibody fragments and recombinantly produced. In this antibody format, all three scFvs showed concentration dependent binding to the target and the isotype control. The binding specificity to the target, observed in phage context, could not be reproduced. Competition experiments with fVIII confirmed that none of the scFvs bound the paratope of their target inhibitor.
The selection of anti-idiotypic scFvs from phage display libraries proves to be effortful. Polyclonal anti-fVIII antibodies purified from hemophilic plasma appear to be unsuitable as a target for phage display, likely due to the high diversity of the target molecules. Furthermore, the preparation of an individualized anti-idiotypic pools for patients by selecting scFvs against single inhibitory mAbs proves to be difficult. The selection of scFvs against anti-C1 inhibitors GMA8011 and LE2E9 produced three promising scFv-carrying phages. However, analysis could not detect anti-idiotypic behavior. Further research with inhibitors, monoclonal and polyclonal, and anti-idiotypic antibodies should be performed to bring better insight into the highly complex paratope-epitope interaction.
S100A12 ist ein Entzündungsmarker, der inflammatorische Prozesse präzise anzeigt. Entzündungsprozesse mit erhöhten S100A12 Konzentrationen spielen vor allem bei Autoimmunerkrankungen wie der der rheumatischen Arthritis (RA), autoinflammatorischen Erkrankungen wie der juvenilen idiopathische Arthritis (JIA) oder weiteren Erkrankungen wie dem familiären Mittelmeerfieber (FMF) eine wichtige Rolle. Das S100A12 Protein besitzt drei verschiedene Konformationen: das Dimer, das Tetramer und das Hexamer. In verschiedenen Studien konnte gezeigt werde, dass das Hexamer an proinflammatorische Rezeptoren wie dem Toll-like Rezeptor-4 (TLR-4) und dem „receptor for the advanced glycation end products“ (RAGE) bindet und so die Produktion von weiteren Entzündungsmediatoren stimuliert. Daher besitzt die S100A12 Hexamerkonformation eine entscheidende Rolle in Entzündungsprozessen. Das Ziel bestand somit in der Selektion von Peptiden oder „single chain variable fragment“ (scFv)-Konstrukten, die exklusiv an die hexamere Konformation von S100A12 binden.
Mittels Biopanning von Peptid- und scFv-Phagen Bibliotheken konnten Peptide und scFvs selektiert werden. Die selektierten Peptide und die selektierten scFvs wurden in ELISAs weiter auf ihre Bindungseigenschaften charakterisiert. Durch Umklonierung in einen Fc-Konstrukt Vektor konnten die scFvs als vollständige scFv-Fc-Konstrukte exprimiert werden. Die Bindung der selektierten Peptide bestätigte sich als Biotin-Fusion im anschließenden ELISA. Es zeigte sich eine sehr hohe Bindungsspezifität der Peptide und der produzierten scFv-Fc-Konstrukte an das S100A12 Hexamer.
Mit den selektierten Liganden ist es gelungen einen Test zu entwickeln: an Streptavidin immobilisierte Peptide binden spezifisch das S100A12 Hexamer aus dem Testmedium und mittels selektiertem scFv-Fc-Konstrukten lassen sich die gebundenen S100A12 Proteine detektieren. Ein Detektionsantikörper ermöglichte die Visualisierung der gebundenen scFv-Fc-Konstrukte mittels Farbreaktion. Das S100A12 Hexamer konnte durch den Testaufbau auch im Plasma spezifisch detekiert werden.
Dieser Test könnte es ermöglichen, die exakte Diagnose und vor allem das Überwachung von Patienten mit steigenden Entzündungsmarkern, wie im Rahmen der autoinflammtorischen Erkrankung JIA oder einer Erkrankung wie dem FMF, zu verbessern. Mit einem verbessertem Krankheitsmonitoring könnte ebenfalls die Therapie im frühen Stadium optimiert werden.
Zusätzlich könnte ein mögliches therapeutische Potential der S100A12 Hexamer Liganden getestet werden. Sollten die hexamerspezifischen Liganden die Interaktion von S100A12 mit ihren Rezeptoren wie TLR-4 oder RAGE blockieren, ist eine therapeutische Verwendung in der Behandlung von Autoimmun- und autoinflammatorischen Erkrankungen möglich.