Huntington’s disease (HD) is a fatal neurodegenerative disease with a worldwide prevalence of 5 to 10 in 100000 people. Clinical symptoms manifest typically in the fourth life decade and progress to a severe neurological and psychiatric condition involving changes of the immune system and metabolism, and is ultimately fatal. This rare monogenetic disorder is caused by a single, well-defined mutation, causing a polyglutamine stretch accumulation at the Huntingtin gene locus. The mutation leads to a structurally modified mutant Huntingtin protein (mtHTT), which becomes biochemically modified and induces pathogenesis by forming aggregates and neurotoxic fragments following proteolytic cleavage.
Using computational methods, including molecular dynamics simulations and artificial intelligence-supported molecular modeling, humanized antibody variants of the anti-HTT antibodies were proposed. Their expression titers reached up to three-fold of the prototypic chimeric variants featuring mouse variable and human constant domains and met the high expectations required for therapeutic applications. Further antigen affinity maturation, based on directed evolution using yeast display platform, resulted in antibody candidates that show the specific antigen-affinity binding within the range of the initial mouse counterparts.
Scientists at acib in collaboration with HD Immune GmbH have delved into the challenging task of exploring the antigen-degradation function of anti-HTT antibodies. They elucidated in detail the dynamics of antigen-antibody complex internalization into phagocytic immune cells, mediated by Fc-gamma-receptors, as well as the molecular mechanism behind the rapid degradation of the pathogenic HTT. The alternative cellular uptake pathways are the hot topic of current research, involving innovative antibody modifications required for specific interaction with the relevant extracellular structures.
Another mechanism of action of the studied anti-HTT antibodies is the blockade of the Caspase-6 enzymatic activity, which cleaves the mutant HTT into toxic fragments. The achieved high-affinity antibody variants indeed tested superior in enzyme inhibition, underlining the importance of quest for even more potent entities.
With this important contribution, acib scientists rendered the anti-HTT antibody sequences suitable for further experimentation, paving the way towards clinical trials. At the same time, they have explored the mechanisms of antibody’s subcellular trafficking and removal of mutant pathogenic HTT, which will have a decisive impact on the final format of the medication. The project is running in close cooperation of the company partner and acib scientists, ensuring prompt information exchange and transfer of novel concepts to application in “close-to-human” in vivo disease models.
