Development of TDP‐43 immunotherapy blocking transmission of seeding‐competent species from ALS/FTD

Abstract

AbstractBackgroundAccumulation of pathological transactive response DNA binding protein 43 (TDP‐43) into intracellular inclusions underlies frontotemporal lobar degeneration with TDP‐43 pathology (FTLD‐TDP), amyotrophic lateral sclerosis (ALS) and limbic‐predominant age‐related TDP‐43 encephalopathy (LATE). TDP‐43 pathology is present as a co‐pathology in other neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and chronic traumatic encephalopathy (CTE). Multiple mechanisms contribute to spreading of TDP‐43 pathology including transmission across synaptic terminals, exosomes and release of misfolded TDP‐43 from dying neurons. In fact, cerebrospinal fluid (CSF) obtained from ALS/FTLD‐TDP patients contains seeding‐competent TDP‐43 species. Therefore, antibody‐mediated clearance of pathological TDP‐43 represents an attractive therapeutic strategy. Our approach is to develop a TDP‐43‐specific immunotherapy that exploits Fcγ receptor‐mediated removal mechanisms to limit neuronal damage while maintaining physiological TDP‐43 function.MethodHigh affinity monoclonal antibodies (mAbs) were generated against various regions of TDP‐43 using AC Immune’s SupraAntigen® platform and evaluated in mechanistic assays in vitro and in vivo models of TDP‐43 proteinopathies. A real‐time quaking‐induced conversion (RT‐QuIC) assay was established using patient’s CSF to evaluate the inhibitory properties of the lead therapeutic mAb on the seeding mechanism. Studies to evaluate the pharmacology and safety of the antibody were carried out in non‐human primates.ResultTargeting the C‐terminal domain of TDP‐43 but not the RNA recognition motifs reduced TDP‐43 pathology and prevented neuronal loss in vivo. This rescue was dependent on Fcγ receptor‐mediated immune complex uptake by microglia. The latter also promoted phagocytic capacity of ALS patient‐derived microglia. Importantly, the antibody efficiently neutralized seeding‐competent pathological TDP‐43 species in CSF from ALS patients. These beneficial effects were achieved while preserving physiological TDP‐43 function demonstrating safety of targeting TDP‐43 by immunotherapy. Modelling from non‐clinical pharmacokinetic studies of the antibody predicted a half‐life supporting target saturation in humans when administered monthly.ConclusionOur studies confirm the presence of extracellular seeding‐competent TDP‐43 species in the CSF of patients with ALS/FTLD‐TDP patients, providing an explanation for the spread of pathology including the non‐contiguous pattern of clinical manifestations observed in ALS. In addition, the binding and inhibitory properties of our lead therapeutic mAb in multiple patho‐mechanistic assays support clinical development in TDP‐43‐driven neurodegenerative diseases.