A single dose of a vectorized mAb targeting TDP-43 potently inhibits the neuropathology in a model of ALS/FTD

Transactive response DNA binding protein-43 (TDP-43)-mediated pathology is a hallmark of devastating neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Thus, monoclonal antibodies (mAbs) are being developed to target the pathological forms of this protein. To improve mAb exposure within the central nervous system, a potent anti-TDP-43 mAb, ACI-5891, was generated as a vectorized full-length antibody (vmAb) and evaluated for brain delivery using adeno-associated virus 9 (AAV9). Among the expression cassettes explored, the selected construct utilized an internal ribosome entry site (IRES), which produced high expression yields in vitro (>200 mg/L) with comparable quality, binding, and functional properties to the conventionally produced mAb. A single intracisternal administration of vmAb ACI-5891 demonstrated a broad brain distribution and sustained expression (i.e., months) in the serum, cerebrospinal fluid, and brain of mice. In a mouse model of ALS/FTD, treatment with a vmAb reduced the amount of pathological phospho-TDP-43 in neurons by 58% and 68% when expressed using either a ubiquitous promoter or a brain-selective promoter, respectively. This innovative approach sufficiently delivers effective immunotherapy with a single dose and illustrates the enormous potential of using vectorized antibodies to target neuropathology, including TDP-43 in patients suffering from ALS, FTD, and other TDP-43 proteinopathies.