Intrabody B1 targeting TDP-43 modulates neuroinflammatory and metabolic pathways in a preclinical ALS model

TDP-43 pathology is a hallmark of Amyotrophic Lateral Sclerosis (ALS), yet no therapeutic strategy effectively targets its upstream molecular consequences. Here, we investigated whether the anti-TDP-43 intrabody scFv B1 modulates neuroinflammatory and metabolic pathways in a preclinical ALS model, and whether these effects translate into functional benefit after symptom onset. Using phage display, we previously identified single-chain variable fragments (scFvs) binding TDP-43, including the candidate therapeutic scFv B1. In NSC-34 motor neuron-like cells overexpressing human wildtype TDP-43, B1 reduced NF-κB activation, consistent with disruption of TDP-43-driven inflammatory signaling. For in vivo assessment, B1 was delivered via AAV-CAP.B10 after symptom onset in the hTDP-43(WTxA315T) transgenic mouse model, enabling neuro-specific expression. Two cohorts were analyzed - longitudinal (nine months) and terminal (six months post-treatment) - through behavioral testing, PET imaging, metabolomics, transcriptomics, and plasma biomarker analyses. B1 achieved robust CNS expression and modulated several disease-relevant molecular pathways. RNA-sequencing revealed attenuation of NF-κB-related inflammatory signatures and partial normalization of metabolic and trophic gene expression. Metabolomic profiling identified shifts toward wild-type-like levels in oxidative stress, mitochondrial, and membrane phospholipid metabolites. Despite these molecular effects, symptomatic B1 administration did not improve motor behavior or reduce plasma neurofilament light chain (NfL) concentrations. Notably, plasma TDP-43 levels were stabilized, indicating systemic target engagement. Collectively, scFv B1 modulates upstream pathogenic processes associated with TDP-43 proteinopathy but is insufficient to reverse established neurodegeneration after symptom onset, underscoring the need for earlier and likely combinatorial intervention strategies in ALS.