Objectives/Goals: Lowering of FUS with antisense oligonucleotide (ASO) has shown promise in a subtype of amyotrophic lateral sclerosis (FUS-ALS). As inflammation is associated with ALS progression, we characterized immune trajectories in FUS-ALS patients treated with FUS ASO to understand the relationship inflammation may have with treatment response. Methods/Study Population: Twelve participants (10 with a diagnosis of ALS, 1 symptomatic carrier, and 1 asymptomatic carrier) received monthly intrathecal administrations of FUS ASO (i.e., jacifusen). Motor function was measured using the ALS Functional Rating Scale-Revised. Axonal injury was measured by cerebrospinal fluid (CSF) neurofilament light chain (NfL) concentration. 10x Genomics single-cell RNA sequencing (scRNA-seq) with T- cell receptor (TCR) sequencing was performed on paired peripheral blood mononuclear cells (PBMCs) and CSF cells. Proteomic analysis was conducted using the Olink Explore HT platform. Complementary analyses included spectral flow cytometry validation and immunohistochemical staining of post-mortem lumbar spinal cord. Results/Anticipated Results: We observed a proportional shift starting at 6 months, whereby T-cell proportions decreased, and myeloid cell proportions increased over treatment. Decreases in T-cell proportions over treatment were not accompanied by increased CD8+ T-cell infiltration in the ventral horn of the lumbar spinal cord. Differential expression revealed long-term, chronic activation and lysosomal dysregulation in myeloid cells. While CSF monocyte proportions were positively associated with CSF NfL concentration, positive associations with ALSFRS-R score were observed only in PBMC T-cell proportions, particularly cytotoxic subclusters. Proteomic analysis also highlighted a shift toward long-term innate immune cell activation associated with reduced ALSFRS-R score, accompanied by decreases in CSF lysosomal proteases. Discussion/Significance of Impact: These findings provide insight into the immune dynamics of FUS-ALS in the context of CNS FUS knockdown, as well as their potential relationship with clinical outcomes. Further, the long-term shift toward monocyte activation and persistent lysosomal dysregulation signature outside the CNS highlights potential avenues for combination therapy.
Rifai et al. (Wed,) studied this question.