CSF Leukocytes Transiently Increase Before Onset of Huntington Disease in Association with a Stage-Specific CSF Cytokine/Chemokine Pattern

BACKGROUND AND OBJECTIVES:CSF inflammatory biomarkers in Huntington disease (HD), a neurodegenerative CAG-triplet expansion disorder, usually increase with disease progression. CSF leukocytes as an inflammatory marker have not been explored in HD. We explored high-precision CSF-leukocyte counts across different HD stages in the multicenter prospective biosample HD study HDClarity and their association with CSF neurofilament light chain (NFL) and cytokine and chemokine patterns. METHODS:A cross-sectional case-control study of the first average CSF leukocyte count of HDClarity study control participants (N = 94) and those carrying a repeat-expanded Huntingtin (HTT) allele (N = 335) categorized as having successive stages of presymptomatic and motor manifest HD as predefined by the HDClarity protocol (early presymptomatic [N = 48]: disease burden score [DBS] <250; late presymptomatic [N = 93]: DBS ≥ 250; early manifest HD [N = 171]: total functional capacity [TFC] 7-11; and late motor manifest HD [N = 23]: TFC < 11) was performed. CSF-NFL was available in 165. Results were juxtaposed with an independent single-center data set of 18 CSF cytokines and chemokines (57 CSFs, 19 control, 6 early and 8 late presymptomatic HD CSFs, and 19 manifest HD CSFs). RESULTS:CSF leukocytes peaked in late premanifest (median, interquartile range: 1.0/µL, 0.33-1.33/µL) when compared with early premanifest (0.0/µL, 0.0-1.0/µL) but also early (0.33/µL, 0.0-1.0/µL) and late manifest HD (0.0/µL, 0.0-0.67/µL). CSF leukocytes in late premanifest HD were higher than in controls (0.0/µL, 0.0-1.0/µL). A CSF-leukocyte peak at a DBS between 256 and 344 closely corresponded to the late premanifest HD peak. Higher CSF leukocytes in late premanifest HD were associated with higher CSF-NFL levels. Exploratory analysis of CSF cytokine and chemokine levels revealed that low interleukin (IL)-7 but high vascular endothelial growth factor (VEGF) and C-C motif chemokine ligand (CCL)22 levels may distinguish HD from control CSF; high VEGF, IL-6, and IL-15 early from late premanifest HD CSF; and low CCL2, CCL17, and IL-8 late premanifest from manifest HD CSF. When consecutively applied, these patterns identified late premanifest HD participants with a 75% sensitivity (95% CI 41%-96%) and 90% specificity (78%-96%). DISCUSSION:CSF leukocytes peaking in late premanifest HD, their association with increased CSF-NFL, and the corresponding stage-specific chemokine/cytokine changes indicate a temporally dynamic, probably neurotoxic inflammatory signaling network in HD.