Clonal CD8⁺ T cells populate the leptomeninges and coordinate with immune cells in human degenerative brain diseases

Meningeal immune cells monitor the central nervous system (CNS) and influence neuroinflammation in mice, but the human leptomeningeal immune landscape and the changes that occur in this immunological niche in neurodegeneration remain underexplored. Here we performed single-cell RNA and T cell receptor (TCR) sequencing of 99,625 high-quality immune cells from 57 leptomeninges and brain samples from donors with Alzheimer's disease (AD), amyotrophic lateral sclerosis and Parkinson's disease and found that although the leptomeninges are home to highly clonally expanded CD8 tissue-resident memory (T_RM) T cells, the maximal level of clonal expansion was decreased in AD in comparison to non-neurodegenerative controls. Intra-patient paired tissue analysis further revealed that brain and leptomeningeal TCR repertoires share significant similarities, but tissue-specific clones emerge in AD. Finally, in AD, the degree of CD8 T_RM clonal expansion was positively correlated with microglial TGFB2, suggesting that brain and leptomeningeal immune cells coordinate their activities in AD. In addition to identifying key inflammatory dynamics in the human degenerating CNS, this study establishes a foundational resource for future studies that could inform treatment for AD and other neuroinflammatory diseases.