Role of Clonally Expanded T Cells in Alzheimer's Disease

DownLoad

Summary

They use integrated studies of numerous cohorts to pinpoint the immunological alterations in Alzheimer's disease. First, they discovered an immunological signature of Alzheimer's disease consisting of an increase in CD8⁺ T effector memory CD45RA⁺ (T_EMRA) cells utilizing mass cytometry (CyTOF) on peripheral blood mononuclear cells. The second group of samples revealed a negative correlation between cognition and CD8⁺ T_EMRA cells. Single-cell RNA sequencing showed that the T cell receptor (TCR) signaling was better in these cells. Notably, they identified clonally increased CD8⁺ T_EMRA cells in the cerebral fluid of Alzheimer's patients utilizing several single-cell TCR sequencing techniques in a third cohort. These results show that people with Alzheimer's disease have an adaptive immune response in their blood and cerebrospinal fluid.

Research Criteria

• They integrated analyses of multiple cohorts and used several methods to assess adaptive immunity in AD (Alzheimer's Disease). First, they used mass cytometry to study peripheral blood mononuclear cells (PBMCs) from patients with AD and patients with prodromal mild cognitive impairment (MCI) (cohort 1).
• To further investigate the role of CD8⁺ T cells in MCI and AD, they assessed the relationship between cognition and populations of memory T cells in a separate cohort (cohort 2).
• They next determined whether CD8⁺ T cells were present in the brain of patients with AD. Finally, they assessed post-mortem brains from a third cohort (cohort 3) comprising control individuals (no neurological disease) and patients with AD (by using immunohistochemistry to examine the expression of CD8 and Aβ and analyze the proximity of CD8⁺ T cells to the cerebral vasculature.
• Then they pooled TCRαβ sequences from plate-seq and drop-seq experiments in cohort 4 to broadly assess clonality in neurodegeneration.

Fig.1 Experimental design. (Gate, 2020)

Sample Type

PBMCs were isolated from blood by layering diluted blood (1:1 in PBS) on top of an equal volume of Ficoll, followed by centrifugation and isolation of the buffy coat. CSF was collected by lumbar puncture, then centrifuged at 300g to pellet immune cells. CSF samples were checked for blood contamination by resuspending the pelleted cells in 100 μL CSF and mixing 10 μL (10%) CSF with 10 μL trypan blue to assess red blood cell content and viability.

Result - Integrated Analysis of scRNA-Seq and scTCR-Seq Dataset Revealed the Clonality of T cells in Patients with AD

As T_EMRA cells are associated with immunological memory, cohort 4 examined whether clonally expanded T cells patrol the CSF of healthy individuals, patients with Alzheimer's disease (AD), and patients with Parkinson's disease (PD). They used both plate-based sequencing (plate-seq) and droplet-based sequencing to evaluate clonal expansion (drop-seq). First, plate-seq was performed on TCRs from CSF T cells of healthy controls, AD patients, and PD patients. Most clonally expanded cells were CD8⁺ T cells. The findings provide the first evidence that clonally expanded CD8⁺ T cells patrol the CSF in aging-related neurodegenerative brains. Single cell TCR sequencing (scTCR-seq) was then performed on these cells, revealing that clonal T cells colocalized with CD8⁺ T cells. Quantification of the most highly expanded clone for each subject revealed that the percentage of the most highly expanded clone was greater in patients with MCI or AD than in healthy controls. Analysis of the differential expression of highly expanded clones in MCI and AD. The percentages of T cells that corresponded to highly expanded clones were then quantified, revealing that 49.13% were CD8⁺ T_EMRA cells. In MCI and AD, differential expression analysis of clonally expanded CD8⁺ T_EMRA cells revealed elevated expression of cytotoxic effector genes, including NKG7 and GZMA. These results demonstrate the utility of combining scRNA-seq and scTCR-seq datasets by revealing the pro-inflammatory, cytotoxic function of clonal CD8⁺ T_EMRA cells in the CSF of AD patients.

Fig.2 Clonal expansion of CD8⁺ T_EMRA cells in the CSF of patients with AD. (Gate, 2020)

Creative Biolabs' Services

Single Cell RNA Sequencing Service

Cell populations are rarely homogeneous and synchronized in their characteristics. Single-cell RNA sequencing aims to uncover the transcriptome diversity in heterogeneous samples. Creative Biolabs offers end-to-end workflows including sample preparation, library construction, and data analysis, maximizing your project flexibility, speed, and data accuracy.

Learn More

Single Cell TCR/BCR Profiling Service

The adaptive immune system relies on the vast diversity of B-cell receptors (BCR) and T-cell receptors (TCR) produced by recombination of the variable (V), diversity (D), and joining (J) loci. Our single-cell TCR/BCR profiling service uses customized bioinformatics and ultra-deep sequencing of V(D)J regions to characterize the entire repertoire. Recent microfluidic technology allows single-cell pairing of BCR and TCR chains.

Learn More

Creative Biolabs provides sample preparation, library construction, and data analysis to maximize project flexibility, speed, and accuracy. We have extensive experience and expertise in performing single-cell RNA sequencing and single-cell TCR sequencing. For any information, please contact us.

Reference

1. Gate, D.; et al. Clonally expanded CD8 T cells patrol the cerebrospinal fluid in Alzheimer's disease. Nature. 2020, 577: 399-404.