Resident Memory-like CD8+ T Cells Are Involved in Chronic Inflammatory and Neurodegenerative Diseases in the CNS

Abstract

Background and objectives: Resident memory T (Trm) cells are a unique population that can survive and function in a compartmentalized tissue with inflammatory potential. We aim to investigate the alteration of Trm population in acute/chronic inflammatory and neurodegenerative diseases in the CNS.

Methods: The frequencies of CD4⁺ and CD8⁺ T cells expressing both CD69 and CD103, the markers for Trm cells, were quantified in the peripheral blood and CSF (n = 80 and 44, respectively) in a cross-sectional manner. The transcriptional profile of Trm-like population in the CSF was further analyzed using a public single-cell dataset.

Results: The frequency of CD69⁺CD103⁺CD8⁺ T cells was strikingly higher in the CSF than in the peripheral blood (among memory fraction, 13.5% vs 0.11%, difference (mean [SE]): 13.4% [2.9]). This CD69⁺CD103⁺CD8⁺ T-cell population was increased in the CSF from patients with chronic inflammatory diseases including multiple sclerosis and with neurodegenerative diseases such as Parkinson disease and Alzheimer disease compared with controls (11.5%, 13.0%, 8.1% vs 2.9%, respectively). By contrast, the frequency was not altered in acute inflammatory conditions in the CNS (4.0%). Single-cell RNAseq analysis confirmed Trm signature in CD69⁺CD103⁺CD8⁺ T cells in the CSF, supporting their Trm-like phenotype, which was not clear in controls.

Discussion: Collectively, an increase in CD69⁺CD103⁺CD8⁺ Trm-like population in the CSF is related with both chronic neuroinflammatory and some neurodegenerative diseases in the CNS, suggesting a partially shared pathology in these diseases.

Figure 1. CD69⁺CD103⁺ Trm-like Cells Are Rarely Observed in the Peripheral Blood

(A) Representative flow cytometry panels showing expressions of CD69 and CD103 on naive (CD45RA⁺) and memory (CD45RA⁻) T cells in the peripheral blood. (B) The frequency of CD69⁺CD103⁺ double-positive (DP) population is higher in memory than in naïve CD8⁺ T cells in the peripheral blood. (C) The frequency of CD69⁺CD103⁺ DP population is higher in memory than in naïve CD4⁺ T cells in the peripheral blood. (D) The frequency of CD69⁺CD103⁺ DP population tended to be higher in CD8⁺ T cells in the peripheral blood. Data are mean ± SD; paired t test (B-D) HC = healthy control; NMOSD = neuromyelitis optica spectrum disorder.

Figure 2. CD69⁺CD103⁺ Trm-like Cells Are Abundant in the CSF

(A) The frequency of CD69⁺CD103⁺CD8⁺ Trm-like cells is not different in the peripheral blood from patients with MS and NMOSD compared with that in controls. (B) The frequency of CD69⁺CD103⁺CD4⁺ Trm-like cells is not different in the peripheral blood from patients with MS and NMOSD compared with that in controls. (C) Representative flow cytometry panels showing CD69⁺CD103⁺ Trm-like population among memory CD8⁺ T cells. (D) The frequency of CD69⁺CD103⁺ Trm-like cells is higher in the CSF than in the peripheral blood among memory CD8 T cells. The samples were from 4 patients with MS, and 1with NMOSD. None of them were in a relapse state. Data are mean ± SD; One-way ANOVA with the Holm-Sidak multiple comparisons test with HC as a control (A, B) and paired t test (D). HC = healthy control; NMOSD = neuromyelitis optica spectrum disorder; PB = peripheral blood; RRMS = relapsing-remitting MS; SPMS = secondary progressive MS.

Figure 3. Representative Flow Cytometry Panels Showing the Frequency of Trm-like Cells

(A) Representative flow cytometry panels showing the frequency of CD69⁺CD103⁺ DP population among memory CD8⁺ T cells. (B) Representative flow cytometry panels showing the frequency of CD69⁺CD103⁺ DP population among memory CD4⁺ T cells. Control: idiopathic normal pressure hydrocephalus; acute inflammation: bacterial meningitis; chronic inflammation: MS. PB = peripheral blood; PD = Parkinson's disease.

Figure 4. CD8⁺ Trm-like Cells Are Increased in the CSF in Chronic Inflammatory and Neurodegenerative Diseases

(A) The frequency of CD69⁺CD103⁺CD8⁺ T cells is increased in the CSF in chronic inflammatory conditions, PD, and AD. The samples were analyzed in Kyoto University for the left 6 categories and in National Center of Neurology and Psychiatry for the right MS category (MS*). All 4 patients in MS* category were not in a relapse state. One with RRMS, 2 with SPMS, and 1 with PPMS. (B) CD4⁺ Trm-like cells were analyzed in the same way as in (A). (C) The frequency of CD69⁺CD103⁺ DP population among memory CD8⁺ T cells and the total cell number in the CSF. The total cell count was not determined between 1 and 10/µL in the clinical laboratory in the facility. The count in this range is described as 5/µL in the plot. (D) The frequency of CD69⁺CD103⁺ DP population among memory CD8⁺ T cells and the age of the patients. Data are mean ± SD; One-way ANOVA with the Holm-Sidak multiple comparisons test with HC as a control (A, B). AD = Alzheimer disease; ALS = amyotrophic lateral sclerosis; PB = peripheral blood; PD = Parkinson disease.

Figure 5. CD69⁺CD103⁺ DP CD8⁺ T Cells From Patients With MS Have a Phenotype Closer to Trm Compared With Those From HC

(A) Temporal alteration of the frequency of CD8⁺ Trm-like cells during the recovery period of acute inflammatory diseases. (B) Temporal alteration of the frequency of CD4⁺ Trm-like cells during the recovery period of acute inflammatory diseases. (C) Gene expressions in CD69⁺CD103⁺ DP CD8⁺ T cells in the CSF are analyzed using public single-cell RNA sequencing dataset. Three CD8⁺ T-cell populations are shown; CD69⁺CD103⁺ DP in the CSF, non-DP in the CSF, and total CD8⁺ T cells in the peripheral blood, from patients with MS. The sum of expressions for each gene in each condition are normalized to 1. (D) CD8⁺ T cells from patients with a noninflammatory condition (intracranial idiopathic hypertension) were analyzed in the same way as in (C). PB = peripheral blood.