Tissue-resident memory T cells invade the brain parenchyma in multiple sclerosis white matter lesions

Abstract

Multiple sclerosis is a chronic inflammatory, demyelinating disease, although it has been suggested that in the progressive late phase, inflammatory lesion activity declines. We recently showed in the Netherlands Brain Bank multiple sclerosis-autopsy cohort considerable ongoing inflammatory lesion activity also at the end stage of the disease, based on microglia/macrophage activity. We have now studied the role of T cells in this ongoing inflammatory lesion activity in chronic multiple sclerosis autopsy cases. We quantified T cells and perivascular T-cell cuffing at a standardized location in the medulla oblongata in 146 multiple sclerosis, 20 neurodegenerative control and 20 non-neurological control brain donors. In addition, we quantified CD3+, CD4+, and CD8+ T cells in 140 subcortical white matter lesions. The location of CD8+ T cells in either the perivascular space or the brain parenchyma was determined using CD8/laminin staining and confocal imaging. Finally, we analysed CD8+ T cells, isolated from fresh autopsy tissues from subcortical multiple sclerosis white matter lesions (n = 8), multiple sclerosis normal-appearing white matter (n = 7), and control white matter (n = 10), by flow cytometry. In normal-appearing white matter, the number of T cells was increased compared to control white matter. In active and mixed active/inactive lesions, the number of T cells was further augmented compared to normal-appearing white matter. Active and mixed active/inactive lesions were enriched for both CD4+ and CD8+ T cells, the latter being more abundant in all lesion types. Perivascular clustering of T cells in the medulla oblongata was only found in cases with a progressive disease course and correlated with a higher percentage of mixed active/inactive lesions and a higher lesion load compared to cases without perivascular clusters in the medulla oblongata. In all white matter samples, CD8+ T cells were located mostly in the perivascular space, whereas in mixed active/inactive lesions, 16.3% of the CD8+ T cells were encountered in the brain parenchyma. CD8+ T cells from mixed active/inactive lesions showed a tissue-resident memory phenotype with expression of CD69, CD103, CD44, CD49a, and PD-1 and absence of S1P1. They upregulated markers for homing (CXCR6), reactivation (Ki-67), and cytotoxicity (GPR56), yet lacked the cytolytic enzyme granzyme B. These data show that in chronic progressive multiple sclerosis cases, inflammatory lesion activity and demyelinated lesion load is associated with an increased number of T cells clustering in the perivascular space. Inflammatory active multiple sclerosis lesions are populated by CD8+ tissue-resident memory T cells, which show signs of reactivation and infiltration of the brain parenchyma.

Perivascular tissue resident memory T cells as therapeutic target in multiple sclerosis

“…Frischer et al observed perivascular cuffs only in cases with active progressive disease [70]. In the NBB tissue collection, donors with perivascular cuffs in the brainstem had a higher brain stem lesion load and an overall higher proportion of mixed active/inactive lesions [66]. These observations suggest that presence of perivascular cuffing can be regarded as a detrimental phenomenon in advanced progressive MS, a clinical phenotypic entity not associated with attacks of infiltrating lymphocytes from the circulation.…”

“…This enrichment comprised both CD4 + and CD8 + T cells, in which CD8 + T cells were most prevalent [43,[71][72][73]. Interestingly, the ratio of CD8/CD4 T cells was remarkably consistent within a donor between regions investigated [66]. Where brain T cells were located almost exclusively in the PVS in normal-appearing white matter, they infiltrated the parenchyma in both active and mixed active/ inactive lesions (Figure 2) [43,66].…”

“…In postmortem MS brain normal-appearing white matter, T cells are enriched [65]. On average 2-6 times as many CD3 + T lymphocytes were encountered in MS normal-appearing white matter when compared to control white matter [33,36,66]. Like in control donors, these were more CD8 + than CD4 + T cells, and they were almost exclusively localized in the PVS (Figure 2).…”

“…Perivenular infiltrates, believed to contain infiltrating lymphocytes from the circulation, have been identified in white matter of both acute and chronic MS cases [68,69]. Despite advanced progressive MS not being associated with relapses or gadoliniumenhancing MRI lesions, perivascular cuffs were observed in some autopsy cohorts with advanced progressive MS [35,66]. Frischer et al observed perivascular cuffs only in cases with active progressive disease [70].…”

“…The association of T cells with different white matter lesion types has been quantified both in the NBB and Vienna/Mayo postmortem MS-tissue collections, which show a comparable profile [66,70]. When compared to normal-appearing white matter, active MS lesions showed the most pronounced enrichment of T cells, followed by the mixed active/inactive lesion.…”