Disease exacerbation of multiple sclerosis is characterized by loss of terminally differentiated autoregulatory CD8+ T cells

Abstract

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system (CNS). Although its etiology remains unknown, pathogenic T cells are thought to underlie MS immune pathology. We recently showed that MS patients harbor CNS-specific CD8+ Tregs that are deficient during disease relapse. We now demonstrate that CNS-specific CD8+ Tregs were cytolytic and could eliminate pathogenic CD4+ T cells. These CD8+ Tregs were present primarily in terminally differentiated (CD27−, CD45RO−) subset and their suppression was IFNγ, perforin and granzyme B-dependent. Interestingly, MS patients with acute relapse displayed a significant loss in terminally differentiated CD8+ T cells, with a concurrent loss in expression of perforin and granzyme B. Pre-treatment of exacerbation-derived CD8+ T cells with IL-12 significantly restored suppressive capability of these cells through upregulation of granzyme B. Our studies uncover immune-suppressive mechanisms of CNS-specific CD8+ Tregs, and may contribute to design of novel immune therapies for MS.

Immune regulation of multiple sclerosis by CD8+ T cells

“…This difference in the suppressive potential between CD8-subsets was masked when suppression cultures were polyclonally activated with anti-CD3 antibody. The findings were corroborated in MS patients where reduction in the frequency of terminally differentiated CD8+ T cells underlies the loss in suppressive ability of CD8+ T cells during disease relapse [19]. Other subsets of CD8+ T cells with regulatory functions in MS include CD8+CD25+FoxP3+ [27] and CD8+CD28- T cells [35].…”

“…Several subtypes of CD8+ T cells with regulatory functions have been identified in multiple disease models. Work from our group demonstrated that the most potent neuroantigen-specific CD8+ Tregs were harbored in the terminally differentiated subset (CD27-CD28-CD45RO-CD62L-CD57+) of CD8+ T cells [19]. This difference in the suppressive potential between CD8-subsets was masked when suppression cultures were polyclonally activated with anti-CD3 antibody.…”

Multiparameter Flow Cytometric Assays to Quantify Effector and Regulatory T-Cell Function in Multiple Sclerosis

“…The prominent requirement of such an assay would be its ability to differentiate MS patients from patients with other neurologic disease and healthy subjects. While the generation of such a test has been technologically difficult, we have developed a flow cytometric based proliferation assay that allows for the detection, quantification and phenotyping of CNS-reactive T cell responses following a relatively short-term in vitro culture [16,18-21]. From several reports by others and us, we know the following:

MS patients harbor CD4+ and CD8+ T cell responses targeted to CNS autoantigens.

Healthy subjects also harbor such responses.

…”

“…Thus, CNS-targeted T cells from MS patients are less dependent on CD28-mediated costimulation [5], are more differentiated toward effector status [16], have greater numbers of HPRT mutations [22] and thus, exhibit a memory/effector phenotype.…”

“…This suppression assay, conducted on carefully recruited treatment-naïve patients before administration of steroids, has identified novel features of immune regulation during an MS relapse: A strikingly reduced suppressive potential of CNS-specific CD8+ Tregs during relapse as compared to remission [21]A relative resistance of CD4 effector cells to CD8 suppression [16]Lack of terminally differentiated CNS-specific CD8 T cells during relapse, with concurrent deficit in perforin and granzyme B expression. The assay measures the proliferation and activation of CFSE-stained CD4+CD25- responder T-cells in response to either a mitogenic stimuli such as CD3 or specific antigens such as myelin antigens.…”