Dimethyl fumarate (DMF) alters the phenotype of circulating immune cells and causes lymphopenia in a subpopulation of treated MS patients.
Cross-sectional observational comparisons of peripheral blood from DMF-treated MS patients (n=17 lymphopenic, 24 non-lymphopenic), untreated MS patients (n=17) and healthy controls (n=23) that was immunophenotyped using flow cytometry. Longitudinal samples were analyzed for 13 DMF-treated patients.
Lymphopenic DMF-treated patients had significantly fewer circulating CD8 + and CD4 + T-cells, CD56 dim NK cells, CD19 + B-cells and plasmacytoid dendritic cells compared to controls. CXCR3 + and CCR6 + expression was disproportionately reduced among CD4 + T-cells while the proportion of T regulatory cells was unchanged. DMF did not affect circulating CD56 hi NK-cells, monocytes or myeloid dendritic cells. Whether lymphopenic or not, DMF-treated patients had a lower proportion of circulating central and effector memory T cells and concomitant expansion of naïve T cells compared to controls.
DMF shifts the immunophenotypes of circulating T cells, causing reduction of memory cells and relative expansion of naïve cells regardless of absolute lymphocyte count. This may represent one mechanism of action of the drug. Lymphopenic patients had disproportionate loss of CD8 + T cells, which may affect their immunocompetence.