Trans-Endothelial Migration of Memory T Cells Is Impaired in Alemtuzumab-Treated Multiple Sclerosis Patients

The breakdown of the blood-brain barrier (BBB) and the trans-endothelial migration of lymphocytes are central events in the development of multiple sclerosis (MS). Autoreactive T cells are major players in MS pathogenesis, which are rapidly depleted following alemtuzumab treatment. This modulation, in turn, inhibits CNS inflammation, but alemtuzumab's effect on T cell migration into the CNS has been less studied. Human brain endothelial cells were stimulated with pro-inflammatory cytokines to mimic an inflamed BBB in vitro. Peripheral blood mononuclear cells from healthy controls, untreated or alemtuzumab-treated patients with relapsing-remitting MS (RRMS) were added to the BBB model to assess their transmigratory capacity. Here, the migration of CD4⁺ effector memory T (T^EM) and CD8⁺ central memory T (T^CM) cells across the BBB was impaired in alemtuzumab-treated patients. Naïve T (T^naïve) cells were unable to migrate across all groups. CD38 was lowly expressed on CD8⁺ T^CM cells, particularly for RRMS patients, compared to CD8⁺ T^naïve cells. CD62L expression was lower on CD4⁺ T^EM cells than CD4⁺ T^naïve cells and decreased further in alemtuzumab-treated patients. These data suggest that repopulated memory T cells are phenotypically different from naïve T cells, which may affect their transmigration across the BBB in vitro.