Blood brain barrier disruption is integral to acute lesions in multiple sclerosis (MS), a complex process where auto-aggressive immune cells migrate into the central nervous system (CNS) and induce demyelination. Recent studies have shown a proportion of patients treated with the disease-modifying therapy cladribine achieve prolonged disease suppression after limited dosing schedules, suggesting this agent can modulate interactions between the immune system and the CNS.  Endothelial ICAM-1 binding to leukocyte beta2 integrins LFA-1 and Mac-1 facilitates their trans-endothelial migration at sites of inflammation and their function as costimulatory molecules for T-cell activation.

Primary human brain microvascular endothelial cells, HBMEC/cAP-002, were cultured on collagen-coated multi-well plates. Cells were grown to confluence and stimulated with TNF at 10 ng/ml overnight to induce upregulation of adhesion molecules. After treatment with cladribine (0.35, 1.75 or 3.5 µM) in the presence or absence of TNF, cells were detached by trypsin/EDTA, incubated with PE-conjugated anti-CD54 mAb or anti-CD106 mAb and surface phenotyped by flow cytometry.

Cladribine dose-dependently inhibited TNF-induced ICAM-1 upregulation on brain endothelial cells. In contrast, there was no effect of cladribine on the expression of VCAM-1, the endothelial receptor for the leucocyte integrin VLA-4.

Our results suggest that cladribine modulates the endothelial responsiveness to TNF, a potent pro-inflammatory cytokine that facilitates leukocyte migration. Further studies are necessary to determine if cladribine inhibits trans-endothelial migration.