Through an in vitro study, Argaw et al. 28 found that VEGF-A could degrade the blood-brain barrier by downregulating the tight junction protein Claudin-5, increasing the permeability of brain microvascular endothelial cells (BMECs), while a clinical study by Si et al. 29 found that VEGF-A may be a major factor contributing to blood-brain barrier degradation and CNS metastasis of leukemia cells. Here, CLDN5 is linked to leukemia.