Conversely, immune reconstitution syndrome in patients with progressive multifocal leukoencephalopathy (PML-IRIS), a demyelinating disease caused by JCPyV infection of the brain, was marked by an increase in blood brain barrier (BBB) permeability, suggesting that the extravasation of these JCPyV-specific CD8 T cells across the BBB may not be as strongly dependent on macrophages or virus location [17]. Here, CD8A is linked to progressive multifocal leukoencephalopathy.