Staining with HLA-A*0201-VP1p36 and -VP1p100 tetramers showed that these JCV-specific CD8+ T cells have an effector-memory phenotype (CD62LloCD45RA−CD49dhi) and can be found in the PBMCs of healthy individuals, perhaps contributing to the overall low incidence of PML (44, 45). Here, CD8A is linked to progressive multifocal leukoencephalopathy.