The immune checkpoint inhibitors, pembrolizumab and nivolumab, are also exciting therapeutic prospects for the management of PML and PML-IRIS, and have been shown in very recent studies to reduce JCV viral load, increase CD4+ and CD8+ T-cell activity against JCV, and induce clinical stabilization or improvement in patients with PML [43, 44, 46, 99]. Here, CD4 is linked to progressive multifocal leukoencephalopathy.