Support for this potential immune therapeutic approach is provided by studies showing that checkpoint inhibitors and common γ-chain cytokines, which stimulate CD4+ and CD8+ T cells, have been effective in a number of serious viral infections, including hepatitis C, JC virus–induced progressive multifocal leukoencephalopathy, and HIV (47, 53). Here, CD8A is linked to progressive multifocal leukoencephalopathy.