Tat has been implicated in the activation of cytokine transforming growth factor (TGF)-β in HIV-1-infected cells and in the stimulation of JC virus (JCV) gene transcription and DNA replication in oligodendroglia, the primary central nervous system cell type infected by JCV in progressive multifocal leukoencephalopathy [47]. This evidence concerns the gene TAT and progressive multifocal leukoencephalopathy.