TAT and disease arising from reactivation of latent virus: Although Tat cannot directly initiate transcription, it has been shown that addition of Tat to latently infected T-cell lines, primary models of latent infection (in vitro) and CD4+ T cells derived from HIV infected individuals on cART (ex vivo) activates viral expression outside the context of T cell activation (Lin et al., 2003; Lassen et al., 2006; Razooky et al., 2015; Khoury et al., 2018b; Khoury et al., 2019).