In addition to HDACs, HIV expression is limited by other cellular barriers to effective mRNA transcription, which the virus overcomes through the action of its own activator, Tat. Tat recruits the positive transcription elongation factor b (P-TEFb) kinase to the integrated viral promoter, inducing viral gene expression (Fig. 1B and C) (30). Several kinase agonists, including hexamethylbisacetamide (HMBA)-a compound previously tested in human cancer trials (31), activate intracellular signaling cascades that mobilize P-TEFb in the absence of Tat (32, 33) and can induce the expression of HIV in latently infected cells (Fig. 2) (34).