CD4 and AIDS: In addition, as this paper was going to press, the interim results of the Strategic Timing of AntiRetroviral Treatment (START) study, a global, large-scale randomized trial comparing immediate ART in those with CD4 cell counts >500 cells/mm3 with deferring ART until CD4 cell counts fell below 350 cells/mm3, demonstrated a 53% reduction in the risk of serious AIDS/non-AIDS-related illness or death (http://www.niaid.nih.gov/news/newsreleases/2015/Pages/START.aspx).