CD4 and HIV infectious disease: During the early stages of HIV infection, intestinal CD4+ T-cells are massively depleted as these cells express high levels of the CCR5 co-receptor, permitting the entry of HIV virions into these cells, followed by eventual destruction of the cells and, in the gut, disruption of gut mucosal epithelial barrier integrity, and this may not fully resolve even with early ART initiation (30–32).