To determine whether Treg cells were susceptible to HIV infection, purified Treg cells were first activated through the TCR and were infected with either replication-competent HIV, which uses CCR5 as a coreceptor (R5.HIV), or replication-defective viruses pseudotyped with vesicular stomatitis virus glycoprotein (VSV-G.HIV) that encode green fluorescent protein (GFP) as a marker of infection (Motsinger et al. 2002). This evidence concerns the gene CCR5 and HIV infectious disease.