Although CD4+ T cells, as well as monocytes and macrophages, are the primary cellular targets for productive HIV-1 infection [5,6,7], in the brain, macrophages and microglia are the main cell types productively infected by HIV-1, and virus production in the CNS is not seen before the onset of acquired immunodeficiency syndrome (AIDS) [8,9]. The gene discussed is CD4; the disease is AIDS.