However, it is important to note that the PA-R5 virus from subject IK1 was isolated just prior to the onset of CD4+ T-cell loss and progression toward AIDS [13], whereas the PA-R5 viruses from the cross sectional panel were isolated at earlier stages of HIV-1 infection, including one virus isolated from an acute seroconverter [34]. This evidence concerns the gene CD4 and HIV-1 infection.