CXCR4 and AIDS: When using HIV-1 variants with different coreceptor usage obtained from patients, it was found that down-modulation of CD4 was not associated with CCR5-using viruses that are present early in infection, but were characteristic of CXCR4- or CXCR4/CCR5-using viruses that are mostly seen later in infection during the onset of AIDS [59].