CXCR4 and AIDS: Prediction of coreceptor tropism based on the env gp120 V3 region indicated that 50% (3 of 6) and 58% (7 of 12) of the participants had CXCR4-using viruses in the asymptomatic and AIDS stages, respectively (P = 1.00, two-tailed Fisher’s exact test) (Table 5).