CXCR4-dependent infection of CD8+, but not CD4+, lymphocytes by a primary human immunodeficiency virus type 1 isolate.

We recently isolated from an infant an X4-syncytium-inducing (SI) human immunodeficiency virus type 1 (HIV-1) variant (92US143-T8) that was able to infect CD8+ lymphocytes independently of CD4. Although it was CD4 independent, the 92US143-T8 isolate also maintained the ability to infect CD4+ cells. In the present study, we investigated the role of CXCR4 in the infection of CD4+ and CD8+ cells by this primary isolate. The expression of CXCR4 was down modulated in CD8+ lymphocytes after infection with the 93US143-T8 isolate. Infection of CD8+ lymphocytes by the 93US143-T8 isolate was prevented by treatment with AMD3100, a specific antagonist for CXCR4, indicating CXCR4-dependent infection. Interestingly, AMD3100 treatment had no inhibitory role in the infection of purified CD4+ lymphocytes by the same isolate. Furthermore, AMD3100 treatment failed to prevent infection of known CD4+ CXCR4+ T-cell lines (MT-2 and CEM) by the 93US143-T8 isolate. In fact, virus replication in the CD4+ cells was often enhanced in the presence of AMD3100. Viruses produced from the infected CD4+ cells in the presence of AMD3100 maintained an unchanged envelope genotype and an SI phenotype. For the first time, these results provide evidence of CXCR4-dependent infection of CD8+ lymphocytes by a primary HIV-1 isolate. This study also shows a different mode of infection for the CD4+ and CD8+ lymphocytes by the same HIV-1 variant. Finally, our findings suggest that a more careful evaluation is necessary before the random use of AMD3100 as a new entry inhibitor in patients harboring SI HIV-1 strains.