Infection of U373-Magi-X4 and U373-Magi-R5 cell lines indicate that all our chimeric viruses and the control R5-tropic isolate HIV-1BaL, utilized the CCR5 coreceptor, whereas the parental HIV-1NL4-3 utilized the CXCR4 coreceptor (Table 3). This evidence concerns the gene CXCR4 and infection.