Flow chart of the experimental study design. PBSC from HIV-1–infected volunteers were mobilized with G-CSF for 5 days, apheresis was performed, and CD34⁺ cells were isolated by immunoaffinity. Transduction of the CD34⁺ cell population with retroviral vectors was carried out as described in Materials and Methods, using vector-containing supernatants plus cytokines (SCF, IL-6, and IL-3) with stromal support for 72 hours. After transduction, colony assays were performed, LTBMC were established, and the major portions of the transduced cells were subjected to selection in G418 for 12 days. After a 4-day recovery period, cells were challenged with HIV-1_JR-FL at an MOI of 0.01 TCID₅₀ , or an HIV-1 primary isolate at an MOI of 0.1 TCID₅₀ . Aliquots of the culture media were taken weekly after HIV-1 infection for subsequent evaluation in an HIV-1 p24 assay. In addition, colony assays were performed from cells after G418 selection, and from unselected LTBMC after 5 weeks.