Gene transfer has potential as a once-only treatment that reduces viral load, preserves the immune system, and avoids lifetime highly active antiretroviral therapy. This study, the first randomized, double-blind, placebo-controlled, phase II cell-delivered gene transfer clinical trial, was conducted in 74 HIV-1 infected adults who received a tat/vpr specific anti-HIV ribozyme (OZ1) or placebo delivered in autologous CD34+ hematopoietic progenitor cells. There were no OZ1-related adverse events. There was no statistical difference in viral load between the OZ1 and placebo group at the primary end-point (average at weeks 47 and 48) but time weighted areas under the curve from weeks 40-48 and 40-100 were significantly lower in the OZ1 group. Throughout the 100 weeks, CD4+ lymphocyte counts were higher in the OZ1 group. This study provides the first indication that cell-delivered gene transfer is safe and biologically active in HIV patients and can be developed as a conventional therapeutic product.