The introduction of HIV-resistance genes into blood forming stem cells using lentiviral vectors results in the generation of HIV-resistant (progeny) CD4+ T-cells and monocytes. To date, this process has been fairly inefficient, resulting in less than 1 percent HIV resistant blood cells in patients treated with gene-modified stem cells. We report here on the enhancement of genetic modification of blood forming stem cells using treatment with a widely used drug, rapamycin. We tested the ability of rapamycin to enhance genetic modification of blood forming stem cells using lentiviral vectors encoding HIV-resistance genes. Cells from 9 healthy donors were modified in the presence of rapamycin and demonstrated a 2-3 fold increase in genetic modification compared to those cells modified in the absence of rapamycin. The process was robust and worked for every lentiviral vector and healthy donor sample we tested. We used transplantation of immunodeficient mice to evaluate the ability of rapamycin-treated cells to engraft and produce multiple lineages of blood cells expressing the anti-HIV genes. All mice engrafted and showed an increase in the level of multiple lineages of blood cells (including CD4+ T-cells and monocytes) expressing the introduced gene sequences compared to animals engrafted with cells not treated with rapamycin. There were no safety issues observed in these experiments and the gene modified cells persisted for long periods (>16 weeks) in these mice. These data demonstrate that enhanced transduction of blood forming stem cells results in increased levels of gene-modified blood cells following transplantation of treated rapamycin-treated stem cells. We are currently testing these cells in our clinical trials for HIV gene therapy. These techniques are also useful for other types of gene therapy that utilize lentiviral vectors to genetically modify blood stem cells.