From a previous collaborative program (NCDDG), our group has developed retroviral vectors carrying hammerhead ribozymes targeted against HIV-1 which inhibit HIV-1 replication in vitro. The goals of this project are to test the efficacy of these ribozyme vectors in a clinical trial. Because the entire spectrum of cells involved directly in HIV-1 infection are derived from hematopoietic stem cells, we will transduce CD34+ cells from HIV-1 infected patients with the ribozymes. The planned source of CD34+ cells will be from G-CSF mobilized peripheral blood (PBSC), which yields high numbers of readily transducible progenitor cells. To provide an internal standard to allow detection of improved survival by cells expressing an active ribozyme, 1/2 of the transplanted cells will be transduced with a neutral vector, either containing no ribozyme or a catalytically inactive version. In the first year of the project, we will perform the necessary pre-clinical safety and efficacy studies using cells from HIV-1 + volunteer donors to permit application for approval for a clinical trial. In years 2-4, we will perform a clinical trial in which the transduced CD34+ cells will be returned to the patients without any prior cytoablative chemotherapy, to minimize risks to the subjects. After cell infusion, peripheral blood samples will be obtained on a monthly basis to determine whether the transduced CD34+ cells engraft to produce mature blood cells containing the ribozyme vector, whether the ribozyme mRNA are present in the blood cells and whether expression of the ribozymes confers a relative survival advantage compared to marker gene- transduced cells. This trial design will allow important information to be derived about the efficacy of gene transfer, expression and function, which can then be used for subsequent trials with a more therapeutic intent.
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