Retroviral Transfer of the Glucocerebrosidase Gene into CD34 + Cells from Patients with Gaucher Disease: In Vivo Detection of Transduced Cells without Myeloablation

Retroviral gene transfer of the glucocerebrosidase gene to hematopoietic progenitor and stem cells has shown promising results in animal models and corrected the enzyme deficiency in cells from Gaucher patients in vitro. Therefore, a clinical protocol was initiated to explore the safety and feasibility of retroviral transduction of peripheral blood (PB) or bone marrow (BM) CD34⁺ cells with the G1Gc vector. This vector uses the viral LTR promoter to express the human glucocerebrosidase cDNA. Three adult patients have been entered with follow-up of 6–15 months. Target cells were G-CSF-mobilized and CD34-enriched PB cells or CD34-enriched steady state BM cells, and were transduced ex vivo for 72 hr. Patient 1 had PB cells transduced in the presence of autologous stromal marrow cells. Patient 2 had PB cells transduced in the presence of autologous stroma, IL-3, IL-6, and SCF. Patient 3 had BM cells transduced in the presence of autologous stroma, IL-3, IL-6, and SCF. At the end of transduction, the cells were collected and infused immediately without any preparative treatment of the patients. The transduction efficiency of the CD34⁺ cells at the end of transduction was approximately 1, 10, and 1 for patients 1, 2, and 3, respectively, as estimated by semiquantitative PCR on bulk samples and PCR analysis of individual hematopoietic colonies. Gene marking in vivo was demonstrated in patients 2 and 3. Patient 2 had vector-positive PB granulocytes and mononuclear bone marrow cells at 1 month postinfusion and positive PB mononuclear cells at 2 and 3 months postinfusion. Patient 3 had a positive BM sample at 1 month postinfusion but was negative thereafter. These results indicate that gene-marked cells can engraft and persist for at least 3 months postinfusion, even without myeloablation. However, the level of corrected cells (<0.02%) is too low to result in any clinical benefit, and glucocerebrosidase enzyme activity did not increase in any patient following infusion of transduced cells. Modifications of vector systems and transduction conditions, along with partial myeloablation to allow higher levels of engraftment, may be necessary to achieve beneficial levels of correction in patients with Gaucher disease.

Overview summary

In this study a retroviral vector is used to transduce human hematopoietic cells in order to explore whether gene marking of these target cells can be obtained in vivo following gene transfer and infusion of the transduced cells into nonmyeloablated recipients. Hematopoietic cells containing the glucocerebrosidase cDNA from the vector were detected up to 3 months after infusion of the transduced cells into patients with Gaucher disease. The level of gene marking was low and the glucocerebrosidase enzyme activity was not increased following transduction and infusion. The results show that it is possible to achieve gene marking in vivo following transplantation of gene-transduced hematopoietic cells into nonmyeloablated recipients. However, the efficiency of the procedure needs to be improved greatly to obtain therapeutic effects for genetic disorders of the hematopoietic system.