Long-term expression of retroviral-transduced adenosine deaminase in human primitive hematopoietic progenitors

Adenosine deaminase (ADA) deficiency, a rare autosomal recessive disorder, is an ideal candidate for gene replacement therapy. By means of co-cultivation with a retroviral vector-producing cell line, we have demonstrated efficient transfer and expression of the human ADA gene into human primitive hematopoietic progenitors. At 6 weeks post-transduction in myeloid long-term bone marrow culture, approximately 50% of the clonogenic progenitors were transduced by the provirus, with ADA expression detected in 30% of transduced colonies. The ADA activity increased by 3.7-fold in the nonadherent fraction of transduced bone marrow after 9 weeks. We have also achieved efficient transduction by retroviral supernatant of normal and ADA-deficient bone marrow cells that were allowed to establish a stromal layer in long-term culture, indicating the feasibility of proceeding with attempts to perform stem cell gene therapy on patients with ADA deficiency.