1. ¹Divisions of Virology and Pediatrics, Beckman Research Institute, City of Hope National Medical Center, Duarte, CA 91010, USA
2. ²Division of Cellular Immunotherapy and Cancer Immunology, Beckman Research Institute, City of Hope National Medical Center, Duarte, CA 91010, USA
3. ³Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO 80523, USA
4. ⁴Department of Pediatrics, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA

Correspondence: Jiing-Kuan Yee, E-mail: pyam@coh.org or jyee@coh.org

Received 4 August 2005; Revised 24 February 2006; Accepted 27 February 2006.

Abstract

Hematopoietic progenitor cells (HPCs) represent an ideal target for gene therapy treatment of human immunodeficiency virus (HIV) infection. However, gene delivery into quiescent HPCs by retroviral or lentiviral vectors remains relatively poor. We evaluated a selection scheme based on the expression of a variant of inosine monophosphate dehydrogenase 2 (IMPDH2), the rate-limiting enzyme in the de novo purine biosynthesis pathway. As lymphocytes depend more than other cell types on de novo synthesis of purines, IMPDH inhibitors such as mycophenolic acid (MPA) can selectively expand lymphocytes overexpressing the enzymes. We used HIV vectors to deliver an IMPDH variant into T cells and HPCs. We showed that the transduced T cells became resistant to MPA selection. By expressing a short hairpin RNA gene targeted to the HIV gag transcript, the MPA-selected T cells became resistant to HIV-1 infection. Monocyte/macrophages derived from the transduced HPCs differentiated normally and exhibited normal function as measured by B7 up-regulation and phagocytosis when stimulated. Our results suggest that this system may be applicable as a selection strategy to enrich transduced T lymphocytes and mononuclear cells in vivo for HIV gene therapy.