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TRANSLATIONAL AND CLINICAL RESEARCH

Lentiviral Vector Gene Transfer Is Limited by the Proteasome at Postentry Steps in Various Types of Stem Cells

^aSan Raffaele Telethon Institute for Gene Therapy and
^bVita Salute, San Raffaele University, Milan, Italy;
^cDepartment of Morphophysiology, School of Veterinary Medicine, University of Turin, Grugliasco, Torino, Italy;
^dStem Cell Research Institute, San Raffaele Scientific Institute, Milan, Italy;
^eReproductive Technologies Laboratory, CIZ, Istituto Sperimentale Italiano Lazzaro Spallanzani, Cremona, Italy;
^fDipartimento Clinico Veterinario, University of Bologna, Ozzano Emilia, Italy;
^gDepartment of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland

Key Words. Lentiviral vectors • Gene transfer • Somatic stem cells • Embryonic stem cells • Proteasome • Proteasome inhibitor

Correspondence: Correspondence: Luigi Naldini, M.D., Ph.D., San Raffaele Telethon Institute for Gene Therapy, Via Olgettina 58, 20132 Milano, Italy. Telephone: 02-2643-4681; Fax: 02-2643-4668; e-mail: naldini.luigi{at}hsr.it

Received on October 3, 2007; accepted for publication on May 5, 2008.

First published online in STEM CELLS EXPRESS  May 15, 2008.

The isolation of human embryonic and somatic stem cells of different types has made it possible to design novel gene and cell replacement therapies. Vectors derived from retro/lentiviruses are used to stably introduce genes into stem cells and their progeny. However, the permissivity to retroviral infection varies among cell types. We previously showed that hematopoietic stem cells are poorly permissive to human immunodeficiency virus (HIV)-derived vectors and that pharmacological inhibition of the proteasome strongly enhances gene transfer. Here we report that the proteasome limits lentiviral gene transfer in all stem cell types tested, including embryonic, mesenchymal, and neural, of both human and mouse origin. Remarkably, this inhibitory activity was sharply reduced upon differentiation of the stem cells, suggesting that it represents a novel feature of the stem cell/immature progenitor phenotype. Proteasome-mediated inhibition was specific for lentiviral vectors and occurred at a postentry infection step. It was not mediated by activation of nuclear factor-B, a major signaling pathway modulated by the proteasome, and did not correlate with high proteasome activity. Interaction of the virion core with cyclophilin A was required to maximize the effect of proteasome inhibitor on the infection pathway. These findings are relevant to uncover new mediators of HIV gene transfer and help in designing more effective protocols for the genetic modification of stem cells.

Disclosure of potential conflicts of interest is found at the end of this article.