GENE THERAPY Overexpression of CXCR4 on human CD34 progenitors increases their proliferation, migration, and NOD/SCID repopulation

A major limitation to clinical stem cell– mediated gene therapy protocols is the low levels of engraftment by transduced progenitors. We report that CXCR4 over-expression on human CD34 progenitors using a lentiviral gene transfer technique helped navigate these cells to the murine bone marrow and spleen in response to stromal-derived factor 1 (SDF-1) signal-ing. Cells overexpressing CXCR4 exhib-ited significant increases in SDF-1– mediated chemotaxis and actin polymer-ization compared with control cells. A major advantage of CXCR4 overexpres-sion was demonstrated by the ability of transduced CD34 cells to respond to lower, physiologic levels of SDF-1 when compared to control cells, leading to im-proved SDF-1–induced migration and pro-liferation/survival, and finally resulting in significantly higher levels of in vivo re-population of nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice including primitive CD34/CD38/low cells. Importantly, no cellular transforma-tion was observed following transduction with the CXCR4 vector. Unexpectedly, we documented lack of receptor internaliza-tion in response to high levels of SDF-1, which can also contribute to increased migration and proliferation by the trans-duced CD34 cells. Our results suggest CXCR4 overexpression for improved de-finitive human stem cell motility, reten-tion, and multilineage repopulation, which could be beneficial for in vivo navigation and expansion of hematopoietic progeni-tors. (Blood. 2004;103:2942-2949) © 2004 by The American Society of Hematolog