Retroviral gene therapy in hematopoietic diseases

SDF-1α/CXCL12 enhances retroviral-mediated gene transfer into immature subsets of human and murine hematopoietic progenitor cells

Genetic modification of hematopoietic stem and progenitor cells has the potential to treat diseases affecting blood cells. Oncoretroviral vectors have been used for gene therapy; however, clinical success has been limited in part by low gene transfer efficiencies. We found that the presence of stromal-derived factor 1 (SDF-1alpha)/CXCL12 during retroviral transduction significantly enhanced, in a dose-dependent fashion, gene transfer into immature subsets of high proliferative human and murine hematopoietic progenitor cells. Murine mononuclear bone marrow cells and purified c-Kit(+)Lin(-) bone marrow cells were prestimulated and transduced with the bicistronic retroviral vector MIEG3 on Retronectin-coated surfaces in the presence and absence of SDF-1. SDF-1 enhanced gene transduction of murine bone marrow and c-Kit(+)Lin(-) cells by 35 and 29%, respectively. Moreover, SDF-1 enhanced transduction of progenitors in these populations by 121 and 107%, respectively. SDF-1 also enhanced transduction of human immature subsets of high proliferative progenitors present in either nonadherent mononuclear or CD34(+) umbilical cord blood cells. Transduction of hematopoietic progenitors was further increased by preloading Retronectin-coated plates with retrovirus using low-speed centrifugation followed by increasing cell-virus interactions through brief centrifugation during the transduction procedure. These results may be of clinical relevance.

Reconstitution of NADPH oxidase activity in human X-linked chronic granulomatous disease myeloid cells after stable gene transfer using a recombinant adeno-associated virus 2 vector

X-linked chronic granulomatous disease (X-CGD) is an inherited disorder of host defense that results from mutations in the gene encoding gp91phox, the large subunit of the phagocyte NADPH oxidase flavocytochrome b. In this study, we constructed a recombinant adeno-associated virus-2 (AAV) vector in which the constitutively active promoter from the human elongation factor- 1alpha (EF-1alpha) gene drives expression of the murine gp91phox cDNA, and tested its ability to integrate and express in a human X-CGD myeloid cell line. The nitroblue tetrazolium (NBT) test of NADPH oxidase activity was used to screen transduced cells for vector-mediated expression of recombinant gp91phox. Between 2 - 14% of cells were NBT-positive in the first several weeks after transduction. Clones with NBT-positive cells persisting several months after transduction had integrated vector by Southern blot analyses, with high level reconstitution of NADPH oxidase activity. In some clones, oxidase activity persisted for at least 8 to 14 months. In the majority, however, vector-derived RNA transcripts declined, although integrated rAAV genomes persisted. Decreased transgene expression was not directly correlated with methylation of the provirus. This study indicates that rAAV vectors can be successfully used for stable gene transfer, integration, and expression of recombinant gp91phoxin a human myeloid cell line for at least 8 - 14 months in the absence of any selection. The EF-1alpha promotor, however, was subject to silencing in a high percentage of clones with integrated rAAV, suggesting that alternative promotors may be desirable for achieving long-term expression in myeloid cells.

Alternatives to human blood and blood resources

Biotechnology is increasingly providing alternatives to established transfusion products, with the promise of freedom from infectivity and unlimited supply. Such products must demonstrate a safety and efficacy at least as great as current products, and thereafter an improved cost-benefit ratio. Alternatives to established products may be categorised as: Alternatives made from blood donations. Substitutes (acting by distinct mechanisms). Recombinant analogs. Cellular therapies (including gene therapy). This overview covers the current status in each of these categories, and likely trends in the near future. Recombinant therapeutic proteins are already established in certain indications, and are likely to be extended to a wider range of applications as the methods for bulk production are improved. Alternative products from donated blood should find niche indications, especially for acute therapy, but cellular therapy is unlikely to be widely implemented on this timescale, except as an adjunct in life-threatening indications. Substitutes are perhaps the most interesting category and are expected to have a major impact, particularly through the use of "proteins" to stimulate endogenous production of circulating cell populations.