Efficient retrovirus-mediated gene transfer to transplantable human bone marrow cells in the absence of fibronectin

Biomaterial-mediated retroviral gene transfer using self-assembled monolayers

Biomaterial-mediated gene delivery has recently emerged as a promising alternative to conventional gene transfer technologies that focus on direct delivery of viral vectors or DNA-polymer/matrix complexes. However, biomaterial-based strategies have primarily targeted transient gene expression vehicles, including plasmid DNA and adenovirus particles. This study expands on this work by characterizing biomaterial properties conducive to the surface immobilization of retroviral particles and subsequent transduction of mammalian cells at the cell-material interface. Self-assembled monolayers (SAMs) of functionally-terminated alkanethiols on gold were used to establish biomaterial surfaces of defined chemical composition. Gene transfer was observed to be greater than 90% on NH(2)-terminated surfaces, approximately 50% on COOH-functionalized surfaces, and undetectable on CH(3)-terminated SAMs, similar to controls of tissue culture-treated polystyrene. Gene delivery via the NH(2)-SAM was further characterized as a function of retrovirus coating time, virus concentration, and cell seeding density. Finally, SAM-mediated gene delivery was comparable to fibronectin- and poly-l-lysine-based methods for gene transfer. This work is significant to establishing safe and effective gene therapy strategies, developing efficient methods for gene delivery, and supporting recent progress in the field of biomaterial-mediated gene transfer.

Expression and function of homing-essential molecules and enhanced in vivo homing ability of human peripheral blood-derived hematopoietic progenitor cells after stimulation with stem cell factor

Hematopoietic stem cell (HSC) homing from blood to bone marrow is a multistep process involving rolling, extravasation, migration, and finally adhesion in the correct microenvironment. With view to the hematopoietic recovery after clinical stem cell transplantation, we investigated the effect of stem cell factor (SCF) on the expression and the adhesive function of the alpha4beta1 and alpha5beta1 integrins very-late antigen (VLA)-4 and VLA-5 on peripheral blood-derived hematopoietic progenitor cells. After SCF stimulation, the expression of VLA-4 and VLA-5 on CD34+/c-kit+ cells obtained from healthy donors increased from 54% to 90% and from 3% to 82%, respectively. For patient-derived cells, the increase was 67% to 90% and 12% to 46%. The proportion of mononuclear cells adhering to the fibronectin fragment CH296 increased by stimulation with SCF from 14% to 23%. Accordingly, functional studies showed an approximate 30% increase of adherent long-term culture-initiating cell. The improvement of the homing abilities of SCF-stimulated HSC was confirmed by transplantation into sublethally irradiated nonobese diabetic-scid/scid mice. Six weeks after the transplantation, in eight of eight animals receiving human HSC with the addition of SCF, a profound multilineage hematopoietic engraftment was detected, whereas in the control group receiving only HSC, none of eight animals engrafted. Our data provide the first in vivo evidence that stimulation with cytokines improves the homing ability of transplanted human hematopoietic progenitor cells.

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.

Human stem-progenitor cells from neonatal cord blood have greater hematopoietic expansion capacity than those from mobilized adult blood

OBJECTIVE

In this study we compared the hematopoietic capacity of CD34+ cell preparations from neonatal cord blood (CB) vs adult mobilized peripheral blood (PBSC) before and after ex vivo culture.

METHODS

CD34+ cell preparations purified from CB or PBSC were cultured in serum-free medium containing FKT: FLT-3 ligand (FL), KIT ligand (KL), and thrombopoietin (TPO).

RESULTS

After 1-4 weeks ex vivo culture, CB CD34+ cell preparations had greatly increased numbers of total cells, CD34+ cells, and colony-forming cells (CFC). In contrast, ex vivo-cultured PBSC CD34+ cell preparations generated far less in vitro assessed hematopoietic capacity. Nonobese diabetic severe combined immunodeficient mouse (NOD/SCID) engrafting potential (SEP) was maintained in ex vivo-cultured CB CD34+ cell preparations, whereas ex vivo-cultured PBSC lost SEP. CB CD34+ cells continued to proliferate throughout 3 weeks ex vivo, whereas after 1 week, no additional cell divisions were detected in PBSC CD34+ cells. After 3 weeks in culture, the average CB CD34+ cell had divided more than 5 times, as compared to only 2 times for the average PBSC CD34+ cell.

CONCLUSION

CB CD34+ cell preparations generated massively increased in vitro assessed hematopoietic capacity and maintained SEP during 1- to 4-week ex vivo cultures. In contrast, ex vivo-cultured PBSC CD34+ cell preparations generated far less in vitro assessed hematopoietic capacity and decreased SEP. The differences in the in vitro proliferative indices of membrane dye-labeled CD34+ cells from CB vs PBSC correlated with these functional differences.

High Levels of Transgene Expression Following Transduction of Long-Term NOD/SCID-Repopulating Human Cells with a Modified Lentiviral Vector

Both oncoretroviral and lentiviral vectors have been shown to transduce CD34(+) human hematopoietic stem cells (HSC) capable of establishing human hematopoiesis in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice that support partially human hematopoiesis. We and others have reported that murine stem cell virus (MSCV)-based oncoretroviral vectors efficiently transduced HSC that had been cultured ex vivo for 4-7 days with cytokines, resulting in transgene expression in lymphoid and myeloid progenies of SCID-engrafting cells 4-8 weeks post-transplantation. Although lentiviral vectors have been demonstrated to transduce HSC under minimal ex vivo culture conditions, concerns exist regarding the level of transgene expression mediated by these vectors. We therefore evaluated a novel hybrid lentiviral vector (GIN-MU3), in which the U3 region of the HIV-1 long terminal repeat was replaced by the MSCV U3 region (MU3). Human cord blood CD34(+) cells were transduced with vesicular stomatitis virus G envelope protein-pseudotyped lentiviruses during a 48-hour culture period. After a total of 4 days in culture, transduced cells were transplanted into NOD/SCID mice to examine gene transfer and expression in engrafting human cells. Fifteen weeks post-transplantation, 37% +/- 12% of engrafted human cells expressed the green fluorescence protein (GFP) gene introduced by the lentiviral vector. High levels of GFP expression were observed in lymphoid, myeloid and erythroid progenies, and in engrafted human cells that retained the CD34(+) phenotype 15 weeks post-transplantation. This study provides evidence that lentiviral vectors transduced both short-term and long-term engrafting human cells, and mediated persistent transgene expression at high levels in multiple lineages of hematopoietic cells.

Efficient retrovirus-mediated transduction of primitive human peripheral blood progenitor cells in stroma-free suspension culture

Retroviral transduction of hematopoietic cells has resulted in unsatisfactory gene marking in clinical studies. Since cytokine-stimulated stem cells have engrafted poorly in animal models, we investigated phenotypic changes during culture of peripheral blood progenitor cells (PBPC). Human CD34(+) HLA-DR(low) cells, immunomagnetically separated from PBPC collections, were found to extrude rhodamine-123, which is characteristic for primitive hematopoietic cells. Cells were grown in suspension cultures supplemented with cytokines. While interleukin-3-containing factor combinations promoted cell proliferation they caused loss of rhodamine-123 extrusion and reduced the frequencies of cobblestone area-forming cells (CAFC). Several other cytokines failed to stimulate cell divisions, which are required for retroviral transduction. A combination including Flt-3 ligand (FL), interleukin-6 and stem cell factor (SCF) preserved an immature phenotype for 5 to 6 days and stimulated cell divisions, which was improved upon addition of leukemia inhibitory factor and interleukin-11. Furthermore, the CAFC frequency among cells treated with these cytokines was increased as compared with widely used cocktails containing interleukin-3, interleukin-6 and SCF. Rhodamine-123 appeared to be a particularly sensitive indicator for differentiation of PBPC. For analysis of gene transfer, amphotropic retroviruses conferring an MDR1 cDNA were added repeatedly for 6 days to cytokine-treated PBPC stroma-free cultures. Proviral cDNA was detected by polymerase chain reaction in 68% of cobblestone areas derived from CD34(+)HLA-DR(low) cells that had been exposed to Flt-3 ligand, interleukin-6 and SCF. In summary, conditions were identified that facilitate efficient transduction of early PBPC with amphotropic retroviruses while preserving a primitive phenotype for extended periods.