CD34 stem/progenitor cells purified from cryopreserved normal cord blood can be transduced with high efficiency by a retroviral vector and expanded ex vivo with stable integration and expression of Fanconi anemia complementation C gene

Human umbilical cord blood mononuclear cells activate the survival protein Akt in cardiac myocytes and endothelial cells that limits apoptosis and necrosis during hypoxia

We have previously reported that human umbilical cord blood mononuclear cells (HUCBC), which contain hematopoietic, mesenchymal, and endothelial stem cells, can significantly reduce acute myocardial infarction size. To determine the mechanism whereby HUCBC increase myocyte and vascular endothelial cell survival, we treated cardiac myocytes and coronary artery endothelial cells in separate experiments with HUCBC plus culture media or culture media alone and subjected the cells to 24 h of hypoxia or normoxia. We then determined in myocytes and endothelial cells activation of the cell survival protein Akt by Western blots. We also determined in these cells apoptosis by annexin V staining and necrosis by propidium iodide staining. Thereafter, we inhibited with API, a specific and sensitive Akt inhibitor, Akt activation in myocytes and endothelial cells cultured with HUCBC during hypoxia and determined cell apoptosis and necrosis. In cells cultured without HUCBC, hypoxia only slightly activated Akt. Moreover, hypoxia increased myocyte apoptosis by ≥ 226% and necrosis by 58% in comparison with myocytes in normoxia. Hypoxic treatment of endothelial cells without HUCBC increased apoptosis by 94% and necrosis by 59%. In contrast, hypoxia did not significantly affect HUCBC. Moreover, in myocyte + HUCBC cultures in hypoxia, HUCBC induced a ≥ 135% increase in myocyte phospho-Akt. Akt activation decreased myocyte apoptosis by 76% and necrosis by 35%. In endothelial cells, HUCBC increased phospho-Akt by 116%. HUCBC also decreased endothelial cell apoptosis by 58% and necrosis by 42%. Inhibition of Akt with API in myocytes and endothelial cells cultured with HUCBC during hypoxia nearly totally prevented the HUCBC-induced decrease in apoptosis and necrosis. We conclude that HUCBC can significantly decrease hypoxia-induced myocyte and endothelial cell apoptosis and necrosis by activating Akt in these cells and in this manner HUCBC can limit myocardial ischemia and injury.

The assessment of human erythroid output in NOD/SCID mice reconstituted with human hematopoietic stem cells

The third-generation NOD/LtSz-scid/IL2Rγ(null) (NOD/SCID IL2Rγ(null)) mouse represents a significantly improved xenograft model allowing high levels of human leukocyte engraftment over extended follow up. One remaining limitation of this mouse model, however, is the low level of circulating human erythrocytes. We established a practical ex vivo erythroid culture system of xenograft marrow progenitors to enrich for human erythroid progeny. At various time points after transplant, erythroid cells were easily assayed after 17 days of ex vivo culture of xenograft marrow, with nearly all nucleated cells of human origin and approximately 60% human GPA or CD71 positive. We then transplanted cord blood CD34(+) cells marked with a lentiviral vector encoding green fluorescent protein (GFP). Three months later, ex vivo culture of xenograft marrow progenitors showed 41.3% of the cultured erythroid cells were positive for GFP and human CD71, and 56.2% were positive for GFP and human GPA, similar to that of circulating leukocytes at the same time point. Next, G-CSF mobilized peripheral blood CD34(+) cells from a sickle cell trait subject were infused in this mouse model to determine if the hemoglobin pattern could be modeled. CD34(+) cells from the sickle cell trait subject engrafted equally compared to CD34(+) cells from normal subjects, establishing the sickle cell trait phenotype. Lastly, a comparison of adult-derived peripheral blood CD34(+) cells and cord blood-derived CD34(+) cells xenografted mice was made, and long term follow-up demonstrated a recapitulation of the fetal to adult hemoglobin switch. This approach should prove a useful tool for testing strategies for genetic manipulation of erythroid progeny and the study of hemoglobin switching.

High-efficiency recovery of functional hematopoietic progenitor and stem cells from human cord blood cryopreserved for 15 years

Transplanted cord blood (CB) hematopoietic stem cells (HSC) and progenitor cells (HPC) can treat malignant and nonmalignant disorders. Because long-term cryopreservation is critical for CB banking and transplantation, we assessed the efficiency of recovery of viable HSCHPC from individual CBs stored frozen for 15 yr. Average recoveries (+/- 1 SD) of defrosted nucleated cells, colony-forming unit-granulocyte, -macrophage (CFU-GM), burst-forming unit-erythroid (BFU-E), and colony-forming unit-granulocyte, -erythrocyte, -monocyte, and -megakaryocyte (CFU-GEMM) were, respectively, 83 +/- 12, 95 +/- 16, 84 +/- 25, and 85 +/- 25 using the same culture conditions as for prefreeze samples. Proliferative capacities of CFU-GM, BFU-E, and CFU-GEMM were intact as colonies generated respectively contained up to 22,500, 182,500, and 292,500 cells. Self-renewal of CFU-GEMM was also retained as replating efficiency of single CFU-GEMM colonies into 2 degrees dishes was >96% and yielded 2 degrees colonies of CFU-GM, BFU-E, and CFU-GEMM. Moreover, CD34(+)CD38(-) cells isolated by FACS after thawing yielded >250-fold ex vivo expansion of HPC. To assess HSC capability, defrosts from single collections were bead-separated into CD34(+) cells and infused into sublethally irradiated nonobese diabetic (NOD)severe combined immunodeficient (SCID) mice. CD45(+) human cell engraftment with multilineage phenotypes was detected in mice after 11-13 wk; engrafting levels were comparable to that reported with fresh CB. Thus, immature human CB cells with high proliferative, replating, ex vivo expansion and mouse NODSCID engrafting ability can be stored frozen for >15 yr, can be efficiently retrieved, and most likely remain effective for clinical transplantation.

Preclinical protocol for in vivo selection of hematopoietic stem cells corrected by gene therapy in Fanconi anemia group C

Fanconi anemia (FA) is an autosomal recessive disorder characterized by birth defects, increased incidence of malignancy, progressive bone marrow failure, and cellular hypersensitivity to DNA cross-linking agents. Bone marrow transplantation is therapeutic and therefore FA is a candidate disease for hematopoietic gene therapy. We have previously used mitomycin C (MMC) to achieve in vivo selection of wild-type hematopoietic stem cells (HSC) transplanted into FANCC knockout mice. However, clinical application of MMC in human FA gene therapy is unlikely because of its unknown toxicity profile in human FA patients. In contrast, cyclophosphamide (CPA) and gamma-irradiation (IR) are already in use with human FA patients and we therefore tested these regimens for their ability to achieve selection of genetically corrected HSCs in vivo. We found that nonmyeloablative doses of CPA or IR or combinations of CPA + IR were highly efficient at achieving in vivo selection of transplanted wild-type HSC. Furthermore, this nontoxic regimen also selected FANCC-mutant HSC corrected by ex vivo retroviral gene therapy. We suggest those nontoxic doses of CPA and/or IR could also be used to enhance gene therapy in human FA patients.

Umbilical cord blood collection, banking, and transplantation: current status and issues relevant to perinatal caregivers

As a result of recent media coverage of cord blood transplantation, expectant parents increasingly ask perinatal caregivers about the possibility of collecting and saving their newborn child's umbilical cord blood. Umbilical cord blood has been used as a source of hematopoeitic stem cells for the treatment of human disease since 1988. As a result of these initial successes, cord blood collection, banking, and transplantation has become increasingly used worldwide, giving rise to several controversies. We have reviewed the current status of the indications for cord blood collection, the methods of collection, and safety issues related to the cyropreservation of cord blood units. In addition, the clinical success of cord blood transplants from related and unrelated donors is detailed. We have examined the major issues concerning cord blood transplantation as it exists in the year 2000 to provide insight into this exciting area of clinical investigation.

In utero hematopoietic stem cell transfer: current status and future strategies

Successful prenatal treatment of severe immunodeficiencies by allogeneic hematopoietic stem cell transplantation in utero has been reported. Though other diseases like hemoglobinopathies or storage diseases are potentially amenable to this novel therapeutic approach, no success has yet been achieved in recipients without severe immunodeficiency. Graft rejection by the developing fetus and/or lack of selective, competitive advantage of donor versus host stem cells preventing stable engraftment seem to be the major obstacles. Several strategies to overcome these hurdles are being explored in preclinical settings, including timing and repeated dosing of stem cell administration to the fetus, ex vivo modification of the transplant, using different fetal compartments as targets for early stem cell transfer, or inducing microchimerism for postnatal transplantation from the same donor. In addition, the exact definition of the basic concept of early fetal immunologic naivete and the understanding of the molecular basics of migration and homing in fetal hematopoiesis system seem mandatory for a successful approach. Gene therapy using ex vivo transduced autologous cord blood cells or direct gene targeting in utero are other potential means to correct hematopoietic and immunologic single gene disorders in utero, though this approach is still away from the stage of clinical trials.

Quantitative immunophenotypic characterization, cryopreservation, and enrichment of second- and third-trimester human fetal cord blood hematopoietic stem cells (progenitor cells)

OBJECTIVE

The aims of this study were (1) to assess the hematopoietic stem cell (progenitor cell) contents of umbilical cord blood samples from second-trimester and early-third-trimester fetuses versus term fetuses and (2) to determine the feasibility of cryopreservation and enrichment of cord blood from fetuses of different gestational ages.

STUDY DESIGN

Cord blood between 13 and 42 weeks' gestation (n = 31) was sampled after delivery or fetal expulsion. Fluorescence-activated cell sorting was used to measure CD34(+) and CD34(+)CD38(-) cell numbers. Samples were cryopreserved with 10% dimethylsulfoxide, and CD34(+) enrichment was performed by magnetically activated cell sorting with the MiniMACS system (Miltenyi Biotech, Bergisch Gladbach, Germany). Kruskal-Wallis analysis of variance and the Mann-Whitney U test were used for analysis of data.

RESULTS

CD34(+) and CD34(+)CD38(-) cell contents were significantly higher in second- and early third-trimester fetuses than in term fetuses (CD34(+) 2.57% +/- 0.38%, 1.48% +/- 0. 31%, and 0.7% +/- 0.13%, respectively, P =.0067; CD34(+)CD38(-) 0. 72% +/- 0.26%, 0.18% +/- 0.05%, and 0.06% +/- 0.02%, respectively, P =.0132). Mononuclear cell recovery, viability, and CD34(+) cell purity after cryopreservation and enrichment were similar among different gestational ages.

CONCLUSION

Cord blood stem cell content decreases significantly from the second trimester to term. Cryopreservation and enrichment of these cells from earlier gestational ages is feasible. This might be especially useful for allogeneic stem cell transplantation and for in utero gene therapy.

Gene transfer into human haematopoietic stem cells

This review of gene transfer to the human haematopoietic system (1) describes the different vectors used to transduce genes into stem cells, emphasizing retroviruses that have already shown their efficiency and innocuousness; (2) analyses which human cells should be targeted to ensure long-lasting engraftment; (3) indicates the different means of infecting these targets ex vivo, underscoring the role of cytokines and stromal cells; (4) recollects the methods used to evaluate transduction efficiency; and (5) gathers the results of clinical trials recently performed using human stem cells. The major conclusions are that good practice can ensure safe gene delivery to human beings and that long-lasting, multilineal precursors can be transduced using retroviral vectors of marker genes or genes of therapeutic interest. However, transduction rates appear to remain relatively low, which should stimulate ongoing research on both vector design and means of ex vivo gene transfer.

Inhibitory effects of interleukin 12 on retroviral gene transduction into CD34 cord blood myeloid progenitors mediated by induction of tumor necrosis factor-alpha

Interleukin 12 (IL-12), a heterodimeric cytokine with potent biologic activity, was evaluated for effects on retroviral-mediated gene transduction into human myeloid progenitor cells in vitro. Cord blood CD34 cells were prestimulated with Steel factor (SLF), IL-3, GM-CSF, and erythropoietin (Epo) in the presence and absence of 5-80 ng/ml IL-12 for 40 hr in suspension culture prior to gene transduction using viral supernatant collected from a packaging cell line containing the pLNL6 vector encoding Neo sequences. After gene transduction, cells were assayed for colony formation stimulated by Epo, GM-CSF, IL-3, and SLF, and gene transduction efficiency was determined by the percentage of G418 resistant (R) colonies and confirmed by PCR analysis. IL-12 dose-dependently inhibited retroviral-mediated gene transduction into human cord blood CD34 granulocyte-macrophage (CFU-GM) and erythroid (BFU-E) progenitors. These suppressive effects could be neutralized by incubation of IL-12 with polyclonal antihuman IL-12. IL-12 had no inhibitory effects directly on colony formation. To understand the possible mechanisms for this suppression, ELISA assays were used to detect the release of interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha, which could potentially have been induced by IL-12 from CD34 cells. TNF-alpha protein release was significantly increased in CD34 cells incubated with IL-12. No detectable levels of IFN-gamma were noted. Anti-TNF-alpha, but not anti-IFN-gamma, blocked the inhibitory effects of IL-12 on gene transduction. Moreover, TNF-alpha, but not IFN-gamma, suppressed gene transfer to the same degree as IL-12. No change of amphotropic receptor mRNA expression was noted by Northern blot analysis in cells treated with or without IL-12. The results suggest that the suppressive effects of IL-12 on retroviral gene transduction are, at least in part, mediated by IL-12 induction of the release of TNF-alpha.