Implication of delayed TNF-alpha exposure on dendritic cell maturation and expansion from cryopreserved cord blood CD34+ hematopoietic progenitors

Most currently used systems for dendritic cell (DC) production from progenitors entail tumor necrosis factor alpha (TNF-alpha) at the onset of cell culture, based on the notion that TNF-alpha might be required in the early stages of DC development. To optimize conditions for DC expansion from cryopreserved cord blood (CB) CD34+ hematopoietic progenitors, we took a dynamic approach to define the timing of TNF-alpha exposure to the culture. We cultured cord blood CD34+ cells in RPMI-1640 with 10% human AB plasma, stem cell factor (days 1-6), granulocyte-macrophage colony-stimulating factor (days 1-18), interleukin-4 (days 6-18) and varying schedules of TNF-alpha (0-144 h after thawing). Expression of the DC-associated markers, including CD83/CD1a, HLA DR/CD86/CD80, CD14/CD40, was monitored every 3 days. Our data demonstrate that delayed TNF-alpha exposure by 48-72 h after thawing gave rise to two- to three-fold increase in the yield of CD83+ DCs that were highly active in stimulating allogeneic T-cell proliferation compared to immediate TNF-alpha exposure. Thus, the immediate exposure of cryopreserved cord blood CD34+ cells to TNF-alpha, potentially compromising DC expansion, should be avoided. This finding should be of significant consideration when using cryopreserved CD34+ progenitor cells as a source of immunologically competent DCs in a clinical setting.     

Efficient gene transfer into normal human B lymphocytes with the chimeric adenoviral vector Ad5/F35

The failure to efficiently introduce genes into normal cells such as human B lymphocytes limits the characterization of their function on cellular growth, differentiation and survival. Recent studies have shown that a new adenoviral vector Ad5/F35 can efficiently transduce human haematopoietic CD34+ progenitor cells. In this study, we compared the gene transfer efficiencies of the Ad5/F35 vector to that of the parental vector Ad5 in human B lymphocytes. Peripheral blood B cells obtained from healthy individuals were cultured in vitro using CD40-CD154 system. Normal B lymphocytes were infected with replication-defectives Ad5 and Ad5/F35, both containing the GFP reporter gene, and transduction efficiencies were monitored by flow cytometry. Ad5 was highly ineffective, infecting only about 5% of human B lymphocytes. In contrast, Ad5/F35 transduced up to 60% of human B lymphocytes and GFP expression could be detected for up to 5 days post infection. Importantly, physiology of B lymphocytes such as proliferation, viability and antibodies secretion were unaffected following Ad5/F35 transduction. Finally, we observed that memory B lymphocytes were more susceptible to Ad5/F35 infection than na?ve B lymphocytes. Thus, our results demonstrate that the adenoviral vector Ad5/F35 is an efficient tool for the functional characterization of genes in B lymphopoiesis.     

Maintenance of proliferative capacity and retroviral transduction efficiency of human fetal CD38(-)/CD34(++) stem cells

Methods for the efficient transduction and expansion of fetal hematopoietic stem cells could lead to novel in utero therapies for blood cell disorders and enzymatic deficiencies. Here we describe a new assay to measure rapidly the effects of cytokines on the differentiation or expansion of primitive progenitors and stem cells found among CD38(-)CD34(++) lineage() cells isolated from human midgestation liver. Importantly, conditions that otherwise supported the expansion of clonogenic progenitors reduced their proliferative capacity. A combination of megakaryocyte growth and development factor and granulocyte-macrophage colony-stimulating factor maintained proliferative potential while also yielding an intermediate level of progenitor expansion. Retroviral transduction was achieved using Moloney murine leukemia virus-based vectors. Freshly isolated candidate stem cells could be transduced at almost 17% efficiency by a 1-h exposure to virus with centrifugation to aid transduction. This was increased to a mean 35.5% transduction efficiency after 1 day of culture. Additionally, the transduction efficiency of candidate stem cells isolated from fetal placental blood was 33.0%. These findings encourage further investigation into the feasibility of ex utero gene therapy whereby fetal cells are isolated from the circulation, transduced, and expanded ex utero before being returned to the fetus.     

Transduction of umbilical cord blood CD34+ NOD/SCID-repopulating cells by simian foamy virus type 1 (SFV-1) vector

Foamy viruses are nonpathogenic retroviruses that offer unique opportunities for gene transfer into various cell types including hematopoietic stem cells. We used a simian foamy virus type 1 vector (SFV-1) containing a LacZ reporter gene with a titer of 1-5 x 10(6) viral particles/ml that was free of replication-competent retrovirus to transduce human umbilical cord blood CD34+ cells. Transduced CD34+ cord blood cells were transplanted into NOD/SCID mice and plated in serum-free methylcellulose culture to determine the transduction efficiency of human hematopoietic progenitor cells. A transduction efficiency of about 20% was obtained. At 6-10 weeks posttransplantation, human hematopoietic cell engraftment and marking were determined. Marrow from transplanted mice demonstrated human cell engraftment by the presence of human (CD45+) cells containing both CD19+ lymphoid and CD33+ myeloid cells. Serial sampling of NOD/SCID bone marrow revealed the presence of 6.7-14.0% CD45+ cells at 6 weeks posttransplant as compared to 3.6-27.2% CD45+ cells at 9-10 weeks posttransplant. Human progenitors examined from NOD/SCID bone marrow cells 9 weeks posttransplant revealed from 7.4 to 25.9% of the colonies exhibiting X-gal staining. Our study demonstrates the ability of a simian foamy virus vector to transduce the SCID-repopulating cell and offers a promising new gene delivery system for use in hematopoietic stem cell gene therapy.     

5型腺病毒载体对人T淋巴细胞的转染及细胞毒性分析

 目的:利用5型腺病毒载体转染人T淋巴细胞,对其转染T淋巴细胞的效率以及细胞毒性进行分析。方法:选取T淋巴瘤Jurkat细胞及原代T细胞,腺病毒按感染复数(multiplicity of infection, MOI)为20、50、100、200和400对其转染,转染48 h后利用流式细胞术检测转染效率;选取腺病毒转染后的不同时点,利用碘化丙啶染色法分析转染对于细胞周期的影响;利用Annexin V/7-AAD染色法分析转染诱导细胞凋亡情况;利用台盼蓝染色计数法分析转染对活细胞数目的影响。结果:5型腺病毒载体转染T淋巴瘤的效率最高,转染效率随着MOI值的增大而增加;CD8+ T细胞和CD4+ T细胞的转染效率大致相同,T细胞经刺激活化后,CD8+ T细胞的转染效率下降;病毒转染未导致明显细胞凋亡;病毒转染对细胞周期与活细胞数目没有显著影响。结论:5型腺病毒载体转染T细胞呈现较低细胞毒性。     

Transduction of CD34+ cells by a vesicular stomach virus protein G (VSV-G) pseudotyped HIV-1 vector. Stable gene expression in progeny cells, including dendritic cells

OBJECTIVE: To use HIV-1 vectors to mediate stable gene transfer into hematopoietic stem/progenitor cells. STUDY DESIGN/METHODS: Purified human CD34+ cells were transduced with HIV-1 vectors pseudotyped with VSV-G and subjected to colony-forming assays and differentiation in liquid culture. Transduction was determined by DNA-polymerase chain reaction (PCR) for the transgene. GFP reporter gene expression and phenotypes of progeny cells were assessed by microscopy and flow cytometry. RESULTS: The HIV-1 vector transduced CD34+ cells with high efficiency. Transduction did not interfere with CD34+ cells differentiation in vitro. Transduced genes are expressed in different subsets of progeny cells, including those with normal dendritic cells (DC) morphology and phenotypes (HLADR+/CD1a+/CD86+/CD14-). CONCLUSIONS: We have demonstrated efficient transduction of hematopoietic progenitor cells by HIV-1 vectors. The transgenes are expressed in different subsets of progeny cells, which suggests stable integration. The generation of DCs stably expressing HIV antigens provides a new approach for vaccine development.     

靶向型辅助腺病毒的构建及其功能研究

目的构建一种新型辅助腺病毒,并用于靶向型第三代腺病毒载体的制备,提高其对造血细胞的感染效率。方法采用重叠PCR的方法合成含有不完全包装信号序列A1-A4和loxP序列的DNA片段SynES,替换穿梭质粒pShuttle中原有的包装信号序列,得到穿梭质粒pShuttle-SynES;将所得穿梭质粒与骨架质粒Ad5/F11p在大肠杆菌BJ5183中同源重组,获得重组腺病毒质粒载体pAd5/F11p-HV,将其转染293细胞包装重组腺病毒Ad5/F11p-HV。参照第三代腺病毒包装策略,利用Ad5/F11p-HV包装获得携带绿色荧光蛋白(GFP)基因的第三代腺病毒HD-Ad5/F11p-GFP;将其以不同的感染强度感染人白血病细胞系K562、U937、Jurkat和人脐带血CD34+细胞后,采用荧光显微镜和流式细胞术检测GFP的表达。结果采用DAN片段SynES替换穿梭质粒pShuttle上的包装信号,获得新的穿梭质粒pShuttle-SynES;进一步构建获得重组腺病毒质粒pAd5/F11p-HV,并制备了辅助腺病毒Ad5/F11p-HV。采用该辅助腺病毒包装pC4HSU-GFP,获得了第三代腺病毒HD-Ad5/F11p-GFP;CsCl密度梯度离心分离HD-Ad5/F11p-GFP和Ad5/F11p-HV,获得了高质量的HD-Ad5/F11p-GFP。与对照病毒HD-H14-GFP相比,HD-Ad5/F11p-GFP可明显提高对人白血病细胞U937、Jurkat和人脐带来源CD34+细胞的感染效率。结论设计并构建了一种靶向性辅助腺病毒,并以此为基础成功制备了对造血细胞高效感染的第三代重组腺病毒。     

Correlation between IL-3 receptor expression and growth potential of human CD34+ hematopoietic cells from different tissues.

CD123 (alpha-subunit of IL-3 receptor) expression on primitive and committed human hematopoietic cells was studied by multicolor sorting and single-cell culture. The sources of cells included fetal liver (FLV), fetal bone marrow, umbilical cord blood, adult bone marrow and mobilized peripheral blood. Three subsets of CD34+ cells were defined by the levels of surface CD123: CD123negative, CD123low, and CD123bright. Coexpression of lineage markers showed that a majority of CD34+CD123bright cells were myeloid and B-lymphoid progenitors, while erythroid progenitors were mainly in the CD34+CD123negative subset. The CD34+CD123low subset contained a heterogeneous distribution of early and committed progenitor cells. Single CD34+ cells from the CD123 subsets were cultured in a cytokine cocktail of stem cell factor, interleukin 3 (IL-3), IL-6, GM-CSF, erythropoietin, insulin-like growth factor-1, and basic fibroblast growth factor. After 14 days of incubation, a higher cloning efficiency (CE) was observed in the CD34+CD123negative and CD34+CD123low fractions (37+/-23% and 44+/-23%, respectively) than in the CD34+CD123bright fraction (15+/-21%). Using previously published criteria that colonies containing dispersed, translucent cells (dispersed growth pattern, DGP) were derived from primitive cells and that colonies composed solely of clusters were from committed cells, early precursors were distributed evenly in the CD34+CD123negative and CD34+CD123low subsets. When CD38 and CD90 (Thy-1) were used for further characterization of CD34+ cells from FLV, CE increased from 37+/-23% in CD123negative to 70+/-19% in CD123negativeCD38- and from 44+/-23% in CD123low to 66+/-19% in CD123lowCD38-. No significant increase in CE or DGP progenitors was observed when CD34+ cells were sorted by CD90 and CD123. We concluded that: A) high levels of CD123 were expressed on B-lymphoid and myeloid progenitors; B) early erythroid progenitors had little or no surface CD123, and C) primitive hematopoietic cells are characterized by CD123negative/low expression.     

Down-regulation of the beta-chemokine receptor CCR6 in dendritic cells mediated by TNF-alpha and IL-4

Chemokines are involved in the control of dendritic cell (DC) trafficking, which is critical for the immune response. We have generated DC from human umbilical cord blood CD34+ progenitors cultured with granulocyte-macrophage colony-stimulating factor, tumor necrosis factor alpha (TNF-alpha), and stem cell factor. Using an anti-CCR6 monoclonal antibody, we observed that these cells showed maximum expression of this beta-chemokine receptor when they were immature, as determined by their relatively low expression of several DC maturation markers such as CD1a, CD11c, CD14, CD40, CD80, and CD83. Immature DC responded strongly to macrophage inflammatory protein-3alpha (MIP-3alpha), the CCR6 ligand, in migration and calcium mobilization assays. CCR6 expression decreased in parallel with the DC maturation induced by prolonged TNF-alphaq treatments. Interleukin-4 was also able to decrease CCR6 protein levels. Our findings suggest that the MIP-3alpha/CCR6 interaction plays an important role in the trafficking of immature DC to chemokine production sites such as injured or inflamed peripheral tissues, where DC undergo maturation on contact with antigens.     

Rapid and efficient generation of lentivirally gene-modified dendritic cells from DC progenitors with bone marrow stromal cells

Since dendritic cells (DC) play pivotal roles in both innate and adaptive immunity, DC can be a good target for immuno-gene therapy. However, the optimal generation method for gene-modified DC has not yet been well exploited. CD34+ cells from cord blood (CB), bone marrow (BM), or peripheral blood (PB) were expanded in a medium containing stem cell factor (SCF), flt 3 ligand (Flt3L) and thrombopoietin (TPO) with or without HESS-5, a murine BM stromal cell line, for 2 weeks (the first expansion step), then differentiated to DC in a medium containing granulocyte-macrophage colony-stimulating factor (GM-CSF), flt 3 ligand (Flt3L), stem cell factor (SCF), tumor necrosis factor-alpha (TNF-alpha), IL-4, and lipopolysaccharide (LPS) for 9 days (the second differentiation step). DC progenitors were transduced with human immunodeficiency virus (HIV) vectors at different time points during the second step. Use of HESS-5 during the first step resulted in more DC generation than without it (cell expansion: CB, 10,461 vs. 354-fold; BM, 962 vs. 225-fold; peripheral blood mononuclear cell (PBMC), 8,506 vs. 240-fold; %DC: CB, 83.4% vs. 76.9%; BM, 83.6 vs. 69.8%; PBMC, 85.9 vs. 60.5%). Gene transduction to the in vitro expanded DC progenitors at day 3 during the second step, resulted in better final yield of the gene-modified DC than that to those at day 0 or day 6 (as much as 44% of DC expressed green fluorescence protein (GFP) as a transgene) and the transduction efficiency correlated with endocytic ability and percent of S phase. DC transduced with an HIV vector encoding a melanoma antigen, MART-1, were adequately recognized by specific anti-MART-1 CTL. The two-step culture method with HESS-5 is useful for rapid expansion of DC progenitors and subsequent lentiviral gene transduction to DC.     

Human hematopoietic (CD34+) stem cells possess high-affinity receptors for adenovirus type 11p

Gene transfer into human hematopoietic stem cells using Ad5 is inefficient due to lack of the primary receptor CAR and the secondary receptors alphavbeta3 integrin and alphavbeta5 integrin, and due to the high seroprevalence of Ad5 antibodies in most adults, resulting in diminished gene transduction. In the present study, we screened six species (species A-F) of adenovirus, displaying different tropisms for interaction with CD34+ cells, at the level of virus attachment and expression. Virus particles were biotinylated and their binding capacity was determined by FACS analysis using streptavidin-FITC. Ad11p, Ad35, and Ad3 (species B) showed high binding affinity, while Ad7, Ad11a (species B), and Ad37 (species D) displayed intermediate affinity. Virions of Ad4 (species E), Ad5 (species C), Ad31 (species A), and Ad41 (species F) hardly bound to hematopoietic progenitor cells. Using a double-labeling system, we demonstrated that adenoviruses bind to quiescent CD34+ cells. Ad11p virions showed the highest affinity among the adenoviruses detected. We further confirmed that virus fiber-specific receptors were present on the hematopoietic progenitor cell surface, because both recombinant fiber of Ad11p and specific antiserum against rfiber could block virus attachment. The ability of the adenoviruses to infect hematopoietic cells was studied by immunofluorescence staining. The adenoviruses from species B and Ad37 showed higher infectivity than Ad31, Ad5, Ad4, and Ad41. Among the studied species B adenoviruses, Ad11p manifested a superior infectivity. Thus, we have confirmed that these cells have high-affinity receptors for species B:2 human adenovirus, Ad11p, and this virus may be used as candidate vector to target therapeutic genes to hematopoietic stem cells.     

High efficiency electroporation of human umbilical cord blood CD34+ hematopoietic precursor cells.

Human umbilical cord blood provides an alternative source of hematopoietic cells for purposes of transplantation or ex vivo genetic modification. The objective of this study was to evaluate electroporation as a means to introduce foreign genes into human cord blood CD34+ cells and evaluate gene expression in CD34+/CD38(dim) and committed myeloid progenitors (CD33+, CD11b+). CD34+ cells were cultured in X-VIVO 10 supplemented with thrombopoietin, stem cell factor, and Flt-3 ligand. Electroporation efficiency and cell viability measured by flow cytometry using enhanced green fluorescent protein (EGFP) as a reporter indicated 31% +/- 2% EGFP+ /CD34+ efficiency and 77% +/- 3% viability as determined 48 hours post-electroporation. The addition of allogeneic cord blood plasma increased the efficiency to 44% +/- 5% with no effect on viability. Of the total CD34+ cells 48 hours post-electroporation, 20% were CD38(dim)/EGFP+. CD34+ cells exposed to interleukin-3, GM-CSF and G-CSF for an additional 11 days differentiated into CD33+ and CD11b+ cells, and 9% +/- 3% and 8% +/- 7% were expressing the reporter gene, respectively. We show that electroporation can be used to introduce foreign genes into early hematopoietic stem cells (CD34+/CD38(dim)), and that the introduced gene is functionally expressed following expansion into committed myeloid progenitors (CD33+, CD11b+) in response to corresponding cytokines. Further investigation is needed to determine the transgene expression in functional terminal cells derived from the genetically modified CD34+ cells, such as T cells and dendritic cells.     

Low-level expression of functional foamy virus receptor on hematopoietic progenitor cells.

Foamy viruses have several qualities favorable for vector development: they are not known to cause disease; they can transduce stationary cells; and the foamy virus receptor is expressed on a wide variety of cells. Here, we analyzed the level of virus receptor expression on hematopoietic progenitor cells. Foamy virus binding was measured by a flow cytometric assay and was found to be considerably reduced in hematopoietic progenitors cell lines as well as in primary CD34(+) cells when compared to fibroblasts. Retroviral vectors based on murine leukemia virus (MLV) pseudotyped with a foamy virus envelope transduced hematopoietic cell lines with a more than 10-fold lower efficiency than fibroblasts. Moreover, less than 1% of primary CD34(+) hematopoietic progenitor cells were transduced with the foamy virus pseudotypes, while gene transfer efficiencies of 8-40% were achieved using pseudotypes with amphotropic envelope or the G protein of vesicular stomatitis virus. In conclusion, the expression of functional foamy virus receptors on hematopoietic progenitors cells was found to be insufficient to achieve high levels of gene transfer into CD34(+) hematopoietic progenitor cells with cell-free vector supernatants using current transduction protocols.     

Dendritic cell subsets generated from CD34+ hematopoietic progenitors can be transfected with mRNA and induce antigen-specific cytotoxic T cell responses

Human dendritic cells (DCs) generated in culture from either monocytes or CD34+ hematopoietic progenitor cells (CD34-HPCs) have been used in cancer immunotherapy protocols with encouraging results. Yet an optimal strategy for the delivery of antigen(s) to DCs still remains to be established. Recent studies demonstrated the feasibility of mRNA transfection to load monocyte-derived DCs. It is not known, however, whether DCs derived by culturing CD34-HPC with GM-CSF and TNF-alpha for 9 days (CD34-DCs) can be efficiently transduced with mRNA. Here we show that clinical-grade CD34-DCs generated after 8 days of culture can be transfected with mRNA without significant alteration of cell viability. About 90% of cells transfected with GFP-RNA express GFP 24 h post-transfection. Remarkably, transfected CD34-DCs retain high levels of GFP expression for at least 14 days. CD34-DCs transfected with Flu-MP RNA were highly efficient in inducing the proliferation of Flu-MP-specific CD8+ T cells as measured by tetramer staining. Furthermore, the stimulated CD8+ T cells produced IFN-gamma upon antigenic stimulation and were able to kill targets pulsed with Flu-MP peptide. Both DC subsets in CD34-DCs, CD1a+-DC (Langerhans cells) and CD14+-DC (interstitial DC), were equally transfected with GFP-RNA, and yielded Flu-specific cytotoxic T cells upon transfection with Flu-MP RNA. Thus, RNA can be used to deliver antigens to two distinct myeloid DC subsets in CD34-DC cultures.     

Physiopathology of myelodysplastic syndromes

Myelodysplastic syndromes are clonal diseases of the hematopoietic stem cell with normal or increased bone marrow cellularity and peripheral cytopenias. Pathophysiology of these diseases is complex with frequent ras mutations, a growth defect of immature progenitors mainly erythroid progenitors, and increased apoptosis of differentiated cells. This growth defect could be linked to (1) a resistance to hematopoietic cytokine stimulation although, erythropoietin receptor expression and functionality are normal and/or (2) increased susceptibility to apoptosis due to overexpression of the death domain receptor Fas on CD34+, CD33+ and GPA+ cells. Stromal cells are thought to produce increased quantities of inhibitory cytokines such as TNF-alpha, TGF-beta, IFN gamma et IL-1. Better understanding of MDS pathophysiology is required for applying adequate therapy either blocking apoptosis or stimulating hematopoiesis.     

Phenotypic and functional characteristics of CD34+ cells are related to their anatomical environment: is their versatility a prerequisite for their bio-availability?

Human CD34+ hematopoietic progenitors (HP) are mainly resident in adult bone marrow (BM). However, their recent revelation in nonhematopoietic tissues implies their circulation through peripheral blood (PB). The intimate mechanisms of this physiological process are not yet understood. Our results showed that steady-state CD34+ HP exhibit a differential phenotypic profile according to their BM versus PB localization. We demonstrated that this phenotype could be modulated by incubation in the presence of their counterpart mononuclear cells (MNC) through cell interactions and cytokine production. Such a modulation mainly concerns migration-mediated cytokine and chemokine receptors as well as some adhesion molecules and partly results from MNC specificity. These phenotypic profiles are associated with distinct cell-cycle position, cloning efficiency, and migration capacity of CD34+ cells from the different anatomical sources. We therefore propose a definition for a circulating versus resident CD34+ cell profile, which mostly depends on their cellular environment. We suggest that blood would represent a supply of cells for which phenotypic and functional characteristics would be a prerequisite for their bio-availability.     

Centrifugation enhances integrin-mediated transduction of dendritic cells by conventional and RGD-modified adenoviral vectors

The level of antigen loading can impact on the capacity for dendritic cells (DC) to activate T cell responses. Several different approaches to adenoviral (Ad)-based transduction were therefore assessed for their effect on both transgene expression and T cell activation. While a conventional E1(-)/E3Delta Ad vector (Ad/GFP) produced a concentration-dependent expression of GFP, a modified vector expressing Arginine-Glycine-Aspartic Acid (RGD) sequence on its fiber knob (Ad-RGD/GFP) enhanced transgene expression by 9-20-fold at each MOI. The addition of centrifugal force (2000xg) during DC transduction with Ad/GFP also increased expression up to 20-fold. However, combining centrifugation with the Ad-RGD/GFP vector produced no effect on transduction rate and only a 1.5- to 2-fold increase in GFP expression, suggesting overlapping mechanisms of action. Consistent with this, exogenous RGD peptide blocked transduction regardless of the vector used, or the addition of centrifugal force, and transduction was primarily limited to DC expressing the CD51 integrin receptor. Ad vectors expressing ovalbumin (OVA) were used to assess transduced DC for their capacity to activate OVA-specific T cells. We observed a significant relationship between transgene expression and the capacity for T cell activation regardless of whether transgene expression was increased by using a higher MOI, an RGD-modified vector, or by employing centrifugal force. Furthermore, combining these approaches produced synergistic effects on T cell activation. We conclude that RGD-modified vectors and centrifugation both enhance DC transduction by increasing entry via integrin receptors and that the capacity for T cell activation can be optimized by combining approaches to achieve the highest possible level of transgene expression.     

Purified canine CD34+Lin- marrow cells transduced with retroviral vectors give rise to long-term multi-lineage hematopoiesis.

Human CD34+ cells have been shown to retain long-term hematopoietic engrafting potential in preclinical and clinical studies. However, recent studies of human and murine CD34- stem cells suggest that these are functionally important early progenitors. Using autologous transplantation, we investigated whether canine CD34 and CD34- marrow cells could be transduced and give rise to long-term hematopoiesis. CD34+Lin- and CD34-Lin- cell populations purified by fluorescence-activated cell sorting were separately cocultivated with retroviral vectors LN (CD34+Lin-) and LNY (CD34-Lin-), which carry the neomycin (neo) gene. After myeloablative total body irradiation (920 cGy), 3 dogs received transplants of both CD34+Lin- cells and CD34-Lin- cells and 2 dogs received only CD34-Lin- cells. Untransduced autologous marrow cells were given to ensure hematopoietic recovery. Using CFU-C assays, transduction efficiencies of CD34+Lin- cells ranged from 6% to 18% with no CFU-C formation from CD34-Lin- cells. PCR-based detection of the neo gene from WBCs was used to detect transduced cells weekly after transplantation. Additional PCR studies in 3 dogs given both CD34+Lin- and CD34-Lin- cells were performed on monocytes, granulocytes, and T cells (2 dogs, one at 7.5 months and the other at 9 months) and granulocytes (1 dog at 12 months). LN was detected up to 12 months posttransplantation in WBCs and mono-myeloid and lymphoid populations from 3 dogs receiving transplants of transduced CD34+Lin- cells. LNY was not detected at any time after transplantation in 5 dogs that received transduced CD34-Lin- cells. Whereas canine CD34+Lin- marrow cells contributed to long-term multilineage hematopoiesis, progeny of CD34-Lin- progenitor cells were not detected after transplantation in these experiments.     

Expression of CXCR4, the receptor for stromal cell-derived factor-1 on fetal and adult human lympho-hematopoietic progenitors.

Stromal cell-derived factor-1 (SDF-1) is a CXC chemokine produced by stromal cells that acts as a chemoattractant for human CD34+ progenitor cells. We investigated the expression of CXCR4, the receptor for SDF-1, on CD34+ cells from different hematopoietic sites and developmental stages. CXCR4 was detected by flow cytometry on 37 % of fetal bone marrow (BM) [gestation weeks (gw) 14-23] and 40% of adult BM CD34+ cells. Interestingly, in fetal liver CD34+ cells, CXCR4 was expressed at lower levels at later stages (9%, gw 20-23) compared to early stages of development (39%, gw 7.5-18), suggesting a development-related change in the migratory capacity of progenitors. CXCR4 was detected at similar levels on both phenotypically primitive and committed progenitors from fetal and adult sites. However, B cell lineage progenitor and precursor cells expressed CXCR4 at the highest density (80% of BM CD34+/CD10+ pro-B cells are CXCR4+). CXCR4 was also expressed in the fetal thymus in early T cell precursors and found to be down-regulated during T cell maturation. Finally, we found that stem cell factor, alone or in combination with other cytokines, can up-modulate CXCR4 expression on CD34+ cells by three- to fourfold. In conclusion, our results suggest that CXCR4 may play an important role in the local and systemic trafficking of human CD34+ cells as well as in human B lymphopoiesis and that its expression can be modulated by cytokines.     

Suppression of protein phosphatase 2A activity enhances Ad5/F35 adenovirus transduction efficiency in normal human B lymphocytes and in Raji cells

Investigation of the molecular processes which control the development and function of lymphocytes is essential for our understanding of humoral immunity, as well as lymphocyte associated pathogenesis. Adenovirus-mediated gene transfer provided a powerful tool to investigate these processes. We have previously demonstrated that adenoviral vector Ad5/F35 transduces plasma cell lines at a higher efficiency than primary B cells, owing to differences in intracellular trafficking. Given that phosphatases are effectors of intracellular trafficking, here we have analyzed the effects of a panel of phosphatase inhibitors on Ad5/F35 transduction efficiency in B lymphocytes in the present study. FACS analysis was conducted to determine Ad5/F35-EYFP transduction efficiency in lymphoid cells, including human primary B cells, following serine/threonine phosphatase (PSP) inhibitor treatment. We further used confocal microscopy to analyze intracellular trafficking and fate of CY3 labeled Ad5/F35 vectors, in PSP treated lymphoid cell. Finally, we analyzed the MAPK pathway by Western blot in PSP treated cells. Adenoviral transduction efficiency was unresponsive to inhibition of PP1 whereas inhibition of PP2A by cantharidic acid, or PP1 and PP2A by okadaic acid, substantially increased transduction efficiency. Importantly, confocal microscopy analyses revealed that inhibition of PP2A shut down adenovirus recycling. Moreover, inhibition of PP2A resulted in increased phosphorylation of AKT, ERK1/2 and MEK1/2. Taken together, these results suggest that Ad5/F35 is more efficiently transduced in cells following PP2A inhibition. Our results are in agreement with reports indicating that PP2A is involved in the formation of recycling vesicles and might be of interest for gene therapy applications.