[Show abstract][Hide abstract] ABSTRACT: The earliest stages of lymphoid commitment from human pluripotent hematopoietic stem cells have not been defined. A clonogenic subpopulation of CD34(+)CD38(-) cord blood cells were identified that expressed high levels of the CD7 antigen and possessed only lymphoid potential. CD34(+)CD38(-)CD7(+) (CD7(+)) cells uniformly coexpressed CD45RA and HLA-DR; c-kit and Thy-1 expression was absent to low. Clonal analysis demonstrated that single CD7(+) cells could generate B cells, natural killer cells, and dendritic cells but were devoid of myeloid or erythroid potential. In contrast, control CD34(+)CD38(-)CD7(-) (CD7(-)) cells generated both lymphoid and myelo-erythroid cells. The lymphoid potential (generation of lymphoid progeny in bulk and single cell cultures) of CD7(+) cells was equivalent to that of the pluripotent CD7(-) cells. RNA expression studies showed that CD7(+) cells expressed PU.1 and GATA-3, but did not express Pax-5, terminal deoxynucleotide transferase, or CD3epsilon. In contrast to the previously described murine common lymphoid progenitor, the alpha chain of the receptor for interleukin-7 was not detected by fluorescence-activated cell sorting analysis or RNA polymerase chain reaction in CD7(+) cells. These studies identify a clonogenic lymphoid progenitor with both B-cell and natural killer cell lineage potential with a molecular profile that suggests a developmental stage more primitive than previously identified lymphoid progenitors. The CD7(+) phenotype distinguishes primitive human lymphoid progenitors from pluripotent stem cells, thus allowing the study of regulation of early human lymphopoiesis and providing an alternative to pluripotent stem cells for genetic manipulation and transplantation. (Blood. 2001;97:3683-3690)
[Show abstract][Hide abstract] ABSTRACT: The effect of IL-3 on the B lymphoid potential of human hemopoietic stem cells is controversial. Murine studies suggest that B cell differentiation from uncommitted progenitors is completely prevented after short-term exposure to IL-3. We studied B lymphopoiesis after IL-3 stimulation of uncommitted human CD34+CD38- cells, using the stromal cell line S17 to assay the B lymphoid potential of stimulated cells. In contrast to the murine studies, production of CD19+ B cells from human CD34+CD38- cells was significantly increased by a 3-day exposure to IL-3 (p < 0.001). IL-3, however, did not increase B lymphopoiesis from more mature progenitors (CD34+CD38+ cells) or from committed CD34-CD19+ B cells. B cell production was increased whether CD34+CD38- cells were stimulated with IL-3 during cocultivation on S17 stroma, on fibronectin, or in suspension. IL-3Ralpha expression was studied in CD34+ populations by RT-PCR and FACS. High IL-3Ralpha protein expression was largely restricted to myeloid progenitors. CD34+CD38- cells had low to undetectable levels of IL-3Ralpha by FACS. IL-3-responsive B lymphopoiesis was specifically found in CD34+ cells with low or undetectable IL-3Ralpha protein expression. IL-3 acted directly on progenitor cells; single cell analysis showed that short-term exposure of CD34+CD38- cells to IL-3 increased the subsequent cloning efficiency of B lymphoid and B lymphomyeloid progenitors. We conclude that short-term exposure to IL-3 significantly increases human B cell production by inducing proliferation and/or maintaining the survival of primitive human progenitors with B lymphoid potential.
The Journal of Immunology 09/2000; 165(5):2382-9. DOI:10.4049/jimmunol.165.5.2382 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The lack of human B lymphocyte development in beige/nude/XID (bnx) mice is in sharp contrast to the robust development observed in another immune deficient strain, the NOD/SCID mouse. The ability to generate human B lymphocytes in the NOD/SCID, but not bnx mouse has been hypothesized to be caused by differences in the microenvironments or systemic cytokine concentrations. In the current studies we report that the differences in development can be primarily attributed to the source of the progenitors transplanted into the mice. The prior studies in bnx mice used cultured pediatric or adult bone marrow (BM) as the source of the CD34+ cells, whereas the NOD/SCID studies have predominantly used fresh or cultured umbilical cord blood (UCB). We have analyzed BM and UCB for the number of human CD34+/CD38- cells capable of in vitro B lymphocyte development, and have found a lower frequency of B lymphocyte generation in BM. The individual B lymphocyte clones that developed from bone marrow produced 100-fold fewer cells than the UCB-derived clones. In agreement with the in vitro studies, human B lymphocytes developed in bnx mice from both CD34+ and CD34+/CD38- cells isolated from human umbilical cord blood, but not from equivalent numbers of CD34+ and CD34+/CD38- progenitors from bone marrow. Therefore, the lower generative capacity, and frequency of B lymphocyte precursors in human marrow may be responsible for the previous results that showed a lack of B lymphocyte development in bnx mice.
Bone Marrow Transplantation 01/2000; 24(11):1167-76. DOI:10.1038/sj.bmt.1702048 · 3.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Genetic modification of hematopoietic stem cells with genes that inhibit replication of human immunodeficiency virus-1 (HIV-1) could lead to development of T lymphocytes and monocytic cells resistant to HIV-1 infection after transplantation. We performed a clinical trial to evaluate the safety and feasibility of this procedure, using bone marrow from four HIV-1-infected pediatric subjects (ages 8 to 17 years). We obtained bone marrow, isolated CD34(+) cells, performed in vitro transduction with a retroviral vector carrying a rev-responsive element (RRE) decoy gene, and reinfused the cells into these subjects with no evidence of adverse effects. The levels of gene-containing leukocytes in peripheral blood samples in the 1 year after gene transfer/cell infusion have been extremely low. These observations support the potential of performing gene therapy for HIV-1 using hematopoietic cells, but emphasize the need for improved gene transfer techniques.
[Show abstract][Hide abstract] ABSTRACT: We describe a long-term, in vitro culture system initiated with CD34(+) or CD34(+)CD38(-) umbilical cord blood hematopoietic progenitors that supports normal human B-lineage development, including the production of mature Ig-secreting B cells. In the first stage (human B-progenitor long-term culture [HB-LTC]), CD34(+) hematopoietic progenitors are cultured on the murine stromal cell line, S17, leading to the sustained production of large numbers of CD10(+), CD19(+) early B progenitors. Reverse transcriptase-polymerase chain reaction (RT-PCR) and three-parameter flow cytometry for VpreB (surrogate light chain), cytoplasmic mu chain, and surface IgM expression were used to characterize the CD19(+) B progenitors present within these cultures. This analysis showed distinct B-lineage subpopulations, including pro-B cells, cycling pre-B cells, and IgM+, IgD-/+ immature B cells. The limited expansion of IgM+ B cells and the immature surface phenotype of this population (IgM+, IgD+, CD10(+), CD38(+)) suggested that HB-LTC conditions were unable to provide appropriate signals for further differentiation. A second culture stage was used to determine if these immature B cells were functionally competent. Purified CD19(+) cells were transferred onto fibroblasts expressing human CD40-ligand in the presence of IL-10 and IL-4. This lead to cell proliferation, modulation of the IgM+ cell surface phenotype to one consistent with an activated mature B cell, secretion of Ig, and isotype switching. Notably, IgM and IgG producing B cells were also generated using two-stage cultures established with highly purified multipotent CD34(+)CD38(-) hematopoietic stem cell progenitors. This culture model should permit detailed in vitro analysis and genetic manipulation of the major transition points in human B ontogeny, beginning with commitment to the B lineage and leading to development and activation of mature B cells.
[Show abstract][Hide abstract] ABSTRACT: Human hematopoietic stem cells are pluripotent, ie, capable of producing both lymphoid and myeloid progeny, and are therefore used for transplantation and gene therapy. An in vitro culture system was developed to study the multi-lineage developmental potential of a candidate human hematopoietic stem cell population, CD34+CD38- cells. CD34+CD38- cells cocultivated on the murine stromal line S17 generated predominantly CD19(+) B-cell progenitors. Transfer of cells from S17 stroma to myeloid-specific conditions ("switch culture") showed that a fraction of the immunophenotypically uncommitted CD19- cells generated on S17 stroma had myeloid potential (defined by expression of CD33 and generation of colony-forming unit-cells). Using the switch culture system, single CD34+CD38- cells were assessed for their lymphoid and myeloid potential. Nineteen of 50 (38%) clones generated from single CD34+CD38- cells possessed both B-lymphoid and myeloid potential. 94.7% of the CD34+CD38- cells with lympho-myeloid potential were late-proliferating (clonal appearance after 30 days), demonstrating that pluripotentiality is detected significantly more often in quiescent progenitors than in cytokine-responsive cells (P = .00002). The S17/switch culture system permits the in vitro assessment of the pluripotentiality of single human hematopoietic cells.
[Show abstract][Hide abstract] ABSTRACT: Umbilical cord blood CD34+CD38- cells are a rare, quiescent, primitive progenitor subpopulation lacking expression of lymphoid and myeloid lineage specific antigens. Although myeloid, erythroid, and megakaryocytic differentiation from these cells has been described, B lineage differentiation has not been demonstrated previously. We report here that highly enriched human B cell progenitors can be consistently generated from CD34+CD38- cord blood cells using long-term culture on the murine stromal line, S17, in the absence of added cytokines. After 6-8 weeks, cell numbers increased up to 160-fold, and cultures contained > 80-90% CD10+CD19+ B progenitors. Consistent with previous reports describing delayed myeloid cell differentiation from CD34+CD38- cells, production of B cell progenitors from CD34+CD38- cord blood cells was delayed 2-4 weeks relative to cultures initiated with either CD34+CD38bright or CD34+CD38dim progenitors. Addition of Flt3 ligand to long-term cultures resulted in a 2-3-fold greater increase in the number of CD19+ cells generated after 4-8 weeks. The selective outgrowth of B cell progenitors using this culture model will be useful for a range of in vitro studies using primitive hematopoietic progenitors.
[Show abstract][Hide abstract] ABSTRACT: Long-term culture-initiating cells (LTC-IC) are hematopoietic progenitors able to generate colony-forming unit-cells (CFU) after 5 to 8 weeks (35 to 60 days) of culture on bone marrow (BM) stroma and represent the most primitive progenitors currently detectable in vitro. We have recently reported that long-term cultures initiated with CD34+CD38- cells from BM or cord blood are able to continue generating CFU for at least 100 days, ie, beyond the standard LTC-IC period. In this report, single-cell cultures from cord blood and retroviral marking of cord blood and BM were used to study whether the subpopulation of CD34+CD38- cells able to generate CFU beyond 60 days ("extended long-term culture-initiating cells" or ELTC-IC) are functionally distinct from LTC-IC in terms of timing of initial clonal proliferation and generative capacity. All cord blood LTC-IC formed clones of greater than 50 cells by day 30. In contrast, cord blood ELTC-IC proliferated later in culture, 50% forming clones after day 30. Although efficient retroviral marking of LTC-IC was seen (25% to 45%), marking of ELTC-IC was inefficient (< 1%), consistent with a more quiescent progenitor population. There was a positive correlation between time of clonal proliferation and generative capacity. ELTC-IC generated threefold to fourfold more progeny than did LTC-IC (P < .002). These studies show that there is a functional hierarchy of progenitors in long-term culture which correlates with their level of quiescence. By extending the LTC-IC assay, a more primitive progenitor may be studied that may be functionally closer to the human long-term repopulation stem cell in vivo.
[Show abstract][Hide abstract] ABSTRACT: Genetic modification of hematopoietic stem cells with a synthetic "anti-human immunodeficiency virus type 1 (HIV-1) gene" which inhibits replication of HIV-1 may allow production of mature lymphoid and monocytic cells resistant to HIV-1 growth after autologous transplantation. Because productive HIV-1 replication requires binding of the Rev protein to the Rev-responsive element (RRE) within the viral transcripts for the HIV-1 structural proteins, anti-HIV-1 gene products which interfere with Rev-RRE interactions may inhibit HIV-1 replication. One such strategy involves overexpression of the RRE sequences in transcripts derived from retroviral vectors to act as decoys to sequester Rev protein and prevent its binding to the RRE element in HIV-1 transcripts. We developed an in vitro model to test the efficacy of this gene therapy approach in primary human hematopoietic cells. Human CD34+ hematopoietic progenitor cells from normal bone marrow or umbilical cord blood were transduced with retroviral vectors carrying RRE decoy sequences as part of a long terminal repeat-directed transcript expressing the neo gene (L-RRE-neo) or with a control vector expressing only the neo gene (LN). The transduced progenitors were allowed to differentiate into mature myelomonocytic cells which were able to support vigorous growth of the monocytotropic isolate of HIV-1, JR-FL. HIV-1 replication was measured in unselected cell populations and following G418 selection to obtain uniformly transduced cell populations. Inhibition of HIV-1 replication in the unselected cell cultures was between 50.2 and 76.7% and was highly effective (99.4 to 99.9%) in the G418-selected cultures. Progenitors transduced by either the L-RRE-neo vector or the control LN vector were identical with respect to hematopoietic growth and differentiation. These findings demonstrate the ability of an RRE decoy strategy to inhibit HIV-1 replication in primary human myelomonocytic cells after transduction of CD34+ progenitor cells, without adverse effects on hematopoietic cell function.
Journal of Virology 08/1996; 70(7):4352-60. · 4.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present cell cycling and functional evidence that the CD34+CD38- immunophenotype can be used to define a rare and primitive subpopulation of progenitor cells in umbilical cord blood. CD34+CD38- cells comprise 0.05% +/- 0.08% of the mononuclear cells present in cord blood. Cell cycle analysis with the fluorescent DNA stain 7-aminoactinomycin D showed that the percentage of CD34+ cells in cycle directly correlated with increasing CD38 expression. CD34+CD38- cord blood cells were enriched for long-term culture-initiating cells (LTCIC; cells able to generate colony-forming unit-cells [CFU-C] after 35 to 60 days of coculture with bone marrow stroma) relative to CD34+CD38- cells. In an extended LTCIC assay, CD34+CD38- cells were able to generate CFU-C between days 60 and 100, clearly distinguishing them from CD34+CD38+ cells that did not generate CFU-C beyond day 40. When plated as single cells, onset of clonal proliferation was markedly delayed in a subpopulation of CD34+CD38- cells; clones (defined as > 100 cells) appeared after 60 days of culture in 2.9% of CD34+CD38- cells. In contrast, 100% of CD34+CD38+ cells formed clones by day 21. Although the CD34+CD38- immunophenotype defines highly primitive populations in both bone marrow and cord blood, important functional differences exist between the two sources. CD34+CD38- cord blood cells have a higher cloning efficiency, proliferate more rapidly in response to cytokine stimulation, and generate approximately sevenfold more progeny than do their counterparts in bone marrow.
[Show abstract][Hide abstract] ABSTRACT: Gene therapy is a potential treatment for hemophilia, wherein cells transduced with a normal factor IX gene could provide a continuous in vivo source of circulating factor IX. In this study, we examined the potential use of hematopoietic cells as a target for factor IX gene therapy. Human myeloid leukemia cells (HL-60) were transduced by retroviral vectors carrying a normal human factor IX cDNA under control of either the Moloney murine leukemia virus long terminal repeat (MoMuLV LTR) (LIXSN), the SV40 promoter (LNSVIX), or a cytomegalovirus (CMV) promoter (LNCIX). Factor IX production was measured in the transduced cells both in the uninduced state and after induction of granulocytic differentiation [with dimethylsulfoxide (DMSO)] or monocytoid differentiation [with phorbol myristic acetate (PMA)]. Transcription of factor IX from the MoMuLV LTR was seen in all cells, with a two-fold increase upon differentiation. Induction with PMA led to an 8- to 15-fold increase in factor IX transcripts from an internal CMV promoter. No factor IX transcripts from the internal SV40 promoter were detected. Immunoreactive factor IX protein was identified by Western blot from induced HL-60 cells transduced by either LIXSN or LNCIX. Factor IX production by HL-60 cells transduced by LNCIX ranged from 38-93 ng/10(6) cells/24 hr following induction of monocytic differentiation. The factor IX antigen titer was directly related to factor IX coagulant titer (r = 0.98; p < 0.001). These data indicate that human myelomonocytic cells are capable of performing the necessary post-translational modifications to produce functional factor IX.(ABSTRACT TRUNCATED AT 250 WORDS)
Human Gene Therapy 07/1995; 6(7):873-80. DOI:10.1089/hum.1995.6.7-873 · 3.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: trans-Dominant inhibitory mutant versions of the human immunodeficiency virus type 1 (HIV-1) regulatory genes tat and rev have previously been described. We have constructed a series of retroviral vectors to transduce these genes and compare their inhibitory activities. The inhibitory activities were measured with transient transfection assays by using a reporter which expresses an HIV-1 gag-Escherichia coli lacZ fusion protein with strict dependence on coexpression of both tat and rev. Additionally, the vectors were packaged as amphotropic virions and used to stably transduce human CEM T lymphocytes. The transduced CEM cells were challenged with HIV-1, and the effects of the mutant HIV-1 genes were determined by measuring the levels of HIV-1 p24gag produced. A tat gene substituted at amino acid 41 (tatk41a) retained partial trans-activating activity and lacked inhibitory activity. A tat gene with a premature stop codon at amino acid 54 (tat54ter) showed moderate trans-dominant inhibition of the reporter plasmid but failed to significantly inhibit HIV-1 replication. The M10 rev mutant, with a 2-amino-acid substitution, showed strong trans-dominant inhibitory activity both in the reporter plasmid and in the HIV-1 infection assay. The greatest inhibition of HIV-1 growth was seen when M10 was expressed under the transcriptional control of a human cytomegalovirus promoter; slightly less inhibition was achieved when expression of M10 was controlled by the Moloney murine leukemia virus long terminal repeat, and minimal inhibition was seen when the HIV-1 long terminal repeat controlled the M10 gene. These results demonstrate the potential utility of retroviral vectors expressing trans-dominant inhibitory mutant HIV-1 genes for gene therapy approaches to AIDS.
Journal of Virology 07/1993; 67(6):3199-207. · 4.44 Impact Factor