Gene transfer into hemopoietic stem cells using retroviral vectors

Retrovirus-mediated gene transfer into human CD34+38low primitive cells capable of reconstituting long-term cultures in vitro and nonobese diabetic-severe combined immunodeficiency mice in vivo

Factors that may improve retroviral transduction of primitive human hematopoietic cells were studied using MFG-based vectors containing a LacZ gene and produced either by a murine (psi-Crip) or a human (Tasaf) cell line. Cord blood (CB) or bone marrow (BM) CD34+ cells were stimulated and transduced in the presence of three cytokines (interleukin 3 [IL-3], IL-6, and stem cell factor [SCF; c-Kit Ligand]). In the supernatant infection protocol, hematopoietic progenitor cells as measured by X-Gal staining of colony-forming unit cells (CFU-Cs) were transduced more effectively with Tasaf (20%) than with psi-Crip (8%). In contrast, there was no difference between these two cell lines in a coculture protocol. However, gene transfer into more primitive CD34+CD38- subsets and in LTC-IC-derived colonies was low. The use of a large number of cytokines including FLT3-L and PEG-rhMGDF increased the transduction efficiency into CD34+CD38(-)-derived CFU-Cs (35% by PCR) or LTC-ICs (10%). A virus pseudotyped with gibbon ape leukemia virus (GALV) envelope further improved gene transfer to 60 and 48% for LacZ+ CFU-C- and LTC-IC-derived colonies, respectively. These conditions of transduction allowed multilineage engraftment of primitive cord blood cells in NOD-SCID mice. Moreover, 10% (at least) of the human hematopoietic cells recovered from the marrow of these immunodeficient animals were transduced. These data suggest that the efficiency of transduction of human hematopoietic primitive cells can be significantly improved by judicious combinations of recombinant cytokines and high retroviral titers.

Human gene therapy

Human gene therapy and its application for the treatment of human genetic disorders, such as cystic fibrosis, cancer, and other diseases, are discussed. Gene therapy is a technique in which a functioning gene is inserted into a human cell to correct a genetic error or to introduce a new function to the cell. Many methods, including retroviral vectors and non-viral vectors, have been developed for both ex vivo and in vivo gene transfer into cells. Vectors need to be developed that efficiently transfer genes to target cells, and promoter systems are required that regulate gene expression according to physiologic needs of the host cell. There are several safety and ethical issues related to manipulating the human genome that need to be resolved. Current gene therapy efforts focus on gene insertion into somatic cells only. Gene therapy has potential for the effective treatment of genetic disorders, and gene transfer techniques are being used for basic research, for example, in cancer, to examine the underlying mechanism of disease. There are still many technical obstacles to be overcome before human gene therapy can become a routine procedure. The current human genome project provides the sequences of a vast number of human genes, leading to the identification, characterization, and understanding of genes that are responsible for many human diseases.

Stem cells from bone marrow, umbilical cord blood and peripheral blood for clinical application: current status and future application

Bone marrow transplantation (BMT) has progressed rapidly during the past two decades to that of a treatment of choice as a therapeutically effective modality for the treatment of selected patients with malignant disease and non-malignant hematological disorders. However, its use is limited by availability of human leukocyte antigens (HLA)-matched donor cells, engraftment and graft-versus-host disease (GVHD). Prevention of GVHD, improvement in the speed and quality of marrow reconstitution, and screening of new immunomodulating agents which improve engraftment and augment hemopoiesis are intense areas of investigation. To this end there has clearly been progress in purification and characterization of human stem cells from different tissue sources. Discussed in this review are: (a) stem cell purification, characterization and ex vivo expansion; (b) bone marrow stem cell transplantation; (c) cord blood stem cell transplantation; (d) peripheral blood stem cell transplantation; (e) fetal liver stem cell transplantation; (f) in utero stem cell transplantation; and (g) evaluation of the capacity of stem cells to serve as targets for gene therapy.

Retroviral vector for gene therapy of X-linked severe combined immunodeficiency syndrome

X-linked severe combined immunodeficiency syndrome (X-SCID) is a genetic disorder characterized by profound impairment of cell-mediated and humoral immunity. Affected children die of recurrent infections within 2 years of birth unless rescued by allogeneic transplantation from a suitable donor. Recently, the genetic defect responsible for X-linked SCID has been identified as a mutation in the gamma chain of the IL-2 receptor, a protein also shared by the IL-4 and IL-7 receptors and therefore now denoted the common gamma chain (gamma c). We report here the development of a high-titer amphotropic retroviral vector for transfer of gamma c. This vector was used to transfer a copy of the gamma c cDNA to murine 3T3 fibroblasts, CD34-enriched hematopoietic progenitor cells obtained from bone marrow and umbilical cord blood of normal donors, and to transplanted murine bone marrow progenitors. Murine 3T3 cells transduced by the retroviral vector were analyzed by Southern blot hybridization and Western transfer. Southern analysis confirmed the integration of unrearranged proviral DNA, and Western blot analysis demonstrated the expression of gamma c protein. CD34-enriched cells were infected with viral vectors bearing gamma c and grown in methylcellulose media. Individual colonies and pools of cells were analyzed 2 weeks later by polymerase chain reaction assay, which confirmed the proviral marking. The vector was also used to transfer a copy of the gamma c cDNA to murine bone marrow cells in a transplantation model. Infected marrow was transplanted into syngeneic Balb/c mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and characterization of the cDNA encoding a novel human pre-B-cell colony-enhancing factor

A novel gene coding for the pre-B-cell colony-enhancing factor (PBEF) has been isolated from a human peripheral blood lymphocyte cDNA library. The expression of this gene is induced by pokeweed mitogen and superinduced by cycloheximide. It is also induced in the T-lymphoblastoid cell line HUT 78 after phorbol ester (phorbol myristate acetate) treatment. The predominant mRNA for PBEF is approximately 2.4 kb long and codes for a 52-kDa secreted protein. The 3' untranslated region of the mRNA has multiple TATT motifs, usually found in cytokine and oncogene messages. The PBEF gene is mainly transcribed in human bone marrow, liver tissue, and muscle. We have expressed PBEF in COS 7 and PA317 cells and have tested the biological activities of the conditioned medium as well as the antibody-purified protein in different in vitro assays. PBEF itself had no activity but synergized the pre-B-cell colony formation activity of stem cell factor and interleukin 7. In the presence of PBEF, the number of pre-B-cell colonies was increased by at least 70% above the amount stimulated by stem cell factor plus interleukin 7. No effect of PBEF was found with cells of myeloid or erythroid lineages. These data define PBEF as a novel cytokine which acts on early B-lineage precursor cells.

Cloning and characterization of the cDNA encoding a novel human pre-B-cell colony-enhancing factor

A novel gene coding for the pre-B-cell colony-enhancing factor (PBEF) has been isolated from a human peripheral blood lymphocyte cDNA library. The expression of this gene is induced by pokeweed mitogen and superinduced by cycloheximide. It is also induced in the T-lymphoblastoid cell line HUT 78 after phorbol ester (phorbol myristate acetate) treatment. The predominant mRNA for PBEF is approximately 2.4 kb long and codes for a 52-kDa secreted protein. The 3' untranslated region of the mRNA has multiple TATT motifs, usually found in cytokine and oncogene messages. The PBEF gene is mainly transcribed in human bone marrow, liver tissue, and muscle. We have expressed PBEF in COS 7 and PA317 cells and have tested the biological activities of the conditioned medium as well as the antibody-purified protein in different in vitro assays. PBEF itself had no activity but synergized the pre-B-cell colony formation activity of stem cell factor and interleukin 7. In the presence of PBEF, the number of pre-B-cell colonies was increased by at least 70% above the amount stimulated by stem cell factor plus interleukin 7. No effect of PBEF was found with cells of myeloid or erythroid lineages. These data define PBEF as a novel cytokine which acts on early B-lineage precursor cells.

Transplantable myeloproliferative disease induced in mice by an interleukin 6 retrovirus

Lethally irradiated mice transplanted with bone marrow cells infected with a novel recombinant retrovirus (murine stem cell virus-interleukin 6 [MSCV-IL-6]) bearing a mouse IL-6 gene developed a fatal myeloproliferative disease within 4 wk of engraftment. The hematologic manifestations of the syndrome included elevated peripheral leukocyte counts (up to 430 x 10(3) cells/mm3) with a predominance of neutrophilic granulocytes, microcytic anemia, and thrombocytosis or thrombocytopenia. The mice showed extensive neutrophil infiltration of the lungs, liver, and occasionally lymph nodes, plus splenomegaly resulting from enhanced splenic myelopoiesis (30-60-fold increase in progenitor numbers). Despite the chronic stimulation of neutrophil excess by IL-6, bone marrow from affected mice was capable of repopulating the hematopoietic tissues (bone marrow and spleen) of lethally irradiated hosts during repeated serial transplantation. In the longest documented case, the progeny of a single MSCV-IL-6-marked cell transferred the myeloproliferative disease to two secondary, four tertiary, and two quaternary recipients (the clone endured for a total of 72 wk). These results, demonstrating considerable proliferative longevity of the IL-6-producing cells, support an in vivo role of IL-6 in the maintenance of hematopoietic precursors. Dysregulated IL-6 production also had significant systemic effects. The mice displayed increased mesangial cell proliferation in the kidney, frequent liver abnormalities, and marked alterations in plasma protein levels. Unlike previous studies where constitutive expression of exogenous IL-6 genes resulted in lymphoproliferative disorders characterized by massive plasmacytosis, minimal plasma cell expansion occurred in the MSCV-IL-6 mice during the observation period. Potential explanations for the differences in disease phenotypes observed in the present and previous studies are different cell types expressing the exogenous IL-6 genes, higher sustained circulating levels of IL-6 achieved using the MSCV-IL-6 retroviral delivery system, and/or the premature death (3-15 wk after transplantation) of the MSCV-IL-6 mice before the onset of plasmacytosis. This animal model should prove useful for further investigation of the function of IL-6 in normal and abnormal hematopoiesis and in inflammatory responses.

IL-6 production by retrovirus packaging cells and cultured bone marrow cells

Retrovirus integration into the host cell genome occurs most efficiently in replicating cells. In agreement with this notion, it was observed that the efficiency with which hemopoietic stem cells (HSC) can be transduced is greatly enhanced when the hemopoietic growth factor (HGF) interleukin 3 (IL-3) is added to co-cultures of bone marrow cells with retrovirus-producing cells. The HGF IL-6, which enhances the IL-3-induced formation of blast cell colonies in vitro, is also believed to improve the transduction of HSC. Because IL-6 can be produced by a number of different cell types, we investigated whether IL-6 was present in the culture supernatant of retrovirus packaging cells and bone marrow cells. We found that the six retrovirus packaging cells tested produced large amounts of IL-6. Bone marrow cells cultured with IL-1 alpha and IL-3 also make IL-6, and, following co-cultivation of both cell types, the concentration of IL-6 in the medium is even up to 10-fold higher than the sum of the concentrations obtained when both are cultured separately. Considering that IL-6 is produced in large amounts during co-cultivations, we believe that its effect on the transduction of HSC cannot be measured by adding extra growth factor to the co-culture medium.

Expression of a swine class II gene in murine bone marrow hematopoietic cells by retroviral-mediated gene transfer

As a first step in assessing the efficacy of a gene transfer approach to the induction of transplantation tolerance in our miniature swine model, double-copy retroviral vectors engineered to express a drug-resistance marker (neomycin) and a swine class II DRB cDNA were constructed. Infectious particles containing these vectors were produced at a titer of greater than 1 x 10(6) G418-resistant colony-forming units/ml using both ecotropic and amphotropic packaging cell lines. Flow cytometric analysis of DRA-transfected murine fibroblasts subsequently transduced with virus-containing supernatants demonstrated that the transferred sequences were sufficient to produce DR surface expression. Cocultivation of murine bone marrow with high-titer producer lines leads to the transduction of 40% of granulocyte/macrophage colony-forming units (CFU-GM) as determined by the frequency of colony formation under G418 selection. After nearly 5 weeks in long-term bone marrow culture, virus-exposed marrow still contained G418-resistant CFU-GM at a frequency of 25%. In addition, virtually all of the transduced and selected colonies contained DRB-specific transcripts. These results suggest that a significant proportion of very primitive myelopoietic precursor cells can be transduced with the DRB recombinant vector and that vector sequences are expressed in the differentiated progeny of these cells.

Retrovirus-mediated gene transfer into CD4+ and CD8+ human T cell subsets derived from tumor-infiltrating lymphocytes and peripheral blood mononuclear cells

Studies were undertaken to test the susceptibility of individual T cell subpopulations to retroviral-mediated gene transduction. Gene transfer into human tumor-infiltrating lymphocytes (TIL) or peripheral blood mononuclear cells (PBMC) was carried out by transduction with an amphotropic murine retroviral vector (LNL6 or N2) containing the bacterial neoR gene. The presence of the neoR gene in the TIL population was demonstrated by Southern blot analysis, detection of the enzymatic activity of the gene product and by the ability of transduced TIL to proliferate in high concentrations of G418, a neomycin analog that is toxic to eukaryotic cells. The presence of the neoR gene in TIL did not alter their proliferation or interleukin-2 dependence compared to nontransduced TIL. The differential susceptibility of CD4+ and CD8+ lymphoid cells to the retro-virus-mediated gene transfer was then tested. Transduction of heterogeneous TIL cultures containing both CD4+ and CD8+ cells resulted in gene insertion into both T cell subsets with no preferential transduction frequency into either CD4+ or CD8+ cells. In other experiments highly purified CD4+ and CD8+ T cell subpopulations from either TIL or PBMC could be successfully transduced with the neoR gene as demonstrated by Southern blot analysis and detection of the gene product neophosphotransferase activity. No such activity of vector DNA could be detected in controls of nontransduced cells. In these highly purified cell subsets the distinctive T cell phenotypic markers were continually expressed after transduction, G418 selection and long-term growth. Clinical trials have begun in patients with advanced cancer using heterogeneous populations of CD4+ and CD8+ gene-modified TIL.

Targeted gene modification for gene therapy of stem cells

Ideally, gene therapy would correct the specific gene defect without adding potentially harmful extraneous DNA sequences. Such correction can be obtained with homologous recombination between input DNA sequences and identical (homologous) sequences in the genomic target gene. The development of techniques for obtaining virtually pure populations of hematopoietic stem cells should permit the use of the highly efficient nuclear microinjection methods for transfer of DNA. These techniques combined with new highly sensitive methods for detecting cells with the specified genetic modification of nonexpressed genes would make homologous recombination-mediated gene therapy feasible for hematopoietic stem cells. These advances are reviewed with particular emphasis on approaches to targeted gene modification of hematopoietic stem cells and speculation on directions for future research.