Retroviral Vector-Mediated Gene Transfer into Hematopoietic Cells: Prospects and Issues

Efficient delivery of DNA and morpholinos into mouse preimplantation embryos by electroporation

Mouse preimplantation development is characterized by three major transitions and two lineage segregations. Each transition or lineage segregation entails pronounced changes in the pattern of gene expression. Thus, research into the function of genes with obvious changes in expression pattern will shed light on the molecular basis of preimplantation development. We have described a simplified and effective method–electroporation–of introducing plasmid DNA and morpholinos into mouse preimplantation embryos and verified effectiveness of this approach by testing the procedure on the endogenous gene Oct4. Before electroporation, the zona pellucida was weakened by the treatment of acid Tyrode’s solution. Then we optimized the parameters such as voltage, pulse duration, number of pulses and repeats, and applied these parameters to subsequent experiments. Compared with the control groups, the number of apoptotic cells and the expression and localization of OCT3/4 or CDX2 was not significantly changed in blastocysts developed from 1-cell embryos, which were electroporated with pIRES2-AcGFP1-Nuc eukaryotic expression vector or mismatched morpholino oligonucleotides. Furthermore, electroporated plasmid DNA and morpholinos targeting the endogenous gene Oct4 were able to sharply down regulate expression of OCT4 protein and actually cause expected phenotypes in mouse preimplantation embryos. In conclusion, plasmid DNA and morpholinos could be efficient delivered into mouse preimplantation embryos by electroporation and exert their functions, and normal development of preimplantation embryos was not affected.

Electroporation of antibodies, DNA, and other macromolecules into cells: a highly efficient method

While antibodies are a major extracellular tool of the highest specificity to answer important biomedical questions, the improvements in electroporation discussed below may make it feasible to also use antibodies as an intracellular deletion tool to study (a) viruses inside the cell, (b) cancer cells, (c) signal transduction, (d) genetics, (e) metabolism, and (f) other structures and mechanisms. Already, others have succeeded in depositing macromolecules, including antibodies (Abs), and nucleic acids inside cells, using many techniques, including electroporation (EP). However, EP has limitations that have precluded its widespread use, particularly its high kill rate for cells and the low percentage of cells that are able to incorporate macromolecules. If these limitations could be overcome for Abs and nucleic acids, then it would be practical to use them as highly specific probes for intracellular molecules. In our experiments using EP, we were able to largely prevent lethality for cells during EP by employing a commercially available cold-storage solution for organ transplants containing high K(+) and Mg(++) (ViaSpan, Belzer UW cold-storage solution, DuPont Pharmaceuticals). This solution decreased cell death after standard EP by an average of 50% for a number of cell lines. Viability of WISH cells after EP approached 100%. In transfection studies, ViaSpan medium strongly increased both P3HR1 cell survival as well as the total number of cells transfected with DNA for green fluorescent protein (GFP). In additional experiments with Abs, we were able to strongly increase the percent of cells that incorporated Ab by using two serial EPs. This enhanced the intracellular protection by Abs against viruses in Vero cells from 64% to a maximum of 98%. We were able to further simplify the EP technique by using unpurified antiserum in place of purified IgG. Thus, this EP technique offers multiple advantages: simplicity, high cell viability, high effectiveness, high specificity, rapid action, usefulness with adherent or non-adherent cells, and no requirement for purification of antibodies from antiserum.

High-level transgene expression in primary human T lymphocytes and adult bone marrow CD34+ cells via electroporation-mediated gene delivery

The design of effective gene delivery systems for gene transfer in primary human blood cells is important both for fundamental hematopoiesis research and for cancer gene therapy strategies. Here, we evaluated electroporation as a nonviral means for transfection of activated human T lymphocytes and adult bone marrow (BM) CD34+ cells. We describe optimal culture and electroporation parameters for efficient gene delivery in prestimulated T lymphocytes (16.3 +/-1.3%), as well as 2-day cultured adult BM CD34+ cells (29.6+/-4.6%). PHA-stimulated T cells were most receptive for transfection after 48h of in vitro culture, while T cells stimulated by CD3 cross-linking and interleukin (IL)-2 achieved maximum transfection levels after 72 h of prestimulation. Kinetic analysis of EGFP expression revealed that activated T lymphocytes maintained transgene expression at high levels for a prolonged period. In addition, fresh unstimulated BM CD34+ cells were consistently transfected (5.2+/-0.4%) with minimal cytotoxicity (<5%), even without preliminary CD34+ cell purification. Both T cells and CD34+ cells retained their phenotype and functional capacity after electroporation. These results demonstrate that electroporation is a suitable nonviral transfection technique that may serve applications in gene therapy protocols using T lymphocytes or CD34+ cells.

Large-scale manufacturing of safe and efficient retrovirus packaging lines for use in immunotherapy protocols

BACKGROUND

The use of gene modified T lymphocytes for immunotherapy in a cancer or AIDS clinical trial requires an efficient, safe ex vivo method for modification of these cells at manufacturing scale. Since retroviruses have been shown to be a moderately effective means of stably integrating therapeutic genes into T lymphocytes, we wanted to create packaging and producer cell lines that would produce replication competent retrovirus (RCR)-free supernatants, at large scale (> 200 l), and transduce with high efficiency.

METHODS

cDNA expression plasmids containing only coding sequences for gagpol or env were built and sequentially transfected into human 293 cells. Packaging and producer clones were characterized for stability, titer and RCR. A producer clone delivering chimeric immune receptors was scaled-up and supernatants used to transduce patient T lymphocytes for clinical studies. PCR and RT-PCR assays were utilized to evaluate the transmission of HERV-H sequences. Relative infectivity of producer clones pseudotyped with different envelopes was determined by transduction and RT assays.

RESULTS

RCR-free, human 293 split-genome packaging lines, pseudotyped with amphotropic, xenotropic, or 10A1 envelopes, were created. A CC49 zeta producer clone was scaled-up to 5 x 54 l lots and supernatants used to safely and efficiently transduce patient T lymphocytes with minimal ex vivo manipulation. While 293 cells express HERV-H mRNA, the transmission frequency in our packaging clones was less than 1 HERV-H sequence per 5 x 10(5) proviral integrations. Additionally, 10A1 and xenotropic packaging lines had higher infectivities than the amphotropic clone.

CONCLUSION

These packaging lines represent the safest configuration for the large-scale production of retroviral vectors, and are capable of producing high titer, RCR-free retroviral vector for large scale clinical use. While all three clones efficiently transduce human T lymphocytes, the 10A1 clone has the highest infectivity. These packaging cell lines will be valuable for use in human gene therapy protocols.

Antibodies for targeted gene therapy: extracellular gene targeting and intracellular expression

Antibody genes of human origin and human antibodies directed against human proteins have become widely available in recent years. These are valuable reagents for gene therapy applications, in which the use of human proteins and genes allows for increased therapeutic benefit. Engineered human antibodies can be used in gene therapy both as a component of a gene delivery system and as a therapeutic gene. As the targeting moiety of a gene delivery system, the antibody should meet certain criteria that have been previously determined from other clinical applications of antibodies. These include bioavailability, specificity for the target cell, and rapid clearance. In addition, if repeat delivery of therapeutic genes is going to be needed, then gene delivery vectors should be non-immunogenic to allow repeated administration. The use of human antibodies in this application should therefore be superior to approaches which use rodent-derived antibodies. Another application of antibodies in gene therapy is the use of antibodies expressed inside the cell (intrabodies) as therapeutic agents. The power of the immune system to rearrange a limited set of genes to create recognition sites for any known molecule is well documented. The ability to harness this information and use these highly specific binding molecules as medicines to inhibit an unwanted cellular function is a promising advance in the field of molecular medicine, and in particular, in the field of intracellular immunization.

Peripheral blood stem cells for autografting

High-dose therapy with autologous hematopoietic progenitor cell support is effective treatment for patients with a variety of high-risk malignancies. Accelerating of marrow recovery from near-lethal or lethal toxicity with hematopoietic cell support improves the safety and cost effectiveness of the high-dose regimens. Peripheral blood progenitor cells will soon replace marrow as the major source of hematopoietic support. This chapter reviews the techniques of peripheral blood progenitor cell collection, mobilization, purification (for tumor removal), and ex vivo expansion.

Gene transfer and therapeutic drug monitoring

During the next decade, gene therapy will evolve from a medical curiosity into an essential component of medical practice. One of the elements necessary for this transition will be the development of simple and accurate ways of monitoring both the vectors used to transfer the genes of interest and the function of the genes themselves. This article reviews the difficulties in achieving these aims and describes ways in which the technology of gene transfer offers a novel means of monitoring current therapies.

Large volume ex vivo expansion of CD34-positive hematopoietic progenitor cells for transplantation

A large volume culture system was developed for the ex vivo expansion of CD34 positive (+) hematopoietic progenitors, using cell donated by 15 patients receiving high-dose chemotherapy with autologous hematopoietic progenitor cell support (AHPCS). Substantial expansion of myeloid (181-fold) and megakaryocyte (41-fold) progenitors cells was demonstrated, using the conditions that we determined to be optimal: CD34+ progenitors cultured unperturbed for 7 (marrow) or 10 (blood) days in Teflon-coated bags with X-Vivo-10 medium containing 10% autologous plasma, 100 ng/ml, respectively, of recombinant stem cell factor (SCF), interleukin 3 (IL-3), interleukin 6 (IL-6), and granulocyte colony-stimulating factor (G-CSF). The studies demonstrated that (a) CD34 selection was necessary to obtain large, clinically relevant numbers of hematopoietic progenitors, (b) the addition of G-CSF to the baseline regimen of SCF/IL-3/IL-6 significantly enhanced the expansion of myeloid progenitors, (c) the addition of IL-1 to SCF/IL-3/IL-6 did not significantly enhance myeloid progenitor cell expansion, (d) CD34+ G-CSF-mobilized peripheral blood progenitor cells (PBPC) produced higher numbers of myeloid progenitors in culture than CD34+ marrow cells, and (e) long-term tissue culture (LTC) assays demonstrate the preservation of long-term initiating cells in ex vivo culture. The short-term and long-term reconstituting capability of CD34+ PBPC cultured in this system remains to be determined and will be evaluated in a clinical trial where they will be used as the sole source of AHPCS following high-dose therapy.

Gene marking and autologous bone marrow transplantation

If residual cancer cells in harvested bone marrow could be marked and subsequently detected in patients at relapse, valuable information would be obtained about the source of recurrent disease after autologous marrow transplantation. If normal progenitor cells were also marked, the study would provide useful data on the susceptibility of these human cells to gene transfer and their capacity to express newly introduced genes. We transferred the neomycin-resistance gene (NeoR) into bone marrow cells harvested from 20 children with acute myeloid leukemia (n = 12) or neuroblastoma (n = 8) in clinical and cytological remission using a retrovirus vector. The cells were then returned to the patients as part of an autologous bone marrow transplantation protocol. Two AML and three neuroblastoma patients have relapsed. In all, the resurgent cells contained the NeoR marker by analysis with PCR. These results prove that so-called remission marrow can contribute to relapse in patients who receive autologous transplants. The gene marking technique is now being used to evaluate techniques of pretransplant purging.

Gene transfer into human hematopoietic progenitor cells: a review of current clinical protocols

Recent reviews by Clay Smith (1992) in this journal and by W. French Anderson (1990) and A. Dusty Miller (1992) have described the technologies used for gene transfer, the potential applications of the approach, and the safety issues that require consideration. This review will have a narrower focus. It will deal specifically with current and forthcoming clinical protocols for gene transfer into hemopoietic progenitor cells, because a major goal of gene therapy for malignant and nonmalignant disease is to transfer and express genes on a long-term basis in these cells or their progeny.