Gene therapy in peripheral blood lymphocytes and bone marrow for ADA- immunodeficient patients

Gene therapy in Duchenne muscular dystrophy

Experiments in dystrophin gene transgenic mice have supported the concept of treating Duchenne muscular dystrophy (DMD) by demonstrating that regional expression of recombinant dystrophin in dystrophic muscle leads to regional restoration of normal muscle morphology and that dystrophin mini-genes driven by muscle specific regulatory elements are probably more effective than the full-length dystrophin gene. As a gene therapy trial for DMD, dystrophin cDNAs were introduced into skeletal muscle fibers of dystrophin-deficient mice (mdx) through direct DNA injection into plasmid expression vectors, and by replication-defective recombinant retrovirus or adenovirus vectors. With direct injection of dystrophin cDNA into a plasmid expression vector or retrovirus vectors, less than 10% of adult mdx fibers of the injected muscle expressed dystrophin. On the other hand, greater efficiency has been reported for recombinant adenovirus injection into young mdx muscle. However, it is necessary to develop vectors, viral or plasmid DNA, which can be injected intravenously and directed to muscle tissues. This will involve designing vectors possessing appropriate cell-type specific tropism and/or gene transcriptional activity for DMD treatment. This is anticipated to be a vital component in the second stage of experiments aimed at DMD treatment.

Gene therapy for cancer, the course ahead

Previous chapters have shown that there are a large number of therapeutic approaches under consideration for the gene therapy of cancer. Many of these have progressed into Phase I clinical trials. However, many of the early results are perceived to be disappointing in terms of low levels of gene transfer and systemic efficacy. In this concluding chapter, possible solutions to this state of unease are addressed, so that gene therapy of cancer can resume on its course to become a major contributor to clinical oncology in the years ahead.

Gene therapy for cancer--in the dock, blown off course or full speed ahead?

Gene therapy no longer seems to generate the unlimited optimism that it once inspired. So much so that the field has recently attracted the close scrutinies of the Director of the NIH himself. In this introductory chapter, the background is presented to the rise, and apparent decline, of the gene therapy of cancer and serves as a prelude to this issue of Cancer Metastasis Reviews which is designed to ask whether the field is worthy of its highly-priced and highly-hyped market profile.

Human fetal gene therapy: moral and ethical questions

This two-part paper discusses moral and ethical questions raised by future trials of human fetal gene therapy. The first part examines broad moral issues to explore whether fetal gene therapy is a morally praiseworthy goal. Ought it be done at all? These issues include (i) how the concept of fetal gene therapy originally arose as a goal envisioned at the beginning of prenatal diagnosis, (ii) preimplantation genetic diagnosis as a better preconceptual alternative for parents at higher genetic risk, (iii) alternatives to genetic abortions, (iv) the social and economic priority of fetal gene therapy, and (v) whether fetal gene therapy is a "slippery slope" that will end in germ-line gene therapy. This part concludes that far more reasons exist to commend fetal gene therapy than to reject it, given its limits and modest social and economic priority. The second part responds to specific ethical questions that must be raised about any protocol for human gene therapy. These questions and issues are adapted to the prenatal situation: (i) how the previable fetus becomes a "patient," (ii) concern for clinical benefit and minimizing risks to the fetus and pregnant woman, (iii) concern for the voluntary and informed participation of the pregnant woman, the father, and for protection of their privacy, (iv) concern for fair selection of subjects, (v) considerations of harm to germ line cells, and (vi) the role of public oversight of fetal gene therapy. The article concludes by recommending a continuation of the consolidated Recombinant Advisory Committee (RAC) for the near future.

A method to codetect introduced genes and their products in gene therapy protocols

To monitor the presence of introduced genes and the distribution of the encoded proteins in host tissues after gene transfer, we combined fluorescence in situ hybridization (FISH) and immunohistochemistry in two separate gene therapy paradigms. In brain tissue sections from animals injected with pHSVlac vector, we localized nuclei containing vector DNA both in cells expressing and not expressing beta-galactosidase (beta-gal). This suggests that the efficiency of gene transfer is affected not only by gene delivery, but also by cellular controls on gene expression. In a second paradigm, following myoblast transplantation, we detected donor nuclei in the muscle of a patient with Duchenne's muscular dystrophy. The donor nuclei were either surrounded by host nuclei or apparently fused in the patient's muscle fiber producing dystrophin. The combined FISH and immunohistochemistry assay offers greater sensitivity and more information than currently used polymerase chain reaction and protein detection methods.

Colocalization of retrovirus and target cells on specific fibronectin fragments increases genetic transduction of mammalian cells

Hematopoietic cells are important targets for genetic modification with retroviral vectors. Attempts at human gene therapy of stem cells have achieved limited success partly because of low gene transfer efficiency. Chymotryptic fragments of the extracellular matrix molecule fibronectin used during infection have been shown to increase transduction of human hematopoietic progenitor cells. Here, we demonstrate that this enhanced gene transfer into mammalian target cells is due to direct binding of retroviral particles to sequences within the fibronectin molecule. Transduction of mammalian cells, including murine long-term repopulating hematopoietic cells, is greatly enhanced when cells are adherent to chimeric fragments containing these retroviral binding sequences. In addition, colocalization of retrovirus and target cells on fibronectin peptides allows targeted transduction of specific cell types by exploiting unique ligand/receptor interactions.

In vitro correction of JAK3-deficient severe combined immunodeficiency by retroviral-mediated gene transduction

Mutations affecting the expression of the Janus family kinase JAK3 were recently shown to be responsible for autosomal recessive severe combined immunodeficiency (SCID). JAK3-deficient patients present with a clinical phenotype virtually indistinguishable from boys affected by X-linked SCID, a disease caused by genetic defects of the common gamma chain (gamma c) that is a shared component of the receptors for IL-2, IL-4, IL-7, IL-9, and IL-15. The specific interaction of JAK3 and gamma c represents the biochemical basis for the similarities between these two immunodeficiencies. Both forms of SCID are characterized by recurrent, severe infections leading to death in infancy unless successfully treated by allogeneic bone marrow transplantation. Because of the potentially lethal complications associated with allogeneic bone marrow transplantation and the frequent lack of suitable marrow donors, the development of alternative forms of therapy is highly desirable. To this end, we investigated a retroviral-mediated gene correction approach for JAK3-deficiency. A vector carrying a copy of JAK3 cDNA was constructed and used to transduce B cell lines derived from patients with JAK3-deficient SCID. We demonstrate restoration of JAK3 expression and phosphorylation upon IL-2 and IL-4 stimulation. Furthermore, patients' cells transduced with JAK3 acquired the ability to proliferate normally in response to IL-2. These data indicate that the biological defects of JAK3-deficient cells can be efficiently corrected in vitro by retroviral-mediated gene transfer, thus providing the basis for future investigation of gene therapy as treatment for JAK3-deficient SCID.

In vitro T lymphopoiesis: a model system for stem cell gene therapy for AIDS

Stable introduction of therapeutic genes into hematopoietic stem cells has the potential to reconstitute immunity in individuals with HIV infection. However, many important questions regarding the safety and efficacy of this approach remain unanswered and may be addressed in a non-human primate model. To facilitate evaluation of expression of foreign genes in T cells derived from transduced hematopoietic progenitor cells, we have established a culture system that supports the differentiation of rhesus macaque and human CD34+ bone marrow derived cells into mature T cells. Thymic stromal monolayers were prepared from the adherent cell fraction of collagenase digested fetal or neonatal thymus. After 10-14 days, purified rhesus CD34+ bone marrow-derived cells cultured on thymic stromal monolayers yielded CD3+CD4+CD8+, CD3+CD4+CD8-, and CD3+CD4-CD8+ cells. Following stimulation with mitogens, these T cells derived from CD34+ cells could be expanded over 1,000-fold and maintained in culture for up to 20 weeks. We next evaluated the ability of rhesus CD34+ cells transduced with a retroviral vector containing the marker gene neo to undergo in vitro T cell differentiation. CD34+ cells transduced in the presence of bone marrow stroma and then cultured on rhesus thymic stroma resulted in T cells containing the retroviral marker gene. These studies should facilitate both in vitro and in vivo studies of hematopoietic stem cell therapeutic strategies for AIDS.

Long-term restoration of immunity against Epstein-Barr virus infection by adoptive transfer of gene-modified virus-specific T lymphocytes

Adoptive transfer of antigen-specific cytotoxic T lymphocytes (CTLs) offers safe and effective therapy for certain viral infections and could prove useful in the eradication of tumor cells. Whether or not the infused T cells persist for extended periods, retaining their ability to expand in response to antigenic stimulation, is not known. We now report long-term detection of gene-marked Epstein-Barr virus (EBV)-specific CTLs in immunocompromised patients at risk for the development of EBV lymphoproliferative disease. Infusions of CTLs not only restored cellular immune responses against EBV, but also established populations of CTL precursors that could respond to in vivo or ex vivo challenge with the virus for as long as 18 months. Our findings support wider use of antigen-specific CTLs in adoptive immunotherapy.

A chimeric human immunodeficiency virus type 1 (HIV-1) minimal Rev response element-ribozyme molecule exhibits dual antiviral function and inhibits cell-cell transmission of HIV-1

We have previously shown that hairpin ribozymes targeting the human immunodeficiency virus (HIV) genome can effectively inhibit virus replication in a variety of primary and cultured hematopoietic cells. To further increase antiviral potency and minimize the chance of viral resistance, we have now cloned the stem-loop II sequences of the HIV type 1 Rev response element into ribozyme transcription cassettes. Fusion RNA molecules were shown to function both as RNA decoys and ribozymes. Stable Molt-4/8 cell lines expressing fusion RNA of stem-loop II and a ribozyme directed at the HIV-type 1 U5 sequence (MSLMJT) or its disabled counterpart (MSLdMJT) were generated. The expression of fusion RNA was persistent for at least 6 months without apparent cytotoxicity. When virus inhibition was examined after the cocultivation of transduced cells with chronically infected Jurkat cells, much greater protection was observed in MSLMJT cells than in MSLdMJT or MMJT (expressing only the ribozyme) cells. Furthermore, to specifically compare the ribozyme activities in various transduced cells, we determined the quantitative levels of proviral DNA in the first round of virus replication (7 h after infection with HXB2). By competitive PCR, the proviral DNA levels in MSLMJT and MMJT cells were found to be reduced to 1/7 and 1/3, respectively, compared with those in MSLdMJT and MdMJT cells. These results suggest not only that the greater inhibition afforded by this fusion RNA was due to its function both as decoy and ribozyme but also that the ribozyme activity may be facilitated.