Gene therapy for adenosine deaminase deficiency

Towards a rAAV-based gene therapy for ADA-SCID: from ADA deficiency to current and future treatment strategies

Adenosine deaminase deficiency fosters a rare, devastating pediatric immune deficiency with concomitant opportunistic infections, metabolic anomalies and multiple organ system pathology. The standard of care for adenosine deaminase deficient severe combined immune deficiency (ADA-SCID) includes enzyme replacement therapy or bone marrow transplantation. Gene therapies for ADA-SCID over nearly two decades have exclusively involved retroviral vectors targeted to lymphocytes and hematopoetic progenitors. These groundbreaking gene therapies represent a revolution in clinical medicine, but come with several challenges, including the risk of insertional mutagenesis. An alternative gene therapy for ADA-SCID may utilize recombinant adeno-associated virus vectors in vivo, with numerous target tissues, to foster ectopic expression and secretion of adenosine deaminase. This review endeavors to describe ADA-SCID, the traditional treatments, previous retroviral gene therapies, and primarily, alternative recombinant adeno-associated virus-based strategies to remedy this potentially fatal genetic disease.

T-cell receptor gene transfer by lentiviral vectors in adoptive cell therapy

Adoptive cell therapy can be envisioned as a promising strategy for tumour immunotherapy. However, existing protocols of adoptive cell therapy still require optimisation as many factors, such as specificity, avidity, level of differentiation and amount of transferred T lymphocytes, can influence their immunocompetence and in vivo functionality. In particular, the need to reduce the in vitro expansion phase and to obtain large numbers of tumour-reactive T cells, as a favourable condition for cancer regression, make TCR gene transfer a potentially ideal tool to overcome the limits of adoptive cell therapy strategies. Here, the authors review the state-of-the-art and recent advances in TCR transfer with particular emphasis on lentiviral vector systems. Initial data from preclinical models and recent clinical trials encourage optimisation of a safe, simplified and stable transfer system. In this regard, HIV-based vectors are emerging as good alternative candidates over the most widely used oncoretroviral vectors due to their peculiar molecular features that fit the ideal conditions for donor T cell in vitro manipulation.

Stem cells in the lung parenchyma and prospects for lung injury therapy

Until recently, it was thought that only embryonic stem cells were pluripotent and that adult stem cells were restricted in their differentiative and regenerative potential to become the tissues in which they reside. However, the discovery that adult stem cells in one tissue can contribute to the formation of other tissues, especially after injury or cell damage, implies that stem cells have developmental plasticity. For example, haematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) from bone marrow can be used to regenerate diverse tissues at distant sites, including the lung. This article reviews the character of stem cells in the lung parenchyma and focuses on the potential uses of adult stem cells in research of lung injury and lung disease therapies.

Primary human T lymphocytes engineered with a codon-optimized IL-15 gene resist cytokine withdrawal-induced apoptosis and persist long-term in the absence of exogenous cytokine

IL-15 is a common gamma-chain cytokine that has been shown to be more active than IL-2 in several murine cancer immunotherapy models. Although T lymphocytes do not produce IL-15, murine lymphocytes carrying an IL-15 transgene demonstrated superior antitumor activity in the immunotherapy of B16 melanoma. Thus, we sought to investigate the biological impact of constitutive IL-15 expression by human lymphocytes. In this report we describe the generation of a retroviral vector encoding a codon-optimized IL-15 gene. Alternate codon usage significantly enhanced the translational efficiency of this tightly regulated gene in retroviral vector-transduced cells. Activated human CD4+ and CD8+ human lymphocytes expressed IL-15Ralpha and produced high levels of cytokine upon retroviral transduction with the IL-15 vector. IL-15-transduced lymphocytes remained viable for up to 180 days in the absence of exogenous cytokine. IL-15 vector-transduced T cells showed continued proliferation after cytokine withdrawal and resistance to apoptosis while retaining specific Ag recognition. In the setting of adoptive cell transfer, IL-15-transduced lymphocytes may prolong lymphocyte survival in vivo and could potentially enhance antitumor activity.

Hematopoietic stem cell gene therapy with drug resistance genes: an update

Transfer of drug resistance genes into hematopoietic stem cells (HSCs) has promise for the treatment of a variety of inherited, that is, X-linked severe combined immune deficiency, adenosine deaminase deficiency, thalassemia, and acquired disorders, that is, breast cancer, lymphomas, brain tumors, and testicular cancer. Drug resistance genes are transferred into HSCs either for providing myeloprotection against chemotherapy-induced myelosuppression or for selecting HSCs that are concomitantly transduced with another gene for correction of an inherited disorder. In this review, we describe ongoing experimental approaches, observations from clinical trials, and safety concerns related to the drug resistance gene transfer.

Therapeutic potential of stem cells in perinatal medicine

Increasing evidence suggests that stem cells have tremendous potential to facilitate repair of damaged tissue and to exert protective influences that limit the extent of damage. Their inherent capacity to respond to signals generated by damaged tissue, migrate to these regions and either replace dead tissue or deliver protection by secretion of specific growth hormones and protective factors, suggests that they might have unrivalled therapeutic potential in perinatal medicine. A further potential of stem cells is their use in gene repair strategies for genetic disorders; an application which is exceedingly interesting from a perinatal perspective. Because of the relatively small size of infants and their capacity for future growth, stem cell therapy could be more successful in newborns than in older children or adults. In practical terms, the placenta, with its large reservoir of fetal blood, offers the ideal source of autologous stem cells. This affords the opportunity for stem cells to be collected and used, either directly ex vivo or after in vitro modulation, both for disorders in the neonatal period and for those arising later in life. The organs most affected from tissue damage in the neonatal period are the brain and the lung. So far, the most promising application of stem cells might be in the treatment of neurological injury. In this review we discuss recent research findings with adult stem cell therapy and their potential use in perinatal medicine. Furthermore, specific animal models suitable to explore the patho-physiological mechanisms of stem cell transplantation after neurological injury will be discussed. This review gives an overview of basic science findings and their possible role for clinical application with regards to the therapeutic potential of stem cells in perinatal medicine. Medline was searched for journal selection in peer-reviewed journals with high impact scores, which were relevant to this topic. All articles were in English and the search was not limited by publication year. However, the oldest publication was dated 1988 (reference 1).

A novel purification strategy for retrovirus gene therapy vectors using heparin affinity chromatography

Membrane separation and chromatographic technologies are regarded as an attractive alternative to conventional academic small-scale ultracentrifugation procedures used for retrovirus purification. However, despite the increasing demands for purified retroviral vector preparations, new chromatography adsorbents with high specificity for the virus have not been reported. Heparin affinity chromatography is presented here as a novel convenient tool for retrovirus purification. The ability of bioactive retroviral particles to specifically bind to heparin ligands immobilized on a chromatographic gel is shown. A purification factor of 63 with a recovery of 61% of functional retroparticles was achieved using this single step. Tentacle heparin affinity supports captured retroviral particles more efficiently than conventional heparin affinity chromatography supports with which a lower recovery was obtained (18%). Intact, infective retroviral particles were recovered by elution with low salt concentrations (350 mM NaCl). Mild conditions for retrovirus elution from chromatographic columns are required to preserve virus infectivity. VSV-G pseudotyped retroviruses have shown to be very sensitive to high ionic strength, losing 50% of their activity and showing membrane damage after a short exposure to 1M NaCl. We also report a complete scaleable downstream processing scheme for the purification of MoMLV-derived vectors that involves sequential microfiltration and ultra/diafiltration steps for virus clarification and concentration respectively, followed by fractionation by heparin affinity chromatography and final polishing by size-exclusion chromatography. Overall, by using this strategy, a 38% yield of infective particles can be achieved with a final purification factor of 2,000.

Molecular imaging applications for immunology

The use of multimodality molecular imaging has recently facilitated the study of molecular and cellular events in living subjects in a noninvasive and repetitive manner to improve the diagnostic capability of traditional assays. The noninvasive imaging modalities utilized for both small animal and human imaging include positron emission tomography (PET), single photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), ultrasound, and computed tomography (CT). Techniques specific to small-animal imaging include bioluminescent imaging (BIm) and fluorescent imaging (FIm). Molecular imaging permits the study of events within cells, the examination of cell trafficking patterns that relate to inflammatory diseases and metastases, and the ability to rapidly screen new drug treatments for distribution and effectiveness. In this paper, we will review the current field of molecular imaging assays (especially those utilizing PET and BIm modalities) and examine how they might impact animal models and human disease in the field of clinical immunology.

Synthesis and release of human (pro)insulin in human BM progenitor cells

BACKGROUND

Pancreatic insulin-producing g-cells are permanently destroyed in Type I diabetic patients, leading to hypoglycemica. Various somatic cells have been studied for their ability to deliver insulin as an alternative source of pancreatic g-cells. We investigated the potential of human BM progenitor cells for this purpose.

METHODS

Two BM-derived hematopoietic cell lines, Tf-1 (CD34+) and K562 (CD34m) cell and primary human BM stromal cells were transduced with the human preproinsulin cDNA, and the ability of these cells to synthesize, store and release insulin was analyzed.

RESULTS

All cells produce and released (pro)insulin at 116-295 wU/10(6) cells/day respectively. No storage of insulin was detected in either cell line or in stromal cells.

DISCUSSION

We conclude that human BM-derived progenitor cells can be induced to produce and release basal levels of (pro)insulin.

Clinical gene therapy for nonmalignant disease

Gene therapy is envisioned as a potentially definitive treatment for a variety of diseases that have a genetic etiology. We reviewed trials of clinical gene therapy for nonmalignant, single-gene, and multifactorial disorders and infectious diseases, and found limited evidence suggesting that gene therapy may benefit patients who have severe, combined, immunodeficiency disorder; cystic fibrosis; coronary artery disease or peripheral arterial disease; or hemophilia. Effective gene therapy requires the targeted transfer of exogenous genetic material into human cells and the subsequent regulated expression of the corresponding gene product. Because no phase 3 randomized controlled trials have been completed that fulfill these criteria, it is difficult to correlate signs of clinical benefit with the administration of gene therapy in any disease. Additional clinical and basic research is needed to determine the future role of gene therapy.

Lentivirus-mediated gene transfer and expression in established human tumor antigen-specific cytotoxic T cells and primary unstimulated T cells

In this report, we evaluated the efficiency of stable gene transfer into established CD8(+) human tumor antigen-specific cytotoxic T cell (CTL) lines and peripheral blood lymphocytes (PBL) by oncoretroviral and lentiviral vectors. In the oncoretroviral vector, the green fluorescent protein (GFP) reporter gene was regulated by the murine stem cell virus (MSCV) promoter. In three human immunodeficiency virus type 1 (HIV-1)-based lentiviral vectors, the GFP transgene was regulated by either a chimeric MSCV/HIV-1 promoter, or cellular promoters from human housekeeping genes PGK and EF1 alpha. We found that several lines of proliferating tumor-specific CTL were poorly (=2%) transduced by the oncoretroviral vector that transduced Jurkat T cell line efficiently (=80%). In contrast, three lentiviral vectors transduced 38-63% of these proliferating CTL. More interestingly, all lentiviral vectors packaged without the HIV-1 accessory proteins transduced human bulk PBL and purified CD4(+) and CD8(+) lymphocyte subsets without prior stimulation. Detailed analysis indicated that the lentiviral vectors containing the EF1 alpha or PGK ubiquitous promoter can transduce unstimulated PBL and achieve low-level transgene expression in the absence of any T-cell activation. However, T-cell activation subsequent to the transduction of unstimulated PBL is required for high-level transgene expression. Transduced PBL expressing transgene delivered by the lentiviral vectors still preserved resting and naïve cell phenotypes. Taken together, prior T cell stimulation and HIV-1 accessory proteins are dispensable for lentivirus-mediated gene transfer into resting naïve and memory T lymphocytes. These results will have significant implications for the study of T-cell biology and for the improvement of clinical gene therapies of acquired immune deficiency syndrome (AIDS) and cancer.

Current developments in the design of onco-retrovirus and lentivirus vector systems for hematopoietic cell gene therapy

Over the past dozen years, the majority of clinical gene therapy trials for inherited genetic diseases and cancer therapy have been performed using murine onco-retrovirus as the gene delivery vector. The earliest systems used were relatively inefficient in both the rates of transduction and expression of the transgene. Formidable obstacles inherent in the cell biology and/or the immunology of the target cell systems limited the efficacy of gene therapy for many target diseases. Development of novel retrovirus gene transfer systems that are in progress have begun to overcome these obstacles. Evidence of this progress is the recent successful functional correction of the immune T and B lymphocyte deficiency in patients with X-linked severe combined immunodeficiency (X-SCID) and adenosine deaminase (ADA)-deficient SCID following onco-retrovirus vector ex vivo transduction of autologous marrow stem cells [Science 296 (2002) 2410; Science 288 (2000) 669; N. Engl. J. Med. 346 (2002) 1185]. These achievements of prolonged clinical benefit from gene therapy were tempered by the finding of insertional mutageneses in two of the treated X-SCID patients [N. Engl. J. Med. 348 (2003) 255].

Toward the development of a virus-cell-based assay for the discovery of novel compounds against human immunodeficiency virus type 1

The emergence of human immunodeficiency virus type 1 (HIV-1) strains resistant to highly active antiretroviral therapy necessitates continued drug discovery for the treatment of HIV-1 infection. Most current drug discovery strategies focus upon a single aspect of HIV-1 replication. A virus-cell-based assay, which can be adapted to high-throughput screening, would allow the screening of multiple targets simultaneously. HIV-1-based vector systems mimic the HIV-1 life cycle without yielding replication-competent virus, making them potentially important tools for the development of safe, wide-ranging, rapid, and cost-effective assays amenable to high-throughput screening. Since replication of vector virus is typically restricted to a single cycle, a crucial question is whether such an assay provides the needed sensitivity to detect potential HIV-1 inhibitors. With a stable, inducible vector virus-producing cell line, the inhibitory effects of four reverse transcriptase inhibitors (zidovudine, stavudine, lamivudine, and didanosine) and one protease inhibitor (indinavir) were assessed. It was found that HIV-1 vector virus titer was inhibited in a single cycle of replication up to 300-fold without affecting cell viability, indicating that the assay provides the necessary sensitivity for identifying antiviral molecules. Thus, it seems likely that HIV-1-derived vector systems can be utilized in a novel fashion to facilitate the development of a safe, efficient method for screening compound libraries for anti-HIV-1 activity.

Hematopoietic stem cell gene therapy

Gene therapy applications that target hematopoietic stem cells (HSCs) offer great potential for the treatment of hematologic disease. Despite this promise, clinical success has been limited by poor rates of gene transfer, poor engraftment of modified cells, and poor levels of gene expression. We describe here the basic approach used for HSC gene therapy, briefly review some of the seminal clinical trials in the field, and describe several recent advances directed toward overcoming these limitations.

Efficient gene transfer into spleen cells of newborn mice by a replication-competent retroviral vector

A murine leukemia virus-derived replication-competent retroviral vector with a translational cassette for the enhanced green fluorescence protein (EGFP) was previously found to function efficiently in cell culture (Jespersen et al., 1999, Gene 239, 227-235). We here report that infection of newborn NIH Swiss mice gives rise to EGFP expression in a majority of spleen cells within the first days after infection. Among the nonadherent spleen cells, B, T, and NK lymphocytes were found to be efficiently marked by EGFP by flow cytometry analysis, whereas the adherent spleen cells were negative in most animals. Analysis at time points up to 60 days after infection reveals a decline in EGFP-positive spleen cells over time. Viremia analysis and PCR analysis of spleen DNA indicate that viruses that have lost the translation cassette predominate at later stages. The results provide a model for efficient gene delivery to spleen cells in a time window of 1 to 2 weeks after infection of newborns. Although this type of vector will not in itself be applicable in the clinic, we envision that efficient in vivo gene delivery will be valuable by analysis of differentiation and proliferation of hematopoietic cells in animal models and by development and evaluation of effectors interfering with these processes.

Adenosine deaminase deficiency with mosaicism for a "second-site suppressor" of a splicing mutation: decline in revertant T lymphocytes during enzyme replacement therapy

Four patients from 3 Saudi Arabian families had delayed onset of immune deficiency due to homozygosity for a novel intronic mutation, g.31701T>A, in the last splice acceptor site of the adenosine deaminase (ADA) gene. Aberrant splicing mutated the last 4 ADA amino acids and added a 43-residue "tail" that rendered the protein unstable. Mutant complementary DNA (cDNA) expressed in Escherichia coli yielded 1% of the ADA activity obtained with wild-type cDNA. The oldest patient, 16 years old at diagnosis, had greater residual immune function and less elevated erythrocyte deoxyadenosine nucleotides than his 4-year-old affected sister. His T cells and Epstein-Barr virus (EBV) B cell line had 75% of normal ADA activity and ADA protein of normal size. DNA from these cells and his whole blood possessed 2 mutant ADA alleles. Both carried g.31701T>A, but one had acquired a deletion of the 11 adjacent base pair, g.31702-12, which suppressed aberrant splicing and excised an unusual purine-rich tract from the wild-type intron 11/exon 12 junction. During ADA replacement therapy, ADA activity in T cells and abundance of the "second-site" revertant allele decreased markedly. This finding raises an important issue relevant to stem cell gene therapy.

Molecular mechanism of transforming growth factor beta-mediated cell-cycle modulation in primary human CD34(+) progenitors

The mechanisms by which transforming growth factor beta (TGF-beta) exerts a negative effect on cell-cycle entry in primary human hematopoietic stem/progenitor cells were examined at the molecular and cellular levels. After treatment of primary human CD34+ progenitors with TGF-beta there was a decrease in the levels of cyclin D2 protein and an increase in levels of the cyclin-dependent kinase inhibitor (CDKI) p15 as compared to the levels in untreated cells. The converse was true after addition of neutralizing anti-TGF-beta antibody. Administration of TGF-beta to CD34+ cells in the presence of cytokines prevented retinoblastoma protein (pRb) phosphorylation, which occurred in the same cells treated with cytokines alone or cytokines and anti-TGF-beta antibody. Neutralization of TGF-beta during 24 to 48 hours of culture with cytokines significantly increased the number of colony-forming progenitors, but did not modulate the human stem cell pool, as measured in 6- to 12-month xenotransplantation assays. Equivalent numbers of human B, T, and myeloid cells were obtained after transplantation of cells treated with or without neutralization of TGF-beta.

An overview of the immune system

We are continually exposed to organisms that are inhaled, swallowed, or inhabit our skin and mucous membranes. Whether these organisms penetrate and cause disease is a result of both the pathogenicity of the organism (the virulence factors at its disposal) and the integrity of host defence mechanisms. The immune system is an interactive network of lymphoid organs, cells, humoral factors, and cytokines. The essential function of the immune system in host defence is best illustrated when it goes wrong; underactivity resulting in the severe infections and tumours of immunodeficiency, overactivity in allergic and autoimmune disease. In this review we have covered the normal function of the immune system in recognising, repelling, and eradicating pathogens and other foreign molecules.

The role of oncology nurses in gene therapy

In February 2001, the Human Genome Project international consortium announced the publication of a draft sequence and initial analysis of the human genome. Although a definitive count of human genes must await further experimental and computational analysis, scientists now estimate that the human genome contains 30000-35000 genes--a much smaller number than initially estimated. The advances in treatment which will result from this research and our improved understanding of cancer at a molecular level will rapidly change the management of cancer. Gene therapy represents one new approach to treatment, but is currently still experimental. This article reviews the important role of the oncology nurse as a member of the multidisciplinary team caring for patients who receive gene therapy as part of a clinical trial.

Gene therapy for genetic haematological disorders and immunodeficiencies

Gene transfer and autologous transplantation of haematopoietic stem cells (HSCs) from patients with genetic haematological disorders and immunodeficiencies could provide the same benefits as allogeneic HSC transplantation, without the attendant immunological complications. Inefficient gene delivery to human HSCs has imposed the major limitation to successful application of gene therapy. A recently reported clinical trial of gene transfer into HSCs of infants with X-linked severe combined immunodeficiency (SCID) has achieved immune restoration because of the selective outgrowth of the gene-corrected lymphocytes. Newer methods for manipulating HSCs may lead to efficacy for other disorders. The problems and progress in this area are reviewed herein.