Current Gene Therapy - Volume 9, Issue 1, 2009

Gene therapy has been a clinical possibility since 1989 and the steadily increasing number of clinical trials now includes strategies targeting neurodegenerative conditions such as lysosomal storage disease, multiple sclerosis, Alzheimer 's and, Parkinson's disease. In spite of lack of knowledge of the molecular causes of these diseases, results so far in these trials have been promising. Thus there is gaining confidence in the potential to develop effective treatments based on gene transfer for neurological diseases in the near future. Furthermore, the accelerating progress in knowledge of the molecular pathologies of neurogenetic disorders, including rare diseases such as the ataxias, makes them even more amenable to gene therapy. Here we review recent preclinical studies relevant to gene therapy of ataxias and discuss developments needed to bring these strategies into the clinic.

Numerous studies have investigated the potential use of TNF-related apoptosis-inducing ligand (TRAIL) as a cancer therapeutic since its discovery in 1995 - because TRAIL is a potent inducer of apoptosis in tumor cells but not in normal cells and tissues. Consequently, a great deal is known about TRAIL/TRAIL receptor expression, the molecular components of TRAIL receptor signaling, and methods of altering tumor cell sensitivity to TRAIL-induced apoptosis. Our laboratory was the first to report the possibility of TRAIL gene transfer therapy as an alternative method of using TRAIL as an antitumor therapy. As with recombinant proteins administered systemically, intratumoral TRAIL gene delivery also has limitations that can restrict its full potential. Translating the preclinical TRAIL studies into the clinic has started, with the hope that TRAIL will exhibit robust tumoricidal activity against human primary tumors in situ with minimal toxic side effects.

AIDS is the result of infection by a lentivirus, HIV-1, which primarily infects CD4+ T cells and macrophages. There is presently no vaccine and none will be available in the foreseeable future. Highly active antiretroviral drug therapy has led to a dramatic reduction of viral load in many infected individuals, and has decreased mortality in the developing world. However, besides long-term drug toxicity and eventual emergence of drug-resistant strains, withdrawal from the therapy (even after effective and continuous treatment) results in re-emergence of the virus since cells harbouring the latent viral reservoirs persist. These issues highlight the need for alternative therapies, e.g. gene therapy. This review summarizes various gene therapy strategies that target early stages of HIV-1 life cycle. We will cover strategies that allow interference at the level of the released virion RNA, reverse transcriptase, pre-integration complex, integrase, dsDNA and provirus DNA in gene-modified cells.

Fanconi anemia (FA) is an inherited chromosomal recessive syndrome characterized by cellular hypersensitivity to DNA crosslinking agents and bone marrow failure, which cause aplastic anemia, and an increased incidence of malignancy. 13 complementation groups are currently discovered, and 13 distinct genes have been cloned (FANCA, FANCB, FANCC, FANCD1, FANCD2, FANCE, FANCF, FANCG, FNACI, FANCJ, FANCL, FANCM, FANCN). Stem cells can theoretically divide to other cells without limit as long as a person is still alive. The stem cells that form blood and immune cells are known as hematopoietic stem cells. Hematopoietic stem cells can be acquired from a Fanconi anemia patient, whereas genomic DNA can be obtained easily from blood cells of a normal person. Normal genes also can be synthesised by PCR method. Normal genomic DNA will be delivered into a patient's stem cells via microinjection or transfection after enzyme digestion; the defective genes might be repaired by homologous genetic recombination. The gene-corrected stem cells can be transplanted into the same patient finally. It is possible that human genomic DNA to be considered as materials for homologous genetic recombination to repair defective genes in vivo. This might be an efficient method for gene therapy, which has no or less immunological rejection for Fanconi anemia and some genetic diseases. Several related observations and experiments are discussed to support this possible means of stem cell gene therapy of Fanconi anemia.

The cornea is a particularly attractive target for gene therapy designed to improve the outcome of corneal transplantation. First, there is a clear and well-defined clinical need. Second, because donor corneas can be preserved for days if not weeks within an eye bank, ex vivo transduction of a donor cornea can be carried out without the urgency associated with many other forms of transplantation. Finally, the partial sequestration of the eye from the systemic circulation decreases the likelihood of spillover of vector and transgene, and the immune privileged nature of the cornea and anterior segment affords a degree of protection from immune responses directed against the vector. A wide range of vectors has been investigated for gene transfer to the cornea. A number of viral vectors, in particular, have proved to be efficient at transducing the cornea and in association with a variety of transgenes, have been used successfully to prolong corneal allograft survival significantly in animal models. The most suitable such vector for future clinical studies in corneal transplantation has yet to be determined, but the most likely include recombinant adenoviral, adeno-associated viral and lentiviral vectors. In this review, we examine the ability of these viral vectors to transduce the cornea, and summarise those studies in which gene therapy has been used to prolong experimental corneal allograft survival.

Tremendous strides have been made in proteogenomics and RNA interference technologies. Hence “personalized” cancer gene therapy has become a foreseeable rather than a predictable reality. Currently, the lack of an optimized, systemic gene delivery vehicle remains a key limiting factor for developing effective treatment applications. Since their introduction by Felgner in 1987, cationic lipids have been an attractive consideration for gene delivery, in view of their biocompatibility, biodegradability, low toxicity, and low immunogenicity. Successful in vivo transgene expression by cationic lipid- or cationic polymer-based delivery depends critically on a long circulating half life (>48 h), a definable systemic biodistribution with target-specific cancer localization, and efficient cell entry and internalization. Ideally, the agent should have a hydrophobic, stabilized core that ensures integrity of the therapeutic entity in vivo, a biocompatible, neutrally charged shell (ξ potential of ∼ ±10 mv) for enhanced, “stealth” circulation, and a suitable size (∼50-200 nm in diameter) for access into the tumor neovasculature and reduced reticuloendothelial system (RES) uptake. “Smart” receptortargeting moieties can redirect intracellular trafficking. Additional engineered features have also been incorporated to minimize lysosomal degradation (membrane fusogenic lipids or proton sponge), promote endosomal escape into cytoplasm (cell penetrating peptides, triblock copolymer construction), and enhance nuclear entry and activate the endogenous transcriptional machinery (inclusion of a nuclear localization signal). Improvements in each of these respective areas of study have converged to yield promising in vivo results.