Current Gene Therapy - Volume 10, Issue 2, 2010

The last few years have seen the transfer of two decades of research into Chimeric Antigen Receptors (CARs) into clinical trials. Despite this extensive research, there is still a great deal of debate into the optimal design strategy for these, primarily, anti-cancer entities. The archetypal CAR consists of a single-chain antibody fragment, specific to a tumour- associated antigen, fused to a component of the T-cell receptor complex (typically CD3ζ) which on antigen binding primes the engrafted T-cell for anti-tumour activity. The modular nature of these artificial receptors has enabled researchers to modify aspects of their structure, including the extracellular spacer, transmembrane and cytoplasmic domain, to achieve laboratory defined optimal activity. Despite this there is no consensus on the optimal structure, a problem exacerbated by conflicting results using identical receptors. In this review, we provide a structural overview of CAR development and highlight areas that require further refinement. We also attempt to identify possible reasons for conflicting results in the hope that this information will inspire future rational design strategies for optimal tumour targeting using CARs.

Gene therapy is a rapidly developing field in which recombinant nucleic acid sequences are introduced to individuals to regulate, repair, replace, add or delete a genetic sequence. Recombinant adeno-associated viral (AAV) vectors, especially AAV2, are frequently used in gene therapy. Knowledge on the biodistribution and potential shedding of AAV2 is crucial to evaluate the risks of infection with the viral vector for the patient and the environment. Literature was analysed for biodistribution and shedding data for AAV2. Preclinical and clinical studies were included with a focus on the influence of the administration route on spreading. Based on biodistribution and shedding data, a qualitative model for the biodistribution and shedding of AAV2 related to the administration route is presented. It is concluded that biodistribution and shedding of AAV2 depend on the route of administration. Some routes lead to local biodistribution and thus to no shedding or shedding via one route only. Other routes lead to systemic biodistribution and to shedding via several excretion routes. The qualitative model presented can help to determine the possible biodistribution in the body and the risk of shedding via the different excretion routes. In addition, it can help to predict the different shedding routes after a certain administration route of AAV2 and thus in deciding which studies are warranted or which safety precautions are needed after administration to patients.

Gene therapy is a rapidly developing field in which recombinant nucleic acid sequences are introduced to individuals. Its therapeutic, prophylactic or diagnostic effect relates directly to the sequence it contains or to the product of genetic expression of this sequence. Recombinant adenoviral vectors (in particular HAdV-5 vectors) are frequently used in gene therapy. Knowledge on biodistribution and shedding is crucial in the risk assessment for the patient and the patient's environment. This review presents a critical overview on biodistribution and shedding data of non-replicating viral vector HAdV-5, related to the used administration route. Based on these data, a qualitative model for the biodistribution and shedding of HAdV-5-based viral vectors is presented. Biodistribution and shedding depend on the route of administration. Some routes lead to local biodistribution and no shedding or one shedding route only. Other routes lead to systemic biodistribution and to shedding via several excreta. Shedding via semen and transport across the blood-brain barrier is not expected for HAdV-5. The presented qualitative model can help researchers and risk assessors to determine the possible distribution in the body and the risk of shedding via the different excretion routes. Furthermore, it can help regulators to predict the different shedding routes after a certain administration route and thus in deciding which studies are warranted or which safety precautions are needed after administration to patients.

Muscle electrotransfer covers the delivery of molecules to muscle tissue by means of electric pulses. This method has proven highly efficient in transferring, in particular, plasmid DNA to muscles, resulting in long-term expression of the transferred genes. DNA electrotransfer to muscle tissue has clinical potential within DNA vaccination, systemic delivery of therapeutic proteins and correction of gene defects in muscles. In the recent years, DNA electrotransfer to muscle tissue has reached clinical advancement with 8 on-going clinical trials. In the present review, I will draw on the experiences obtained from the clinical studies, in understanding the mechanistic and practical advantages and limits of muscle electrotransfer. The effect of applying electric pulses to muscle tissue will be described in details, while present and future clinical applications are reviewed.

Small interfering RNAs (siRNA) are one of the most recent additions used to silence gene expression. At present, siRNA is the most extensively used gene-silencing technique over other nucleic-acid based approaches to treat diseases including cancer, hepatitis, respiratory disease, cardiovascular diseases, neuronal disease and autoimmune disease. However, systemic delivery of siRNA remains to be the biggest challenge to be overcome. Various strategies have been developed to deliver siRNA efficiently into target cell such as chemical modification of siRNA, physical strategies, viral and non viral-vectors mediated delivery. Among all the approaches non viral vectors including lipoplexes, polyplexes and inorganic nanoparticles were found to be most successful which have been reviewed in this article. Further therapeutic applications of RNAi have also been briefly reviewed.

Acute liver failure (ALF) is a life-threatening medical emergency and occurs when the liver rapidly loses its function within a short period. ALF can develop secondary to a variety of causes. Currently, the orthotopic liver transplantation is the “Gold Standard” therapy for the disease. However, due to the limited availability of donor organs and rapid progression of the disease, the mortality of ALF remains high. Therefore, it is imperative to develop novel therapeutic reagents for ALF. Gene therapy by delivering a target gene to the patients appears to be a promising approach for the treatment of ALF. Here, we review the recent advance of gene therapy for ALF, focusing on the three technical elements, animal models, vehicles for gene delivery and technique for gene delivery, which are important for the success of gene therapy as well as the potential targets used for the treatment of ALF.