Vectors in gene therapy

More than twenty patients have been treated in France and Britain, with a high rate of immune system reconstitution observed.

Gendicine, an adenoviral p53-based gene therapy was approved by the Chinese food and drug regulators in 2003 for treatment of head and neck cancer.

Advexin, a similar gene therapy approach from Introgen, was turned down by the US Food and Drug Administration (FDA) in 2008.

[4] Concerns about the safety of adenovirus vectors were raised after the 1999 death of Jesse Gelsinger while participating in a gene therapy trial.

CMV's tropism for hematopoietic progenitor cells and its large genome (230 kbp) initially attracted researchers.

[6] More recently, CMV containing telomerase and follistatin was intravenously and intranasally delivered in mouse studies with the intention of extending healthspan.

It was found that in the absence of the E1B-55Kd viral protein, adenovirus caused very rapid apoptosis of infected, p53(+) cells, and this results in dramatically reduced virus progeny and no subsequent spread.

These are denominated cis-acting elements, because they need to be on the same piece of DNA as the viral genome and the gene of interest.

The wild type HSV-1 virus is able to infect neurons and evade the host immune response, but may still become reactivated and produce a lytic cycle of viral replication.

Though the latent virus is not transcriptionally apparent, it does possess neuron specific promoters that can continue to function normally.

[9] Caution for rare cases of encephalitis must be taken and this provides some rationale to using HSV-2 as a viral vector as it generally has tropism for neuronal cells innervating the urogenital area of the body and could then spare the host of severe pathology in the brain.

Clinical trials carried out of intramuscular injection of a naked DNA plasmid have occurred with some success; however, the expression has been very low in comparison to other methods of transfection.

This shock is thought to cause temporary formation of pores in the cell membrane, allowing DNA molecules to pass through.

More recently a newer method of electroporation, termed electron-avalanche transfection, has been used in gene therapy experiments.

Hydrodynamic delivery involves rapid injection of a high volume of a solution into vasculature (such as into the inferior vena cava, bile duct, or tail vein).

However, in spite of the facts that there is little toxicity associated with them, that they are compatible with body fluids and that there was a possibility of adapting them to be tissue specific; they are complicated and time-consuming to produce so attention was turned to the cationic versions.

It was also found that although cationic lipids themselves could condense and encapsulate DNA into liposomes, the transfection efficiency is very low due to the lack of ability in terms of "endosomal escaping".

Polymersomes are synthetic versions of liposomes (vesicles with a lipid bilayer), made of amphiphilic block copolymers.

Advantages of polymersomes over liposomes include greater stability, mechanical strength, blood circulation time, and storage capacity.

As a result, co-transfection with endosome-lytic agents such as inactivated adenovirus was required to facilitate nanoparticle escape from the endocytic vesicle made during particle uptake.

[21] Due to their low toxicity, high loading capacity, and ease of fabrication, polycationic nanocarriers demonstrate great promise compared to their rivals such as viral vectors which show high immunogenicity and potential carcinogenicity, and lipid-based vectors which cause dose dependence toxicity.

In addition to the variety of polymers and copolymers, the ease of controlling the size, shape, surface chemistry of these polymeric nano-carriers gives them an edge in targeting capability and taking advantage of enhanced permeability and retention effect.

When in the presence of genetic material such as DNA or RNA, charge complementarity leads to a temporary association of the nucleic acid with the cationic dendrimer.

The Michigan-based company Dendritic Nanotechnologies discovered a method to produce dendrimers using kinetically driven chemistry, a process that not only reduced cost by a magnitude of three, but also cut reaction time from over a month to several days.

These new "Priostar" dendrimers can be specifically constructed to carry a DNA or RNA payload that transfects cells at a high efficiency with little or no toxicity.

Nanosized materials less than 100 nm have been shown to efficiently trap the DNA or RNA and allows its escape from the endosome without degradation.

Inorganics have also been shown to exhibit improved in vitro transfection for attached cell lines due to their increased density and preferential location on the base of the culture dish.

Quantum dots have also been used successfully and permits the coupling of gene therapy with a stable fluorescence marker.

Examples of cargo molecules of CPPs include nucleic acids, liposomes, and drugs of low molecular weight.

This has been shown to have more efficient gene transfer in respiratory epithelial cells than either viral or liposomal methods alone.