Gene therapy is when DNA is introduced into a patient to treat a genetic disease. The new DNA usually contains a functioning gene to correct the effects of a disease-causing mutation.
The process of gene therapy includes many approaches like:
- Replacing of mutated gene (work incorrectly or no longer work at all) with copy of healthy gene
- Inactivating, or “knocking out,” a mutated gene that is functioning improperly.
- Introducing a new gene into the body which helps to fight against disease.
There are number of diseases which are probably treated with the help of gene therapy includes: inherited disorders, some types of cancer, and certain viral infection.
A gene that is introduced directly into a cell usually does not function. Instead, a genetically engineered carrier called vector is used to deliver the gene. Viruses are often used as vectors because they can deliver the new gene by infecting the cell. The viruses needs to be modified so that they can’t cause disease when used. Depending upon the cell cycle of the virus, some types of virus, such as retroviruses, integrate their genetic material including the new gene (going to insert) into a chromosome in the human cell. Other viruses, such as adenoviruses, introduce their DNA into the nucleus of the cell, but the DNA is not integrated into a chromosome.
The introduction of the vector into the body may either by intravenously directly into a specific tissue in the body, after which it is taken up by individual cells or Exposure of the removed patient’s cells sample to the vector in a laboratory setting. The transformed cells containing the vector are then returned to the patient. If the process of those transformation become successful, the new gene delivered by the vector will make a functioning protein.
The introduction of DNA into cells can be done by various methods. The two major classes are recombinant viruses (viral methods) and naked DNA or DNA complexes (non-viral methods).
Viruses are not able to replicate by itself and uses the machinery of the host cell. Ex. Rotaviruses, during its life cycle having their genetic material copied into the genome of the host cell. A number of viruses have been used for human gene therapy, including herpes simplex , retroviruses ,adenoviruses, vaccinia, and adeno-associated viruses. Like the genetic material (DNA or RNA) in viruses, therapeutic DNA can be designed to simply serve as a temporary blueprint that is degraded naturally or (at least theoretically) to enter the host’s genome, becoming a permanent part of the host’s DNA in infected cells.
Non-viral methods are designed to have more advantages than viral methods such as large scale production and low host immunogenesity. However, non-viral methods initially produced lower levels of transfection and gene expression, and thus lower therapeutic efficacy. Later technology remedied this deficiency.
Methods for non viral gene therapy
Non viral methods includes the injection of naked DNA by Electroporation, the gene gun, sonoporation, magnetofection, the use of oligonucleotides and inorganic nanoparticles
Electroporation also known as electropermeabilization, is a technique uses electrical field which applied to cells leads to increase in the permeability of the cell membrane due to which chemicals, drugs, or DNA can be easily inserted into the cell.
Electroporation allows cellular introduction of large highly charged molecules such as DNA which would never passively diffuse across the hydrophobic bilayer core.
The gene gun method: the method is also known as biolistic method. In this technique the particles are coated with small DNA Sequences. The particles are delivered to the cells by the use of device. The gun is fired at the cluster of the cells and the DNA Sequences enter to the desired cell.
Magnetofection is simple and highly efficient method to transfect cells in culture. It is novel technique used magnetic field applied to the gene vectors which are associated with magnetic particles leads the vectors forced into the target cells. In this way, the vectors applied gets exposed on the cells within a few minutes due to which 100% of the cells get in contact with a significant vector. This has several important consequences:
- Increased rate of transfection as compare to other standard way of transfection.
- At short-term incubation high level of increase of transgene expression compared to standard transfections.
- The low vector doses are required to achieve High transfection rates and transgene expression which allows to save expensive transfection reagents.
- The time required for the process is very low. At short process time of incubation of cells high transfection efficiency has been generated compared to several hours with standard procedures.
Sonoporation, or cellular sonication, is the use of sound of ultrasonic frequencies which enhance the permeability of the cell plasma membrane. This technique is usually used for non-viral gene therapy in order to allow uptake of large molecules such as DNA into the cell, in a cell disruption process called transfection or transformation. Sonoporation leads to the acoustic cavitation of microbubbles to enhance delivery of these large molecules. The bioactivity of this technique is similar to, and in some cases found superior to, electroporation. Extended exposure to low-frequency (<MHz) ultrasound has been demonstrated to result in complete cellular death (rupturing), thus cellular viability must also be accounted for when employing this technique.
Use of nanoparticles : to cure the genetic and acquired diseases in human the most important step is gene delivery in case of gene therapy.
The vector used for gene delivery must possess high transfection efficiencies and low cytotoxicity.On this base, the investigations on non-viral gene vectors with the ability to overcome physiological barriers are increasing. Among the non-viral vectors, nanoparticles showed remarkable properties regarding gene delivery such as the ability to target the specific tissue or cells, protect target gene against nuclease degradation, improve DNA stability, and increase the transformation efficiency or safety.
Use of synthetic oligonucleotides: In gene therapy is to inactivate the genes involved in the disease process. One method of use of antisense which is specific to the target gene help to disrupt the transcription of the faulty gene. Other method is uses of small molecules of RNA called siRNA to signal the cell to cleave specific unique sequences in the mRNA transcript of the faulty gene, disrupting translation of the faulty mRNA, and therefore expression of the gene.