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What is Gene Therapy, and what are its advantages ?

Gene therapy is a novel approach to deal with various diseases. A simple explanation of Gene Therapy: Introduction of the functional gene into the effective cell which produces sufficient amount of appropriate protein encoded by transferred gene. The field of Gene Therapy is still a developing field in the world of medical science.

Three main strategies in gene therapy:-
1. Gene addition
2. Usage of antisense nucleotide or ribozymes
3. Control of gene expression

Why gene therapy over drug therapy?
• Reinstate dysfunctional gene with functional gene
• Continuous secretion of therapeutic protein
• Cell specific

Types of gene therapy:-
Somatic cells:-
When a morbid somatic cell is cured by changing the gene expression. The genetical changes that take place do not get transferred into the succeeding generation.
Germ Cells:-
The aim of the Germ line gene therapy is to transfer the genomic changes to the offspring.

Although plans of conducting it on larger animals and humans has not been executed. There is a misconception that it has already been put into practice widely but actually the genetic information are just being used for selection of eggs/sperms, no alteration has taken place.

Two main approaches:-
• Ex-Vivo Approach is used for the cells that can be re-implanted. They are taken out of the human body, transgened and introduced into the cell which is reset in the body.eg: lymphocytes, fibroblasts, myoblasts, umbilical cord blood, stem-cells etc.
• In-Vivo Approach in which transgene is commenced into the objective cell to comprehend the working of the gene therapy and help reassess the facts about human genes and gene delivery technique.

Fundamentals of gene therapy are:-
1. Identification of disease causing gene
2. Cloning of the gene
3. Gene mutation identification
4. Detection of gene expression and protein function
5. Gene transfer efficacy and safety testing system. It makes sure transgenes have all the components mandatory for transcription, translation and RNA polyadenylation.

Methods of gene Therapy:

The vector that is introduced should be non immunogenic and safe. The following methods are used :-
– PHYSICAL:- Parental injections, micro-injections, aerosol, electroporation (high voltage current passed to the target cell to produce pores through which transgene enters the cell) and gene guns.
– CHEMICAL:- Calcium phosphate, DEAE-dextran, liposomes and lipoplexes (for oral delivery of gene), surfactants and perflurochemical liquids for aerosol delivery of gene.
– VIRAL VECTORS:- advantageous over the other two:-
a) More specific
b) Single dose is sufficient
DISADVANTAGES:-
a) limited packaging capacity
b) unknown long term physiological effects
c) risk of immunological activation
d) regeneration of wild type of virus
examples of vectors:- retro virus, adeno-virus, herpes simplex virus etc.

Other advancements:-

– NEW ORGAN TRANSPLANT OR TISSUE IMPLANT:-
Used in the treatment of lysosomal storage disease
– HUMAN ARTIFICIAL CHROMOSOME:-
Laboratory engineered chromosome consisting of all mandatory information
– RECEPTOR MEDIATED DELIVERY
DNA of particular size is transferred to a specific receptor cell as ligand to deliver transgene
– VIRALLY DIRECTED ENZYME PRODRUG THERAPY:-
Vector is expressed only in tumour cells not in normal cells.
– THERAPEUTIC ANTISENSE AND RIBOZYMES:-
Consisting of the use of oligonucleotide sequences that are complimentary to a gene that has to be inhibited by forming triplex with the regulatory component of chromosomal DNA or by complexing a region of mRNA.

Gene vaccines:-
DNA vaccine can stimulate cell mediated and humoral immunity. However there are risks of provocation of autoimmune response and insertional metagenesis.
We hope that clinical trials of 20th century may become a clinical reality in 21st century and we can fight fatal genetic disorders in a better way.

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