GENE THERAPY - Molecular Biology

8/9/2019 GENE THERAPY - Molecular Biology

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GENE

THERAPY


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INTRODUCTIONA Brief History

1980s - Gene therapy studies began with the introduction ofhuman genes into bacterial plasmid (e.g. for production ofinsulin)

1990 1st

approved experiment on human: DNA in white bloodcells of 4 yr-old girl with severe immunodeficiency syndrome(SCID) inserted with missing generesulted in strengthenedimmune system.

2002 Gene therapy methods repair errors in mRNA derivedfrom defective genes

2003 Blood-brain barrier crossed by genes (too large to passalone) via liposomes containing the inserted genes; major step inParkinsons disease research

2006 Immune system is prevented from rejecting newlydelivered gene; Killer T cells retargeted to attack cancer cellssuccessfully used as treatment for 2 patients with metastatic

melanoma


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WHAT

ISGENE THERAPY? It is the alteration, substitution, or insertion of a

gene into an individuals cells and tissues totreat a disease that involves one or moredefective mutant alleles

The defective gene is manipulated to produce aprotein that changes the function of those cells,consequently eliminating the root cause of thedisease.

It is not an approved medical therapy But it has been approved in more that 400

clinical trials for diseases such as cystic fibrosis,emphysema, adenosine deaminase deficiency,and some cancers.


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More on GENE THERAPY If it is successful, gene therapy provides a

way to fix a problem at its source.

Gene therapy differs from traditional drug-based approaches, which may treat theproblem, but which do not repair theunderlying genetic flaw.

But gene therapy is not a simple solution -it's not a molecular bandage that willautomatically fix a disorder.


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The Discovery of Gene Therapy

Gene therapy is commonly thought of as a new theorythat was introduced to the public only recently, but in

reality, it goes back several decades.

It was first shown (by Avery, McLeod, and McArthy) thata gene can be transferred within nucleic acids in 1944.Later, the ability of viruses to transmit genes (inSalmonella) was first demonstrated in 1952.

Speculations of gene therapy were made by variousscientists, including Tatum in his 1966 speech in NewYork.


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The Discovery of Gene Therapy(Contd)

Among the first animals to undergo gene therapy werePeking ducklings, which were injected with DNA extractfrom Khaki Campbell ducks; all the characteristics found

in the Peking ducklings that were injected with KhakiCampbell duck DNA were passed onto their offspring.

The first attempt ofgene therapy on human beings wasdone in the 1960s by S. Rogers; he injected a virus intothree patients with arginase deficiency hoping to raisearginase levels higher. Because of different results fromother scientists, much debate was debated about thepatients arginine levels, but concluded that the patientslevel of arginine did not change with the use of theShope papilloma virus. Successful attempts on humanbeings were made subsequent to this experiment.


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Types of Gene Therapy 2 main types exist: somatic-cell therapy &

germ-line therapy Somatic-Cell Therapy: genetic malfunctions in

body cells are repaired; alterations occur only intreated individuals and do not affect offspring;performed on humans ex vivo: cells are modified outside the body and then

transplanted back in again in vivo: genes are changed in cells still in the body

Germ-Line Therapy: gametes are altered totreat inherited diseases; alterations affectunborn individuals and are passed on to the nextgeneration; not yet performed on humans


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How Gene Therapy is Accomplished

Using a Retrovirus: Genes in virus that cause leukemia in mice (but do not affect

humans) are removed and replaced with RNA copy of healthygene; promoter is added to turn on gene to produce protein;however, genes are prone to insertion at wrong site

Using an Adenovirus: Disease-causing gene is removed from virus and replaced with

healthy (but impermanent) genes; works in more cell types thanretroviruses

Using the Herpes Simplex Virus: More than one therapeutic gene may be inserted; infects wide

variety of tissues, but is cytopathic and may cause encephalitis Using Lipoplexes:

Plasmid DNA complexed to liposome (forms lipoplex); cationiclipids of liposome allow interaction with plasma membrane thatfavors endocytosis so that DNA is easily taken in the cell


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An Example of a

GENE THERAPY PROCEDURE

In one type of genetherapy, geneticallyengineered virusesare used to insertnew, functioninggenes into the cells ofpeople who are unableto produce certainhormones or proteinsnecessary for thebody to function

normally.


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Gene Testing(May Be Required Prior to Gene Therapy)

An individual must be confirmed to have a geneticdisorderto undergo gene therapy

Accurate diagnosis of the genetic defect can be made

by one of the following methods: Scientist can scan a patient's DNA sample (e.g. from blood) formutated sequences using probes to seek complement basesamong the three million human base pairs, bind to it and flag themutation

The sequence of DNA bases in a patients genome can be

compared to the normal version of the gene Disease can be pinpointed rapidly using gene testing

Cost of testing can range from hundreds to thousands ofdollars ($US), depending on the sizes of the genes andthe numbers of mutations tested.


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The Key to Gene TherapyI. Choosing a Good Candidate for Therapy

1. The disorder must result from the mutation of1 ormore gene.

2. Know the genes involved and know biology of

disorder, e.g. role of encoding protein.3. Have available the normal gene.4. Normal gene should be able to fix the problem and

be readily delivered to affected tissue.

II. Successful Delivery of Gene1. The right cells are targeted.2. The gene is activated.3. The gene is integrated in cells.4. Harmful side effects are avoided.


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What is Gene Therapy Used For? Gene therapy is used to

treat inherited diseasesand conditions that arecaused by genetic defects.

Because this techniquehas not yet beenapproved, it is not anestablished treatment forany disease.Improvements in the

techniques and furtherresearch in this area aimfor it to be used in medicaltherapy.

Some Diseases Targeted in Gene Therapy Alzheimer's disease

Gaucher disease

Cystic fibrosis

Hemophilia A and B Hereditary Hemochromatosis

Huntington's disease

Phenylketonuria

Sickle cell disease

Spinal muscular atrophy

Tay-Sachs Disease


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CONCLUSIONExpectations for Gene Therapy

Scientists expect that within the first decades of the 21stcentury, gene therapy will offer unprecedentedopportunities to treat, cure, and ultimately prevent a vastrange of diseases.

Gene therapists hope to reduce or eliminate the geneticsusceptibility to conditions such as heart disease,diabetes mellitus, arthritis, and Alzheimer's disease.

Eventually, gene therapy might help older people toregain strength in withered muscles and density inthinned bones, and to increase pumping power in their

aging hearts. Some researchers predict that in the distant future gene

therapy technology could be used to eliminate geneticdefects from families or even to produce designerbabies with more muscle strength, higher intelligence,sweeter dispositions, or whatever traits parents desire.


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Gene therapy originally aimed to replace a healthy genefor a defective one, or to repair a faulty gene, therebyeliminating symptoms of disease. Today, however, genetherapy has applications beyond inherited geneticdisorders. Approximately, 75% percent of all clinical trialsinvolving gene therapy are now aimed at treatments forcancer and acquired immunodeficiency syndrome(AIDS), two devastating diseases whose cures are yet tobe discovered.

Continued studies in gene therapy will increaseknowledge in the field of genetics and will bring furtherlight to the manipulation of genes to improve health.

CONCLUSION(Contd)


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REFERENCES U.S. Dept. of Energy. Gene Testing. 19 April 2007.

Yang, Steven. History of Gene Therapy. 17 April 2007.

Noguchi, Phillip. Risks and Benefits of Gene Therapy.19 April 2007..

Rocholl, Brandi.Gene Therapy: RevolutionizingMedicine. 20 April 2007.

Wikimedia Foundation. Gene Therapy. 23 April 2007.

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