Diraj Gene Therapy Final

8/8/2019 Diraj Gene Therapy Final

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Gene Therapy-a novel

approach to treat diseases

By: Dhiraj kumar Bhuyan

2007V92M
http://images.google.com/imgres?imgurl=peer.tamu.edu/curriculum_modules/Cell_Biology/images/gene.therapy.jpg&imgrefurl=http://peer.tamu.edu/curriculum_modules/Cell_Biology/module_4/whyitmatters.htm&h=196&w=200&sz=13&tbnid=jfUy_-tUS0AJ:&tbnh=97&tbnw=98&prev=/images%3Fq%3Dgene%2Btherapy%26start%3D40%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DN


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What is gene therapy?

Gene therapy is a technique for correctingdefective genes responsible for diseasedevelopment.

The basic definition of gene therapy is altering apersons genes in order to achieve a more desirabletrait

In most gene therapy studies, a "normal" gene isinserted into the genome to replace an

"abnormal,or disease-causing gene.


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Aim Of Gene Therapy

Is to introduce Therapeutic Materialinto Target cells.

Gene therapy typically aims tosupplement a defective mutant allelewith a functional one.

At Present Gene Therapy is still at theclinical research stage.


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Successful gene therapy requires

1. Genetic nature of disease is understood.

2. The affected tissues are known and

accessible.3. Correct gene expression is achieved.

4. Harmful side effects if any are

manageable.


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Naked DNANaked DNATargetTarget

CellCell

TherapeuticTherapeuticProteinProtein

AAVAAV

Retrovirus/LentivirusRetrovirus/Lentivirus

AdenovirusAdenovirus

NucleusNucleus

Gene Therapy Principle


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Types Of Gene Therapy

Germ line gene therapy: Gene therapy can betargeted to germ (egg and sperm) cells.

Somatic cell gene therapy: Gene therapy canbe targeted to somatic (body cells).- most common

three types

1. in vivo2. ex vivo

3. Gene targeting


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In Vivo Gene Therapy

The genetic material is transferred directlyinto the body of patient.

Only available option for tissues that

cannot be grown in vitro; or if grown cellscannot be transferred back.

It is more or less a random process,

require less manipulations. Requires an efficient and selective delivery

system.


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Ex Vivo Gene Therapy

The genetic materialis first transferredinto the cells grownin vitro

Controlled process,transfected cells areselected andamplified

more manipulations.

Cells are usuallyautologous, they arethen returned backto the patient


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in vivo and ex vivo schemes

IN VIVO

EX VIVO


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Methods of gene delivery

(therapeutic constructs)

It Includes two methods:

virus-mediated gene-deliverysystems

nonviral gene-delivery systems


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Non viral gene-delivery

systems

Naked DNA injection

Gene gun

Electroporation

Lipofection


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Naked DNA gene therapy

This is the simplest method i.e. the

direct introduction of therapeuticDNA into target cells.

Very cheap.


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Limitations of naked DNA gene

therapy

This approach is limited as it can

be used only with certain tissues

and requires large amount of

DNA. Results in a prolonged low level

expression


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Microprojectile gene transfer (gene gun)

therapy

Gene guns which shoots

DNA coated gold particles

into the cell using highpressure gas.

Fire particles in cells at

high speed so particles

enter cells. Invented for DNA transfer toplant cells.

Yet not available in human

G f h h
http://www.brown.edu/Courses/Bio_160/Projects2000/RCC/genegun.jpg


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Gene transfer through

Liposomes

Therapeutic drugs

Positively charged lipid droplets can

interact with negatively charged DNA

to wrap it up and deliver to cells.

Inside liposomes DNA is resistant to

degradation and is capable of passing

the DNA through the target cell's

membrane.

Used in cystic fibrosis, cancer,

parkinsons disease.


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Non viral gene-delivery

systems

Advantages: DNA can be of any size

Non-infectious and Cant replicate; no inflammatory

responseDisadvantages: low efficiency

non-specific


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virus-mediated gene-delivery systems

Include Biological vehicles (vectors) such asviruses and bacteria.

Viruses are currently the most efficient means ofgene transfer.

Viruses attack their hosts and introduce theirgenetic material into the host cell as part of theirreplication cycle.


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Some viral vectors used in genetherapy are:

Retroviruses Adenoviruses Adeno-associated viruses

Herpes simplex virus Lentiviruses


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Ideal Viral Characteristics

Insert size:should be large

Targeted: limited to a cell type.

Immune response: none.

Stable: not mutated.

Production: easy to produce highconcentrations.

Regulatable:produce enough protein to makea difference.


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Applications include a variety of

diseases:

Monogenic inherited disease, Cancer,

Cardiovascular disease,

Infectious disease, Autoimmune disease.


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In humans

Cancer 69%


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Genetic Defects that are

Candidates for Gene Therapy


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SCID caused by a number of defects:

Example: ADA (adenosine deaminase) gene

defect.X linked SCID.

Lack of functional lymphocytes.

No T-cell dependent antibody response.

Successful Gene Therapy for

Severe Combine Immunodeficiency


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SCID: Ex vivo gene therapy


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The First Case

The first gene therapy was performed on

September 14th, 1990

Ashanti DeSilva was treated for SCID

Doctors removed her white blood cells,

inserted the missing gene into the WBC, and

then put them back into her blood stream.

This strengthened her immune system


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Gene Therapy Successes

Ashanti de Silvasuccessfully treated for

ADA deficiency - 1990

Ryes Evans successfully

treated for SCID - 2001

Photocourtes

yofVandeSilva


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Gene Therapy Problems

Two boys treated for SCID developed

leukemia due to disruption of a gene that

regulates cell division.

Extremely labour intensive.

Repeated many times to achieve success.


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Cancer gene therapy

Three ways

1. Construcing antisense of oncogene

2. Introducing correct functional version of tumor

suppresser gene

3. Introducing a gene encoding a toxic protein


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Adenovirus p53

First commercially approvedgene therapy product


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Applications For elevated milk production.

Provide nutrition to milk

Mice with a genetically engineered deficiencywhich mimics some human disease.

Methods for Tissue Specific Targeting .

Ad f


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Advantages of gene

therapies

Treatment of a genetic disease at the root of the

problem, at the DNA level.

Potential to treat a disease for which no treatmentis currently available.

Potential for life-long treatment from a single

injection.

Once a treatment for one genetic disease has been

developed, similar diseases should be equally

treatable, using a different disease-specific gene.


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Hurdles In Gene Therapy

Short lived nature of gene therapy

Immune response

Problems with viral vectors

Multigene disorders

Specific scientific knowledge and regulatory

expertise has to be available. Insertional mutagenesis.


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Major Problems that Scientists

Must Overcome

Develope more efficient ways to deliver the genes to the

patients genetic material

Develop vectors that can specifically focus on the targeted cells

Ensure that vectors will successfully insert the desired genes

into each of these target cells

Deliver genes to a precise location in the patients DNA

Ensure that transplanted genes are precisely controlled by the

bodys normal physiologic signals


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Diraj Gene Therapy Final

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