diraj gene therapy final
TRANSCRIPT
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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
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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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