Study Gene Therapy Flash Cards

 
Pile Management Card
Gene Therapy

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• Liposomes
– No limit to the amount of DNA that can be packaged
– Lipid-based, similar to cellular membrane
– Not specific, but does not enter cells as effectively as viral vectors
– Not immunogenic, but may be toxic
– Needs to be integrated to allow DNA to integrate
– May be best suited for ex vivo therapies

-no size limit
-no immune reponse b/c no proteins
-can't replicate/recombine so less risk of infectious form
-hard to infect in vivo
-inefficient
-can't target tissues
• Adeno-associated virus
– Does not cause illness
– Dividing and resting cells
– Can target specific cells
– 90% integration into chromosome 19
– Usually no immune response
– Max capacity 5 kb

-small amt DNA allowed
-no viral genes
-safe
-non-dividing cells
-stable expression
-labor-intensive
• Adenovirus
– Both dividing and resting cells
– Can target specific types of cells
– Does not integrate into DNA
– Causes immune response
– Max capacity 7.5 kb

-responsible for respiratory infections
-efficient
-high titer
-don't integrate into DNA
low level of viral antigens produces robust immune response that eliminated transduced cells
-delete viral genes that are most immunogenic?
-but, there will always be some level of immunity
• Retroviral vectors
– Target actively dividing cells
– RNA must be converted to DNA before activation
– Random integration
– Causes immune response
– Max capacity: 8 kb

-only transduce dividing cells
-but, most in vivo cells are quiescent!
-but, low titer
Jesse Gelsinger
partial OTC deficiency
Rhys Evans
SCID
• Allogeneic transplants
-stem cells received from brother, sister or parent, or, if necessary, and unrelated donor.
• Syngeneic transplants
patients receive
stem cells from their identical twin
• Autologous transplants
- patients receive their own stem cells
3 Graft Types
Autologous transplant
Syngeneic transplants
Allogeneic transplants
Hematapoietic Stem Cells
• Different from embryonic stem cells
• Found in bone marrow, blood and
umbilical cord blood
• Can mature into three types of blood cells
– White blood cells
– Red blood cells
– Platelets
• Naked DNA
– Plasmid
– Some cells will take up, but not specific
– No maximum
– Little or no integration
– No immunogenicity or toxicity
– Best for ex vivo
Viral Vectors for Gene Therapy
-Retroviral vectors
-Adenovirus
-Adeno-associated virus
-Herpes simplex virus
• Herpes simplex virus
– Targets nervous cells
– Will not integrate, but can remain episomal, will be copied and passed on
– Causes immune response
– Max capacity 20 kb
First gene therapy approval
(1990)- Ashanti de Silva
-ADA deficiency
ADA deficiency
• Adenosine deaminase (ADA) deficiency
-one form of SCID (severe combined
immunodeficiency)
• Adenosine deaminase breaks down a toxic substance, deoxyadenosine
• Autosomal recessive disease (inherit one copy from each parent)
• Most babies die within months
• rare
Nonviral Vectors
-Liposomes
-Naked DNA
SCID patients (bubble boy)
-gene therapy was successful, but 2 patients got leukemia due to improper integration of gene
Jesse Gelsinger
rare liver disorder, died in 1999 as
a result of immune response to gene therapy
Problems w/gene therapy in the past
-delivery method
-activation of gene expression
– Introducing gene in correct cells
– Immune response (Jesse)
– Disrupting other important genes (bubble boy)
• In vivo versus ex vivo therapies
– In vivo- cells are treated in patient’s body
– Ex vivo- cells are removed, treated and put back into patient
• Necessary components of Gene Therapy
– Target the appropriate cells/tissues
– Activate gene expression
– Integrate the gene into the DNA
– Avoid harmful side effects (immune response)
• Gene inhibition therapy
– Infectious diseases, cancer & inherited disorders
– Gene product inhibits or interferes w/defect
• Gene augmentation therapy
– Inherited disorders caused by loss of function
– Only if effects are reversible
Types of Gene Therapy
• Killing of specific cells (like cancer)
• Somatic and germ line therapy
• Gene augmentation therapy
• Gene inhibition therapy
How is gene therapy used to treat disease?
-A normal gene is inserted into a nonspecific location to replace nonfunctional gene.
– A normal gene may be swapped for an abnormal copy through homologous recombination
– Abnormal gene can be repaired
– The regulation of gene could be altered
Gene Therapy
– Technique for correcting defective genes responsible for disease development
Level 3 Genetic Disorder
-Multifactorial disorders
– Mutations in multiple genes, often w/
environmental factors (many cancers, alzheimer
Level 2 Genetic Disorder
-Chromosomal abnormalities
– Entire chromosomes or large segments are missing, duplicated or altered (ex: Down syndrome, cri-du-chat)
Level 1 Genetic Disorder
-Single gene disorders
– Mutation results in protein product being altered or missing (ex: ADA, SCID, Huntingdon’s disease, cystic fibrosis)
Modes of Inheritance
• Dominant
• Recessive
• X-linked recessive
• X-linked dominant
• Y-linked
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