Gene therapy Flashcards
What is gene therapy?
novel approach to teating diseases baseed on modifying the expression of a person’s genes toward a therapeutic goal
What is somatic gene therapy?
involves the manipulation of gene expression in cells so as to be corrective for the patient, but this correction is not inherited by the next generation
What is germline gene therapy?
involves genetic modification of germ cells that will pass the seleccted change on to the next generation
What is required for gene identification and cloning?
must have identified the gene (genes) responsible for a particular disease state and have demonstrated concordance of disease state with a defect in the particular gene or gene product
What is the first task of any gene therapy strategy?
delivery of genetic material to the appropriate cells of patients in a way that is specific, efficient and safe
What is an ex vivo strategy of gene therapy?
cells are removed from the body and treated with a gene vector that take up the selected gene then reintroduced back into the body
What is the in vivo strategy for gene therapy?
direct injection of viral vector into the body
What was the first ex vivo gene therapy trial used?
ADA deficiency
What was the first in vivo gene therapy used to treat?
treat cystic fibrosis
What are the most widely used indications for gene therapy?
cancer
genetic deficiencies (LPL deficiency)
viral infections
autoimmunity
diseases in which several genes and environment interact
What is the therapeutic strategy for gene therapy applications?
vector carries a gene that encodes a protein that is either defective or that is not present due to mutation(s) in the patients’ endogenous gene(s)
What is the cytolytic strategy for gene therapy applications?
vector is designed to destroy or eliminate a diseased cell or tissue
example=> virus carrying the gene for thymidine kinase from herpes simplex virus
What is the drawback from the cytolytic strategy?
difficulty in targeting the specific cell
Delivery of gene therapy requires vectors. What are the most important factors?
most vectors are based on attenuated or modified versions of viruses => challenge to remove the disease-causing components of virus and insert recombinant gene
utiliz non-viral vectors => a) liposome transfection, b) gene gun technology
What is important about controlling gene expression?
making the correct amount of therapeutic protein at the right time
maintaining long-term expression of the gene
What is important wrt the host immune response and gene therapy?
use of vectors that give minimal or no adverse immune resonses
ability to give multiple doses of vector
For vector systems, what are the properties of adenovirus?
episomal
high transduction effeciency
infects replicating and non-replicating cells
elicits an immune response
insert capacity 8-36kb
What are the properties for adeno-associated virus vectors?
integrates genome into specific region on human chromosome 19
low immunogenicity
no associated disease
infects dividing and non-dividing cells
limited insert capapcity of 5kb
What are properites of herpesvirus vector?
large insert capacity
broad host range
infects dividing and non-dividing cells
What is the liposomes/naked DNA virus vector?
no liit to size of genes that can be delivered
low immunogenicity
poor levels of gene transfer
What is the properties of the retrovirus vector?
non-pathogenic in humans
stably transduces dividing but not non-dividing cells
inserts genome into host cell’s DNA
long term expression
insert capacity of 8kb
inactivated by human complement
How is a retrovirus used?
- reverse transcriptase codes RNA back to DNA
- integrase integrates DNA into host chromosome
only dividing cells
How is a adenovirus used?
is uses DNA but does not integrate into the host chromosome
both dividing and non dividing cells
How do you make a retroviral vectors?
insert packaging signal in viral genome (virus must be killed after delivery)
gene is placed on a plasmid onto a packaging cell line to finally get a producer cell
what are the most used viral vectors?
adeno virus and retroviruses
What are the steps to initiate a gene therapy trial?
involves internal institutional reviews
external government reviews
What are problems that must be solved before gene therapy can be used?
avoid immune response in patient (inflammation or Abs)
get genes into non-diving cells like liver, muscle, neurons
get gene integrated so that it will be replicated and expressed indefinitely as needed
Describe adeno-associated virus (AAV)
often found in cells that are simultaneously infected with adenovirus
generally harmless
What are the main ways that AAV is not like adenovirus?
does not stimulate inflammation in host
does not elicit Abs against itself
integrates ssuccessfully into one spot in genome of host (chromosome 19 in humans)
can enter non-dividing cells
What are factors influencing future development of gene therapy?
optimizing vector safety to reduce adverse event risks
overcoming the technlogical obstables
analysis of human genome
expansion of diagnostic industry
public acceptance of gene therapy
