Gene Therapy
Genetic Therapeutics
Introduction to Gene Therapy
Gene therapy has potential to treat many disorders
o Inherited diseases- e.g. Cystic Fibrosis
o Cancers
o Infectious diseases
o Immune disorders
What do we meant by gene therapy?
Definition
Describes any procedure intended to treat or alleviate disease by genetically modifying cells of patient
Method of gene therapy can include- use of DNA, RNA or oligonucleotides
Categories of Gene Therapy
There are two broad categories of gene therapy:
Germ line cells- genetically modified to produce permanent modification
o This can be transmitted to descendants
o Its achieved by modifying DNA of gamete (egg or sperm), zygote, or early embryo
o Germ-line therapy is banned in humans for ethical reasons
Somatic cells- genetically modified
o Somatic cells are any adult cells that isn’t gametes, germ cells or stem cells
o This seeks to modify specific cells or tissues of patient in a way that its not passed on and is confined only to
that patient
Somatic Cell Gene Therapy: Strategies
Cells that are targeted are typically cells that are involved in pathogenesis of disease
There are usually two strategies:
1. Modify disease cells to alleviate disease
2. Selectively kill disease cell
Strategy can depend on type of mutation in disease cells
Strategy 1- modifying disease cell can include gene augmentation, gene silencing or repair of mutant gene
Gene Augmentation
Gene augmentation- where functional copied of gene are added back into
cells that lack it
Works well if disease is caused by loss of function mutation
Gene Silencing
Gene silencing- where expression of gene is selectively inhibited
Useful if gene being expressed is harmful
o E.g. gain of function mutation
Can be achieved by turning off transcription of harmful gene- leading to
gene silencing
Gene Repair
Strategy involves trying to repair gene mutation
Restore normal gene function or to minimise effect of
mutation
Selectively killing
diseased cells
Directly kill disease causing cells
, o Involved directly targeting harmful cells with gene that will kill them- called
suicide gene
Targeting disease cells in more INDIRECT way- assisted killing- where immune system
is modified to enhance its response to disease cells and initiate cell death
Gene Transfer
Gene transfer relies on delivery of genetic material into
patient
Identifying best delivery mechanism possible for cell types being targeted
Two general approaches for gene transfer:
o In-vivo- direct delivery
o Ex-vivo- cell-based delivery
Gene transfer in different cell types
Challenge to gene therapy- life span of cells being
targeted
o Some cells are much shorter lived than others
Short lived cells- need to divide to replenish last cells and genetic material being used
for gene therapy might not be passed onto newly divided cells
o Consequence- loss of therapeutic effectiveness
Long lived cells- non-dividing; genetic information isn’t lost
o Consequence- easier to treat that short lived cells
But, therapeutic effect still depends on efficiency of transferring therapeutic genetic material into cells
Technology of Gene Therapy
Gene transfer- potential of this technique to treat disease relies on method to get DNA into patient cell
o Non-toxic
o Target DNA to particular cells
o Introduce DNA into cell in transcriptionally active form
o Express gene at reasonable level for sufficient time
DNA must be packaged in delivery vehicle
Non-viral
o Liposomes
Viral
o Retrovirus
o Lentivirus
o Adenovirus
o Adeno-associated viruses
Liposomes
Liposomes contain therapeutic gene
Take up into cell via endocytosis or clathrin coated pits
DNA avoids degradation by lysosomes and is taken up into nucleus
Once in nucleus, gene needs to be expressed
Plasmid Expression Vector
To achieve high levels of expression gene must be placed into plasmid
expression vector
Genetic Therapeutics
Introduction to Gene Therapy
Gene therapy has potential to treat many disorders
o Inherited diseases- e.g. Cystic Fibrosis
o Cancers
o Infectious diseases
o Immune disorders
What do we meant by gene therapy?
Definition
Describes any procedure intended to treat or alleviate disease by genetically modifying cells of patient
Method of gene therapy can include- use of DNA, RNA or oligonucleotides
Categories of Gene Therapy
There are two broad categories of gene therapy:
Germ line cells- genetically modified to produce permanent modification
o This can be transmitted to descendants
o Its achieved by modifying DNA of gamete (egg or sperm), zygote, or early embryo
o Germ-line therapy is banned in humans for ethical reasons
Somatic cells- genetically modified
o Somatic cells are any adult cells that isn’t gametes, germ cells or stem cells
o This seeks to modify specific cells or tissues of patient in a way that its not passed on and is confined only to
that patient
Somatic Cell Gene Therapy: Strategies
Cells that are targeted are typically cells that are involved in pathogenesis of disease
There are usually two strategies:
1. Modify disease cells to alleviate disease
2. Selectively kill disease cell
Strategy can depend on type of mutation in disease cells
Strategy 1- modifying disease cell can include gene augmentation, gene silencing or repair of mutant gene
Gene Augmentation
Gene augmentation- where functional copied of gene are added back into
cells that lack it
Works well if disease is caused by loss of function mutation
Gene Silencing
Gene silencing- where expression of gene is selectively inhibited
Useful if gene being expressed is harmful
o E.g. gain of function mutation
Can be achieved by turning off transcription of harmful gene- leading to
gene silencing
Gene Repair
Strategy involves trying to repair gene mutation
Restore normal gene function or to minimise effect of
mutation
Selectively killing
diseased cells
Directly kill disease causing cells
, o Involved directly targeting harmful cells with gene that will kill them- called
suicide gene
Targeting disease cells in more INDIRECT way- assisted killing- where immune system
is modified to enhance its response to disease cells and initiate cell death
Gene Transfer
Gene transfer relies on delivery of genetic material into
patient
Identifying best delivery mechanism possible for cell types being targeted
Two general approaches for gene transfer:
o In-vivo- direct delivery
o Ex-vivo- cell-based delivery
Gene transfer in different cell types
Challenge to gene therapy- life span of cells being
targeted
o Some cells are much shorter lived than others
Short lived cells- need to divide to replenish last cells and genetic material being used
for gene therapy might not be passed onto newly divided cells
o Consequence- loss of therapeutic effectiveness
Long lived cells- non-dividing; genetic information isn’t lost
o Consequence- easier to treat that short lived cells
But, therapeutic effect still depends on efficiency of transferring therapeutic genetic material into cells
Technology of Gene Therapy
Gene transfer- potential of this technique to treat disease relies on method to get DNA into patient cell
o Non-toxic
o Target DNA to particular cells
o Introduce DNA into cell in transcriptionally active form
o Express gene at reasonable level for sufficient time
DNA must be packaged in delivery vehicle
Non-viral
o Liposomes
Viral
o Retrovirus
o Lentivirus
o Adenovirus
o Adeno-associated viruses
Liposomes
Liposomes contain therapeutic gene
Take up into cell via endocytosis or clathrin coated pits
DNA avoids degradation by lysosomes and is taken up into nucleus
Once in nucleus, gene needs to be expressed
Plasmid Expression Vector
To achieve high levels of expression gene must be placed into plasmid
expression vector
