GENE THERAPY

What is Gene Therapy?• It is intracellular delivery of genes to

generate a therapeutic effect by correcting an existing abnormality.

• The Human Genome Project provides information that can be used to help replace genes that are defective or missing in people with genetic diseases.

What is the outcome of gene therapy?

1. GENE AUGMENTATION THERAPY

2. TARGETED MUTATION CORRECTION

3. INHIBITION OF GENE EXPRESSION

4. GENE THERAPY TO ACHIEVE PHARMACOLOGICAL EFFECTS

STEPS IN GENE THERAPY1. Identification of the defective gene.

2. Cloning of normal healthy gene.

3. Identification of target cell / tissue / organ.

4. Insertion of the normal functional gene into the host DNA.

METHODS OF GENE DELIVERY 1. PHYSICAL METHODS: -Parenteral injection -Microinjection -Aerosol -Gene gun

2. CHEMICAL METHODS: -Calcium phosphate

-Liposomes 3. BIOLOGICAL METHODS: Viral Vectors like -Retrovirus -Adenovirus -HSV

• METHODS OF GENE DELIVERY contd…

4. NEO-ORGAN IMPLANTS 5. TISSUE TRANSPLANTATION 6. HUMAN ARTIFICIAL CHROMOSOMES

How to introduce the genes ?

Two Approaches to deliver genes: 1. Ex vivo approach 2. In vivo approach

1. Ex vivo approach: -Target cells are removed from the body and grown

in vitro. -The gene is then introduced into the cultured cells. -These cells are then re-introduced into the same

individual -Examples: Fibroblast cells, Hematopoietic cells.

IN -VIVO

2. In vivo approach:(Direct GeneTransfer) -Cloned therapeutic gene is introduced

directly into the affected tissue, without removing cells from the body.

-Specially designed vehicles are needed. -Examples are: Lungs, Brain

Where to introduce the genes ?

Somatic cells or the Germ line cells are the cells to accept the introduced genes.

TYPES OF GENE THERAPY:

1. SOMATIC CELL THERAPY 2. GERM LINE THERAPY

1.SOMATIC CELL THERAPY:

• Insertion of therapeutic gene into somatic cells like fibroblasts,myoblasts,epithelial cells, nervous cells,glial cells etc.

• This can correct the genetic defect in the patient

• However,in somatic cell therapy, Transgene cannot be passed on to the siblings etc.

2. GERMLINE THERAPY:

• Introduction of the foreign gene into germ cells like sperm / ovum / fertilized egg.

• Results in expression of modified features in both somatic as well as germ cells of the offspring.

• Considered unethical, and is not advocated in humans.

COMMON VECTORS USED FOR GENE THERAPY:

• 1.Retro viruses

• 2. Adeno viruses

• 3. Liposomes

3.LIPOSOMES:• These are lipid bilayers surrounding an aqueous

vesicle.• Can be used to introduce foreign DNA into a target

cell.

Advantages:• Safer when compared to Viral vectors.• Can carry large DNA molecules.

Disadvantages:• Inefficient transfer.• Transient expression.

Accomplishments of Gene Therapy• Severe combined

Immuno deficiency (SCID)- It is caused by the deficiency of adenosine Deaminase enzyme. The first trial of gene therapy was done on this disease. Follow up studies show the presence of normal immune functions in recipients compatible with life.

Some results of gene therapy:

1. Severe Combined Immuno Deficiency:

Adenosine Deaminase deficiency: First attempt at gene therapy.

2. Hemophilia A & Hemophilia B: -Ex vivo method using fibroblasts -Clinical improvement was present.

3. Cystic Fibrosis: -In vivo trials with Transmembrane Conductance

Regulator CFTR.

Targets for gene therapyGenetic disorders –

1) Duchenne Muscular dystrophy2) Cystic fibrosis3) Familial hypercholesterolemia4) Hemophilia5) Haemoglobinopathies6) Gaucher’s disease7)Albinism8) Phenyl ketonuria.

Acquired diseases• Cancers• Infectious disease- HIV• Neurological disorders• Cardiovascular diseases• Rheumatoid arthritis• Diabetes mellitus

RISKS OF GENE THERAPY

• 1.Adverse reactions due to the virus or new genes.

• 2.Activation of proto-oncogene leading to formation of oncogene.

• 3.Introduction of a mutation to the next generation.

GENE THERAPY (Summary)• Steps in Gene therapy• Approaches: - Ex-vivo -In-vivo• Types:

-Somatic cell therapy -Germ line therapy

• Methods of delivery:-Physical -Chemical -Biological etc etc

• Strategies.