Gene Gene

By Pankaj Kukreti

Therapy

CONTENTS• DEFINITION• TYPES• APPROACH• METHODS• IMPORTANCE• DISEASES• ETHICS• CONCLUSION• REFERENCES

WHAT IS GENE THERAPY ?• Gene therapy is the insertion of genes into an

individual’s cells and tissues to treat A disease, such as A hereditary disease in which A deleterious mutant allele is replaced with A functional one.

TYPES OF GENE THERAPY Germ line gene therapy• In this case, germ cells, i.E., Sperm or eggs are modified by the introduction of functional genes, which are integrated into their genomes.•The change due to therapy would be heritable n would be passed on later generation.

Somatic gene therapy• In this, therapeutic genes are transferred into the somatic cells of a patient.•Any modification and effects will be restricted to the individual patient only, & will not be inherited.

NEED OF GENE THERAPY• To overcome the disease.• Targeting the cells of diseased tissues.• Genes can be inserted into the cells of

patients by direct and indirect routes, and the inserted genes can integrate into the chromosomes or remain extra chromosomal.

STRATEGIES OF GENE THERAPY

• Gene augmentation therapy (GAT).

• Targeted killing of specific cells.

• Targeted mutation correction.

• Targeted inhibition of gene expression.

GENE AUGMENTATION THERAPY

• For diseases caused by loss of function of a gene, introducing extra copies of the normal gene may increase the amount of normal gene product to a level where the normal phenotype is restored.

• Targeted to clinical disorders where the pathogenesis is reversible.

• Applied to autosomal recessive disorders.

DISEASE CELLS

NORMAL PHENOTYPE (increase in gene X product)

GENE X

TARGETED KILLING OF SPECIFIC CELLS

• Popular in cancer gene therapies.• Genes are directed to the target cells and then

expressed to cause cell killing.• Direct cell killing – inserted gene are expressed

to produce a lethal toxin or a gene encoding a prodrug is inserted, conferring susceptibility to killing by a subsequently administered drug.

DISEASE CELLS

DISEASE CELLS

CELLS KILLED BY EXPRESSED TOXIN

CELLS KILLED BY DRUG

DIRECT KILLING OF DISEASE CELLS

PRODRUG GENE

TOXIN GENE

DRUG

TARGETED MUTATION CORRECTION

• It can be done at different level:

• At gene level, based on homologous recombination.

• At rna transcript level, by using particular types

• of therapeutic ribozymes.

DISEASE CELLS (mutant gene X)NORMAL PHENOTYPE (genetic mutation corrected to restore

functional gene)

CORRECTED GENE

GENE X

TARGETED GENE MUTATION CORRECTION

mutant

TARGETED INHIBITION OF GENE EXPRESSION

• If diseases cells display an inappropriate expression of a gene (in case of many cancers), a variety of different system can be used specifically to block the expression of a single gene at the DNA,RNA or PROTEIN levels.

Disease cells containing mutant or harmful gene

Block of expression of pathogenic gene

ANTISENSE GENE

m

m

Inhibition

N C

AAAA

METHODS OF GENE TRANSFER• VIRAL METHODS

• RETROVIRUS VECTORS

• ADENOVIRUS VECTOR

• HERPES SIMPLEX VECTORS

• NON VIRAL METHOD

• BY OLIGONUCLEOTIDES

• BY LIPOSOME

LTR LTRGENE X

Packaging Signal

10 KB in size

Packaging Cells

Gag PolEnv

Non-replication competentvirus containing gene X,pseudotyped with selectedenvelope

polgag envLTR LTR

= Vector

Retroviruses are used for Gene Therapy

Packaging Signal

Gene Transfer

BY RETROVIRAL VECTOR

VIRAL METHOD BY ADENOVIRUS VECTOR

BY LIPOSOMAL METHOD

GENE THERAPY FOR INHERITED DISORDERS

• Recessively inherited disorders are conceptually the easiest inherited disorders to treat by gene therapy.

• The first apparently successful gene therapy was initiated in 1990 for adenosine deaminase deficiency.

• Cystic fibrosis.• Familial hypercholesterolemia (fh).• Gaucher’s diseases• For neoplastic disorders & infectious disease

GENE THERAPY SUCCESSES AND FAILURES

A recessive disorder of a mutation in the adenosine deaminase (ADA) gene causes SCID. Gene therapy successfully replaced this gene in several ADA patients

SCID is often called "bubble boy disease". SCID became widely known during the 1970's and 80's, when the world learned of David Vetter, a boy with X-linked SCID, who lived for 12 years in a plastic, germ-free bubble. He died after a bone marrow transplant.

GENE THERAPY TRIALS FOR INHERITED DISORDERS

• DISORDER CELLS ALTERED GENE THERAPY STRATEGY ADA DEFICIENCY T-CELLS & HEMOPOITIC STEM CELLS EX VIVO GAT USING RECOMBIN-

ANT RETROVIRUSES CONTAINING

AN ADA GENE.

CYSTIC FIBROSIS RESPIRATORY EPITHELIUM IN VIVO GAT USING RECOMBIN-

ANT ADENOVIRUSES OR LIPOSOME-

TO DELIVER THE CFTR GENE

FAMILIAL LIVER CELLS EX VIVO GAT USING RETROVIRUS

HYPERCHOLESTEMIA TO DELIVER THE LDL RECEPTOR

GENE.

GAUCHER’S DISEASE HEMOPOITIC STEM CELLS EX VIVO GAT USING RETROVIRU-

SES TO DELIVER THE GLUCO-

CEREBROSIDASE GENE.

PROBLEMS AND ETHICS• SHORT-LIVED NATURE OF GENE THERAPY.

• IMMUNE RESPONSE.

• PROBLEMS WITH VIRAL VECTORS.

• MULTIGENE DISORDERS.

• CHANCE OF INDUCING A TUMOR.

CONCLUSIONS• It is believed that gene therapy will revolutionize the

practice of medicine. This technique has the ability to cure many of the diseases that have effected our society for years i.E. People that have serious genetic diseases.

• As scientist discover more genes & their functions, the potential for this treatment is limitless. As we know our fate is indeed in our gene.

REFRENCES• ASCADI G, DICKSON G, LOVE DR ET AL. NATURE, 352,815-818• ANDERSON WF.(1985) J. MED. PHILOSOPH., 10,275-191.• ARBONES ML, AUSTIN HL, CAPON DJ, GREENBURG G. (1994) NATURE

GENETICS,6,90-97.• BARINAGA M. (1993) SCIENCE, 262, 1512-1514.• BOCK LC, GRIFFIN LC, LATHAM JA, VERMAAS EH, TOOLE JJ. (1992) NATURE,

355, 564-566.• BORIS,LAWRIE K,TEMIN HM (1994) ANN. NY ACAD.SCI, 716, 59-71.• BRODY SL,CRYSTAL R.(1994)ANN. NY ACAD .SCI,716,90-103.• CECH T (1995) BIOTECHNOLOGY,13,323-326.• CHUBB JM,HOGAN ME,(1992)TRENDS BIOTECHNOL.,10,132-136.

• CULVER KW, BLAESE RM. (1994) TRENDS GENT., 10,174-178. CURIEL DT. (1994)ANN.NY ACAD.SCI,716,36-58.

• ENGLAND SB,NICHOLSON LV, JOHNSON MA ET AL

.(1990)NATURE,343,180-182.

• GRLBA E,SMIT C. (199)TRENDS GENT.,10,139-144.GREEN LL, HARDY MC,MAYNARD-CURRIE CE ET AL.(1994)NATURE GENETICS,7,13-21.

• GROSSMAN M, RAPER E,KOZARSKYR K ET AL.(1994) SCIENCE,232,1548-1553.HODGOSON CP.(1995),

• HAHN BH, SHAW GM, TAYLOR ME ET AL. (1986) SCIENCE, 232, 1548-1553.

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