Gene Therapy

1. GENE THERAPY Basics Dr.T.V.Rao MD

2. What Genes can do • Genes, which are carried on chromosomes, are the basic physical and functional units of heredity. Genes are specific sequences of bases that encode instructions on how to make proteins. it’s the proteins that perform most life functions and even make up the majority of cellular structures.

3. Why Genetic Disorders • When genes are altered so that the encoded proteins are unable to carry out their normal functions, genetic disorders can result.

4. All of us carry some defective Genes, some are apparent and many in apparent • Each of us carries about half a dozen defective genes. We remain blissfully unaware of this fact unless we, or one of our close relatives, are amongst the many millions who suffer from a genetic disease. About one in ten people has, or will develop at some later stage, an inherited genetic disorder, and approximately 2,800 specific conditions are known to be caused by defects (mutations) in just one of the patient's genes.

5. We Inherit from Parents • Most of us do not suffer any harmful effects from our defective genes because we carry two copies of nearly all genes, one derived from our mother and the other from our father. The only exceptions to this rule are the genes found on the male sex chromosomes. Males have one X and one Y chromosome, the former from the mother and the latter from the father, so each cell has only one copy of the genes on these chromosomes

6. Law of Inheritance • In the majority of cases, one normal gene is sufficient to avoid all the symptoms of disease. If the potentially harmful gene is recessive, then its normal counterpart will carry out all the tasks assigned to both. Only if we inherit from our parents two copies of the same recessive gene will a disease develop.

7. 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. Although the technology is still in its infancy, it has been used with some success.

8. How It Works • A vector delivers the therapeutic gene into a patient’s target cell • The target cells become infected with the viral vector • The vector’s genetic material is inserted into the target cell • Functional proteins are created from the therapeutic gene causing the cell to return to a normal state

9. Gene Therapy is Experimental • Advances in understanding and manipulating genes have set the stage for scientists to alter a person's genetic material to fight or prevent disease. Gene therapy is an experimental treatment that involves introducing genetic material (DNA or RNA) into a person's cells to fight disease.

10. Majority are Trails • Gene therapy is being studied in clinical trials (research studies with people) for many different types of cancer and for other diseases. It is not currently available outside a clinical trials

11. Vivo to Vitro

12. What Gene therapy can Achieve • Replacing a mutated gene that causes disease with a healthy copy of the gene. • Inactivating, or “knocking out,” a mutated gene that is functioning improperly. • Introducing a new gene into the body to help fight a disease.

13. Uses of gene therapy • Replace missing or defective genes; • Deliver genes that speed the destruction of cancer cells; • Supply genes that cause cancer cells to revert back to normal cells; • Deliver bacterial or viral genes as a form of vaccination; • Provide genes that promote or impede the growth of new tissue; and; • Deliver genes that stimulate the healing of damaged tissue.

14. Genes are Medicine? • Gene therapy is ‘the use of genes as medicine’. It involves the transfer of a therapeutic or working gene copy into specific cells of an individual in order to repair a faulty gene copy. Thus it maybe used to replace a faulty gene, or to introduce a new gene whose function is to cure or to favourably modify the clinical course of a condition.

15. Goal of Gene therapy • A normal gene may be inserted into a non-specific location within the genome to replace a non-functional gene. This approach is most common. • An abnormal gene could be swapped for a normal gene through homologous recombination. • The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function. • The regulation (the degree to which a gene is turned on or off) of a particular gene could be altered.

16. Delivering desired Genes

17. Gene Therapy Corrects • Gene therapy is a technique for correcting defective genes responsible for disease development. Researchers may use one of several approaches for correcting faulty genes:

18. Steps in Gene Therapy

20. Manipulation corrects the Defective Genes

21. Gene Therapy delivers Proteins • Today, gene therapy is the ultimate method of protein delivery, in which the delivered gene enters the body's cells and turns them into small "factories" that produce a therapeutic protein for a specific disease over a prolonged period.

22. Antisense therapy • Antisense therapy is a form of treatment for genetic disorders or infections. When the genetic sequence of a particular gene is known to be causative of a particular disease, it is possible to synthesize a strand of nucleic acid (DNA, RNA or a chemical analogue) that will bind to the messenger RNA (mRNA) produced by that gene and inactivate it, effectively turning that gene "off".

23. Antisense Therapy • Antisense therapy is not strictly a form of gene therapy, but is a genetically-mediated therapy and is often considered together with other methods

25. First Approved Gene Therapy • On September 14, 1990 at the U.S. National Institutes of Health, W. French Anderson M.D. and his colleagues R. Michael Blaese, M.D., C. Bouzaid, M.D., and Kenneth Culver, M.D., performed the first approved gene therapy procedure on four-year old Ashanthi DeSilva. Born with a rare genetic disease called severe combined immunodeficiency (SCID),

26. What did they do • In Ashanthi's gene therapy procedure, doctors removed white blood cells from the child's body, let the cells grow in the laboratory, inserted the missing gene into the cells, and then infused the genetically modified blood cells back into the patient's bloodstream.

27. A success story • As of early 2007, she was still in good health, and she was attending college. Some would state that the study is of great importance despite its indefinite results, if only because it demonstrated that gene therapy could be practically attempted without adverse consequences.

28. Principles of Gene therapy • A normal gene may be inserted into a non-specific location within the genome to replace a non-functional gene. This approach is most common. • An abnormal gene could be swapped for a normal gene through homologous recombination. • The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function. • The regulation (the degree to which a gene is turned on or off) of a particular gene could be altered.

29. Gene Therapy Depends on Delivery of Corrective Genes • Viral vectors are a tool commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism (in vivo) or in cell culture (in vitro). Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect.

30. Viruses are used as Delivery Tolls • Viruses are used as vectors to introduce the genetic material inside the bodies. • These viruses are inactivated, they are not able to reproduce • Adenoviruses • Herpes viruses DNA tumor viruses • Retroviruses RNA tumor viruses

31. Making the new Genetic Material Functional • Gene that is inserted directly into a cell usually does not function. Instead, a carrier called a vector is used to introduce the therapeutic gene into the patient's target cells. The most common vector that is used is a virus that has been genetically altered to carry normal human DNA. Viruses cause diseases in humans by encapsulating and delivering the genes into cells.

32. Somatic and Germ Line Gene Therapy • Gene therapy can target somatic (body) or germ (egg and sperm) cells. In somatic gene therapy the recipient's genome is changed, but the change is not passed on to the next generation; whereas with germ line gene therapy the newly introduced gene is passed on to the offspring.

33. Safety • Safety: Although viral vectors are occasionally created from pathogenic viruses, they are modified in such a way as to minimize the risk of handling them.

34. Making safe Protocols • Low toxicity: The viral vector should have a minimal effect on the physiology of the cell it infects. • Stability: Some viruses are genetically unstable and can rapidly rearrange their genomes. This is detrimental to predictability and reproducibility of the work conducted using a viral vector and is avoided in their design.

35. Cell type specificity • Cell type specificity: Most viral vectors are engineered to infect as wide a range of cell types as possible. • However, sometimes the opposite is preferred. The viral receptor can be modified to target the virus to a specific kind of cell.

36. Lentivirus • Lentivirus (lenti-, Latin for "slow") is a genus of slow viruses of the Retroviridae family, characterized by a long incubation period. Lentiviruses can deliver a significant amount of genetic information into the DNA of the host cell, so they are one of the most efficient methods of a gene delivery vector. HIV, SIV, and FIV are all examples of lentiviruses.

37. Retroviruses • Retroviruses can infect only dividing cells. The viral genome in the form of RNA is reverse-transcribed when the virus enters the cell to produce DNA, which is then inserted into the genome at a random position by the viral integrase enzyme

38. Vectors deliver the Genetic Materials • The vector, now called a provirus, remains in the genome and is passed on to the progeny of the cell when it divides.

39. Adenoviruses • As opposed to lenti viruses, adenoviral DNA does not integrate into the genome and is not replicated during cell division. Adenoviral vectors are occasionally used in in vitro experiments.

40. Choosing non infective Adenovirus • Their primary applications are in gene therapy and vaccination. Since humans commonly come in contact with adenoviruses, which cause respiratory, gastrointestinal and eye infections, they trigger a rapid immune response with potentially dangerous consequences To overcome this problem scientists are currently investigating adenoviruses to which humans do not have immunity.

41. Adeno-associated viruses • Adeno-associated virus (AAV) is a small virus which infects humans and some other primate species. AAV is not currently known to cause disease and consequently the virus causes a very mild immune response. AAV can infect both dividing and non-dividing cells and may incorporate its genome into that of the host cell. These features make AAV a very attractive candidate for creating viral vectors for gene therapy

42. Limitation of Direct Gene Induction • The simplest method is the direct introduction of therapeutic DNA into target cells. This approach is limited in its application because it can be used only with certain tissues and requires large amounts of DNA.

43. Nonviral approach • Nonviral approach involves the creation of an artificial lipid sphere with an aqueous core. This liposome, which carries the therapeutic DNA, is capable of passing the DNA through the target cell's membrane

44. Nonviral Vectors: Liposome'sless Immunogenic • DNA/lipid complexes are easy to prepare and there is no limit to the size of genes that can be delivered. Because carrier systems lack proteins, they may evoke much less immunogenic responses. More importantly, the cationic lipid systems have much less risk of generating the infectious form or inducing tumorigenic mutations because genes delivered have low integration frequency and cannot replicate or recombine.

45. Nanoengineered substances • Nonviral substances such as Ormosil have been used as DNA vectors and can deliver DNA loads to specifically targeted cells in living animals. (Ormosil stands for organically modified silica or silicate)

46. Transfection and Nanoengineering • Transfection is the process of introducing nucleic acids into cells by non-viral methods. The term "transformation" is preferred to describe non-viral DNA transfer in bacteria and non-animal eukaryotic cells; "transduction" is often used to describe virus-mediated DNA transfer.

47. Gene Therapy should not Interfered Germ Line • The germ line of a mature or developing individual is the line (sequence) of germ cells that have genetic material that may be passed to a child • Germ line cells are immortal, in the sense that they can reproduce indefinitely. This is largely due to the activity of the enzyme known as telomerase. This enzyme extends the telomeres of the chromosome, preventing chromosome fusions and other negative effects of shortened telomeres.

48. Creating New Chromosome • Researchers are also experimenting with introducing a 47th artificial chromosome to the body. • It would exist autonomously along side of the other 46, not affecting their workings or causing any mutations. • It would be a large vector capable of carrying substantial amounts of genetic information and the body’s immune system would not attack it.

49. ADA deficiency was selected for the first approved human gene therapy trial for several reasons • The disease is caused by a defect in a single gene, which increases the likelihood that gene therapy will succeed. • The gene is regulated in a simple, “always-on” fashion, unlike many genes whose regulation is complex. • The amount of ADA present does not need to be precisely regulated. Even small amounts of the enzyme are known to be beneficial, while larger amounts are also tolerated well

50. Problems of Large Gene • It would be a large vector capable of carrying substantial amounts of genetic code, and scientists anticipate that, because of its construction and autonomy, the body's immune systems would not attack it. A problem with this potential method is the difficulty in delivering such a large molecule to the nucleus of a target cells.