Gene therapy : Gene therapy Presented By:
1st M.PHARM(Pharmaceutics) What’s gene ? : What’s gene ? • Gene is the biological unit of heredity.
• Genes determine obvious traits, such as hair and eye color, as well as more subtle characteristics such as the ability of the blood to carry oxygen.
• A gene is a part of DNA molecule, and humans have 30.000 genes.
• Genes carry instructions that allow the cells to produce specific proteins such as enzymes.
• Only certain genes in a cell are active at any given moment. As cell mature, many genes become permanently inactive. The pattern of active and inactive genes in a cell and the resulting protein composition determine what kind of cell it is and what it can do and cannot do. Flaws in genes can result in disease. What is gene therapy ? : What is gene therapy ? • An experimental treatment that involves introducing genetic material (DNA or RNA) into a person’s cells to fight disease
• A novel approach to treat, cure, or ultimately prevent disease by changing the expression of a person’s genes
• The insertion of genes into an individual’s cells and tissues to treat a disease, and hereditary diseases in particular
•A technique for correcting defective genes responsible for disease development Background : Background • In the 1980, advances in molecular biology had already enabled human genes to be sequenced and cloned. Scientist looking for a method of easily producing protein, such as the protein deficient in diabetics-insulin, investigated introducing human genes to bacterial DNA. The modified bacteria then produce the corresponding protein which can be harvested and injected in people who cannot produce it naturally.
Scientist took the logical step of trying to introduce genes straight into human cells, focusing diseases caused by single-gene defects, such as cystic fibrosis, hemophilia, muscular dystrophy and sickle cell anemia. However this has been much harder than modifying simple bacteria, primarily because of the problems involved in carrying large section of DNA and delivery it to the right site on the genome Concept of Gene Therapy : Concept of Gene Therapy • Gene therapy utilizes two theoretically possible approaches :
1. Somatic gene therapy
2.Germline gene therapy Somatic Gene Therapy : Somatic Gene Therapy • Transfer of a gene or genes into body cells
other than germ cells with effect only on the
patient. The new genetic material cannot be
passed on to offspring
• Somatic gene therapy can be broadly split into two categories (types) :
1. Ex vivo
2. In vivo Types of gene therapy...............continued : Types of gene therapy...............continued • Ex vivo : Cells from the patient’s blood or bone marrow are removed and grown in the laboratory. The cells are exposed to the virus that is carrying the desired gene. The virus enters the cells and inserts the desired gene into the cell's DNA. The cells grow in the laboratory and then returned to the patient by injection into a vein. The gene is transferred into the patient’s cells while the cells are outside the patient’s body.
• In vivo :The vectors be injected directly into the body. ( The gene is transfered to cells inside the patient’s body). Ex vivo : Ex vivo In vivo : In vivo Germline gene therapy : Germline gene therapy Involve the genetic modification of germ cells.
Such therapy would change the genetic make
up of the egg or sperm of an individual and
would be carried on to future generations.
This would offer the possibility of removing an
inherited disorder from a family line forever.
• Although it has potential for preventing
inherited disease, this form of gene therapy is
controversial and currently very little research
is being done in this area, both for technical
and ethical reasons. How does gene therapy work : How does gene therapy work • In most gene therapy studies, a normal gene is inserted into the genome to replace an “abnormal” disease-causing gene.
• A carrier molecule called a vector must be used to deliver the therapeutic gene to the patients target cells.
• The most common vector is a virus that has been genetically altered to carry normal human DNA How does gene therapy work.......continued : How does gene therapy work.......continued • Target cell such as the patient’s liver or lung cells are infected with the viral vector. The viral vector then unload its genetic material containing the therapeutic human gene into the target cell. The generation of a functional protein product from therapeutic gene restores the target cell to a normal state.
• Some of the different types of viruses as
gene therapy vectors :
3. Adeno-associated viruses
4. Herpes simplex viruses Retroviruses : Retroviruses • The genetic material in retroviruses is in the form of RNA molecule, while the genetic material of their hosts is in the form of DNA
• When retrovirus infects a host cell, it will introduce its RNA together with some enzymes into the cell.
• The RNA molecule must produce a DNA copy before it can be considered part of the genetic material of the host cell.
• The process of of producing a DNA copy from RNA molecule is termed reverse transcription, and the enzymes carried in the virus called reverse transcriptase. Retroviruses continued........ : Retroviruses continued........ • DNA copy must be incorporated into the large DNA molecules in the cell or the chromosomes of the cell (genome of the host cell). This process is done by enzyme integrase.
• The host cell now contains a new gene, and when it devides later, its descendants will contain the new genes.
• Retrovirus can only invade cells that devide often, therefore blood cells, skin cells and many other tissues can not be invaded by this vector. Also, they do not insert their genetic material in any specific places within the cell’s chromosomes, but in the middle of an important gene. The important gene could become defective, stop functioning and could do more harm than good.
• The body also has its immunereponse, destroying retrovirus. Retroviruses carrying healthy gene are mixed with unhealthy cells taken from a patient. Retroviruses infect unhealthy cells with healthy gene, adding the gene to patient’s DNA. Healthy cells then injected back to the patient. : Retroviruses carrying healthy gene are mixed with unhealthy cells taken from a patient. Retroviruses infect unhealthy cells with healthy gene, adding the gene to patient’s DNA. Healthy cells then injected back to the patient. Adenoviruses : Adenoviruses • Adenoviruses carry their genetic material in the form of DNA.
• When these viruses infect a host, they introduce their DNA
molecule into the host but not incorporated into the host
• These extra genes are not replicated, so when the host
undergo cell division, the descendants of the cell will not have the extra gene.
• This means that treatment with adenovirus will require
regular doses to add the missing gene every time.
• Adenoviruses can invade slower dividing cells, such as lung cells
• Like retroviruses, immune response may reduce its effectiveness Adeno-associated viruses : Adeno-associated viruses • Adeno-associated viruses are believed to occur naturally in humans, existing without causing disease or instigating in immune response from the body. This type of virus is being used, because it is non-pathogenic (most people carry this harmless virus).
• AAV are small viruses with a genome of single stranded DNA. They insert their material specifically into chromosome 19, at a specific site.
• Disadvantages in using AAV are the small amount of DNA it can carry (only 2 genes) and the difficulty in producing it. AAV continued............. : AAV continued............. • Most people treated with AAV will not build an immune response to remove the virus and the cells that have been successfully treated with it.
• Several trials with AAV are ongoing or in preparation, mainly trying to treat muscle and eye disease, the two tissues where the virus seems particularly useful. Herpes simplex viruses : Herpes simplex viruses • A class of double stranded DNA virus that
usually used to target the nervous system
because herpes simplex virus usually infects neurons. Non viral options for gene delivery : Non viral options for gene delivery 1. Direct introduction of therapeutic cDNA into target cells. This approach can be used only with certain tissues and requires large amount of DNA.
2. Artificial liposome which carry therapeutic cDNA. It is capable of passing the DNA through the target cells membrane.
3. Chemically linking therapeutic cDNA to a molecule that will bind to special cell receptors. Once bound to these receptors the cDNA construct are engulfed by the cell membrane and passed into the interior of the target cell. This method is not very effective
4. Introducing 47th artificial human chromosome into target cells. This chromosome would exist autonomously alongside the standard 46. However, a method for inserting the chromosome into the cell, or the nucleus is yet to be found Direct delivery : Direct delivery What diseases could be treated withgene therapy : What diseases could be treated withgene therapy • About 4000 diseases have been traced to gene disorders.
• Current and possible candidates for gene therapy include cancer, AIDS, cystic fibrosis, Parkinson's, Alzheimer’s disease, Lou Gehrig’s disease, cardiovascular disease and arthritis. Has gene therapy been successfullyused in humans : Has gene therapy been successfullyused in humans • Gene therapy is likely to be most successful with diseases caused by single gene defects.
• The 1st successful gene therapy on humans was performed in 1990 by researchers at the National Institute of Health for treatment patient with adenosine deaminase (ADA) deficiency, a rare genetic disease. Patients with this condition do not have normal ADA genes and do not produce ADA enzyme, causes severe immunodeficiency and prone to repeated serious infections.
• In 2003, more than 600 gene therapy clinical trials were under way in the US but only a handful of these are in advanced stages. What factors have kept gene therapy frombecoming an effective treatment for geneticdisease ? : What factors have kept gene therapy frombecoming an effective treatment for geneticdisease ? • Short-lived nature of gene therapy.
• Immune response
• Problem with viral vector : viruses may present a variety of potential problems to the patient – toxicity, immune and inflammatory response and also cause disease
• Multigene disorder : multigene or multifactorial disorders would be difficult to treat effectively using gene therapy What risk are associated with currentgene therapy trials ? : What risk are associated with currentgene therapy trials ? • Viruses can usually infect more than one type of cell, thus they might infect healthy cells.
• Another danger is that the new gene might be inserted in the wrong location in the DNA, possibly causing cancer or harmful mutations to the DNA.
• There is a slight chance that the DNA could unintentionally be introduced into the patient’s reproductive cells, so it may be passed on if the patient has children after treatment.
• The possibility that transferred genes could be “overexpressed", producing so much of the missing protein as to be harmful ; that the viral vector could cause inflammation or an immune reaction ; and that the virus could be transmitted from the patient to other individuals or into the environment. Are genetic alterations from genetherapy passed on to children ? : Are genetic alterations from genetherapy passed on to children ? • In somatic gene therapy, the patient’s genome is changed, but the change is not passed along to the next generation.
• In germ line gene therapy, the patient’s egg or sperm cells are changed with the goal of passing on changes to their offspring.
• Existing gene therapy treatments and experiments are all somatic. What is the current status of gene therapyresearch ? : What is the current status of gene therapyresearch ? • FDA has not yet approved any human gene therapy product for sale. Current gene therapy is experimental and has not proven very successful in clinical trials.
• Little progress has been made since the 1st gene therapy clinical trial in 1990, but in 1999 suffered a major set back with the death of patient participating in gene therapy trial, from multi organ failured. Is gene therapy safe ? : Is gene therapy safe ? Gene therapy is under study to determine whether it could be used to treat disease. Current research is evaluating the safety of gene therapy; future studies will test whether it is an effective treatment option. Several studies have already shown that this approach can have very serious health risks, such as toxicity, inflammation, and cancer. Because the techniques are relatively new, some of the risks may be unpredictable; however, medical researchers, institutions, and regulatory agencies are working to ensure that gene therapy research is as safe as possible. Bibliography : Bibliography 1. Gene Therapy
2. Gene Therapy
3. Gene Therapy
4. Gene Therapy
5. Gene Therapy for Cancer : Questions and Answers
6. Gene Therapy and Children
7. encarta.msn.com/media_461561269/Gene_Therapy.html Thank you : Thank you