Gene Therapy

Gene Therapy - Background The first gene therapy journal published, Human Gene Therapy The first approved gene therapy clinical trial took place when Ashanthi DeSilva, a 4 year old girl with ADA- deficient Severe Combined Immunodeficiency, was given her own T cells engineered with a retroviral vector carrying a normal ADA gene The first gene therapy cure was reported when Alain Fischer (Paris) succeeded in totally correcting children with SCID-X1, or “bubble boy” syndrome (X-linked severe combined immunodeficiency) “Bubble Boy”

What Are Genetic Disorders? Genetic disorder is a disease caused by a "variation" or "mutation“ of a gene. Genetic disorders can be passed on to family members who inherit the genetic abnormality. A small number of rare disorders are caused by a mistake in a single gene. Most disorders involving genetic factors, such as heart disease and most cancers, arise from a interplay of multiple genetic changes and environmental factors.

What Are Genetic Disorders? Thee categories of genetic disorders: –Single gene disorders caused by a mistake in a single gene. Sickle cell, cystic fibrosis and Tay-Sachs disease are examples. –Chromosome disorders caused by an excess or deficiency of the genes. Down syndrome is caused by an extra copy of a chromosome, but no individual gene on the chromosome is abnormal. –Multifactorial inheritance disorders caused by a combination of small variations in genes. Heart disease, most cancers and Alzheimer's disease are examples. Sickle Cell Disorder

What is Gene Therapy? Researchers may use one of several approaches for correcting faulty genes: –A normal gene may be inserted into a location within the genome to replace a nonfunctional gene. Most common approach. –An abnormal gene could be swapped for a normal gene through homologous recombination. –An 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.

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 patient's target cells. The most common vector is a virus that has been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Scientists manipulate the virus genome to remove disease-causing genes and insert therapeutic ones. Target cells, such as the patient's liver or lung cells, are infected with the viral vector.

How Does Gene Therapy Work? Non-viral options: –Direct introduction of therapeutic DNA into target cells. Can be used only with certain tissues and requires large amounts of DNA. –An artificial lipid sphere with an aqueous core, called a liposome, which carries the therapeutic DNA, is capable of passing the DNA through the target cell's membrane.

Problems With Gene Therapy? Short-lived nature of gene therapy- patients will have to undergo multiple rounds of gene therapy. Immune response- risk of stimulating the immune system in a way that reduces gene therapy effectiveness is always a potential risk. Problems with viral vectors- viruses, the carrier of choice, present potential problems to the patient, like toxicity, immune and inflammatory responses, and gene control and targeting. Multi-gene disorders- most common disorders, such as heart disease, high blood pressure, Alzheimer's disease, arthritis and diabetes, are caused by the combined effects of variations in many genes.

Types of Gene Therapy Prominent forms include postnatal gene delivery via viral vectors for insertion within the genome, imparting expression of the newly incorporated gene, and so-called “gain of function” RNA interference, or RNAi, borrows from the principals of naturally occurring process within biological systems, used to affect relative levels of expression of certain genes. Present research and ongoing efforts are also being made in the development of human prenatal gene therapy

In vivo gene therapy: delivery of new genetic material directly to target cells within the body –The challenge lies in ensuring the specificity and in reaching the correct target cells within the body Ex vivo therapy: target cells are removed from the body and then genetically modified –The cells are then returned to the body after selection and amplification –This is a safe method but dependent on the type of cells being targeted

Benefits of prenatal gene therapy Provides early phenotypic correction, reducing or avoiding otherwise devastating effects of genetic disease Demonstration of long-term postnatal therapeutic protein production Tolerance to the transgenic protein can be induced by in utero expression

Adverse Effects of Gene Therapy Vector induced oncogenesis Germline transfer of transgenic DNA sequences Developmental aberrations caused by expression of the transgenic proteins and vector induced oncogenesis Without proper specificity, delivery to the right cell type in the right organ, at the right time, there could be detrimental immunological effects.

Is Gene Therapy Ethical? Questions we will consider: –What is normal and what is a disability or disorder, and who decides? –Who will have access to your genetic information? –Is somatic gene therapy (done in the adult cells of people known to have the disease) more or less ethical than germline gene therapy (done in egg and sperm cells and prevents the trait from being passed on to further generations)? –Preliminary attempts at gene therapy are expensive. Who will have access to these therapies? Who will pay for their use?

Problems With Scientific Reductionism Epigenetics - some gene regulatory information not expressed in DNA sequences are transmitted from one generation to the next –Twin studies…

HUGO Ethics Committee Statement on Gene Therapy Research Germ-line cell gene therapy avoided, only confronts somatic cell therapy Main Objectives of Statement: –respond to public concerns about ethical conduct, quality, and safety of somatic gene therapy research –make distinction between somatic therapy from germ- line therapy

HUGO Ethics Committee Statement on Gene Therapy Research (continued) Common principles previously established by HUGO in 1996 Statement of the Principled Conduct of Genetics Research: – Recognition that the human genome is part of the common heritage of humanity –Adherence to international norms of human rights –Respect for the values, traditions, culture, and integrity of participants –Acceptance and upholding of human dignity and freedom

HUGO Ethics Committee Statement on Gene Therapy Research (continued) Recommendations by HUGO Committee: –researchers and governments must respond to public concerns about the benefits, risks and ethical conduct of research –all research conducted must abide by stringent quality and safety controls and be in conformity with international norms

4 Ethical Yardsticks: Review Nonmaleficence: Do no harm, avoiding the causation of harm. Beneficence: Do good. Respect for autonomy: Respect for the fundamental self-worth, dignity,and decision-making capacity of individuals. Justice: Distribute benefits, risks and costs fairly.

Risks of Gene Therapy New gene might be inserted into wrong location in the DNA (misfire) Immune system complications Vector viruses can infect more than one type of cell Over-expression of missing protein DNA could accidentally be introduced into reproductive cells (germ-line gene therapy)

Case Studies of Gene Therapy

Gene Therapy used to Treat Type I Diabetes Study by Lee, Kim, Kim, Shin, and Yoon performed in Korea (2000). Their results were published in Nature Type I diabetes is caused by the destruction of insulin-producing pancreatic β cells by an inappropriate autoimmune response

This experiment was performed on mice and rats but the results may result in future implications for humans Scientists used a recombinant adeno-associated virus (rAAV) to insert a gene that results in the expression of a single-chain insulin analogue (SIA) into streptozotocin- induced diabetic rats and autoimmune diabetic mice. First, the gene was cloned under the L-type pyruvate kinase (LPK) promoter, which regulates the expression of SIA in response to glucose levels

In addition to eight months of controlled glucose levels, there were no visible side affects from the gene therapy. While the results did not show permanent remission, the control of glucose levels from the insertion of the SIA gene was promising. This form of gene therapy may provide a cure for type I diabetes for humans in the future (but a lot more research would be required before that can happen).

Gene Therapy as a Treatment for X- SCID X-linked severe combined immunodeficiency (X- SCID) is a disease that affects young children and is usually fatal within their first year of life. Bone marrow transplants are usually the best option for treatment, but with the difficulty in finding a donor who matches the patient, gene therapy has become a new alternative. Clinical trials for treating X-SCID patients have been marked by mixed results

One of the patients involved in the Fischer trials has developed leukemia two and a half years after the initial gene therapy treatment (Gene Therapy). Two of eleven patients involved in a similar study in France have also developed leukemia (Trends in Biotechnology). The gene therapy treatments have resulted in the overexpression of the a gene that may be an oncogene and is located at the site of the retroviral insertion. The site of insertion is the first intron of the LMO-2 gene, which is located on chromosome eleven. LMO-2 is also the site of a translocation that occurs in leukemia. This observation clearly correlates the retroviral insertion as the cause of leukemia in the patients.

It is still unknown whether the development of leukemia in these clinical studies was the result of a premature treatment (which could be eliminated with further research and development) or if it is a permanent risk. Despite the fact that without treatment, X-SCID is a fatal disease, there is still an ethical question of whether or not it is right to subject a sick child to the possibility of developing another disease through the risks of gene therapy treatments. The parents of the young children who participated in the study were informed of this risk prior to the treatment.

1) What do you think that having a map of the entire human genome impacts our understanding of human nature? 2) Do you think using HGT to prevent diseases is a medical goal or enhancement goal? 3) Do you approve the therapeutic use of gene transfer? Why or Why not? 4) Problems? 5) Is there any difference between sending a child to a high-school to enhance his or her intellectual capabilities and trying to do this through genetic interventions?