27 November 2018 Today’s Title: CW: Gene therapy Learning Question: What are the ethical implications of gene therapy?

Aims from specification (q) explain the term gene therapy; (r) explain the differences between somatic cell gene therapy and germ line cell gene therapy;

Key words Gene therapy Augmentation Germline cell Somatic cell Transgenic Genetically modified organism Liposomes

Gene Therapy Gene therapy is the treatment of a disease by manipulating the genes in a person’s cells. Depends on whether the disorder is caused by dominant or recessive allele If 2 recessive alleles, working dominant allele can be added to make up for them If caused by dominant allele, you can “silence” the dominant allele (e.g. sticking DNA to the middle of the DNA sequence so it does not work properly) Two examples of gene therapy SCID Cystic fibrosis

Somatic cell gene therapy Involves altering the alleles in the body cells, particularly those most affected by the disorder E.g. Cystic Fibrosis (CF) damages the respiratory system Somatic gene therapy for CF targets the epithelial cells lining the lungs Somatic therapy does not affect gametes, therefore offspring could inherit disorder

Somatic cell gene therapy Gene therapy by adding genes (augmentation) Inheritance of defective genes or loss of functional gene product can be overcome by engineering a functioning copy of the gene inserting gene into relevant specialised cell means desired protein is synthesised and functioning normally Gene therapy by killing specific cells Cancers can be treated by eliminating populations of cells Cancer cells can be manipulated to express genes/produce surface antigens to make cell vulnerable to attack from immune system

Germline cells Each cell of an early embryo is a stem cell It can divide and specialise to become any cell type within the body It has the potential to become a new being These are germline cells

Germline cell gene therapy Involves altering the alleles in the sex cells This means every cell of any offspring would be affected by gene therapy and therefore will not suffer from the disease Currently illegal in humans

Gene Therapy Somatic therapy Germline therapy Alleles in body cells genetically modified Modified genes will not be passed on to any offspring Germline therapy Changing genes in cells that would go on to form gametes All of the cells in the new organism would carry the genetic modification Modified genes in gametes could be passed on to offspring

Ethical concerns Accidental genetic modification could create new human diseases or interfere with evolution in some way Permanent modifications to human genome could raise moral, social and ethical issues that need to be explored in detail

Somatic cell gene therapy Germline cell gene therapy The functioning allele of the gene is introduced into target cells – therefore techniques to get the gene to the target location are needed, or specific cells must be removed, treated and then replaced (this is called ex vivo therapy) The functioning allele of the gene is introduced into germline cells – delivery techniques are more straightforward Introduction into somatic cells means that any treatment is short-lived and has to be replaced regularly. The specialised cells containing the gene will not divide to pass on the allele. Introduction into germline cells means that all cells derived from these germline cells will contain a copy of the functioning allele. The offspring may also contain the allele There are difficulties in getting the allele into the genome in a functioning state. Genetically modified viruses have been tried but the host becomes immune to them so cells will not accept the virus vector on second and subsequent treatments. Liposomes are used but these may be inefficient Although more straightforward, it is considered unethical to engineer human embryos. It is not possible to know whether the allele has been successfully introduced without any unintentional changes to it, which may damage the embryo. Genetic manipulations are restricted to the actual patient Genetic manipulations could be passed on to the patient’s children.

Somatic cell gene therapy Germline cell gene therapy functioning allele of the gene is introduced into target cells – therefore techniques to get the gene to the target location are needed, or specific cells must be removed, treated and then replaced (this is called ex vivo therapy) The functioning allele of the gene is introduced into germline cells – delivery techniques are more straightforward Introduction into somatic cells means that any treatment is short-lived and has to be replaced regularly. The specialised cells containing the gene will not divide to pass on the allele. Introduction into germline cells means that all cells derived from these germline cells will contain a copy of the functioning allele. The offspring may also contain the allele There are difficulties in getting the allele into the genome in a functioning state. Genetically modified viruses have been tried but the host becomes immune to them so cells will not accept the virus vector on second and subsequent treatments. Liposomes are used but these may be inefficient Although more straightforward, it is considered unethical to engineer human embryos. It is not possible to know whether the allele has been successfully introduced without any unintentional changes to it, which may damage the embryo. Genetic manipulations are restricted to the actual patient Genetic manipulations could be passed on to the patient’s children.

SCID SCID severe combined immunodeficiency disease Caused by a faulty allele coding for the enzyme adenosine deaminase (ADA) This enzyme is essential for the healthy working of the immune system

Gene therapy for SCID Gene therapy Alternative treatment Removal of patient’s T cells and insertion of the correct allele into them using a vector (retrovirus) Cells that have taken the allele up successfully are cloned and replaced into the patient’s body Alternative treatment Daily injections of adenosine deaminase

Problems with SCID gene therapy Some patients who appeared to have been successfully treated, went on to develop leukaemia Is the risk of cancer acceptable when the patients would have died anyway from this rare and fatal disease?

Cystic Fibrosis Abnormally thick mucus is produced in the lungs and other parts of the body. Caused by a recessive allele of the gene that codes for the CFTR protein. CFTR gene Sits on chromosome 9 Commonest defective allele is a result of the deletion of three bases Machinery of cell recognises that the protein is not right and does not insert it in the cell membrane

The CFTR protein forms channels for chloride ions in the plasma membrane

Gene therapy for cystic fibrosis Normal allele inserted into liposomes Sprayed as an aerosol into the nose Liposomes are lipid soluble and able to move through the lipid layers of the plasma membrane of the cells lining the respiratory passages Effect only lasted a week Cells have a short lifespan and are continually replaced Introducing the gene using adenovirus Unpleasant side effects – trials stopped

Questions A patient suffering from cystic fibrosis was offered gene therapy targeted at his lung epithelial cells to help treat the disease. What does gene therapy involve? (1) What type of gene therapy was the patient offered? (1) 2. Give three possible disadvantages of somatic gene therapy (3) 3. Erin has a family history of breast cancer. She has agreed to be screened for the mutated BRCA1 gene, which can cause breast cancer. A sample of her DNA is digested and separated using gel electrophoresis. Describe how a DNA probe could be used to identify the mutated BRCA1 gene (4)

Answers (a)Gene therapy involves altering/supplementing defective genes (mutated alleles) inside cells to treat genetic disorders and caner (b)Somatic gene therapy 2. The effective treatment may be short-lived The patient might have to undergo multiple treatments It might be difficult to get the allele into specific body cells The allele may be inserted into the wrong place in the DNA, which could cause more problems The allele may be overexpressed

Answers 3. The separated DNA fragments are transferred to a nylon membrane and incubated with a fluorescently labelled DNA probe The probe is complementary to the sequence of the mutated BRCA1 gene If the sequence is present in one of the DNA fragments, the DNA probe will hybridise to it The membrane is then exposed to UV light and if the sequence is present in one of the DNA fragments, then that band will fluoresce

Learning Outcomes Discuss the ethical concerns raised by the genetic manipulation of animals (including humans), plants and microorganisms.

Face transplant patient http://www.bbc.co.uk/news/world-us-canada-17534646

Ethics of organ donation - Is it wrong to sell organs?

Ethics of organ donation - Is it wrong to sell organs? Senior NHS doctors have complained about botched transplant surgeries done abroad Doctors in India see poor donors dying after selling one of their kidneys In March 2007, China published new rules governing human organ transplants – buying and selling organs is forbidden. Written permission from doctors is required before operation is carried out

Xenotransplantation Animal – human transplantations are being studied by some transplant centres. Pigs may be a possible source of transplant organs….what do you think? What are the implications of this?

Ethical issues and gene therapy People are worried that the technology could be used in ways other than for medical treatment e.g. cosmetic effects of aging Worries that gene therapies do more harm than good by using the technology (e.g. risk of overexpression of genes) Also concern that gene therapy is expensive – some people believe that health service resources could be better spent on other treatments that have passed clinical trials

Benefits and risks of genetic engineering organism benefit Risk Micro-organism GM bacteria can be used to produce useful products Antibiotic resistance genes are used as genetic markers Plants Animals Humans Use your textbooks to complete this table, p185