Part 2

READING PASSAGE 2

You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2 below.

GENE THERAPY

A. Gene therapy is the introduction of genes into existing cells to prevent or cure a wide range of diseases. The most common form of gene therapy involves using DNA that encodes a functional, therapeutic gene to replace a mutated gene. Gene therapy was first conceptualised in 1972, with the authors urging caution before commencing human gene therapy studies. The first attempt, an unsuccessful one, at modifying human DNA was performed in 1980 by Martin Cline. The first successful nuclear gene transfer in humans, approved by the National Institutes of Health, was performed in May 1989. The first therapeutic use of gene transfer as well as the first direct insertion of human DNA into the nuclear genome was performed by French Anderson in a trial starting in September 1990. The first commercial gene therapy, Gendicine, was approved in China in 2003 for the treatment of certain cancers. In 2011, Neovasculgen was registered in Russia as the first-in-class gene-therapy drug for treatment of peripheral artery disease, including critical limb ischemia. In 2012, Glybera, a treatment for a rare inherited disorder, lipoprotein lipase deficiency, was approved by the European Commission.

B. Although the technology is still in its infancy, it has been used with some success. It is a potential therapy for a number of diseases (such as cystic fibrosis, sickle cell anaemia, adrenoleukodystrophy and haemophilia) as well as several inherited retinal diseases. Current gene therapy has primarily focused on treating individuals by targeting the therapy to somatic (body) cells, such as bone marrow cells. Gene therapy may be classified into the two following types:

Somatic gene therapy: In somatic gene therapy, the therapeutic genes are transferred into the somatic cells (cells that do not make sperm or eggs) of a patient. Any modifications and effects will be restricted to the individual patient only, and will not be inherited by the patient’s offspring or later generations. Somatic gene therapy represents mainstream basic and clinical research, in which therapeutic DNA is used to treat disease.

Germline gene therapy: In germline gene therapy, germ cells (sperm or eggs) are modified by the introduction of functional genes, which are ordinarily integrated into their genomes. The change due to therapy would therefore be heritable and would be passed on to later generations. In some jurisdictions, germline gene therapy is the only feasible option for some diseases; however, this option is fraught with many bio-ethical considerations. For the present, germline gene therapy is prohibited for application in human beings, at least for the foreseeable future, in most countries.

C. Gene therapy may be classified into two types, ex vivo and in vivo, on the basis of the method of delivery of genes. Ex vivo gene therapy involves the transfer of genes in cultured cells and reinsertion of the genetically altered cells back into the patient. In vivo gene therapy is the direct delivery of genes into the cells of a particular tissue in the body. The in vivo gene delivery can be divided into two categories: the therapeutic gene is directly injected into the body tissues; the therapeutic DNA is delivered to the target cells through the circulation.

D. Gene therapy uses sections of DNA (usually genes) to treat or prevent disease. The DNA is carefully selected to correct the effect of a mutated gene that is causing disease. The technique was first developed in 1972 but has, so far, had limited success in treating human diseases. For example, in 1999, 18-year-old Jesse Gelsinger died after undergoing gene therapy for ornithine transcarbamylase deficiency, and in 2002 it was reported that two children treated for X-linked severe combined immunodeficiency (X-SCID) in a clinical trial in 1999 had developed leukaemia. However, more than 1,800 gene therapy clinical trials have been conducted since the technique was first developed. Gene therapy can be used to modify cells inside or outside the body. When it’s done inside the body, a doctor will inject the vector carrying the gene directly into the patient. This method is useful when only certain tissues require correction. When it’s done outside the body, doctors will take a sample of the patient’s cells and expose them to the vector in a laboratory. The corrected cells are then returned to the patient. This approach is more useful when only a few cells need to be corrected.

E. Gene therapy has the potential to eliminate and prevent hereditary diseases such as cystic fibrosis and is a possible cure for heart disease, AIDS and cancer. The technology is still in its infancy. If the defects in the gene are corrected, these diseases could be treated. Gene therapy could have the potential to cure many genetic disorders. However, there are concerns that the wide range use of gene therapy in human beings is not safe.

Questions 14-18

Reading Passage 2 has five sections, A-E.

Which section contains the following information?

Write the correct letter, A-E, in boxes 14-18 on your answer sheet.

NB: You may use any letter more than once

14.ABCDE . a reference to a person who resisted the use of gene therapy on humans

15.ABCDE . a reference to the early failure of a gene therapy trial

16.ABCDE . a reference to different methods of delivering gene therapy.

17.ABCDE . a reference to the ethical concerns surrounding inheritable gene therapy.

18.ABCDE . mention of the total recorded attempts to apply gene therapy in clinical research.

Questions 19-22

Complete the summary below.

Choose ONE WORD ONLY from the passage for each answer.

Write your answers in boxes 19-22 on your answer sheet.

TYPES OF GENE THERAPY

Gene therapy can be classified as either somatic or germline. In somatic gene therapy, the 19___________ cells of a patient are targeted for gene replacement. The effects of the therapy will not be passed down to future 20___________. However, in germline gene therapy, the DNA of a patient’s sperm or egg cells is altered. This means that any changes will be passed down to future generations. Although this type of gene therapy is not permitted in humans in most countries, it may be the only possible cure for people with certain 21___________ . In addition, gene therapy can be classified as either ex vivo or in vivo. In ex vivo gene therapy, the genes are altered outside the patient’s body before the 22___________ into the patient. In vivo gene therapy involves injecting the therapeutic DNA directly into the patient’s body.

Questions 23-26

Do the following statements agree with the information given in Reading Passage 2?

In boxes 23-26 on your answer sheet, write

23.TRUEFALSENOT GIVEN . The first gene therapy trial on humans was unsuccessful.

24.TRUEFALSENOT GIVEN . So far, gene therapy has only been used on adults.

25.TRUEFALSENOT GIVEN . X-SCID is more common in boys than girls.

26.TRUEFALSENOT GIVEN . The corrected cells are then returned to the patient.