1""Gene Therapy- From Medicine to Perfection and the Ethical Arguments Carl DeGuzman Biochemistry 118Q Professor Douglas Brutlag 12/3/09 One promising but somewhat less publicized branch of medicine is gene therapy, which involves the insertion of genes into an individual’s cells and tissues in order to treat a disease. Gene therapy can be divided into two main types, somatic gene therapy and genetic gene therapy. Somatic gene therapy involves the transfer of therapeutic genes into the somatic cells of a patient. These cells include every cell type in the human body except for the cells which make up the sperm and ova and undifferentiated stem cells. The second type of gene therapy, genetic gene therapy, involves the modification of the germ cells or the sperm or eggs of the patient. The changed genes of the germ cells then become inheritable by the offspring of the patient. In theory, this approach could be used to treat diseases that are hereditary or passed down as genetic disorders. However, this passing down of traits to one’s offspring is part of the reason that genetic gene therapy is surrounded by more ethical controversy than its somatic counterpart. Furthermore, the development of these two techniques has led to the possibility of genetic modification in not only those who are suffering from a disease, but also those who are in good health. Genetically altering one’s genes could lead to enhancements in strength, cognition, mood, or height. This opens up a whole new side of the ethical debate, whether or not we should try to make ourselves “more perfect” through the use of gene therapy. Scientists however continue to perfect gene therapy and hope that soon it will be able to cure otherwise untreatable diseases.2"" Somatic gene therapy is at a much further stage of development than genetic gene therapy. There are two different types of somatic gene therapy, ex vivo and in vivo. Ex vivo involves altering the cells outside of the body and then transplanting them back in, while in vivo involves modifying the cells while they are still in the body. In order introduce the necessary gene in a patient during somatic gene therapy, a vector is needed. Most often, some sort of viral vector is used in order to implant the new DNA in the cell. Various types of viruses such as retroviruses, adenoviruses, and adeno-associated viruses are used which replace the target gene with a modified gene. Retroviruses must convert the RNA it carries into a strand of DNA before the cell’s genetic make-up is changed, rather than carrying a copy of its own DNA to introduce to the cell. The strand of DNA made by the retrovirus is then introduced into the DNA of the cell by an integrase enzyme. Sometimes the DNA strand is placed in a part of the DNA where it does no good. Therefore, methods have been developed to insure that the DNA is introduced the right way. Unlike retroviruses, adenoviruses carry double-stranded DNA. They also do not integrate with the host cell’s DNA, but instead float free in the nucleus of the host. The instructions in the strand are carried out normally, but when the cell replicates the DNA strand is not passed down to the replicated cell and therefore the therapy must be readministered as the cell population grows. Gendicine, the first gene therapy product to be licensed to treat cancer, is an adenovirus and is used to treat neck and head cancer. Finally, scientists use adeno-associated viruses (AAV), which are small viruses that contain a genome of single stranded DNA. It works either by inserting its genetic material on a certain site of chromosome 19, or by recombining with the host DNA. Although it carries such a small amount of DNA and is difficult to produce, AAV vectors are popular because people usually do not develop an immune system response to them. Also, AAV vectors are able to deliver genes to the3""brain, unlike other vectors. Along with adenoviruses, AAV vectors are able to infect a wider range of cells than retroviruses, which infect only a limited number of host cell types. Although there are other methods that do not involve viral vectors, these vectors are the most used techniques in order to introduce the therapeutic DNA into the host cell. Unlike somatic gene therapy, genetic gene therapy is still in a mostly theoretical stage of development. There are two stages of the germline that work well for genetic gene therapy: when the egg is released either before or after it is fertilized by the sperm, and when the egg is forming blastomeres. It is possible to simply inject DNA into the egg, and the DNA will integrate into one of the chromosomes. However, this method does not always work properly and can result in some cells of the embryo receiving the modified DNA while other cells do not. When the germline is in the blastomere stage it is manipulated in a test tube, creating embryonal stem cells. These cells can later be injected into a blastocyst and implanted in a surrogate mother. This gene therapy then results in an individual who has some cells that contain the modified embryonal stem cells, and some cells that do not have the modified DNA in them, but DNA which comes from the fertilized egg. So far, gene therapy has been successful in modifying various traits of animals, and scientists are rapidly learning more about this technique. While the use of somatic gene therapy in medicine does not face much ethical scrutiny, the same cannot be said of genetic gene therapy. Opponents have two main issues with genetic gene therapy when describing why it is unethical. The first issue involves the progeny of the patient who are affected by the therapy. The second issue centers on the fact that in order to do the gene therapy, in vitro fertilization must be used. Proponents of this therapy point to the potential breakthrough treatments this therapy may offer when they try to answer these ethical problems.4"" Those who support genetic gene therapy bring up two strong arguments in favor of it. The first is that by modifying the genes of the embryo, they believe one will be able to avoid the onset of diseases that would have been unavoidable otherwise. Embryos could be screened to determine the likelihood of developing certain diseases, and could be treated accordingly. Very severe genetic disorders that do not allow the embryo to develop properly could be treated before they are able to affect the
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