Activity 6: Gene Therapy
Students will assess the risks and benefits of different gene therapies.
Gene Therapy involves the insertion
of new genetic material into cells in a patient's body. By inserting manipulated
DNA directly into the body, doctors can correct or enhance a particular
cellular function, such as enzyme production; increase the vulnerability
of diseased cells; or, in some cases, block the operation of particular
cells or cell functions.
Developing specific therapies requires several steps. First, researchers
must determine the gene or genes that cause or affect the disorder. Next,
they must decide on the best approach for solving the problem and determine
how to modify DNA sequences to carry out that solution. And then researchers
must find safe, efficient vehicles--called vectors--to carry the modified
DNA to targeted cells. There are several vectors already in use, including
chemical solutions, synthetic fat molecules, and viruses that have been
modified so that they are harmless.
In each step of the process there is some degree of difficulty and risk.
It is not always clear how modifying one gene may affect other genes in
the DNA sequence, and if more than one gene needs to be modified, the chances
of other genes being affected goes up. It is also possible that the integration
of viral DNA into a cell's genome might
accidentally activate genes that can trigger the growth of cancer. And it
is difficult to target the correct cells to modify. For example, the cells
responsible for producing mucous in cystic fibrosis patients are located
in the patients' lungs. There is no easy way to remove and insert cells
directly into the lungs, so current experimental procedures involve using
a tube that drips a solution containing modified cells into the lungs. Doctors
hope that enough cells will be reached by this process to effect a change.
In addition, there are many ethical issues involved in gene therapy.
For example, some of the current questions being debated include: Which
diseases should be targeted? How will the genetic manipulation be regulated?
How much money should be spent on developing gene therapies for disorders
for which alternative therapies already exist? Should genetic manipulation
be used to eliminate defective genes from egg or sperm cells? Will genetic
manipulation be used to "improve" the human species by selectively
controlling for certain traits? Who should make these decisions?
A modified virus carrying the gene for the defective protein
in people with cystic fibrosis enters a lung cell. The virus breaks down,
and the modified DNA enters the nucleus of the cell. In the nucleus, transcription of the viral DNA produces
single strands of messenger RNA, which
migrate to the cytoplasm and begin producing a correct version of the defective
For each pair of students:
Duplicate Gene Therapy Project Summaries and distribute to pairs of students.
- Divide the class into groups of four to six. Explain that each group
represents a committee that oversees the development of new gene therapies.
The committee decides which projects should be given money for research
and development of a therapy. However, funds are limited, and only one
new project can be funded.
- Ask the students to carefully read through the project summaries on
the handout. Then ask each student to do a risk/benefit analysis for the
projects to describe the issue and record information upon which to base
his or her decisions. Explain that their risk/benefit analyses should contain
the following five parts:
- At least five facts about the proposed therapies
- At least five opinions about the proposed therapies
- At least five risks involved in developing the therapies
- At least five benefits involved in developing the therapies
- A decision statement that includes a rationale based on the risks and
If necessary, you may want to help students get started by asking questions
such as: How many people does the therapy affect? Are there specific ethnic
groups that the therapy affects? Is the disorder fatal or debilitating?
Does the therapy require modifying a single gene or more than one gene?
Will modifying the genes cause unintended changes? Will the changes produced
by the modified genes be inheritable? Are alternative treatments available
for the disorder? If so, how effective are they?
- Once students have completed their risk/benefit analyses, have each
group use the information to decide which project should be funded. Then
have the groups present their decisions, along with their rationales, to
the class. They should also indicate any additional information they might
need to make a better decision.
- Which factors were most important to you in deciding which gene therapy
project to fund? Which factors were least important? Why? Did all the members
of your group agree on which project to fund? If not, what factors helped
your group reach the final decision?
- Suppose there were a fourth project that involved developing a gene
therapy to "change" skin color. Do you think such a project should
be funded? Why or why not? What other information might you want to have
about the project before you decide?
- Suppose it were possible to eliminate genes from egg or sperm cells
that make us vulnerable to disease or aging. What are some of the consequences
of changing the egg or sperm cells? Under what conditions do you think
this practice should be allowed? Give reasons for your answers.