19 Biopharming Edible Vaccines As y o u r e a d in Activity 1, A Genetically Modified Solution? scientists

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1 19 Biopharming Edible Vaccines As y o u r e a d in Activity 1, A Genetically Modified Solution? scientists have been using genetically modified E. coli for more than 30 years to manufacture proteins for medicinal and industrial purposes. In the early 1990s, pharmaceutical researchers began working with genetically modified organisms to insert vaccines against diseases into the foods we eat. Their goal was to find a way to engineer a cheap, easy way to vaccinate people without needles. In many developing countries, making sure that people get their shots has been difficult because there are not enough qualified personnel and equipment. An edible vaccine contained in food would help to address these problems. Throughout this unit you have been learning about genetic modification techniques the same ones that are involved in the research on edible vaccines. In this activity you will read about how these techniques can be combined to engineer genetically modified organisms that are edible and carry vaccines. Scientists are researching ways to genetically modify plants, such as this lettuce, to create edible vaccines. 393

2 Science & Global Issues/Biology genetics Challenge 00What are the benefits and trade-offs of genetically modifying crops to contain edible vaccines? Materials For each pair of students set of 8 Genetic Modification of Lettuce Cards Procedure 1. Spread the Genetic Modification of Lettuce Cards out on the table in front of you. Each card shows a step required to genetically modify lettuce. With your partner discuss what each card shows. 2. You performed processes similar to those shown on the cards in Activity 2, Creating Genetically Modified Bacteria, Activity 9, Isolating DNA, and Activity 18, Which Corn Is Genetically Modified? With your partner look back in your science notebooks and this book to identify which of these three activities correlate to which cards. Note that an activity may correlate to just one or to multiple cards, and some cards discuss processes you have not studied. 3. Copy the table below into your science notebook, and write your ideas from Step 2 in the table. Card Summary of step Activity from Genetics unit 4. With your partner, arrange the cards in the correct order for genetically modifying lettuce. Record the predicted order in your science notebook, and add any new information to the KWL chart (What do I Know? What do I Want to Know? What did I Learn?) that your class started at the beginning of the activity. 5. Complete the reading that follows. As you read, record any new information or questions you have in your KWL chart. 6. When you finish the reading, review the order of the cards with your partner. Revise the order to reflect the information given in the reading. Refer back to the text if necessary. 7. Compare the card order with the other pair in your group. Discuss any differences in the way you have ordered the cards, and come to an agreement about the order. Record the final order your group decides on in your science notebook. Add any new information to your KWL chart. 394

3 Reading: Edible Vaccines Imagine there was a way to be vaccinated against hepatitis B simply by eating a bowlful of lettuce instead of getting a shot. Currently most vaccines come in the form of an injection given by a doctor, nurse, or skilled technician. The vaccines must be kept refrigerated, and some of the shots hurt more than others. Edible vaccines, such as a vaccine in lettuce, would eliminate these problems. Vaccine lettuce is just one example of a genetically modified organism engineered by scientists working in the growing field of molecular farming, also known as bio pharming. They are researching ways to insert genes into plants and animals. These genes would cause the organisms to produce proteins for pharmaceutical purposes. Making an Edible Vaccine Vaccines have been successful weapons against diseases since the 1800s. They have nearly eradicated polio and smallpox around the world and have prevented millions of children from getting measles, mumps, and rubella. Most vaccines are based on a protein from the virus that causes the particular disease, which triggers an immune system response in our bodies. The virus protein in the vaccine is not enough to actually cause the disease. Instead, when the vaccine is injected the immune system responds the same way it would to fight the disease, eventually making the person immune to the disease. Creating an edible vaccine from a genetically modified organism relies on the same principles as making other genetically modified organisms. Scientists must first isolate the DNA from the disease agent. Just as you did in Activity 9, Isolating DNA, scientists lyse (break down) the cell membrane with a detergent and then apply alcohol to precipitate (separate) out the DNA from the other material. biopharming edible vaccines Activity 19 isolating Dna detergent alcohol sample lyse PreciPitate dna other material dna other material 395

4 Science & Global Issues/Biology genetics After the DNA is isolated, scientists extract the correct gene from the DNA and make copies of that gene. To do this, they use a process called PCR (polymerase chain reaction). The gene is heated to separate the DNA double helix strand, and then an enzyme and single nucleotides are added. Each separated strand is copied to form a double-stranded segment of DNA. This process is repeated through many cycles to make multiple copies of the gene. The diagram below shows the eight copies produced by three cycles of PCR. After 20 cycles over one million copies of the gene will be produced. Polymerase chain reaction (PCR) Once the gene has been copied, geneticists engineer a DNA construct. A DNA construct is a piece of DNA that is made of three specific parts: a start region, the desired gene, and a selectable marker. Antibiotic resistance is a common selectable marker. When you transformed E. coli in Activity 2, Creating Genetically Modified Bacteria, ampicillin resistance was the selectable marker. This meant that 396

5 biopharming edible vaccines Activity 19 only E. coli cells transformed with the green fluorescent protein (GFP) protein would grow in Petri dishes with ampicillin in them. In other words, only the bacteria that had taken in the DNA construct containing the ampicillin resistance gene and the gene to make them glow would grow on the ampicillin plates. Bacteria that had not taken up the construct would not grow. Scientists also add a start region, which signals where gene transcription should begin. virus protein gene gene of interest dna construct start virus protein gene antibiotic resistance gene start signal codon antibiotic resistance gene selectable marker gene When all of these steps have been completed, scientists insert the DNA construct into the target organism. This can be done in several ways. In Activity 2, Creating Genetically Modified Bacteria, you worked with a DNA plasmid, a ring of DNA found in bacteria. With bacteria, scientists use enzymes to insert the DNA construct into plasmids. Then the plasmid is introduced to the bacteria, which infects the target organism, bringing along the DNA construct. There are several methods for transmitting the DNA construct into the target organism, three of which are shown in the figure below. or or Particles are coated with dna with desired gene and fired into plant cells using a gene gun dna with desired gene is inserted into a plasmid which is inserted into a bacterium the bacterium infects the plant cells dna with desired gene is transfered into a virus which infects the plant cells 397

6 Science & Global Issues/Biology genetics After the DNA construct is inserted into the DNA of the target organism, the newly modified organism is grown to mature size. Researchers test for the presence of the new gene using electrophoresis, as you did in Activity 18, Which Corn Is Genetically Modified? Scientists also perform a second, more sensitive test, Southern blotting (named for molecular biologist Edward M. Southern), to confirm that the virus protein gene is being created by the cells and is present in the modified organism. If the modified organism produces the virus protein gene, clinical trials are conducted to see if the protein produces the desired vaccine effect. For example, in the vaccine lettuce that was modified to contain the hepatitis B protein gene, scientists first tested the modified lettuce on mice. The mice were fed the modified lettuce, and then tested to see if their immune systems responded to the hepatitis B protein. Once it was determined that the process does work in mice, similar tests were performed on human subjects. Today, testing and research are continuing and will go on until scientists determine if the lettuce consistently and safely produces the desired result in humans. Benefits and Trade-offs of Edible Vaccines The concept of producing edible genetically modified organisms to deliver vaccines has many benefits. Unlike traditional vaccines, many of the plants being tried in this process require little refrigeration, if any. It is easier to grow large amounts of the modified organisms than to produce large amounts of the injectable vaccine. The lettuce could be farmed anywhere that there is adequate soil, sun, and water. Because production does not involve expensive equipment or laboratories, it would cost less than traditional vaccines. There is no need for sterilized needles, or for trained medical staff to administer the vaccine. 398

7 biopharming edible vaccines Activity 19 There are also drawbacks to edible vaccines. Because organisms naturally vary, the dosage of the vaccines may be uneven. This is important because if there is not enough of the vaccine, the immune system will not respond. If there is too much of the vaccine in the organism, the body tolerates the vaccine but the immune system does not respond properly. Also, the edible vaccines still have to be delivered to where they are needed, which is the same problem with the traditional vaccines. Many of the locations where vaccines are most needed are remote areas that are difficult to reach and do not have the farmland needed to grow edible vaccines. Another concern that has been raised is that if the modified organisms are accidentally introduced into regular food crops, there could be unintended consequences. Several edible vaccines are in the early stages of being tested on humans. Corn and potatoes have been modified to produce a vaccine against a harmful strain of E. coli, potatoes have been modified to vaccinate against the Norwalk virus (one cause of the symptoms often called the stomach flu, but not related to influenza), and, as you read earlier, lettuce has been modified to vaccinate against hepatitis B. Other scientists are working on methods to grow the modified plants, and then turn them into vaccine pills, which would help make them easier to distribute and make the doses even. These methods, however, have not yet been fully developed. Currently, there are no edible vaccines approved for use in the United States. Analysis 1. What are the steps involved in genetically modifying an organism? 2. Compare the genetic modification of vaccine lettuce to the process of selectively breeding rice with desirable traits, which you learned about in Activity 7, Breeding Better Rice. In what ways are the processes similar? Different? 3. What are the benefits and trade-offs of using genetic modification to produce an organism with a specific phenotype? Key Vocabulary DNA construct genetic modification vaccine 399