Question: Passage $\mathrm{V}$
For many years, researchers have been interested in developing edible vaccines that would provide protection against various bacterial and viral diseases. An edible vaccine is a genetically modified organism (GMO) that is created when genes from the bacteria or virus being vaccinated against are inserted into plant cells. As the plants grow, they produce proteins from the bacteria or virus that the researchers are attempting to vaccinate against. When a person eats the plant, the viral or bacteria proteins serve as antigens, which initiates a primary immune response.
Some of the plants that are of interest in edible vaccine development are bananas, potatoes, tomatoes, corn, rice, tobacco, and soybeans. While early research focused on growing crops that produced edible products such as bananas, the most recent research is focused on extracting material from the leaves and seeds of the plants, dehydrating it, and putting it into capsules that can be swallowed. This allows for a more predictable dosage of the vaccine and eliminates concerns that the crops containing the vaccine would be accidentally eaten by individuals who are not in need of the vaccine. The term edible vaccine has now been replaced with the term plantderived oral vaccine.
The development of plant-derived oral vaccines solves many problems associated with injectable vaccines. Because plant-derived oral vaccines are grown in crops, there is no problem with storage or refrigeration that is required of most traditional vaccines. These plant-derived vaccines also require no special training to administer. Additionally, when a vaccine is taken orally, it provides mucosal immunity due to the production of IgA antibodies by the immune system-in addition to systemic immunity. Since 90 percent of diseases enter the body through a mucus membrane, a vaccine that coerces mucosal immunity is of great benefit in the prevention of many diseases.
When a vaccine is given orally, it must pass through the digestive system before being absorbed into the bloodstream, whereas injected vaccines enter the bloodstream directly. What problems might vaccine developers be concerned about with a plant-derived oral vaccine that has to pass through the digestive tract?

Options:
A. There would be concern that the vaccine would not work quickly enough if it had to travel through the digestive tract.
B. There would be concern that stomach acidity might damage the bacterial or viral proteins that were expressed by the plant cells of the vaccine.
C. There would be concern that the vaccine might elicit an inflammatory response in the digestive tract.
D. all of the above
Answer: All vaccines take time to work (often weeks before full immunity occurs), so waiting for an oral vaccine to pass through the digestive tract (which takes no more than a few hours) is not of major concern. This eliminates choice A. Choice $\mathrm{C}$ suggests that inflammation in the digestive tract might be a problem. Since the inflammatory response is expected as one of the nonspecific immune defenses, it is not of major concern. Since two choices have been eliminated, choice D is no longer an option. This leaves choice B as the correct response. Since the plant has been engineered to express proteins unique to the virus or bacterium being vaccinated against, it is possible that these proteins might be damaged in the stomach. Recall that the function of the stomach is to digest proteins by using the enzyme pepsin. The correct answer is B.