Biology (Holt)

Vaccines
Many viral diseases, such as smallpox and polio, cannot be treated
effectively by existing drugs. Instead they are combated by preven-
tion—using vaccines. A is a solution containing all or part
of a harmless version of a pathogen (disease-causing microorgan-
ism). When a vaccine is injected, the immune system recognizes the
pathogen’s surface proteins and responds by making defensive pro-
teins called antibodies. In the future, if the same pathogen enters
the body, the antibodies are there to combat the pathogen and stop
its growth before it can cause disease.
Traditionally, vaccines have been prepared either by killing a spe-
cific pathogenic microbe or by making the microbe unable to grow.
This ensures that the vaccine itself will not cause the disease. The
problem with this approach is that there is a small but real danger
that a failure in the process to kill or weaken a pathogen will result in
the transmission of the disease to the very patients seeking protection.
This danger is one of the reasons why, for example, rabies vaccines
are administered only when a person has actually been bitten by an
animal suspected of carrying rabies.
Vaccines made by genetic engineering techniques avoid this dan-
ger. As illustrated in Figure 8,the genes that encode the pathogen’s
surface proteins can be inserted into the DNA of harmless viruses
such as cowpox (Vaccinia). The modified but harmless cowpox
virus becomes an effective and safe vaccine, as illustrated in Figure

8. The surfaces of the modified virus display herpes surface pro-
   teins in addition to the virus’s own surface proteins. When the mod-
   ified virus is injected into a human body, the body’s immune system
   quickly responds to this challenge. The immune system makes anti-
   bodies that attack any virus displaying the herpes surface protein.
   As a result, the body is thereafter protected against infection by the
   herpes virus.

vaccine

SECTION 2 Human Applications of Genetic Engineering 235

Real Life

1.Isolate the gene that

codes for the herpes

surface protein.

2.Insert the gene into a

harmless cowpox virus.

The virus makes the herpes

surface protein. Use this

modified virus in a vaccine.

Genital herpes virus Cowpox virus

(harmless)

Herpes surface protein

Gene

A person vaccinated with a genetically engineered vaccine, such as the genital
herpes vaccine, will make antibodies against the virus.

Figure 8 Making a genetically engineered vaccine

You might get a vaccine

in a banana.

Genetic engineers

are putting genes from

disease-causing microbes

into fruits and vegetables

to create vaccines that

are inexpensive and

easy to take. Clinical

trials using different

foods, including pota-

toes, are underway.

Finding Information

What are the most com-

mon ways vaccines are

now administered?