Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
NOVA Home Find out what's coming up on air Listing of previous NOVA Web sites NOVA's history Subscribe to the NOVA bulletin Lesson plans and more for teachers NOVA RSS feeds Tell us what you think Program transcripts Buy NOVA videos or DVDs Watch NOVA programs online Answers to frequently asked questions
Killer Disease on Campus

Making Vaccines
Naked-DNA vaccine: HIV

 


HIV step 1

Step 1
Use the growth medium, which includes PCR primers, to make billions of copies of a single gene.

 

Genetic vaccines, sometimes called naked-DNA vaccines, are currently being developed to fight diseases such as AIDS. The goal of these vaccines is to use a gene from a pathogen to generate an immune response. A gene contains the instructions to create a protein. With a genetic vaccine, small loops of DNA in the vaccine invade body cells and incorporate themselves into the cells' nuclei. Once there, the cells read the instructions and produce the gene's protein.

Using a technique called PCR, which stands for polymerase chain reaction, you'll make many copies of a specific gene. The work of finding the gene and copying sequences of its DNA is done by "primers."



HIV step 2

Step 2
Combine the virus genes with vectors.

 

To make your genetic vaccine, you'll use vectors. Vectors are agents that are able to enter and instruct cells to create proteins based on the vector's DNA code. In this case, the vectors are loops of double-stranded DNA. You can exploit the vector's ability to create proteins by splicing a gene from the virus into a vector. The cell that the vector later invades will then produce proteins created by the virus.

The vectors and copied genes have been treated with restriction enzymes, which are agents that cut DNA sequences at known locations. The enzymes have cut open the round vectors and trimmed the ends of the copied genes.



HIV step 3

Step 3
Add bacteria to the vectors to allow the altered vectors to replicate.



 

The ends of the vectors have again come together, but now with a gene spliced into the loop. You'll need many copies of the vector/gene loop for your genetic vaccine. These copies can be produced with the help of bacteria.

Vectors are capable of self-replicating when within a bacterial host, as long as that host is in an environment conducive to growing. After you combine the vectors and bacteria, the vectors will be shocked into the bacteria.



HIV step 4

Step 4
Use the purifier to separate the altered vectors from the bacteria.



 

The final vaccine should include only the vectors, so you'll need to separate them from the bacteria after enough copies have been produced. This can be done with a detergent, which ruptures the cell walls of the bacteria and frees the DNA within.

The relatively large bacterial DNA can then be separated from the smaller DNA loop that makes up the vector.



HIV step 5

Step 5
Fill the syringe with the altered vectors.



 

Upon inoculation, billions of copies of the altered vector will enter the body. Of these, only 1 percent will work their way into the nuclei of body cells. But that's enough.

The body's immune system responds to these proteins once they leave the cell. But more importantly, it also reacts to proteins that are incorporated into the cells' walls. So in addition to mounting an attack against the free-floating proteins, the immune system attacks and eliminates cells that have been colonized by a pathogen. The vaccine, then, works like a live vaccine, but without the risk. (With a live vaccine, the pathogen can continue to replicate and destroy cells as it does so.)



HIV done

Done
The naked-DNA vaccine is complete.

Select another pathogen.



 

Congratulations. You have just produced a naked-DNA HIV vaccine.

Trials for a genetic vaccine that may protect against AIDS began in 1995. These vaccines, which contained HIV genes, were given to patients who already were infected with HIV. A year later, the trials were expanded to test people without HIV. These trials are still being conducted and have not yet produced conclusive results.

Human trials for genetic vaccines against herpes, influenza, malaria, and hepatitis B are also underway.

Note: Although the genetic material of HIV is RNA, the procedure for making the vaccine is similar.




Smallpox icon

Similar-pathogen vaccine:
smallpox virus

  Measles icon

Attenuated vaccine:
measles virus

  Polio icon

Killed vaccine:
polio virus

Tetanus icon

Toxoid vaccine:
tetanus

  Hepatitis icon

Subunit vaccine:
hepatitis B

  HIV icon

Naked-DNA vaccine:
HIV



Killer Disease homepage



Send feedback Image credits
   
NOVA Home Find out what's coming up on air Listing of previous NOVA Web sites NOVA's history Subscribe to the NOVA bulletin Lesson plans and more for teachers NOVA RSS feeds Tell us what you think Program transcripts Buy NOVA videos or DVDs Watch NOVA programs online Answers to frequently asked questions

Support provided by

For new content
visit the redesigned
NOVA site