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1. What are the key scientific concepts behind AIDS vaccines?
2. What are the major scientific challenges to making an AIDS vaccine?
3. Will a vaccine that works in one place in the world work in another?
4. If the scientific challenges are so great, why do scientists think an AIDS vaccine is possible?
5. What are the major approaches scientists are using to develop an AIDS vaccine?
6. How many years will it be before the world gets an AIDS vaccine?
7. What are the most promising vaccines candidates currently in clinical testing/in the pipeline?
Vaccine basics - Learn the basics of vaccine science with this quick introduction from the AIDS Vaccine Handbook (2005).
HIV life cycle poster - See how vaccines, microbicides and antiretroviral drugs impact the HIV life cycle
HIV in pictures - Get a better understanding of HIV through this pictorial description of HIV with both diagrams and photographs of the virus. From the AIDS Vaccine Handbook (2005).
The immune system in pictures - Learn about the immune system with easy-to-understand diagrams. From the AIDS Vaccine Handbook (2005).
AIDS vaccine approaches in development - Learn about the different approaches in vaccine development like "naked DNA" vaccines, live vector vaccines and peptide vaccines. Which ones induce the best immune responses and where do these results point the research? From the AIDS Vaccine Handbook (2005).
Vaccines that trigger cellular immunity: what can we hope for? - While most vaccines induce antibody protection against infection, HIV has proven a worthy foe against this traditional method. This chapter from the Handbook outlines what hopes there are for developing vaccines that can target cellular immune responses to provide protection. From the AIDS Vaccine Handbook (2005).
Vaccine development: from concept to licensed product - Learn about the different stages of vaccine development and what's involved in the process that takes a vaccine from a concept in a lab to your doctor's office. From the AIDS Vaccine Handbook (2005).
IAVI's Scientific Blueprint - Read IAVI's biannual blueprint of the AIDS vaccine field and its recommendations for strengthening and accelerating the global search for a preventive AIDS vaccine. (2006)
Ending AIDS - link to the official website and learn more about Ending AIDS: The Search for a Vaccine, the film that transforms the intricacies and jargon of science into a terrifically lucid, fast-paced study of technology and human initiative at their outer limits. (2005)
Challenges in Designing HIV Vaccines - From the NIAID, an overview that outlines the various challenges scientists face in the research and development of HIV vaccines. (2005)
The Science of AIDS Vaccines: An Introduction for Community Groups - From the International Council of AIDS Service Organizations (ICASO), a vaccine science primer geared towards community groups. Available in
English, Spanish, French. (2003) |
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Ever since 1983 when HIV was discovered to be the cause of AIDS, scientists have been trying to develop a vaccine to prevent AIDS. After over two decades of work, there is still no vaccine.
One of the main reasons is that HIV is a much more daunting biological foe compared to the viruses that cause other diseases such as measles, mumps and influenza - for which scientists have developed highly-effective vaccines which are used widely around the world.
Among other characteristics that make HIV so challenging is that the virus mutates much more rapidly than many other viruses. This ability to change its genes and therefore some aspects of its structure make it very difficult to effectively attack with a vaccine-generated immune response.
Most other vaccines, for instance, appear to work by stimulating an antibody response which blocks the activity of an invading virus. Antibodies attach to the surface of viruses and other pathogens and stop them from causing illness or infecting cells. Antibodies which are effective in this way are called neutralizing antibodies.
HIV has developed ingenious ways to avoid control by broadly neutralizing antibodies. Antibodies are generated as the result of a lock-and-key type interaction between various cells in the immune system and the virus itself. In scientific terms, the key holes are called "binding sites." HIV has an outer coating, or envelope, that conceals many of the binding sites for neutralizing antibodies. Some of these binding sites are also concealed by the way that the HIV proteins fold over each other. They are only exposed for a brief instant while the virus is binding to a cell. This makes it very difficult for the immune system to mount an effective antibody-response to control the virus.
Antibodies are part of the humoral immune system, which is one of the two "arms" of the immune system. The other arm is the cellular immune system. This part of the immune response involves many different types of immune cells, including T-cells, which control the virus after it has infected cells.
(If you're feeling a little lost, click
here to see the immune system in pictures!)
It has proved very challenging to develop vaccine candidates with a long-lasting T-cell response that can control HIV. One reason for this is that the virus attacks and kills T helper cells, which play an essential role in orchestrating the overall immune response. Also, although the body produces so-called killer T cells that can attack and kill HIV infected cells, these cells identify their targets by specific protein sequences on the surface of the virus or the infected cell. Because HIV can mutate or change some of its genetic sequences so rapidly, the virus is able to evolve into forms that can escape killer T-cells.
What's more, unlike most other human viruses, HIV is a retrovirus (see pictures of HIV). This means its genetic material is encoded as RNA, not DNA. The virus depends on hijacking our cells genetic machinery to make more copies of itself. Retroviruses were only discovered in the latter portion of the 20th century and are still poorly understood.
A further challenge is that HIV can remain "latent" in cells in the body which are not actively multiplying. These so-called reservoirs could persist even after a vaccine-induced immune response had quelled an active infection. The infection could be re-established if these cells were activated later on.
All of these issues pose enormous hurdles for AIDS vaccine researchers. As we have learned more about the science of HIV and the dynamics of transmission, we have shifted our strategies for vaccine design and our goals for what first and even second generation vaccines might accomplish. And while the challenges still remain, there is also a strong sense of urgency in the field. But whereas 10 years ago many scientists had little hope of developing an AIDS vaccine, scientists are now much more optimistic about the prospects.
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