The active ingredient in these vaccines is an intact virus or bacterium that has been killed or otherwise stripped of its ability to infect humans. Examples include the cholera and injectable polio vaccines. Historically, this approach has not been taken to develop vaccines against HIV due to the risk that the viruses harvested for such preparations may not all have been killed or adequately inactivated.
These vaccines use a form of the targeted pathogen that is highly unlikely to be harmful—one capable, say, of multiplying, but not typically of causing disease. Examples include the measles vaccine and the oral vaccine against polio, which has been widely deployed in global efforts to eradicate the disease. Live-attenuated vaccines can be very effective because they closely mimic the behavior of the targeted pathogen, giving the immune system a clearer picture of what it would be up against. However, this approach has not been applied to the development of preventive AIDS vaccine candidates because of the risk that attenuated HIV might revert to its disease-causing form.
Vaccines of this variety are composed of purified pieces of the pathogen—known as antigens—that generate a vigorous, protective immune response. Common subunit vaccines include the seasonal flu and hepatitis B vaccines. This approach was employed to devise the first AIDS vaccine candidate tested in humans, which failed to induce protection from HIV infection. AIDS researchers, including those affiliated with IAVI, are still pursuing this strategy in novel ways.
DNA vaccine candidates:
These vaccine candidates are also designed to train the immune system to recognize antigens. The difference is that their active ingredients are not the purified antigens themselves, but circles of DNA called plasmids that carry genes encoding those antigens. Human cells passively take up these plasmids and produce the antigens that train the immune system to recognize the targeted pathogen. No vaccines of this sort have yet been approved for human use, but several AIDS vaccine development efforts are employing this approach, including one candidate in IAVI’s portfolio
Recombinant vector vaccine candidates:
These vaccine candidates, like DNA-based candidates, introduce genes for targeted antigens into the body. But the genes are inserted into a virus that actively infects human cells. The viruses chosen as vectors are safe to use because they do not ordinarily cause disease in humans or have been stripped of their ability to proliferate after infecting cells. No vaccines of this sort have yet been approved for human use, but several AIDS vaccine development efforts are employing this strategy, including several candidates in IAVI’s portfolio.