Researchers in the HIV vaccine field have been disappointed in recent years by the failure of trials of promising AIDS vaccine candidates. The most current and perhaps most frustrating was a trial of a vaccine developed by Merck which used an adenovirus serotype 5 vector for antigen delivery. This trial was halted ahead of schedule when no evidence turned up that it protected against HIV infection or controlled the virus once a person became infected. Even worse news was that this vaccine increased the risk of HIV infection in uncircumcised men who had proven adenovirus serotype 5 antibody immunity from natural exposure with the common cold virus.
AIDS Vaccine Research
Some research groups are exploring regimens that use alternate but less-common serotype adenovirus vectors, which include serotypes adenovirus 26 and 35. These elicit different immune responses than adenovirus serotype 5, according to Professor Dan Barouch of Harvard Medical School and chief of vaccine research at Beth Israel Deaconness Medical Center. Dr. Barouch led a study that showed promising results with vaccines containing these vectors.
This particular study found that rhesus macaques could be partially protected from the simian immunodeficiency virus by using serotype adenovirus 26 along with modified vaccinia Ankara, or with serotype adenovirus 35. The simian immunodeficiency virus is considered to be one of the more difficult viruses to
combat with a vaccine. Researchers are now ready to test the adenovirus 26/MVA regimen in Phase I clinical trials with volunteers.
The potential AIDS vaccine will be administered orally and the volunteers will be sequestered for 12 days. The vaccine has been engineered using a dose of the AIDS virus itself, just as other live vaccines have done. Vaccines generally work by promoting immune response in the subject, leading to the formation of antibodies.
A reason for optimism is that activating the immune system through the digestive tract (orally, via a pill) has worked well before, with the polio virus. This allows for ease of distribution and administration, especially in high risk areas of the world.
AIDS Vaccine Difficulties
It has been difficult to engineer a successful AIDS vaccine because the virus attacks the very same immune cells that are mobilized by a vaccine, and because the virus can cover itself in an always changing envelope inside the cell. This particular vaccine was computer designed by a program that chose a batch of the envelope disguises from HIV strains worldwide. If it is successful it will enable the immune system to recognize and react strongly to these disguised HIV proteins. It is hoped that as the harmless adenovirus spreads in the digestive tract the immune cells responsible for destroying intruders will also recognize the attached HIV and react against any future exposure to the HIV virus.
This research and trial are the most recent and most promising in the decades long search for an AIDS vaccine to stem the tide of HIV infection in the developing world, as well as in more technologically advanced societies where people are still being infected with HIV on a daily basis.