Results of a new study indicate that a vaccine against HIV may not necessarily require the production of protective antibodies in the blood the way most traditional vaccines work. A new target of HIV vaccine research and development may involve causing the virus to trigger the body to produce mucosal antibodies in the vagina and rectum.
Researchers have been looking for an HIV vaccine that works like most traditional vaccines, which involves introducing the body to a version of an infectious organism that prompts the immune system to quickly produce antibodies in the blood. These antibodies are then able to bind to and destroy the organism if it is encountered in the future. Unfortunately vaccine research in HIV using this concept has been unsuccessful thus far, displaying a need to use a different strategy for research.
It is known that HIV is mainly transmitted mucosally during sexual intercourse. There have been documented cases where people have been able to resist HIV infection despite repeated high-risk exposures. These individuals did not produce antibodies to the virus in the blood, but had evidence of antibodies (called IgG) in mucosal tissue. This inspired researchers to think that rather than focus on the production of antibodies in the blood, they should look at whether a vaccine can provoke the production of HIV-protective antibodies in the sites most commonly tied to infection, such as the vagina and rectum.
This new study evaluated whether an intranasal or intramuscular vaccine could trigger the body to produce these mucosal antibodies and provide protection against HIV. The researchers administered a vaccine to 5 moneys and a placebo to the other 6. All of the monkeys were exposed vaginally to the monkey version of HIV, called simian immunodeficiency virus (SIV), and were followed for six months.
The study found that all 5 of the vaccinated monkeys failed to become infected with SIV, and all 5 produced both IgG in mucosal tissue as well as another mucosal antibody called IgA. Interestingly, the antibodies in their blood completely lacked the ability to neutralize the virus. All 6 of the monkeys who received a placebo became infected with SIV.
The results of this study challenge the idea that circulating antiviral antibodies in the blood are required for protection against HIV infection, and shed some light on using a different research approach. Further studies will be needed to confirm these results, but the study provides hope in using a new direction for research and development of a human vaccine against HIV.