When applied as part of a rectal gel, the drug tenofovir may prevent HIV transmission, according to an study performed in macaque monkeys. These results were released on August 4, 2008 in the open access journal PLoS Medicine.

In both heterosexuals and homosexuals, rectal intercourse carries a very risk of HIV transmission. Prophylactic measures thus far have focused on condoms and other physical barriers, so there is limited information about the potential use of topical products for this type of transmission.

To investigate this potential new preventative measure, Martin Cranage of St. George’ss University of London and colleagues performed a study in macaque monkeys. After application of the experimental gel, a placebo, or no medication, human rectal exposure to HIV was simulated in the monkeys by exposure to Simian immunodeficiency virus (SIV), a form of the disease that is specific to monkeys.

The researchers found that the macaques pre-treated with rectal tenofovir gel up to two hours before viral exposure were partly or totally protexted from SIV infection. Untreated animals, along with those treated with the placebo were infected with the virus. Notably, some of the macaques given protection also developed T-cell immune responses to the virus.

These findings indicate that prevention of rectal HIV transmission might be achieved through topical treatment with antiretroviral drugs, a powerful new tool for HIV prophylaxis. However, investigating this will provide further challenges for scientists, because true efficacy cannot be concluded in animals alone. Further, recent human trials have had some setbacks — this is shown in a study of women using microbicide vaginally who actually showed increased rates of HIV infection. Also, because of HIV’s mechanism of attack via activated T-cells from the immune system, it is important to establish that the noted immune response does not increase subsequent infection with the virus.

The authors conclude, optimistic despite these limitations, that there is potential for topical applications of antiretroviral drugs. “There may be potential for synergy between topical ARV/microbicide use and vaccination as a two-pronged strategy for preventing infection with HIV,” they say.

Florian Hladik and Charlene Dezzutti, contributed an accompanying Perspective noting the implications of this study on further studies of a similar nature, including continued refinement of the animal models, significant further pre-clinical research, and molecular level investigation.

About PLoS Medicine

PLoS Medicine is an open access, freely available international medical journal. It publishes original research that enhances our understanding of human health and disease, together with commentary and analysis of important global health issues. For more information, visit http://www.plosmedicine.org/

About the Public Library of Science

The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world’s scientific and medical literature a freely available public resource. For more information, http://www.plos.org/

Prevention of SIV rectal transmission and priming of T cell responses in macaques after local preexposure application of tenofovir gel.

Cranage M, Sharpe S, Herrera C, Cope A, Dennis M, et al.

PLoS Med 5(8): e157.

doi:10.1371/journal.pmed.0050157

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Can a topical microbicide prevent rectal HIV transmission?

Hladik F, Dezzutti CS

PLoS Med 5(8): e167.

doi:10.1371/journal.pmed.0050167

Click Here For Full Length Perspective

Written by Anna Sophia McKenney