Published yesterday in Public Library of Science (PLoS), a new study done in mice with human immune systems show that mice given Pre-exposure prophylaxis (PrEP) did not contract HIV vaginally.
Though the study has not been tried in humans, it offers some hope for what may be possible to prevent women from contracting HIV vaginally--especially since the use of PrEP may be done without the consent or knowledge of a (consentual) sex partner. If this proves effective in women, the political hurdles to getting ARVs in the hands of women is going to be a huge battle.
I love the Public Library of Science for providing free access to peer-reviewed studies for people, and providing great summaries for thos of us not scientifically trained or inlcined. Here's what they said:
Editors' Summary
Background.
"Since the first cases of acquired immunodeficiency syndrome (AIDS) in 1981, the AIDS epidemic has spread rapidly. About 33 million people are now infected with the human immunodeficiency virus (HIV), the cause of AIDS. More than half of newly acquired infections now occur in women, mostly through unprotected vaginal sex with an infected male partner. Women are biologically more susceptible than men to HIV infection during vaginal intercourse and often cannot persuade their partner to use a condom. Consequently, alternative strategies that prevent intravaginal transmission of HIV (infection through the vagina) are urgently needed, particularly strategies that women can use without their partner's agreement. A vaccine would be ideal but it could be many years before an effective HIV vaccine is available so researchers are investigating other preventative strategies such as the use of microbicides—compounds that protect against HIV when applied inside the vagina—and pre-exposure treatment (prophylaxis) with antiretroviral drugs.
Why Was This Study Done?
Before any new strategy to prevent intravaginal HIV transmission is tried by women, it has to be tested in animals. Currently, this can only be done in macaques, an expensive option. In this study, the researchers have investigated whether “humanized BLT” mice could be used instead. When HIV enters the human body during vaginal intercourse, it sticks to dendritic cells (a type of immune system cell) in the vaginal lining. These cells carry the virus to the body's lymphoid tissues (collections of immune cells), where it infects and kills CD4+ T cells (another type of immune cell). Dendritic cells and CD4+ T cells have molecules on their surface that HIV recognizes. Mice are not normally susceptible to infection with HIV because their immune system cells lack these molecules. Humanized BLT mice have a nearly human immune system—BLT stands for bone marrow, liver, thymus. They are produced by implanting pieces of human fetal liver and thymus (the organ where T cells learn to recognize foreign invaders) under the kidney capsule of immunodeficient mice (animals born without an immune system) and then transplanting human hematopoietic stem cells (the source of the major immune system cells) into the mice.
What Did the Researchers Do and Find?
When the researchers examined the female reproductive tract of humanized BLT mice for human immune system cells, they found CD4+ T cells, dendritic cells and macrophages, all of which are involved in HIV infection. Furthermore, half of the blood cells of the BLT mice were human. Most of the BLT mice, the researchers report, were susceptible to intravaginal HIV infection as shown, for example, by a rapid loss of human CD4+ T cells from their blood. However, BLT mice pretreated with antiretroviral drugs (a mixture of emtricitabine and tenofovir disoproxil fumarate) were resistant to intravaginal HIV infection. As in human HIV infections, CD4+ T cells were also depleted in several other organs of the BLT mice after intravaginal HIV infection. Again, this depletion was prevented by antiretroviral pre-exposure prophylaxis. Finally, human CD4+ T cells also disappeared from the gut-associated lymphoid tissue (an important site for HIV replication and CD4+ T cell depletion during human HIV disease) of the BLT mice after infection with HIV.
What Do These Findings Mean?
These findings show that humanized BLT mice are susceptible to intravaginal infection with HIV and that many aspects of HIV infection in these mice closely mimic infection in people. In addition, by showing that pre-exposure prophylaxis with antiretroviral drugs prevents HIV infection, these results suggest that humanized BLT mice could be used to test new strategies designed to prevent intravaginal infection. As with all animal models, any approach that works in humanized BLT mice will still have to be tested in people. Nevertheless, these findings provide preclinical evidence that pre-exposure prophylaxis with antiretroviral drugs may be an effective way to prevent intravaginal transmission of HIV and, therefore, provide valuable support for clinical trials of this approach."