Gel Prevention of SIV transmission: The next big thing in HIV research

ResearchBlogging.org Cranage M, et al. “Prevention of SIV rectal transmission and priming of T cell responses in macaques after local pre-exposure application of tenofovir gel” PLoS Medicine; v5,issue 8, 2008.

I’m sure all of you know that AIDS (acquired immune deficiency syndrome) is a big deal.  It hasn’t been in the news as much recently as it has in the past, but AIDS still remains at pandemic levels.  In 2007, about 33.2 million people were thought to be living with HIV or AIDS.  HIV (human immunodeficiency virus) is the virus that causes AIDS, and preventing the spread of HIV has been incredibly important to the medical community since AIDS first appeared on the scene.

This post is actually about current research in the prevention of HIV transmission, but there is a lot more information about AIDS out there if you want it, and I’ll be including some links at the bottom of the post.

Anyway, though biomedicine is trying to find a vaccine to prevent the spread of AIDS, research is ongoing.  HIV is something called a retrovirus.  And as some of you know, viruses can mutate (which is why you have you get a new flu vaccine every year).  HIV in particular mutates very quickly, and is capable of outwitting many of the treatments already out there.  Currently, there are several kinds of antiretroviral drugs out there to treat HIV, but there is still no cure, and patients often have to take several kind of antiretrovirals at once to keep HIV at bay. So other studies are also ongoing to prevent the spread of HIV through other mechanisms while a vaccine is studied.  This study shows some pretty promising results for a new kind of gel.

The authors used rhesus macaques, which are one of the primate types commonly used for research prior to clinical trials.  Monkeys are very useful in HIV research because they can be infected with SIV (simian immunodeficiency virus), which, though very similar to HIV, is safe for humans to use, and yet the structure is similar enough that something that works for SIV will probably work for HIV.   In this case, the antiretroviral drug they were using (Tenofovir) is effective against SIV and HIV, so it’s possible that this gel will be useful to humans fairly soon.  Tenofovir is usually taken as an oral antiretroviral drug in people who already have HIV, but the researchers hoped that application prior to exposure could also help prevent the spread.

The researchers took Tenofovir in gel form and inserted into the rectum of the monkeys.  They then infected the same tissue with SIV at various time points.  The results were quite good, 8 out of 9 monkeys pre-treated with Tenofovir were protected against SIV.  In contrast, those who got a placebo gel or no gel at all almost all got SIV.  The researchers also found a positive correlation between the amount of Tenofovir that got into the blood after just 15 minutes, and the degree of protection, which implies that it is indeed the Tenofovir that is doing its job, as opposed to some other factor.

I’m sure when you think “rectal gel” you think “oh, they’re gearing it toward homosexual men”.  But that’s actually not necessarily the case.   It is far easier to spread HIV rectally than through other measures, because the rectum has only one very thin layer of cells protecting lymphoid cells.  The lymphoid cells are the cells that HIV prefers, and so you can see how easy it might be to get HIV into the system via the rectum.  Also, it’s not just homosexual men having anal sex (in the paper they refer to it as “AI”).  There is also a distinct prevalence in the US of heterosexual anal sex.  21.7% of women in Northern California between the ages of 18-29 report anal intercourse (Misegades, 2001). 

Furthermore, AI is more common in woman at risk for HIV, particularly sex workers and drug users.  Finally, there are many women in Africa forced into sex work, and Africa is where the spread of HIV is of greatest concern.  Some studies show that 40% of female sex workers in South Africa engaged in AI, and most of the time they do so unprotected (Karim 1998, Van Damme, 2002).  So you can see that a rectal protectant would be beneficial in many more demographics than most people think.  Also, this particular study was a rectally applied gel, but these findings could be used to make vaginal gels as well.  Further research into this gel could mean enormous improvements in HIV transmission around the world, especially if it could be produced cheaply.

Cranage, M., Sharpe, S., Herrera, C., Cope, A., Dennis, M., Berry, N., Ham, C., Heeney, J., Rezk, N., Kashuba, A., Anton, P., McGowan, I., Shattock, R., Hladik, F. (2008). Prevention of SIV Rectal Transmission and Priming of T Cell Responses in Macaques after Local Pre-exposure Application of Tenofovir Gel. PLoS Medicine, 5(8), e157. DOI: 10.1371/journal.pmed.0050157

Finally, if you want to learn more about AIDS, try www.aids.org, as well as information from www.aids.gov, and www.unaids.org.  You can learn about the disease, ongoing methods of treatment, and if you want, you can contribute to general human awesomeness by getting involved or donating. The AIDS fight may not be all over the news, but it isn’t over yet.

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