Experimental drug blocks HIV transmission in monkeys

Researchers have developed a protein able to block the transmission of HIV in monkeys.

They say their findings could lead to a new kind of microbicides — creams and gels applied directly to the vagina or rectum to stop transmission of the disease.

Currently, no microbicides are available on the market, but several candidates are being tested in clinical trials.

The new potential microbicide, developed by Michael Lederman of Case Western Reserve University, United States, and colleagues, could lead to a ‘second generation’ of products that would either complement the ones currently in trials or replace them if these were to fail.

Lederman’s candidate drug is based on a modified protein. Unlike the products that are being tested, this protein seems to stop transmission by preventing HIV from getting into host cells — a necessary step for the virus to replicate and spread infection.

The protein does this by blocking a ‘receptor’ molecule, called CCR5, found on the surface of host cells that the HIV virus normally binds to during infection. A very small minority of people are known to lack CCR5 and are, as a result, almost completely protected from acquiring HIV infection.

The researchers applied the protein to the vaginas of 30 monkeys. Fifteen minutes later, they infected them with a high dose of a monkey version of HIV. The protein was effective at blocking infection, without producing side effects.

The researchers believe their protein works by making the monkey’s target cells ‘absorb’ the CCR5 molecule. Once this has occurred, CCR5 is no longer available for HIV to latch onto, and transmission is blocked.

“The result is interesting, but in terms of being a potential option for the developing world, we are still a long way away,” Robin Shattock,  of St. George’s Hospital Medical School, UK, told SciDev.Net.

Lederman’s protein would be expensive to produce and is therefore unlikely to be developed into a product for people in developing nations. However, says Shattock, several pharmaceutical companies own small synthetic molecules that also block CCR5.

“Hopefully, this study will encourage them to get involved in the field,” he says, adding that these molecules could be ten times less expensive to produce.

Through agreements with public bodies that lobby for the development of microbicides, these cheaper products could make it to developing world markets, says Shattock. 

Frédéric Tangy and Clarisse Lorin, of the Pasteur Institute in France, also note that a microbicide composed solely of Lederman’s protein would be effective only against HIV.

“Experts agree it is necessary that a microbicide acts against other sexually transmitted pathogens, as these considerably increase the risk of infection with HIV,” says Tangy.

Nonetheless, Lederman’s findings have been hailed as a significant achievement.

“These findings reflect real progress in the science of microbicides, overall and in the sophistication of the research techniques being applied,” says Polly F. Harrison, director of the Alliance for Microbicide Development.

Link to full research paper in Science

Reference: Science 306, 485 (2004)