Researchers in Canada have developed a vaginal implant that aims to protect women from becoming diagnosed with HIV.

In a paper now published in the Journal of Controlled Release, they report how they successfully tested the vaginal implant in laboratory animals.

HIV, which is the virus that causes AIDS, hijacks activated immune T cells to use their machinery to complete its life cycle—that is, to produce copies of itself and spread. A major site of transmission is in the female genital tract.

The new vaginal implant slowly releases drugs that keep the T cells of the female genital tract in a resting, or "quiescent," state, which is much less productive for the virus.

Unlike activated T cells, quiescent T cells block the early stage of the HIV life cycle, "resulting in a largely inefficient [transmission]."

Some sex workers 'naturally immune' to HIV

Senior study author Emmanuel Ho, who is a professor in the School of Pharmacy at the University of Waterloo in Canada, and colleagues came up with the idea of a vaginal anti-HIV implant after studying sex workers in Kenya, East Africa.

There, they observed that many female sex workers did not become HIV-positive, even though they were having sex with clients who were.

Further investigation revealed that the women's natural resistance to HIV came from the fact that their immune T cells remained in a quiescent state.

When they realized this, the researchers wondered whether it might be possible to induce T cell quiescence in the female genital tract with drugs.

This approach could "provide an excellent women-oriented strategy against HIV [transmission]," they note in their study paper.

Professor Ho says that they decided to pursue the idea of a vaginal implant rather than a drug that is taken by mouth because "some drugs taken orally never make it to the vaginal tract."

A vaginal implant that can block HIV could offer a cheaper, more reliable way of preventing transmission, he adds.

Implant induces 'an immune quiescent state'

There are 36.7 million people living with HIV or AIDS worldwide, including 2.1 million children under the age of 15.

Most of the 160,000 children newly diagnosed with HIV each year live in sub-Saharan Africa. Their mothers transmit the virus either during pregnancy, while giving birth, or when breast-feeding.

The implant is a porous, hollow tube filled with a drug that is secreted slowly and is absorbed into the walls of the female genital tract. The tube has two flexible arms that prevent it from moving around.

In their study, the researchers filled the vaginal implant with hydroxychloroquine and tested it in rabbits.

The implant caused a significant reduction in activated T cells, indicating that it induced "an immune quiescent state" in the female rabbits' genital tracts.

"What we don't know yet is if this can be a stand-alone option for preventing HIV transmission or if it might be best used in conjunction with other prevention strategies."

Professor Emmanuel Ho

"We aim to answer these questions with future research," he concludes.