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.

Prof. 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.