July 24, 2016

Research Roundup: The HIV/AIDS and STIs edition

Senior Program Assistant

Scientists have long known that the composition of the vaginal microbiome—the bacterial environment in the vagina—can be hostile or even toxic to pathogens and sperm. Now, research conducted by the Centre for the AIDS Programme of Research in South Africa (CAPRISA) suggests that the presence of Prevotella bivia bacteria can significantly increase a woman’s risk for contracting HIV, while the Gardnerella vaginalis bacteria can interfere with the preventative antiretroviral drug tenofovir. The team at CAPRISA sequenced the vaginal microbiomes of 120 women in South Africa, and reported that presence of P. bivia was associated with a 20-fold higher risk for HIV/AIDS. Infection with P. bivia results in an inflammatory response, in which immune cells—including CD4 T cells—are sent to the vaginal surface. CD4 T cells are the main target of the HIV virus, and the influx makes it much easier for the virus to take hold in the body. The team also dug into why the efficacy of tenofovir—which both treats and prevents HIV—varies significantly in women. CAPRISA had previously tested an HIV prevention gel containing tenofovir in women, and had frozen and stored vaginal microbiome samples from participants. The samples revealed a correlation between high levels of G. vaginalis and HIV infection, prompting the team to study the two in the lab. Within 24 hours, the bacteria was able to completely consume the antiretroviral, halting any protection the drug may offer.

A vaccine candidate against chlamydia proved promising in animal trials, resulting in a lower presence of the bacteria and reducing damage to reproductive health organs in vaccinated versus unvaccinated mice. Chlamydia is one of the most common sexually transmitted infections (STIs)—with an estimated 131 million new cases each year—and can be cured with antibiotics. While many cases are initially asymptomatic, the disease can cause pelvic inflammatory disorder and infertility if left untreated. The vaccine, developed by researchers at McMaster University in Ontario, contains three different proteins found on the bacterium. The team reported a 95 percent decrease in chlamydial shedding—an indication of the infection spreading throughout the body—and an 87.5 percent decrease in hydrosalpinx, which can damage the fallopian tubes. The team will continue testing the vaccine in varying formulations and in other animal models before initiating human clinical trials.

Dapivirine ring (Photo: International Partnership for Microbicides)
Dapivirine ring (Photo: International Partnership for Microbicides)

Earlier this year, the International Partnership for Microbicides (IPM) announced the results of two large phase 3 clinical trials—The Ring Study and ASPIRE—demonstrating that a monthly vaginal ring containing the antiretroviral dapivirine could reduce HIV risk in women by 31 and 27 percent, respectively. However, new findings suggest that when used consistently, the ring can reduce HIV risk by 56 percent, and in a subset of women who used the ring most effectively, the ring slashed HIV risk by 75 percent. The dapivirine ring, developed by IPM, is the only long-acting, female-initiated HIV prevention method to have successfully completed large efficacy trials. IPM has initiated two open-label studies of the dapivirine ring and is seeking regulatory approval for the ring.