Scientists at Osel Inc. and the National Cancer Institute (NCI) have developed a new way to prevent HIV infection by genetically enhancing the ability of naturally occurring vaginal bacteria to block viral transmission. Bioengineered bacteria introduced into the vaginal cavity of macaques—a commonly used experimental primate—reduced the transmission of simian HIV (SHIV) by nearly two thirds.
The novel approach takes advantage of lactobacilli, which are beneficial bacteria that play an important role in vaginal health and help protect women against a variety of sexually transmitted infections. The Osel team engineered the common strain Lactobacillus jensenii to pump out therapeutic quantities of the HIV inhibitor cyanovirin-N, which is a protein originally discovered by NCI scientists screening natural substances for antiviral activity.
In a study just published online in advance of publication in the Nature journal Mucosal Immunology, the team showed that vaginal administration of Lactobacillus expressing CV-N to rhesus macaques could reduce the transmission of SHIV (a virus developed for research that combines critical components of HIV with the ability to infect monkeys) by 63 percent after repeated challenges with virus. A reduction in the viral load was also seen in infected macaques that received the Lactobacillus product, called MucoCept.
"We were excited to see this reduced rate of transmission in the macaque model," said Dr. Laurel Lagenaur, the leader of the Osel team. "Because this Lactobacillus strain is likely to colonize women at a higher rate than macaques, we could see an even bigger reduction in the rate of HIV infection when this product is tested in women. The lactobacilli themselves are also beneficial to vaginal health."
The scientists believe their approach could provide an affordable and durable method for reducing the continuing worldwide epidemic of HIV, which currently infects more than two million people every year. A major advantage of the novel approach of a live bioshield such as MucoCept is that it would provide sustained protection; women would not need to apply it frequently or immediately before sexual intercourse.
"This approach has potential as a novel 'natural' approach to prevent HIV," said Dr. Salim S. Abdool Karim of Centre for the AIDS Programme of Research In South Africa (CAPRISA) at the University of KwaZulu-Natal, who co-led a study establishing proof-of-concept for microbicides using tenofovir gel. "Data in women are eagerly awaited." Dr. Karim was not involved in the current study.
"It's exciting to be working on a prevention for HIV that people could actually afford," said Dr. Dean H. Hamer, chief of the Gene Structure and Regulation Section at the NCI and senior author of the study. "While there is much interest in the recent results with PrEP [pre-exposure prophylaxis], it's important to realize that the cost of the required antiretroviral drugs is prohibitive in the real world."
The engineered lactobacilli in MucoCept constitute an ideal microbicide because the organisms naturally colonize the vagina—unlike the strains found in dairy products or food supplements—and they continuously produce the HIV inhibitor. Upon administration of MucoCept as a vaginal suppository, these bacteria can take up residence and potentially protect the user for weeks at a time.
The Osel group is hoping to start human trials of MucoCept within the next several years following completion of product development and safety testing.