Scientists have identified a protein in breast milk that may lead to better HIV protection for infants.
Called Tenascin-C, or TNC, the protein had been known to help in wound healing, but researchers at Duke University recently discovered that it could bind to and neutralize the HIV virus, preventing it from being passed from mother to child.
"Even though we have antiretroviral drugs that can work to prevent mother-to-child transmission, not every pregnant woman is being tested for HIV, and less than 60 percent are receiving the prevention drugs, particularly in countries with few resources," senior author Sallie Permar, an assistant professor of pediatrics, immunology and molecular genetics and microbiology at Duke University, said in a statement. "So there is still a need for alternative strategies to prevent mother-to-child transmission, which is why this work is important."
The findings, published in Proceedings of the National Academy of Sciences, went further than previous studies to explain the antiviral properties in breast milk, with a particular focus on HIV. Scientists used mature milk samples from healthy women and divided them up into smaller fractions comprised of specific proteins. Using mass spectrometry, a multistep protein separation process, they eventually identified Tenascin-C as the single protein involved with HIV neutralization.
“The protein works by binding to the HIV envelope, and one of the interesting things is that we were even able to narrow down exactly where on the envelope it binds,” Permar told the Smithsonian. That is, the protein binds on a part outside the human T cell that HIV normally attacks. With this region blocked, the virus is severely inhibited.
Still, Tenascin-C may not act alone. “It’s clearly not the whole story, because we do have samples that have low amounts of this protein but still have HIV-neutralizing activity,” she said.
Permar adds that the new find may be used to develop HIV-prevention treatments. "It's likely that TNC is acting in concert with other anti-HIV factors in breast milk, and further research should explore this," she said. "But given TNC's broad-spectrum HIV-1-binding and neutralizing activity, it could be developed as an HIV-prevention therapy, given orally to infants prior to breastfeeding, similar to the way oral rehydration salts are routinely administered to infants in developing regions."
According to the World Health Organization, transmission of HIV from mother to child can occur during pregnancy, labor, delivery and breastfeeding. Without intervention, transmission rates can be anywhere between 15 to 45 percent, but can be reduced to below 5 percent with proper treatment.
Tenascin-C appears to be safe since it’s a naturally occurring protein in breast milk, and may avoid resistance reactions to antiretroviral treatments typically used in mother and child treatments.
"The discovery of the HIV-inhibiting effect of this common protein in breast milk provides a potential explanation for why nursing infants born to HIV-infected mothers do not become infected more often than they do," Barton F. Haynes, director of the Duke Human Vaccine Institute, said. "It also provides support for inducing inhibitory factors in breast milk that might be even more protective, such as antibodies, that would completely protect babies from HIV infection in this setting."