Scientists have identified a protein in breast milk that may be a key reason why most HIV-positive mothers don't transmit the virus to their babies through breast-feeding. Looking at breast milk samples, researchers isolated a protein called tenascin-C, or TNC, which is already known to play a role in healing wounds and which they found can also neutralize HIV. It does this by capturing the virus and binding to its outer envelope, hindering its ability to enter human cells. Because TNC is a naturally occurring substance in breast milk, it is likely safe and would be less inclined to lead to drug resistance if used as a prophylaxis. While it's probable that TNC is working in tandem with other anti-HIV elements of breast milk, the study's researchers believe its effects are powerful enough on its own that it could be developed as an orally administered HIV-prevention therapy for infants, given before breast-feeding.