It has been shown that HIV transmission is prevented by breast milk with a study done on mice. The infected cells were even killed in some cases. There were signs of the virus dying in mice that had HIV when they were given breast milk. The transmission of the virus to uninfected mice was also prevented in some of the mice tested.
The immune systems of the mice studied were engineered to resemble the human immune system. Breast milk could not transmit the virus, and upon entering breast milk the virus died. It has been documented that mother’s testing positive for HIV have breast feed without transmitting the virus to the infant.