Breast milk may block HIV transmission

While breastfeeding is attributed to a significant number of HIV infections that occur in infants, the majority of infants who are breastfed by HIV-infected mothers do not get infected themselves, despite repeated exposure to the virus.  This apparent conundrum has left researchers to question: Does breast milk transmit HIV or protect against it?

New research indicates that breastfeeding may in fact destroy HIV and prevent its oral transmission from mother to infant, according to scientists from the University of North Carolina School of Medicine.  The findings give rise to the possibility that certain compounds in breast milk could be isolated and utilized to combat the virus responsible for AIDS.

UNC researchers genetically modified mice by introducing human bone marrow, liver and thymus tissues into the animals, so they would have fully functioning human immune systems and be similarly susceptible to HIV.

The researchers then fed the mice with human breast milk containing HIV – but found the mice were never infected with the virus.  The study is the first to look at the effect of breast milk on HIV in a mammalian model, as opposed to prior studies done in test tubes.

"These results are highly significant because they show that breast milk can completely block oral transmission of both forms of HIV that are found in the breast milk of HIV-infected mothers: virus particles and virus-infected cells," Angela Wahl, a post-doctoral researcher at UNC School of Medicine and lead author of the paper, said in a released statement.

"This refutes the 'Trojan horse' hypothesis which says that HIV in cells is more stubborn against the body's own innate defenses than HIV in virus particles,” she continued.

Wahl told that scientists have long wondered whether breast milk was protective against or a facilitating factor in the transmission of HIV.

“What we have shown is that breast milk is indeed a protective agent, so it should not be denied even to children of HIV-infected women,” she said.

As for the infants who do contract HIV during breastfeeding periods, Wahl said a next step in the lab’s research would be to compare the breast milk from HIV-infected mothers who transmitted the virus to their infants against the breast milk from HIV-infected mothers who did not transmit virus for any differences.  She added it was important not to discount the possibility the HIV could have actually been transmitted another way, such as mastitis, which can cause nipple bleeding.

“What we know is that infants who acquire HIV during breastfeeding weren’t infected at the time of birth, and  when you look at virus that eventually infects the infant and virus in mother’s breast milk, it’s the same,” Wahl said.  “But it doesn’t mean it couldn’t be the result of [contact with] blood.”

World Health Organization guidelines recommend mothers, even HIV-infected mothers, breastfeed infants for the first 12 months (exclusively for the first six months) – though the guidelines add that HIV-infected mothers and their infants should be put on a course of antiretroviral medications to reduce chances of transmission.

“Breast milk has several factors that protect against other life threatening illnesses—it shouldn’t be withheld,” Wahl said. “ It protects infants against childhood infections and reduces morbidity and mortality.”

Wahl said another future goal in the research was to identify which compounds in breast milk potentially have HIV-killing capabilities.

“The key is really identifying these factors within breast milk that are blocking transmission and testing if they can serve as natural inhibitor against all types of HIV transmission – oral, rectal and vaginal,” she said.  “Now that we have our [mouse] model, we can start.”

The study was published online Thursday in the journal PLoS Pathogens.