Could breast milk possibly be protective against HIV?
by Chael Needle
The benefits of breastfeeding in resource-poor countries while mothers and infants are on differently tailored antiretroviral regimens have been highlighted in recent years in studies such as the Breastfeeding, Antiretrovirals, and Nutrition (BAN) Study. Enrolling more than 2,300 mother-infant pairs in Malawi, the study showed that mother-to-child transmission of HIV was significantly reduced with paired and prolonged drug interventions compared with standard, abbreviated treatment during labor, delivery and seven days post-partum.
Based in part on the BAN Study results, the World Health Organization revised its guidelines on breastfeeding, replacement feeding, and mixed feeding, with the aim of improving infant survival rates. Stopping breastfeeding early, studies have shown, increases the chances that an infant will die compared with a prolonged period of breastfeeding. But breastfeeding is often characterized as the lesser of two evils.
But what if breast milk itself, or under certain conditions, could prevent HIV transmission or even kill the virus?
Published in the on-line journal PLoS Pathogens, a new animal study out of the University of North Carolina (UNC) School of Medicine has grappled with these possibilities. Led by J. Victor Garcia, PhD, senior author of the study and professor of medicine at the UNC Center for Infectious Diseases and the UNC Center for AIDS Research, the researchers found that breast milk has the ability to completely block oral transmission of both forms of HIV found in breast milk, virus particles and virus-infected cells, as well as the ability to destroy HIV.
What distinguishes this study from past studies is that researchers have been able to show positive results about the anti-HIV effects of breast milk, not in test tubes but in vivo. Researchers pioneered a new model that would allow the oral transmission of HIV—the humanized “BLT” mouse model. The model introduces human bone marrow, liver, and thymus tissues into animals who do not have an immune system of their own. Thus, the human immune system is replicated and the mice can be infected in the same ways as humans. After determining that the mice’s oral cavity and upper digestive tract had the same cells that affect oral transmission of HIV in humans, researchers focused on these possible sites of transmission.
“We made a very striking observation: milk—just human breast milk—has a very strong viricidal activity against HIV. It kills the virus. It makes it non-transmissable,” says Dr. J. Victor Garcia.
Earlier research by Dr. Garcia and his research team had shown that pre-exposure prophylaxis (PrEP)—the use of antiretrovirals to prevent HIV transmission—is effective against intravenous, vaginal and rectal transmission of HIV in humanized BLT mice. The current study showed that a seven-day PrEP regiman was 100 percent effective in blocking the oral transmission of HIV in the mice.
Researchers also discovered that mice given virus in whole breast milk from HIV-negative women did not become infected.
Other questions remain, says Dr. Garcia: “Is milk just a vehicle of transmission or is it a vehicle for protection? Our results strongly suggest that it has a protective effect.”
Another question that needs to be answered through more research, he says, is what in breast milk produces this dramatic effect. Also: “Is there any difference between the milk of non-infected women versus HIV-infected women? Does the virus do anything to the ability of the milk to kill HIV? And we don’t know that because all the samples that we had were from non-infected women.…We hope to test this hypothesis—that maybe there’s something different between the milk of an infected mother and a non-infected mother. If that’s the case then we need to zero in on what that difference is so that we can prevent more transmissions in the future.”
The research team plans on pursuing these and other avenues.
“Having these humanized BLT mice is really going to open the doors to numerous experiments that could never be done before,” notes Dr. Garcia, “because these little mice, because of the human component, can be infected in the same manner that humans can—through vaginal exposure, rectal exposure, and now we can show that they can be infected through oral exposure. We can start looking at prevention of all routes of transmission.”
Dr. Garcia emphasizes the potential at hand: “We have a natural product. It’s not a drug! The [viricidal product] will not be toxic. So, are there any possible uses, alternative uses, for what is in milk? And in order to be able to do that we need to identify what’s in there. What is the active component? And then ask questions like, Can it be used therapeutically? Can it be used for prophylaxis? Can it be regulated in the breast milk? Can the levels of protection be increased?”
Chael Needle wrote about the importance of fourth-generation HIV tests in the June issue.