Certain factors in breast milk may block the transmission of HIV from mother to child during breast feeding when the virus is outside of cells, but have little effect on the transmission of the virus once it has entered them, according to a study published by Dartmouth Medical School researchers in the June issue of the Journal of Acquired Immune Deficiency Syndromes.
Lead author Magdalena Lyimo, a fifth-year Ph.D student, said her work was inspired by first-hand experience with HIV-positive women and children in Tanzania.
Lyimo originally worked to determine whether there are factors in breast milk that could block the transmission of infection to the infant, according to co-author Alexandra Howell, professor of medicine and microbiology and immunology. Lyimo conducted part of her research in Howell's lab, and did other work under DMS professor of microbiology and immunology Ruth Connor.
Lyimo found that, of the two forms of the virus present in breast milk, the cell-free form is inhibited in milk, while cell-associated HIV is not. The study examined breast milk from infected mothers and from healthy donors.
"We think that breast milk itself is able to take care of the cell-free form," Lyimo said.
Anti-retroviral drugs used to treat HIV reduce levels of the cell-free form of the virus, but not the cell-associated form, Lyimo said. When the virus is in the cell-associated form, a cell protects the virus from the breast milk as well as anti-retroviral drugs.
"[Breast milk] has no effect on protecting these cells in the lab from HIV that was contained within an infected blood cell," Howell said.
Since the milk used in the study was obtained from infected African mothers and healthy American mothers, Lyimo is currently repeating the study using race-matched donors to account for differences in nutrition and other factors, Howell said.
Many aspects of HIV transmission through breast milk remain unknown, Howell said, which make the concrete implications of the research difficult to predict.
"It was just a matter of trying to figure out how to take data that you get in the laboratory and how to translate it to the real world," Howell said.
HIV infection is a major problem in Tanzania, Lyimo's home country, and the results of the study may influence future approaches to treatment.
Lyimo said researchers should target both the cell-associated and cell-free forms of the virus in developing treatment protocols.
Children in under-developed countries like Tanzania are especially prone to infection through breast milk because it is difficult to obtain sterile water to make formula, Lyimo said.
"The women in Tanzania don't have the option of putting children on formula," she said.
Mothers who choose to formula-feed their children also face stigma, Howell said, explaining that such women are often assumed to be HIV-positive by their communities.
Breast feeding also provides many nutrients and antibodies that are important to infant health and are not available in formula, according to Howell.
