Researcher Magdalena Lyimo presented her research on the anti HIV-1 properties of human breast milk at the Dartmouth-Hitchcock Medical Center last Wednesday.

Although breast milk is responsible for one-third of new HIV-1 cases from mother to child each year, this method of transmission is relatively inefficient. Lyimo’s work with Ruth Connor and Alex Howell of the department of physiology aimed to explore breast milk’s properties with regard to both cell-free (active virus particles) and cell-associated (proviral DNA in immune cells) HIV-1.

Lyimo’s primary work used breast milk from healthy donors from the Upper Valley to examine its properties with respect to a number of factors. She concluded that breast milk inhibits cell-free HIV-1 infection regardless of the virus tropism by examining the R5, X4, and R5X4 HIV-1 strains. However, breast milk from these donors did not inhibit cell-associated HIV-1 because it proceeds with a different mechanism of infection.

Using dual PCR, Dr. Lyimo was also able to conclude that breast milk from the uninfected donors inhibits the early stages of infection, like reverse transcription and integration, in CD4 cells. Unfortunately, breast milk does not inhibit the release of HIV-1 and the observed decrease in transcription was not sustained beyond five days.

Lyimo then questioned whether or not breast milk from HIV-1 infected donors had the same inhibitory properties. Interestingly, both the breast milk from the ten HIV positive as well as the ten HIV negative donors in TZM-bl assays once again showed inhibition of cell-free HIV-1 independent of virus tropism, and no inhibition of cell-associated HIV-1. Because the number of donors was so small, further studies will be needed to support these reported effects.

Curious as to whether these inhibitory effects were mediated by innate immune factors or HIV-specific antibodies in the milk, Lyimo then examined the presence of chemokines and pathogen-specific antibodies and observed levels of inhibition. There was no correlation between observed levels of inhibition and levels of chemokines responsible for inhibition activity including MIP-1α, MID-1β, and RANTES, suggesting these chemokines may be working in combination with other cytokines, or not mediating the inhibitory properties of breast milk. Lyimo also tried depleting IgG and IgA, two pathogen-specific antibodies, but the altered milk from both HIV-positive and HIV-negative donors maintained its inhibitory effects.

Thus, Lyimo’s continuing work is focused on determining what causes the observed inhibitory effects of breast milk. Glycosaminoglycans are a possible candidate because after the depletion of anionic factors like these glycans, anti HIV-1 activity in breast milk was reduced. Lyimo’s lab is currently performing enzymatic digestion of these glycans to confirm their hypotheses.