Introduction:

The microbiome can be described as the collection of microbes which live on and within us. Recent research on the vaginal and breast milk microbiome has shed light on fascinating findings concerning HIV prevention, acquisition and transmission in pregnant & breastfeeding mothers and their babies. Understanding the role of the microbiome in this process is important for prevention strategies, providing knowledge to mothers living with HIV with guidance on whether to breastfeed and to enable new therapies to be developed in the future.

 

Vaginal dysbiosis is linked to HIV susceptibility:

Dysbiosis is defined as an imbalance of species in a particular environment. An example of dysbiosis would be a wildflower meadow that has become overgrown by stinging nettles. In the vagina however, all the species present are microbes! A healthy vaginal ecosystem should be dominated by a group of bacteria called Lactobacillus. Research has found that women with vaginal dysbiosis who lack important Lactobacillus bacteria were more likely to acquire HIV [1],[2]. It is thought these bacteria are protective against HIV as they play a large role in reducing inflammation, which in turn reduces the number of immune system cells for HIV virus particles to target [3].

 

This intriguing finding has been supported by another study which linked dysbiosis in the gut microbiome to increased likelihood of HIV acquisition in populations at risk of exposure to the virus [4]. Taken together, these intriguing studies demonstrate the importance of keeping our microbiomes in a balanced ‘wildflower meadow’ state, as robust microbial communities play an important role in health and disease prevention.

 

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Breast Milk's Prebiotic Protective Role Against HIV infection:

It is puzzling how infants, who are exposed to substantial amounts of the virus during breastfeeding, often remain uninfected. Recent studies have revealed a possible explanation: the presence of complex prebiotic sugars called human milk oligosaccharides (HMOs). Comprising 20% of breast milk's total carbohydrates, HMOs play a critical role in developing a healthy gut microbiome, as only one group of important specialist bacteria, called Bifidobacteria, can break them down. Intriguingly, HMOs have also demonstrated the ability to bind to the baby’s white blood cells, which means there is less opportunity for HIV virus particles to bind and infect. It has been found that this competition for binding reduces HIV’s ability to infect these cells by 80% [5].

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While HMOs have been found to reduce the chances of HIV acquisition in infants, they need to be present in high enough abundances in breast milk to be truly effective. If HMOs are not present in abundances higher than 1.87 g/L in the mother’s milk, the chances of an infant acquiring HIV from breast milk are greatly increased [6]. These findings open up the possibility for breast milk screening to assess concentration of HMOs present and therefore the likelihood of HIV transmission to their infant. This is important because, as discussed in our previous article, mothers living with HIV face difficult decisions when deciding on whether to breastfeed, and any information which can impact this decision should be accounted for.

 

Supporting Infants of HIV-Positive Mothers:

Some mothers are advised to avoid breastfeeding due to them having a high viral load and therefore increased chances of transmitting HIV to their baby. This means their baby has a reduced chance of achieving a healthy ‘wildflower meadow’ gut microbiome, as they miss out on beneficial breast milk bacteria and associated prebiotic HMOs. To combat this, a South African study supplemented non breastfed infants of mothers living with HIV with acidified formula containing Bifidobacterium lactis [7]. They found these infants had significantly greater weight gain compared to infants fed non-acidified formula. Although the precise mechanisms remain unclear, improved weight gain may be attributed to reduced instances of diarrhea or enhanced gut absorption. Probiotics containing Bifidobacteria therefore present a potential avenue for improving the health outcomes of non-breastfeeding infants born to mothers with HIV.

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Moving Forward: Microbiome Research and New Solutions:

Studying the microbiome's role in HIV is crucial for developing innovative strategies to improve health outcomes for those with HIV and prevent its spread. Understanding the associations between vaginal microbiome imbalances, HMOs and HIV acquisition can pave the way for targeted prevention measures in mothers and their infants. It is also important to increase support for promoting the gut health of infants which cannot be breasted due to HIV risk, as they could benefit from tailored breast milk-derived probiotics. By exploring these connections, we can advance our understanding of the microbiome's impact on HIV and work towards better health outcomes for all.

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