Infants born to women living with HIV (WLWH) who remain uninfected themselves still face markedly higher risks of infection, impaired growth, and neurodevelopmental challenges. Although chronic immune activation is a well-established feature of maternal HIV, how this biology affects the infant remains to be fully understood. A new longitudinal metabolomics study by Tobin and colleagues brings tryptophan metabolism to the center of this discussion.
Profiling 1,426 breast-milk samples from 326 Zambian mothers across 18 months postpartum, the authors uncovered a striking and persistent signature. Milk from WLWH contains significantly less tryptophan and more kynurenine at every stage of lactation. These alterations were tightly correlated with maternal plasma levels, indicating that systemic tryptophan depletion, rather than a localized mammary effect, is a primary driver. The result is a sustained elevation in the kynurenine-to-tryptophan (K/T) ratio, which reflects chronic IDO1 activation and interferon-induced catabolism in the milk that infants consume during a critical developmental window.
For the tryptophan research community, these findings identify an important maternal–infant metabolic axis. Human milk is the sole source of dietary tryptophan during exclusive breastfeeding. Chronic maternal depletion therefore exposes infants to lower tryptophan intake while simultaneously delivering a pro-inflammatory milk metabolome enriched in KP-related and interferon-induced metabolites. This combined exposure may contribute to altered serotonin biosynthesis, disrupted mucosal immunity, and the neurodevelopmental vulnerabilities documented in children who are HIV-exposed but uninfected (CHEU). The authors also validated key components of this metabolic signature in an independent Haitian cohort, demonstrating that the pattern persists even in WLWH receiving antiretroviral therapy.
This work positions tryptophan availability and KP homeostasis as potential risk factors in maternal and infant health. It raises timely questions about whether tryptophan supplementation, modulation of IDO1 activity, or broader KP-targeted strategies could help mitigate the developmental risks faced by CHEU. Further investigation into the effects of long-term exposure to high K/T ratio breast milk on infant development, including neurodevelopment, is warranted.