Effects of preterm birth and gestational diabetes on innate lymphoid cells (ILCs) in human breast milk

Breastfeeding provides key immunological and metabolic benefits for newborns, reducing complications of preterm birth and long-term risks associated with maternal gestational diabetes mellitus (GDM). However, the mechanisms underlying these protective effects, particularly the role of maternal immune cells in breast milk, remain incompletely understood. This study aimed to investigate how preterm birth and GDM influence the composition of breast milk-derived innate lymphoid cells (ILCs) during early lactation and to explore whether these maternal cells affect neonatal immune characteristics in vitro using cord blood T cells as a model system.

Breast milk samples (colostrum and transitional milk) were collected within the first two weeks postpartum from mothers of term and preterm infants. Flow cytometric analysis revealed that total ILC frequencies decreased over time, with no significant differences between term and preterm deliveries. Colostrum from GDM mothers, however, contained significantly higher ILC frequencies compared with samples from normoglycemic controls, indicating that maternal metabolic status alters the immunological composition of breast milk. Cord blood T cells from GDM pregnancies showed elevated expression of the sphingosine-1-phosphate receptor 1 (S1PR1), suggesting an enhanced migratory phenotype. Co-culture experiments with breast milk-derived ILCs did not further increase S1PR1 expression or modify T cell activation markers (CD25, CD69, CTLA-4, PD-1). We emphasize that all functional assays were conducted in vitro using coculture systems with umbilical cord blood cells and were not performed directly on newborns.

Maternal GDM modifies the composition of breast milk-derived ILCs and is associated with altered receptor expression on neonatal cord blood T cells. Nevertheless, in vitro exposure to breast milk ILCs did not enhance T cell activation, suggesting that breastfeeding may help maintain neonatal immune balance despite maternal metabolic stress. These results highlight a potential regulatory role of breast milk immune cells at the maternal-infant interface and underscore the importance of breastfeeding in mitigating pro-inflammatory programming in infants of GDM mothers.