Breastfeeding’s Lasting Impact: How Immune Cells Shape Maternal and Infant Health

Breastfeeding is widely recognized for its benefits to both mother and child, but the intricate biological mechanisms driving these effects are only now coming into focus. Recent research highlights the crucial role of immune cells, particularly T cells, in shaping the health of both individuals, extending far beyond nutritional support. This understanding reframes lactation not merely as a nutritional process, but as a dynamic, immune-regulated state with long-term consequences.

The Immune Connection: T Cells and Lactation

For years, the immune changes associated with lactation were primarily attributed to myeloid cells. However, emerging evidence demonstrates that T cell subsets expand during lactation, playing diverse roles from mammary gland maturation and milk production to long-term protection against breast cancer for the mother. These T cells are not simply present. they actively contribute to the physiological processes of lactation.

Maternal Health Benefits: Reduced Breast Cancer Risk

Studies have shown a strong association between breastfeeding and a reduced risk of breast cancer. Research published in Nature Immunology in 2025 revealed that breastfeeding is linked to longer overall survival in breast cancer patients and an increase in CD8+ tissue-resident memory T (TRM) cells within breast tissue. These TRM cells, maintained for over 30 years in some cases, express genes associated with parity (the number of times a woman has given birth) and appear to protect against tumor development. In animal models, parity and lactation led to increased CD8+ TRM cells and reduced tumor growth after cancer cell injection.

Infant Health: Shaping the Immune System and Gut Microbiome

The benefits of breastfeeding extend to the infant as well. T cells found in breast milk may play a critical role in shaping the baby’s developing immune system, supporting a healthy gut microbiome, and providing direct immune protection. This immune support is crucial during a period of rapid development, and vulnerability.

How Immune Cells Support Lactation

Research is revealing how different types of immune cells contribute to lactation. As highlighted in a review article published in Trends in Immunology, mammary T cells have lasting effects on both maternal and infant health. Understanding this interplay between the immune system and lactation can provide insights into why some individuals experience difficulties with milk production or infections like mastitis.

Future Research Directions

Whereas significant progress has been made, many questions remain. Researchers are working to understand how different T cell subsets function during lactation, what microbial cues guide their recruitment to the mammary gland, and how immune-epithelial communication provides breast cancer protection. Further investigation is also needed to determine how immune cells transferred through breast milk directly impact neonatal immune development.

“We hope the advances in the field resonate with clinicians and public health researchers by reframing lactation as an immune-driven process with long-term health implications,” says Abigail Jaquish of the Salk Institute for Biological Studies. “We expect the review to spark novel cross-disciplinary conversations and highlight the need for increased focus on lactation in immunology research.”

Key Takeaways

• Breastfeeding is not solely a nutritional process; it’s a complex immune-regulated state.
• T cells play a critical role in supporting lactation and influencing both maternal and infant health.
• Breastfeeding is associated with a reduced risk of breast cancer in mothers, potentially due to the action of TRM cells.
• Immune cells in breast milk contribute to the development of the infant’s immune system and gut microbiome.
• Further research is needed to fully understand the intricate interplay between the immune system and lactation.