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Maternal Immunization Boosts Vaccine-Specific T Cells in Breastmilk

Online publication date: Jan. 13, 2023

Researchers in the Center for Global Infectious Disease Research at Seattle Children’s Research Institute yielded new insights into the immunological properties of human breastmilk, including that maternal immunization with COVID-19 mRNA vaccine enriches breastmilk with T cells — infection-fighting blood cells — that are specialized to fight the virus. Their findings help show how breastmilk may be uniquely poised to respond to and protect infants against infections.

The study, published in the journal Mucosal Immunology, was co-first authored by Drs. Blair Armistead and Yonghou Jiang, a postdoctoral fellow and a research scientist, respectively, in the lab of Dr. Whitney Harrington. In addition to her research role, Harrington is a Seattle Children’s infectious disease physician and an assistant professor of pediatrics at the University of Washington School of Medicine. 

Much of what was known about breastmilk passive immunity — the transfer of immunity to the infant by the mother — was limited to maternal antibody transfer. For example, antibodies specific to a variety of viral infections, including influenza and COVID-19, can be found in the breastmilk, and more recently researchers have found that COVID-19 mRNA vaccines also lead to vaccine-specific antibodies in the breastmilk.

This study shows that maternal vaccination can also increase the number of vaccine-specific T cells in breastmilk, indicating that breastmilk may be an underrecognized source of T-cell immunity in nursing infants. T cells provide the immune system with a longer-term “memory” than antibodies do, providing immunity for a lengthier period.

In addition, the researchers found more generally that human breastmilk is enriched with mucosal memory T cells (mucosa is the soft tissue that lines the body’s canals and organs and plays an important part in immunity) distinct from peripheral immunity in the blood. Further, some T cells that were significantly overabundant in the breastmilk compared to blood were specific to microbial and viral pathogens. The findings may have significant implications for optimizing maternal vaccination schedules to increase protection in babies who are nursing.

The researchers next plan to study how vaccines other than COVID-19 mRNA-based vaccines, as well as maternal infections during pregnancy or lactation, influence the presence of T cells in breastmilk.

“Our long-term goal is to demonstrate the transfer of breastmilk-derived T cells to nursing infants and to characterize their role in infant immunity,” Armistead said.

Harrington’s team also included John Houck and Rene Coig and was joined by research institute colleagues Dr. Rhea Coler and lab members Dr. Sasha Larsen and Tiffany Pecor, Dr. Nana Minkah, and Dr. Marc Carlson from Bioinformatics and Research Scientific Computing, in addition to University of Washington and Fred Hutchinson Cancer Center researchers.

“This project embodied team science,” Armistead said. “We worked with scientists across fields of expertise, including maternal and child health, T-cell biology, and bioinformatics to accomplish this work.”

The research was supported by the National Institutes of Health, Burroughs Wellcome Fund, the University of Washington and Seattle Children’s.

— Colleen Steelquist