Profiling of mature stage human breastmilk cells identifies host-defense lactocyte sub-populations

Breastmilk is chock-full of nutrients, immunological factors, and cells that aid infant development. Maternal cells are the least studied breastmilk component, and their unique properties are difficult to identify using traditional techniques. Here, we characterized the cells in mature stage breastmilk from healthy donors at the protein, gene, and transcriptome levels. Holistic analysis of flow cytometry, qPCR, and single cell RNA sequencing data identified the predominant cell population as epithelial with smaller populations of macrophages and T cells. Two percent of epithelial cells expressed four stem cell markers: SOX2, TRA-1-60, NANOG, and SSEA4. Furthermore, milk contained six distinct epithelial lactocyte sub-populations, including three previously unidentified sub-populations programmed towards host-defense and intestinal development. Pseudotime analysis delineated the differentiation pathways of epithelial progenitors. Together, these data define healthy human maternal breastmilk cells and provide a basis for their application in maternal and infant medicine.