Breastmilk stem cells: Recent advances and future prospects

Abstract

Optimally, breastmilk is the only food or drink that infants consume in the first 6 months of life. It is the optimal source of nutrition and protection for the human infant, containing nutritional agents and an array of bioactive factors that confer active immunity to the infant. As breastmilk composition is being researched, more and more factors are discovered in it with beneficial attributes. Interestingly, among its biochemical components, breastmilk contains maternal cells. Most of our knowledge on breastmilk cells comes from studies of leucocytic populations, which often are the dominant cells in colostrum and early lactation milk. However, in mature human milk, leucocytes are usually found in low numbers and the dominant cells are of epithelial origin. With the recent technical advancement in the fields of molecular biology and flow cytometry, the epithelial compartment of human milk has started to be further explored. These initial efforts are revealing a profound cellular hierarchy in breastmilk, from early-stage stem cells to progenitors to more differentiated lactocytes and myoepithelial cells. The origin(s) of these cell populations and their wide variability among and within women is also starting to be explored. Exciting advances are suggesting the existence of pluripotent stem cell populations in breastmilk, and this provides new avenues for examination of the role(s) of these cells in the lactating breast and for the breastfed infant and their potential uses in the study of the biology and pathology of the breast as well as in regenerative medicine. This chapter summarises the current knowledge of the cellular hierarchy of human milk and discusses future applications.