Large Stem/Progenitor-Like Cell Subsets can Also be Identified in the CD45^- and CD45^+/High Populations in Early Human Milk

Background: Stem/progenitor cells have been identified in human milk. However, characterization and percentages of cell subsets in human milk using hematopoietic stem and progenitor cell markers according to the differential expression of CD45, i.e., as CD45^dim/+ (mainly hematopoietic stem/progenitor cells) and CD45^- (mainly non-hematopoietic stem/progenitor cells), have not been assessed to date.

Research aim: To characterize stem/progenitor-like cell phenotypes in human milk and to report the percentages of these cells at two different lactation stages compared to peripheral blood.

Methods: Human milk samples paired with peripheral blood samples (N = 10) were analyzed by flow cytometry using CD45, CD34, CD133, CD38, and lineage-negative markers. The percentage of cell subsets was analyzed in colostrum (Day 3 postpartum) and transitional milk (Day 5/6 postpartum) and compared with the peripheral blood counterpart.

Results: The percentage of CD45^-CD34⁺ cells was predominant in both colostrum and transitional milk. The percentage of CD45^+/highCD133⁺ cells was high in colostrum while the percentage of CD45^-CD133⁺ cells was high in transitional milk. Furthermore, the median percentages of the CD45^-CD34⁺, CD45^-CD133⁺, and CD45^dimCD133⁺ cell subsets were higher in colostrum than its peripheral blood counterpart (0.11% vs. 0.002%; 0.17% vs. 0.0005%; 0.09% vs. 0.05%, p = .04, respectively); also CD45^-CD34^-CD133⁺ and CD45^dimCD34^-CD133⁺ cell subsets were higher in colostrum than peripheral blood (1.32% vs. 0.0% and 2.4% vs. 0.06%, p = .04), respectively).

Conclusion: Early human milk is an abundant reservoir of hematopoietic stem/progenitor-like cells in the CD45^+/high population and non-hematopoietic stem/progenitor-like cells in the CD45^- population.