Transfer and Integration of Breast Milk Stem Cells to the Brain of Suckling Pups

Maternal-driven immune education in offspring

Maternal environmental exposures, particularly during gestation and lactation, significantly influence the immunological development and long-term immunity of offspring. Mammalian immune systems develop through crucial inputs from the environment, beginning in utero and continuing after birth. These critical developmental windows are essential for proper immune system development and, once closed, may not be reopened. This review focuses on the mechanisms by which maternal exposures, particularly to pathogens, diet, and microbiota, impact offspring immunity. Mechanisms driving maternal-offspring immune crosstalk include transfer of maternal antibodies, changes in the maternal microbiome and microbiota-derived metabolites, and transfer of immune cells and cytokines via the placenta and breastfeeding. We further discuss the role of transient maternal infections, which are common during pregnancy, in providing tissue-specific immune education to offspring. We propose a "maternal-driven immune education" hypothesis, which suggests that offspring can use maternal encounters that occur during a critical developmental window to develop optimal immune fitness against infection and inflammation.

Feasibility of intranasal human milk as stem cell therapy in preterm infants with intraventricular hemorrhage

OBJECTIVE

Intraventricular hemorrhage (IVH) is a common cause of preterm brain injury. Fresh parent's own milk (POM) contains pluripotent stem cells (SCs) that produce neuronal cells in-vitro. The permeable neonatal blood brain barrier potentially allows SC delivery. We performed the first prospective trial (clinicaltrials.gov NCT04225286) of feasibility of intranasal POM (IPOM) in preterm infants with IVH and described SC content of POM samples.

STUDY DESIGN

37 Infants (mean gestation 27.7 ± 2.6 weeks, birthweight 1030 ± 320 g) with IVH (35.1% grade IV) were recruited from two tertiary Toronto NICUs. IPOM was given ideally twice daily until 28 days of age. Tolerance and adverse reactions were collected and 162 administering providers surveyed.

RESULTS

There were no major adverse reactions. Provider surveys suggested acceptability, although potential provider and subject stress requires further study. Milk cell analysis suggests wide variability between parents.

CONCLUSIONS

This phase 1 study demonstrated IPOM was tolerated and feasible in preterm infants.

Characterization and comparison of human and mouse milk cells

Recent data has characterized human milk cells with unprecedented detail and provided insight into cell populations. While such analysis of freshly expressed human milk has been possible, studies of cell functionality within the infant have been limited to animal models. One commonly used animal model for milk research is the mouse; however, limited data are available describing the composition of mouse milk. In particular, the maternal cells of mouse milk have not been previously characterized in detail, in part due to the difficulty in collecting sufficient volumes of mouse milk. In this study, we have established a method to collect high volumes of mouse milk, isolate cells, and compare the cell counts and types to human milk. Surprisingly, we found that mouse milk cell density is three orders of magnitude higher than human milk. The cell types present in the milk of mice and humans are similar, broadly consisting of mammary epithelial cells and immune cells. These results provide a basis of comparison for mouse and human milk cells and will inform the most appropriate uses of mouse models for the study of human phenomena.

Where does the time go? Temporal patterns of pumping behaviors in mothers of very preterm infants vary by sociodemographic and clinical factors

Background

Mothers of very preterm (<32 weeks gestational age [GA]) infants are breast pump dependent and have shorter duration of milk provision than mothers of term infants. The opportunity (i.e., time) cost of pumping and transporting mother's own milk (MOM) from home to the NICU may be a barrier. There is a paucity of data regarding how much time mothers actually spend pumping.

Objective

To investigate the variation in pumping behavior by postpartum week, maternal characteristics, and infant GA.

Methods

Prospectively collected pump log data from mothers enrolled in ReDiMOM (Reducing Disparity in Mother's Own Milk) randomized, controlled trial included pumping date and start time and end time of each pumping session for the first 10 weeks postpartum or until the infant was discharged from the NICU, whichever occurred first. Outcomes included number of daily pumping sessions, number of minutes spent pumping per day, and pumping behaviors during 24-h periods, aggregated to the postpartum week. Medians (interquartile ranges) were used to describe outcomes overall, and by maternal characteristics and infant GA.

Results

Data included 13,994 pump sessions from 75 mothers. Maternal characteristics included 55% Black, 35% Hispanic, and 11% White and 44% <30 years old. The majority (56%) of infants were born at GA 28-31 weeks. Mothers pumped an average of less than 4 times per day, peaking in postpartum week 2. After accounting for mothers who stopped pumping, there was a gradual decrease in daily pumping minutes between postpartum weeks 2 (89 min) and 10 (46 min). Black mothers pumped fewer times daily than non-Black mothers after the first 2 weeks postpartum.

Conclusion

On average mothers pumped less intensively than the minimum recommendation of 8 times and 100 min per day. However, these pumping behaviors represent significant maternal opportunity costs that should be valued by the institution and society at large.

Breastfeeding-Related Health Benefits in Children and Mothers: Vital Organs Perspective

Breast milk (BM) is a constantly changing fluid that represents the primary source of nutrition for newborns. It is widely recognized that breastfeeding provides benefits for both the child and the mother, including a lower risk of ovarian and breast cancer, type 2 diabetes mellitus, decreased blood pressure, and more. In infants, breastfeeding has been correlated with a lower risk of infectious diseases, obesity, lower blood pressure, and decreased incidence of respiratory infections, diabetes, and asthma. Various factors, such as the baby's sex, the health status of the mother and child, the mother's diet, and the mode of delivery, can affect the composition of breast milk. This review focuses on the biological impact of the nutrients in BM on the development and functionality of vital organs to promote the benefit of health.

Quantification of Female Chimeric Cells in the Tonsils of Male Children and Their Determinants

The factors influencing mother-to-child cell trafficking and persistence over children's lives have yet to be established. The quantification of maternal microchimerism was previously reported through HLA-based approaches, which introduced bias regarding the tolerogenic environment. We aimed to identify cells of maternal origin irrespective of the HLA repertoire and to ascertain the determinants of microchimeric cells. This case-control study enrolled 40 male infants attending pediatric surgery from January 2022 to October 2022. Female cells were quantified in infants' tonsil tissue by using cytogenetic fluorescent in situ hybridization (FISH) coupled with optimized automated microscopy. Out of the 40 infants, half (47.4%) had been breastfed for more than one month, a quarter for less a month, and 10 children (26.3%) were never breastfed. XX cells were observed in male tonsils in two-thirds of participants at a median density of 5 cells per 100,000 cells. In univariate analyses, child age was negatively associated with a high female cell density. In exploratory multivariate analyses, previous breastfeeding is a likely determinant of the persistence of these cells in the host, as well as the rank among siblings. Part of the benefit of breastmilk for child health may therefore be driven by breastfeeding-related microchimerism.

Potential Epigenetic Effects of Human Milk on Infants' Neurodevelopment

The advantages of human milk feeding, especially in preterm babies, are well recognized. Infants' feeding with breast milk lowers the likelihood of developing a diverse range of non-communicable diseases later in life and it is also associated with improved neurodevelopmental outcomes. Although the precise mechanisms through which human milk feeding is linked with infants' neurodevelopment are still unknown, potential epigenetic effects of breast milk through its bioactive components, including non-coding RNAs, stem cells and microbiome, could at least partly explain this association. Micro- and long-non-coding RNAs, enclosed in milk exosomes, as well as breast milk stem cells, survive digestion, reach the circulation and can cross the blood-brain barrier. Certain non-coding RNAs potentially regulate genes implicated in brain development and function, whereas nestin-positive stem cells can possibly differentiate into neural cells or/and act as epigenetic regulators in the brain. Furthermore, breast milk microbiota contributes to the establishment of infant's gut microbiome, which is implicated in brain development via epigenetic modifications and key molecules' regulation. This narrative review provides an updated analysis of the relationship between breast milk feeding and infants' neurodevelopment via epigenetics, pointing out how breast milk's bioactive components could have an impact on the neurodevelopment of both full-term and preterm babies.

Bovine milk-derived cells express transcriptome markers of pluripotency and secrete bioactive factors with regenerative and antimicrobial activity

The bovine mammary stem/progenitor cell secretome stimulates regeneration in vitro and contains proteins associated with antimicrobial defense. This has led to the exploration of the secretome as a biologic treatment for mastitis, a costly inflammation of the udder commonly caused by bacteria. This study reports on a population of bovine mammary stem/progenitor cells isolated non-invasively from milk (MiDCs). MiDCs were characterized by immunophenotyping, mammosphere formation assays, and single cell RNA sequencing. They displayed epithelial morphology, exhibited markers of mammary stem/progenitor cells, and formed mammospheres, like mammary gland tissue-isolated stem/progenitor cells. Single cell RNA sequencing revealed two sub-populations of MiDCs: epithelial cells and macrophages. Functionally, the MiDC secretome increased fibroblast migration, promoted angiogenesis of endothelial cells, and inhibited the growth of mastitis-associated bacteria, including antibiotic-resistant strains, in vitro. These qualities of MiDCs render them a source of stem cells and stem cell products that may be used to treat diseases affecting the dairy industry, including mastitis.

The cellular and immunological dynamics of early and transitional human milk

Human milk is essential for infant nutrition and immunity, providing protection against infections and other immune-mediated diseases during the lactation period and beyond in later childhood. Milk contains a broad range of bioactive factors such as nutrients, hormones, enzymes, immunoglobulins, growth factors, cytokines, and antimicrobial factors, as well as heterogeneous populations of maternal cells. The soluble and cellular components of milk are dynamic over time to meet the needs of the growing infant. In this study, we utilize systems-approaches to define and characterize 62 analytes of the soluble component, including immunoglobulin isotypes, as well as the cellular component of human milk during the first two weeks postpartum from 36 mothers. We identify soluble immune and growth factors that are dynamic over time and could be utilized to classify milk into different phenotypic groups. We identify 24 distinct populations of both epithelial and immune cells by single-cell transcriptome analysis of 128,016 human milk cells. We found that macrophage populations have shifting inflammatory profiles during the first two weeks of lactation. This analysis provides key insights into the soluble and cellular components of human milk and serves as a substantial resource for future studies of human milk.

Regenerative Potential of Human Breast Milk: A Natural Reservoir of Nutrients, Bioactive Components and Stem cells

Human milk is a complex fluid that contains carbohydrates, lipids, proteins, and other bioactive molecules (immunoglobulins, lactoferrin, human milk oligosaccharides, lysozyme, leukocytes, cytokines, hormones, and microbiome) which provide nutritional, immunological, and developmental benefits to the infant. In addition to their involvement in the development, these bioactive compounds have a key role in anti-oncogenicity, neuro-cognitive development, cellular communication, and differentiation. As a result of technological advancements, it has been discovered that human breast milk contains cells that display many of the characteristics of stem cells with multilineage differentiation potentials. Do these cells have any specific properties or roles? Research efforts on breast milk cells have been mainly focused on leukocytes based on their immunological perspective in the early postpartum period. This review summarizes the nutritional components in human milk, i.e., the macro and micronutrients required for the growth and development of infants. Further, it discusses the research work reported concerning the purification, propagation, and differentiation of breast milk progenitor cells and highlights the advancements made in this newly emerging field of stem cell biology and regenerative medicine.

Ecologies, synergies, and biological systems shaping human milk composition-a report from "Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN)" Working Group 2

Human milk is universally recognized as the preferred food for infants during the first 6 mo of life because it provides not only essential and conditionally essential nutrients in necessary amounts but also other biologically active components that are instrumental in protecting, communicating important information to support, and promoting optimal development and growth in infants. Despite decades of research, however, the multifaceted impacts of human milk consumption on infant health are far from understood on a biological or physiological basis. Reasons for this lack of comprehensive knowledge of human milk functions are numerous, including the fact that milk components tend to be studied in isolation, although there is reason to believe that they interact. In addition, milk composition can vary greatly within an individual as well as within and among populations. The objective of this working group within the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project was to provide an overview of human milk composition, factors impacting its variation, and how its components may function to coordinately nourish, protect, and communicate complex information to the recipient infant. Moreover, we discuss the ways whereby milk components might interact such that the benefits of an intact milk matrix are greater than the sum of its parts. We then apply several examples to illustrate how milk is better thought of as a biological system rather than a more simplistic "mixture" of independent components to synergistically support optimal infant health.

Metabolomic Diversity of Human Milk Cells over the Course of Lactation-A Preliminary Study

Human milk (HM) is a complex biofluid containing a wide cell variety including epithelial cells and leukocytes. However, the cellular compositions and their phenotypic properties over the course of lactation are poorly understood. The aim of this preliminary study was to characterize the cellular metabolome of HM over the course of lactation. Cells were isolated via centrifugation and the cellular fraction was characterized via cytomorphology and immunocytochemical staining. Cell metabolites were extracted and analyzed using ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-QqTOF-MS) in the positive and negative electrospray ionization modes. Immunocytochemical analysis revealed a high variability of the number of detected cells with relative median abundances of 98% of glandular epithelial cells, 1% of leukocytes, and 1% of keratinocytes. Significant correlations between the milk postnatal age with percentage of epithelial cells and leukocytes, and with total cell count were observed. Results from the Hierarchical Cluster Analysis of immunocytochemical profiles were very similar to those observed in the analysis of the metabolomic profiles. In addition, metabolic pathway analysis showed alterations in seven metabolic pathways correlating with postnatal age. This work paves the way for future investigations on changes in the metabolomic fraction of the cellular compartment of HM.

Emergent roles of maternal microchimerism in postnatal development

Maternal microchimerism (MMc) is the phenomenon that a low number of cells from the mother persists within her progeny. Despite their regular presence in mammalian pregnancies, the overall cell type repertoire and roles of maternal cells, especially after birth, remain unclear. By using transgenic mouse strains and human umbilical blood samples, recent studies have for the first time characterized and quantified MMc cell type repertoires in offspring, identified the cross-generational influence on fetal immunity, and determined possible factors that affect their presence in offspring. This review summarizes new findings, especially on the maternal cell type repertoires and their potential role in utero, in postnatal life, and long after birth.

Breast milk mesenchymal stem cells abate cisplatin-induced cardiotoxicity in adult male albino rats via modulating the AMPK pathway

Myocardial injury influenced by cisplatin (Cis) is a compelling reason to hunt out a treatment modality to overcome such a threat in cisplatin-treated patients. Breast Milk mesenchymal stem cells (Br-MSCs) are a non-invasive, highly reproducible source of stem cells. Herein, we investigate Br-MSCs' role in cardiotoxicity induced by cisplatin. Rats were divided into; control, Cis-treated (received 12 mg/kg single intraperitoneal injection), BrMSCs-treated (received single intraperitoneal injection of 0.5 ml sterilized phosphate-buffered saline containing 2 × 107 cells of Br-MSCs); metformin-treated (received 250 mg/kg/day orally) and BrMSCs + metformin + Cis treated groups. At the experiment end, serum creatine kinase (CK-MB) and cardiac troponin T (cTnT) activates were estimated, cardiac malondialdehyde (MDA), superoxide dismutase (SOD), interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α) levels were measured, cardiac expression of Bax and Bcl-2 and AMP-activated protein kinase (AMPK), as well as heart histopathology, were evaluated. Study results showed that Cis explored acute cardiotoxicity evidenced by deteriorated cardiac indices, induction of oxidative stress, and inflammation with myocardium histological alterations. Treatment with Br-MSCs restored heart function and structure deteriorated by Cis injection. The antioxidant/anti-inflammatory/anti-apoptotic results of Br-MSCs were supported by AMPK activation denoting their protective role against cisplatin-induced cardiac injury. These results were superior when metformin was added to the treatment protocol.

The Effect of Infant Gastric Digestion on Human Maternal Milk Cells

SCOPE

Human breast milk contains a variety of cell types that have potential roles in infant immunity and development. One challenge associates with defining the purpose(s) of milk cells in the infant is a poor understanding of the effect of digestion on cell fate.

METHODS AND RESULTS

This study first demonstrates that milk cell death occurs after gastric digestion in mice. Then flow cytometry and RT-PCR are used to understand the mechanism of human milk cell death and quantify live cell types before and after simulated gastric digestion. This study finds that digestion in simulated gastric fluid for 30 min reduces cell viability from 72% to 27%, with most cell death is caused by the acidic pH. The primary mechanism of cell death is caspase-mediated apoptosis. The non-cellular components of milk offer only mild protection against cell death from stomach acid.

CONCLUSIONS

Gastric digestion does not select for a specific resilient cell population to survive-most cell types die in equal proportions in the gastric environment. Taken together, these results provide a foundation with which to understand the fate of human breast milk cells in the infant's intestine and beyond.

Pregnancy-induced maternal microchimerism shapes neurodevelopment and behavior in mice

Life-long brain function and mental health are critically determined by developmental processes occurring before birth. During mammalian pregnancy, maternal cells are transferred to the fetus. They are referred to as maternal microchimeric cells (MMc). Among other organs, MMc seed into the fetal brain, where their function is unknown. Here, we show that, in the offspring’s developing brain in mice, MMc express a unique signature of sensome markers, control microglia homeostasis and prevent excessive presynaptic elimination. Further, MMc facilitate the oscillatory entrainment of developing prefrontal-hippocampal circuits and support the maturation of behavioral abilities. Our findings highlight that MMc are not a mere placental leak out, but rather a functional mechanism that shapes optimal conditions for healthy brain function later in life.

During pregnancy, maternal cells are transferred to the fetus, where they can reach the developing brain. In this study, the authors demonstrate that these maternal cells play an important role in neurodevelopment.

Profiling of mature-stage human breast milk cells identifies six unique lactocyte subpopulations

Breast milk is chock-full of nutrients, immunological factors, and cells that aid infant development. Maternal cells are the least studied breast milk component, and their unique properties are difficult to identify using traditional techniques. Here, we characterized the cells in mature-stage breast milk from healthy donors at the protein, gene, and transcriptome levels. Holistic analysis of flow cytometry, quantitative polymerase chain reaction, 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 subpopulations, including three previously unidentified subpopulations programmed toward mucosal defense and intestinal development. Pseudotime analysis delineated the differentiation pathways of epithelial progenitors. Together, these data define healthy human maternal breast milk cells and provide a basis for their application in maternal and infant medicine.

Factors influencing maternal microchimerism throughout infancy and its impact on infant T cell immunity

Determinants of the acquisition and maintenance of maternal microchimerism (MMc) during infancy and the impact of MMc on infant immune responses are unknown. We examined factors which influence MMc detection and level across infancy and the effect of MMc on T cell responses to BCG vaccination in a cohort of HIV exposed, uninfected and HIV unexposed infants in South Africa. MMc was measured in whole blood from 58 infants using a panel of quantitative PCR assays at day one and 7, 15, and 36 weeks of life. Infants received BCG at birth, and selected whole blood samples from infancy were stimulated in vitro with BCG and assessed for polyfunctional CD4+ T cell responses. MMc was present in most infants across infancy with levels ranging from 0-1,193/100,000 genomic equivalents and was positively impacted by absence of maternal HIV, maternal-infant HLA compatibility, infant female sex, and exclusive breastfeeding. Initiation of maternal antiretroviral therapy prior to pregnancy partially restored MMc levels in HIV exposed, uninfected infants. Birth MMc was associated with an improved polyfunctional CD4+ T cell response to BCG. These data emphasize that both maternal and infant factors influence MMc, which may subsequently impact infant T cell responses.

Human Breast Milk: From Food to Active Immune Response With Disease Protection in Infants and Mothers

Breastfeeding is associated with long-term wellbeing including low risks of infectious diseases and non-communicable diseases such as asthma, cancer, autoimmune diseases and obesity during childhood. In recent years, important advances have been made in understanding the human breast milk (HBM) composition. Breast milk components such as, non-immune and immune cells and bioactive molecules, namely, cytokines/chemokines, lipids, hormones, and enzymes reportedly play many roles in breastfed newborns and in mothers, by diseases protection and shaping the immune system of the newborn. Bioactive components in HBM are also involved in tolerance and appropriate inflammatory response of breastfed infants if necessary. This review summarizes the current literature on the relationship between mother and her infant through breast milk with regard to disease protection. We will shed some light on the mechanisms underlying the roles of breast milk components in the maintenance of health of both child and mother.

Safety and Feasibility of Using Cell-Enriched Human Milk in the Treatment of Early Necrotizing Enterocolitis

Background: Necrotizing enterocolitis (NEC) is a severe intestinal disease that often occurs in preterm infants, and there currently is a lack of specific and effective therapy. Human milk is rich in cells that may become a potential NEC treatment. Research Aim: To evaluate the safety and feasibility of cell-enriched fresh human milk treatment for premature infants with stage I NEC. Materials and Methods: Infants born at <1,500 g birth weight who developed stage I NEC were enrolled. Along with routine treatment for these infants, those in the intervention group were treated with cell-enriched fresh mother's milk (1 mL/kg) once per day for seven consecutive days. The intervention feasibility and safety were monitored and evaluated as primary outcomes. Short-term outcomes, including the duration of antibiotics, days to full enteral feeding and prognosis, were investigated as secondary outcomes. Results: Forty infants were enrolled, and 20 infants were included in each group. The demographic characteristics of the two groups of infants were comparable. All infants in the intervention group completed cell-enriched fresh mother's milk feeding for 7 days without any adverse clinical issues. The infants' vital signs were within the normal range during and after the intervention. None of the enrolled patients progressed to stage II NEC or above. The time interval from milk pumping to feeding was 3.7 ± 0.5 hours. Conclusions: Using cell-enriched fresh mother's milk to treat premature infants with stage I NEC was safe and feasible.

Human milk: From complex tailored nutrition to bioactive impact on child cognition and behavior

Human milk is a highly complex liquid food tailor-made to match an infant's needs. Beyond documented positive effects of breastfeeding on infant and maternal health, there is increasing evidence that milk constituents also impact child neurodevelopment. Non-nutrient milk bioactives would contribute to the (long-term) development of child cognition and behavior, a process termed 'Lactocrine Programming'. In this review we discuss the current state of the field on human milk composition and its links with child cognitive and behavioral development. To promote state-of-the-art methodologies and designs that facilitate data pooling and meta-analytic endeavors, we present detailed recommendations and best practices for future studies. Finally, we determine important scientific gaps that need to be filled to advance the field, and discuss innovative directions for future research. Unveiling the mechanisms underlying the links between human milk and child cognition and behavior will deepen our understanding of the broad functions of this complex liquid food, as well as provide necessary information for designing future interventions.

Whole embryonic detection of maternal microchimeric cells highlights significant differences in their numbers among individuals

During pregnancy in placental mammals, small numbers of maternal cells (maternal microchimeric cells, or MMc cells) migrate into the fetus and persist decades, or perhaps for the rest of their lives, and higher frequencies of MMc cells are reported to correlate with variety of phenomena, such as immune tolerance, tissue repair, and autoimmune diseases. While detection of these MMc cells is considered in all pregnancies, their frequency differs largely according to tissue type and disease cases, and it remains unclear whether the number of MMc cells differs significantly among embryos in normal pregnancies. Here, for the first time, we developed a whole embryonic detection method for MMc cells using transgenic mice and counted live MMc cells in each individual embryo. Using this technique, we found that the number of MMc cells was comparable in most of the analyzed embryos; however, around 500 times higher number of MMc cells was detected in one embryo at the latest stage. This result suggests that the number of MMc cells could largely differ in rare cases with unknown underlying mechanisms. Our methodology provides a basis for testing differences in the numbers of MMc cells among individual embryos and for analyzing differences in MMc cell type repertoires in future studies. These data could provide a hint toward understanding the mechanisms underlying the variety of apparently inconsistent MMc-related phenomena.

Impacts of Enriched Human Milk Cells on Fecal Metabolome and Gut Microbiome of Premature Infants with Stage I Necrotizing Enterocolitis: A Pilot Study

SCOPE

Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality in preterm infants, occurring more often in formula-fed infants than in breastfed infants. Recent animal studies have shown that cells in fresh breast milk survive in the newborns' digestive tract. However, no clinical studies have been conducted on the effects of human milk cells, and their biological roles in the infants' intestines remain unexplored.

METHODS AND RESULTS

Twenty premature infants are enrolled. Cells from fresh milk of their own mothers are enriched and fed to infants with Bell's Stage I NEC once a day for 7 days since the onset of NEC. Fecal samples are collected at enrollment and 2 weeks later. Fecal sphingolipids are observed to be enriched in NEC patients and positively correlated with calprotectin levels. After intervention with enriched human milk cells, inflammation-associated sphingolipids and microbiome profiles are altered and resembled those of the controls.

CONCLUSION

These preliminary findings reveal the potential impacts of enriched human milk cells on premature infants with Bell's Stage I NEC and provide insight into the roles of fecal sphingolipid metabolism in the neonates' intestinal inflammation. However, the limited sample size of the study indicates the need for further investigation.

25 Years of Research in Human Lactation: From Discovery to Translation

Researchers have recently called for human lactation research to be conceptualized as a biological framework where maternal and infant factors impacting human milk, in terms of composition, volume and energy content are studied along with relationships to infant growth, development and health. This approach allows for the development of evidence-based interventions that are more likely to support breastfeeding and lactation in pursuit of global breastfeeding goals. Here we summarize the seminal findings of our research programme using a biological systems approach traversing breast anatomy, milk secretion, physiology of milk removal with respect to breastfeeding and expression, milk composition and infant intake, and infant gastric emptying, culminating in the exploration of relationships with infant growth, development of body composition, and health. This approach has allowed the translation of the findings with respect to education, and clinical practice. It also sets a foundation for improved study design for future investigations in human lactation.

Breast milk MSCs upregulated β-cells PDX1, Ngn3, and PCNA expression via remodeling ER stress /inflammatory /apoptotic signaling pathways in type 1 diabetic rats

Type 1 diabetes mellitus (T1DM) is one of the autoimmune diseases characterized by beta-cell dysfunction with serious health complications. Br-MSCs represent a novel valid candidate in regenerative medicine disciplines. Yet, the full potential of Br-MSCs in managing type 1 diabetes remains elusive. Indeed, this study was designed to explore a novel approach investigating the possible regenerative capacity of Br-MSCs in type1 diabetic islet on the level of the cellular mRNA expression of different molecular pathways involved in pancreatic beta-cell dysfunction. Sixty adult male Sprague-Dawley rats were randomly assigned into 3 groups (20 rats each); the control group, type1 diabetic group, and the type 1 diabetic Br-MSCs treated group. And, for the first time, our results revealed that intraperitoneally transplanted Br-MSCs homed to the diabetic islet and improved fasting blood glucose, serum insulin level, pancreatic oxidative stress, upregulated pancreatic mRNA expression for: regenerative markers (Pdx1, Ngn3, PCNA), INS, beta-cell receptors (IRS1, IRβ, PPARγ), pancreatic growth factors (IGF-1, VEGFβ1, FGFβ), anti-inflammatory cytokine (IL10) and anti-apoptotic marker (BCL2) too, Br-MSCs downregulated pancreatic mRNA expression for: inflammatory markers (NFKβ, TNFα, IL1β, IL6, IL8, MCP1), apoptotic markers for both intrinsic and extrinsic pathways (FAS, FAS-L, P53, P38, BAX, Caspase3), ER stress markers (ATF6, ATF3, ATF4, BIP, CHOP, JNK, XBP1) and autophagy inhibitor (mTOR). In conclusion, Br-MSCs could be considered as a new insight in beta cell regenerative therapy improving the deteriorated diabetic islet microenvironment via modulating; ER stress, inflammatory, and apoptotic signaling pathways besides, switching on the cellular quality control system (autophagy) thus enhancing beta-cell function.

Comparison of the Characteristics of Breast Milk-derived Stem Cells with the Stem Cells Derived from the Other Sources: A Comparative Review

Breast milk (BrM) not only supplies nutrition, but it also contains a diverse population of cells. It has been estimated that up to 6% of the cells in human milk possess the characteristics of mesenchymal stem cells (MSC). Available data also indicate that these cells are multipotent and capable of self-renewal and differentiation with other cells. In this review, we have compared different characteristics, such as CD markers, differentiation capacity, and morphology of stem cells, derived from human breast milk (hBr-MSC) with human bone marrow (hBMSC), Wharton's jelly (WJMSC), and human adipose tissue (hADMSC). Through the literature review, it was revealed that human breast milk-derived stem cells specifically express a group of cell surface markers, including CD14, CD31, CD45, and CD86. Importantly, a group of markers, CD13, CD29, CD44, CD105, CD106, CD146, and CD166, were identified, which were common in the four sources of stem cells. WJMSC, hBMSC, hADMSC, and hBr-MSC are potently able to differentiate into the mesoderm, ectoderm, and endoderm cell lineages. The ability of hBr-MSCs todifferentiate into the neural stem cells, neurons, adipocyte, hepatocyte, chondrocyte, osteocyte, and cardiomyocytes has made these cells a promising source of stem cells in regenerative medicine, while isolation of stem cells from the commonly used sources, such as bone marrow, requires invasive procedures. Although autologous breast milk-derived stem cells are an accessible source for women who are in the lactation period, breast milk can be considered as a source of stem cells with high differentiation potential without any ethical concern.

Maternal Microbiota, Early Life Colonization and Breast Milk Drive Immune Development in the Newborn

The innate immune system is the oldest protection strategy that is conserved across all organisms. Although having an unspecific action, it is the first and fastest defense mechanism against pathogens. Development of predominantly the adaptive immune system takes place after birth. However, some key components of the innate immune system evolve during the prenatal period of life, which endows the newborn with the ability to mount an immune response against pathogenic invaders directly after birth. Undoubtedly, the crosstalk between maternal immune cells, antibodies, dietary antigens, and microbial metabolites originating from the maternal microbiota are the key players in preparing the neonate’s immunity to the outer world. Birth represents the biggest substantial environmental change in life, where the newborn leaves the protective amniotic sac and is exposed for the first time to a countless variety of microbes. Colonization of all body surfaces commences, including skin, lung, and gastrointestinal tract, leading to the establishment of the commensal microbiota and the maturation of the newborn immune system, and hence lifelong health. Pregnancy, birth, and the consumption of breast milk shape the immune development in coordination with maternal and newborn microbiota. Discrepancies in these fine-tuned microbiota interactions during each developmental stage can have long-term effects on disease susceptibility, such as metabolic syndrome, childhood asthma, or autoimmune type 1 diabetes. In this review, we will give an overview of the recent studies by discussing the multifaceted emergence of the newborn innate immune development in line with the importance of maternal and early life microbiota exposure and breast milk intake.

Breast milk stem cells: Are they magic bullets in neonatology?

Each mammal produces milk specific to its newborn that meets all nutritional needs. Breast milk is not only a secretory product but is also a complex liquid containing several components that provide enteral nutrition. The stage of lactation, the fullness of the breast, the feeding of the baby, and the health of the mother during the breastfeeding period cause differences in the composition of breast milk. Although the positive effects of breast milk on the physical and intellectual development of a child in the short and long term have been known for centuries, its mechanism has not been elucidated. Stem cells are defined as the cells that possess specific markers and have not undergone differentiation. Under suitable conditions and stimuli, they can differentiate into desired cells. The detection of stem cells, whose exact origin is not known, in breast milk and their demonstration in the baby's body have prompted the necessity of exploring the possible role of stem cells in the treatment of diseases. In this review, breast milk-derived stem cells and their possible role in neonatology are discussed.

How Knowledge about Stem Cells Influences Attitudes towards Breastfeeding: Case Study of Polish Women

Maternal breastfeeding is associated with multiple health benefits, both for the child and the mother. Since breastfeeding rates are declining, finding new, future-oriented strategies to strengthen and support mothers’ positive attitudes towards breastfeeding need to be developed. In this paper, we describe how information about the presence of stem cells in breast milk can influence the willingness to breastfeed in the population of Polish pregnant women. A cross-sectional study involving a group of 150 pregnant women was conducted to assess the correlation between their knowledge about stem cells and their attitude towards breastfeeding. Among the respondents, only 6% claimed that they did not know anything about stem cells, but general knowledge about stem cells in the research group was poor. The survey results indicated that city residence, university degree, maternal experience and advanced pregnancy correlated with higher general knowledge regarding stem cells. Most respondents (77.3%) had no knowledge regarding the presence of stem cells in breast milk. Approximately two-thirds of mothers with earlier negative breastfeeding experience declared that information about the presence of stem cells in breast milk could have influenced the decision to continue and extend the time of breastfeeding. Hence highlighting the presence of stem cells in breast milk can be used to encourage breastfeeding as a unique activity.

The Gut‒Breast Axis: Programming Health for Life

The gut is a pivotal organ in health and disease. The events that take place in the gut during early life contribute to the programming, shaping and tuning of distant organs, having lifelong consequences. In this context, the maternal gut plays a quintessence in programming the mammary gland to face the nutritional, microbiological, immunological, and neuroendocrine requirements of the growing infant. Subsequently, human colostrum and milk provides the infant with an impressive array of nutrients and bioactive components, including microbes, immune cells, and stem cells. Therefore, the axis linking the maternal gut, the breast, and the infant gut seems crucial for a correct infant growth and development. The aim of this article is not to perform a systematic review of the human milk components but to provide an insight of their extremely complex interactions, which render human milk a unique functional food and explain why this biological fluid still truly remains as a scientific enigma.

Racial and socioeconomic disparities in breast milk feedings in US neonatal intensive care units

Very low birth weight (VLBW; <1500 g birth weight) infants are substantially more likely to be born to black than to non-black mothers, predisposing them to potentially preventable morbidities that increase the risk for costly lifelong health problems. Mothers' own milk (MOM) may be considered the ultimate "personalized medicine" since milk composition and bioactive components vary among mothers and multiple milk constituents provide specific protection based on shared exposures between mother and infant. MOM feedings reduce the risks and associated costs of prematurity-associated morbidities, with the greatest reduction afforded by MOM through to NICU discharge. Although black and non-black mothers have similar lactation goals and initiation rates, black VLBW infants are half as likely to receive MOM at NICU discharge in the United States. Black mothers are significantly more likely to be low-income, single heads of household and have more children in the home, increasing the burden of MOM provision. Although rarely considered, the out-of-pocket and opportunity costs associated with providing MOM for VLBW infants are especially onerous for black mothers. When MOM is not available, the NICU assumes the costs of inferior substitutes for MOM, contributing further to disparate outcomes. Novel strategies to mitigate these disparities are urgently needed. IMPACT: Mother's own milk exemplifies personalized medicine through its unique biologic activity. Hospital factors and social determinants of health are associated with mother's own milk feedings for very low-birth-weight infants in the neonatal intensive care unit. Notably, out-of-pocket and opportunity costs associated with providing mother's own milk are borne by mothers. Conceptualizing mother's own milk feedings as an integral part of NICU care requires consideration of who bears the costs of MOM provision-the mother or the NICU?

Breastfeeding Contributes to Physiological Immune Programming in the Newborn

The first 1,000 days in the life of a human being are a vulnerable stage where early stimuli may program adverse health outcomes in future life. Proper maternal nutrition before and during pregnancy modulates the development of the fetus, a physiological process known as fetal programming. Defective programming promotes non-communicable chronic diseases in the newborn which might be prevented by postnatal interventions such as breastfeeding. Breast milk provides distinct bioactive molecules that contribute to immune maturation, organ development, and healthy microbial gut colonization, and also secures a proper immunological response that protects against infection and inflammation in the newborn. The gut microbiome provides the most critical immune microbial stimulation in the newborn in early life, allowing a well-trained immune system and efficient metabolic settings in healthy subjects. Conversely, negative fetal programming by exposing mothers to diets rich in fat and sugar has profound effects on breast milk composition and alters the immune profiles in the newborn. At this new stage, newborns become vulnerable to immune compromise, favoring susceptibility to defective microbial gut colonization and immune response. This review will focus on the importance of breastfeeding and its immunological biocomponents that allow physiological immune programming in the newborn. We will highlight the importance of immunological settings by breastfeeding, allowing proper microbial gut colonization in the newborn as a window of opportunity to secure effective immunological response.

Single Cell RNA Sequencing of Human Milk-Derived Cells Reveals Sub-Populations of Mammary Epithelial Cells with Molecular Signatures of Progenitor and Mature States: a Novel, Non-invasive Framework for Investigating Human Lactation Physiology

Cells in human milk are an untapped source, as potential "liquid breast biopsies", of material for investigating lactation physiology in a non-invasive manner. We used single cell RNA sequencing (scRNA-seq) to identify milk-derived mammary epithelial cells (MECs) and their transcriptional signatures in women with diet-controlled gestational diabetes (GDM) with normal lactation. Methodology is described for coordinating milk collections with single cell capture and library preparation via cryopreservation, in addition to scRNA-seq data processing and analyses of MEC transcriptional signatures. We comprehensively characterized 3740 cells from milk samples from two mothers at two weeks postpartum. Most cells (>90%) were luminal MECs (luMECs) expressing lactalbumin alpha and casein beta and positive for keratin 8 and keratin 18. Few cells were keratin 14⁺ basal MECs and a small immune cell population was present (<10%). Analysis of differential gene expression among clusters identified six potentially distinct luMEC subpopulation signatures, suggesting the potential for subtle functional differences among luMECs, and included one cluster that was positive for both progenitor markers and mature milk transcripts. No expression of pluripotency markers POU class 5 homeobox 1 (POU5F1, encoding OCT4) SRY-box transcription factor 2 (SOX2) or nanog homeobox (NANOG), was observed. These observations were supported by flow cytometric analysis of MECs from mature milk samples from three women with diet-controlled GDM (2-8 mo postpartum), indicating a negligible basal/stem cell population (epithelial cell adhesion molecule (EPCAM)^-/integrin subunit alpha 6 (CD49f)⁺, 0.07%) and a small progenitor population (EPCAM⁺/CD49f⁺, 1.1%). We provide a computational framework for others and future studies, as well as report the first milk-derived cells to be analyzed by scRNA-seq. We discuss the clinical potential and current limitations of using milk-derived cells as material for characterizing human mammary physiology.

Immunologic Properties of Human Milk and Clinical Implications in the Neonatal Population

Human milk contains various bioactive substances including hormones, immunoglobulins, enzymes, and growth factors in addition to its macro- and micronutrients. It has been suggested that human milk is a vehicle of communication between the maternal and infant immune systems, providing passive protection as well as direct active immunomodulation. Human milk protects newborns against pathogens by acting directly on multiple physiologic systems. Bioactive and immunologic factors regulate the infant's immune, metabolic, and microbiome systems. Breastfeeding protects infants in all socioeconomic groups, showing a pattern of protective dose/duration-response effects. This review summarizes the immune components and immunologic properties of human milk and provides an update of their potential implications in the neonatal population.

Breast Milk Stem Cell Survival in Neonate's Gut, Entery into Neonate Circulation and Adaption by the Body

The stem cell exchange during pregnancy is thought to remain chimeras for life. Few studies recently revealed that maternal transfer of viable stem cells to the offspring continues even after birth during breastfeeding. Some of these stem cells are likely to be integrated into different organs (brain, blood, kidneys, and pancreas) including neurons and insulin-producing cells in the pancreas to become functional cells. This finding opens a new avenue for research on therapeutic uses of breast milk- derived stem cells. Recently Dr. Foteini Hassiotou used glowing mice, which were genetically modified to express a gene called tdTomato that causes cells to appear red under fluorescence light. These mice were mated, and their babies were swapped with the pups of another, unmodified mother mouse. The new pups suckled the modified mouse and, as a result, obtained glowing red stem cells from breast milk. The study has never been replicated in humans, so it is not clear yet if the findings apply to humans as in the case of mice. However, the results of the study are the jumping-off points for future research on human breast milk stem cells and their possible application in stem cell therapies. Additional studies are necessary to understand the passage of human breast milk stem cells through the neonate's GI tract, and passage to the systemic circulation.

Amniotic fluid and breast milk: a rationale for breast milk stem cell therapy in neonatal diseases

Amniotic fluid and breast milk play important roles in structural development throughout fetal growth and infancy. Given their significance in physical maturation, many studies have investigated the therapeutic and protective roles of amniotic fluid and breast milk in neonatal diseases. Of particular interest to researchers are stem cells found in the two fluids. These stem cells have been investigated due to their ability to self-replicate, differentiate, reduce tissue damage, and their expression of pluripotent markers. While amniotic fluid stem cells have received some attention regarding their ability to treat neonatal diseases, breast milk stem cells have not been investigated to the same extent given the recency of their discovery. The purpose of this review is to compare the functions of amniotic fluid, breast milk, and their stem cells to provide a rationale for the use of breast milk stem cells as a therapy for neonatal diseases. Breast milk stem cells present as an important tool for treating neonatal diseases given their ability to reduce inflammation and tissue damage, as well as their multilineage differentiation potential, easy accessibility, and ability to be used in disease modelling.

T Cells in Preterm Infants and the Influence of Milk Diet

Preterm infants born before 32 weeks gestational age (GA) have high rates of late onset sepsis (LOS) and necrotizing enterocolitis (NEC) despite recent improvements in infection control and nutrition. Breast milk has a clear protective effect against both these outcomes likely due to multiple mechanisms which are not fully understood but may involve effects on both the infant's immune system and the developing gut microbiota. Congregating at the interface between the mucosal barrier and the microbiota, innate and adaptive T lymphocytes (T cells) participate in this interaction but few studies have explored their development after preterm delivery. We conducted a literature review of T cell development that focuses on fetal development, postnatal maturation and the influence of milk diet. The majority of circulating T cells in the preterm infant display a naïve phenotype but are still able to initiate functional responses similar to those seen in term infants. T cells from preterm infants display a skew toward a T-helper 2(Th2) phenotype and have an increased population of regulatory cells (Tregs). There are significant gaps in knowledge in this area, particularly in regards to innate-like T cells, but work is emerging: transcriptomics and mass cytometry are currently being used to map out T cell development, whilst microbiomic approaches may help improve understanding of events at mucosal surfaces. A rapid rise in organoid models will allow robust exploration of host-microbe interactions and may support the development of interventions that modulate T-cell responses for improved infant health.

Human milk cortisol and immune factors over the first three postnatal months: Relations to maternal psychosocial distress

Background

Many biologically active factors are present in human milk including proteins, lipids, immune factors, and hormones. The milk composition varies over time and shows large inter-individual variability. This study examined variations of human milk immune factors and cortisol concentrations in the first three months post-partum, and their potential associations with maternal psychosocial distress.

Methods

Seventy-seven healthy mothers with full term pregnancies were enrolled, of which 51 mothers collected morning milk samples at 2, 6 and 12 weeks post-delivery. Maternal psychosocial distress was assessed at 6 weeks post-delivery using questionnaires for stress, anxiety, and depressive symptoms. Immune factors were determined using multiplex immunoassays and included innate immunity factors (IL1β, IL6, IL12, IFNγ, TNFα), acquired immunity factors (IL2, IL4, IL10, IL13, IL17), chemokines (IL8, Groα, MCP1, MIP1β), growth factors (IL5, IL7, GCSF, GMCSF, TGFβ2) and immunoglobulins (IgA, total IgG, IgM). Cortisol was quantified using liquid chromatography-tandem mass spectrometry. A linear mixed effects model was fit to test whether stress, anxiety, and depressive symptoms individually predicted human milk cortisol concentrations after accounting for covariates. Repeated measurement analyses were used to compare women with high (n = 13) versus low psychosocial distress (n = 13) for immune factors and cortisol concentrations.

Results

Virtually all immune factors and cortisol, with the exception of the granulocyte-macrophage colony-stimulating factor (GMCSF), were detected in the human milk samples. The concentrations of the immune factors decreased during the first 3 months, while cortisol concentrations increased over time. No correlation was observed between any of the immune factors and cortisol. No consistent relationship between postnatal psychosocial distress and concentrations of immune factors was found, whereas higher psychosocial distress was predictive of higher cortisol concentrations in human milk.

Conclusion

In the current study we found no evidence for an association between natural variations in maternal distress and immune factor concentrations in milk. It is uncertain if this lack of association would also be observed in studies with larger populations, with less uniform demographic characteristics, or with women with higher (clinical) levels of anxiety, stress and/or depressive symptoms. In contrast, maternal psychosocial distress was positively related to higher milk cortisol concentrations at week 2 post-delivery. Further investigation on maternal psychosocial distress in relation to human milk composition is warranted.

[Research advances in the effect of bioactive substances in breast milk on the growth and development of infants]

There are various types of bioactive substances in human breast milk, such as active proteins, growth factors, cytokines, oligosaccharides, probiotics and cells. Many studies have shown that these bioactive substances in breast milk have important protective effects on infant growth and development, including anti-bacterial and anti-viral effects and the promotion of infant growth and development and immunologic maturation. They can also reduce the incidence rate of infectious diseases in infants, improve neural development in preterm infants, and reduce the risk of obesity and diabetes in future. However, there is still no clinical evidence for the effects of several active substances in breast milk, and their immunoregulatory mechanism remains unclear. Therefore, further studies are needed for clarification.

The Therapeutic Potential of Conditioned Medium from Human Breast Milk Stem Cells in Treating Spinal Cord Injury

Study Design

Experimental animal study.

Purpose

This study investigated the therapeutic effects of human breast milk stem cell (BMSC)-conditioned medium (BMSC-CM) in a model of spinal cord injury (SCI) in male Sprague-Dawley rats.

Overview of Literature

SCI is one of the leading causes of disability in addition to sensory and motor impairment. So far, there have been no successful treatments for SCI. Given the positive outcomes associated with using stem cells and their derivatives as a treatment for various diseases, there is a growing interest in using them as an SCI treatment. Recent research has demonstrated that CM from stem cells has therapeutic advantages.

Methods

Human BMSCs were isolated and characterized, and CM was subsequently collected. Animals received an intrathecal administration of BMSC-CM after SCI. The activity of caspase-3 was measured to assess apoptosis, and levels of tumor necrosis factor-α and interleukin-1β were measured to assess inflammation. Also, sensory and locomotor performances were assessed after SCI and BMSC-CM administration.

Results

Administration of CM from BMSC reduced apoptosis and inflammation at the site of injury in a rat model of SCI (p<0.05). Motor, sensory, locomotor, and sensorimotor performances were significantly improved in rats that received BMSC-CM after SCI.

Conclusions

Intrathecal administration of BMSC-CM improved recovery in a rat model of SCI.

Neurotrophic Factors Mediated Activation of Astrocytes Ameliorate Memory Loss by Amyloid Clearance after Transplantation of Lineage Negative Stem Cells

Alzheimer's disease (AD) is one of the untreatable neurodegenerative disorders with associated societal burden. Current therapies only provide symptomatic relief without altering the rate of disease progression as reported by Lanctot et al. (Therapeutic Advances in Neurological Disorders 2 (3):163-180, 2009). The increased number of failed clinical trials in last two decades indicates the imperative need to explore alternative therapies for AD as reported by Tuszynski et al. (Nature Medicine 11 (5):551-555, 2005) and Liyanage et al. (Alzheimer's & Dementia 4:628-635, 2005). In this study, we aimed to decipher the role of neurotrophic factors in the reversal of memory loss by transplantation of lineage negative (Lin-ve) stem cells in a male mouse model of cognitive impairment induced by intrahippocampal injection of amyloid β-42 (Aβ-42). The efficacy of human umbilical cord blood (hUCB) derived Lin-ve stem cells were analyzed by neurobehavioral parameters, i.e., Morris water maze and passive avoidance after bilateral intra-hippocampal transplantation using stereotaxic surgery. Real-time PCR and immunohistochemistry was carried out in brain tissues in order to analyze the expression of neurotrophic factors, apoptotic, astrocytic, and other neuronal cell markers. The transplantation of Lin-ve stem cells led to reversal of memory loss associated with reduction of Aβ-42 deposition from the brains. The molecular analysis revealed increase in neurotrophic factors, i.e., glial derived neurotrophic factor (GDNF), ciliary derived neurotrophic factor (CNTF), and Brain-derived neurotrophic factor (BDNF) after transplantation. The administration of ANA-12, a TrkB inhibitor, reversed the behavioral and molecular effects of stem cell transplantation suggesting involvement of BDNF-TrkB pathway in the rescue of memory loss. We believe that the amyloid clearance results from activation of astrocytes and anti-apoptotic pathways added by neurotrophic factors.

Stem cells in human breast milk

Recent studies have demonstrated that breast milk contains a population of cells displaying many of the properties typical of stem cells. This review outlines progress made in this newly emerging field of stem cell biology and provides an analysis of the available data on purification, propagation and differentiation of certain types of progenitor cells from breast milk. The possible fates of breast milk cells, including microchimerism caused by their transmission to the distant organs of the infant, are also discussed. Unique properties of breast milk-derived stem cells, such as their unusually low tumorigenic potential and their negligible ability to form teratomas, are highlighted as obvious advantages for using these cells in regenerative therapy.

Milk MicroRNAs in Health and Disease

MicroRNAs are small noncoding RNAs responsible for regulating 40% to 60% of gene expression at the posttranscriptional level. The discovery of circulating microRNAs in several biological fluids opened the path for their study as biomarkers and long-range cell-to-cell communication mediators. Their transfer between individuals in the case of blood transfusion, for example, and their high enrichment in milk have sparked the interest for microRNA transfer through diet, especially from mothers to infants during breastfeeding. The extension of such paradigm led to the study of milk microRNAs in the case of cow or goat milk consumption in adults. Here we provide a comprehensive critical review of the key findings surrounding milk microRNAs in human, cow, and goat milk among other species. We discuss the data on their biological properties, their use as disease biomarkers, their transfer between individuals or species, and their putative or verified functions in health and disease of infants and adult consumers. This work is based on all the literature available and integrates all the results, theories, debates, and validation studies available so far on milk microRNAs and related areas of investigations. We critically discuss the limitations and outline future aspects and avenues to explore in this rapidly growing field of research that could impact public health through infant milk formulations or new therapies. We hope that this comprehensive review of the literature will provide insight for all teams investigating milk RNAs' biological activities and help ensure the quality of future reports.