Breastmilk cell trafficking induces microchimerism-mediated immune system maturation in the infant

Impact of Maternal Exposure to SARS-CoV-2 on Immunological Components of Breast Milk

COVID-19, caused by SARS-CoV-2, has become a global public health threat. Although no replication-competent virus has been found in breast milk samples, breastfeeding practices during the pandemic were impacted. It is well known that breast milk is adapted to meet the needs of infants, providing the appropriate amounts of nutrients and various bioactive compounds that contribute to the maturation of the immune system and antioxidant protection, safeguarding infants against diseases. While its composition is variable, breast milk contains immune cells, antibodies, and cytokines, which have anti-inflammatory, pro-inflammatory, antiviral, and antibacterial properties that strengthen infant immunity. Since COVID-19 vaccines have not yet been approved for infants under six months of age, newborns rely on the passive transfer of antibodies via the placenta and breast milk to protect them against severe SARS-CoV-2 infection. Several studies that analyzed breast milk samples in the context of COVID-19 have demonstrated that a strong antibody response is induced following maternal infection with SARS-CoV-2. Therefore, this review aims to provide a comprehensive overview of the impact of maternal exposure to SARS-CoV-2 through natural infection and/or vaccination on the immunological composition of breast milk based on the studies conducted on this topic.

T lymphocytes in human milk: Their role in immune system maturation through maternal microchimerism

Breastfeeding promotes the trafficking of immune cells and soluble factors from the mother to the neonate during lactation, resulting in maternal microchimerism. Human milk is abundant in T lymphocytes, but little is known about their priming and actions in neonatal mucosal tissues and their role in conferring immune tolerance in early life. This review summarises recent findings on the characteristics of human milk T cells compared to their counterparts in maternal and neonatal blood. We discuss how bioactive components of human milk, such as cytokines, hormones, and miRNA, may modulate the immune suppressive function of this cell subset. We shed light on the presence and possible functions of regulatory T cells (Tregs) in the breastfeeding triad of mother, human milk, and neonate, and how this subset of T lymphocytes may contribute to the prevention of immune pathologies, such as allergies and autoimmune diseases, later in life through human milk-induced maternal microchimerism in the newborn.

Maternal milk cell components are uptaken by infant liver macrophages via extracellular vesicle mediated transport

Milk is a multifaceted biofluid that is essential for infant nutrition and development, yet its cellular and bioactive components, particularly maternal milk cells, remain understudied. Early research on milk cells indicated that they cross the infant's intestinal barrier and accumulate within systemic organs. However, due to the absence of modern analytical techniques, these studies were limited in scope and mechanistic analysis. To overcome this knowledge gap, we have investigated the transintestinal transport of milk cells and components in pups over a 21-day period. Studies employed a mT/mG foster nursing model in which milk cells express a membrane-bound fluorophore, tdTomato. Using flow cytometry, we tracked the transport of milk cell-derived components across local and systemic tissues, including the intestines, blood, thymus, mesenteric lymph nodes, and liver. These experiments identified milk-derived fluorescent signals in intestinal epithelial and immune cells as well as liver macrophages in 7-day-old pups. However, the minute numbers of macrophages in mouse milk suggest that maternal cells are not systemically accumulating in the infant; instead, pup macrophages are consuming milk cell membrane components, such as apoptotic bodies or extracellular vesicles (EVs). Ex vivo experiments using primary macrophages support this hypothesis, showing that immune cells preferentially consumed EVs over milk cells. Together, these data suggest a more complex interplay between milk cells and the infant's immune and digestive systems than previously recognized and highlight the need for future research on the role of milk cells in infant health.

Infant respiratory infections modulate lymphocyte homing to breast milk

Introduction

Chemokines and their receptors are essential for leukocyte migration to several tissues, including human milk. Here, we evaluated the homing of T and B lymphocyte subsets to breast milk in response to ongoing respiratory infections in the nursing infant.

Methods

Blood and mature milk were collected from healthy mothers of nurslings with respiratory infections (Group I) and from healthy mothers of healthy nurslings (Group C). Total lymphocyte, T and B cells, their subset numbers, and the expression of the homing receptors CCR5, CCR6, CCR10, and CXCR3 in these cells were evaluated in milk. Maternal serum and milk chemokine, cytokine, and IgA and IgG antibody levels were also quantified.

Results

All milk lymphocyte numbers were greater in Group I than in Group C. All CD4 T-cell subsets expressing CCR5, CCR6, and CXCR3 were higher in Group I. Within the CD8 T-cell subsets, only CCR6 and CXCR3 were higher in Group I, while CCR5 expression was higher in Group I exclusively for activated CD8 T cells. Group I showed greater numbers of all CCR6+ B-cell subsets and CXCR3+ naive B cells and plasma cells than did Group C. Infection of the nurslings promoted increased CCL20, CXCL10, IL-6, IL-8, total IgA, and IgG levels in the milk.

Conclusion

Respiratory infections in nursing infants stimulate an increase in cytokines and chemokines in breast milk, facilitating the recruitment and activation of lymphocytes. This process may promote immunological tolerance and help in the maturation of the infant's immune system, providing an additional strategy for passive maternal-infant protection.

Clinical relevance of feto-maternal microchimerism in (hematopoietic stem cell) transplantation

Toleration of a semi-allogeneic fetus in the mother's uterus as well as tolerance after allogeneic hematopoietic stem cell transplantation (HSCT) appear to share some immunologic concepts. The existence of microchimeric cells, and the original idea of a bidirectional cell trafficking between mother and child during pregnancy have been known for decades. Today, origins and mechanisms of persistence of microchimeric cells are intensively being elucidated. Both, the translation of the phenomenon of feto-maternal immune tolerance to donor choice or prevention of graft-versus-host disease (GvHD) in HSCT, and the implications of microchimeric cells in and for HSCT are highly intriguing. Yet, differences in detection methods of microchimeric cells, as well as in transplantation protocols impede the comparison of larger cohorts, and limit potential clinical advice. Still, matching of non-inherited maternal antigens (NIMA), which are expressed on maternal microchimeric cells, demonstrated a strong association with decreased risk for the development of acute GvHD in the context of various transplantation strategies. Despite the fact that advances in graft manipulation and immunosuppression ameliorated the safety and outcome after HSCT, NIMA-matching retained a beneficial role in selection of sibling, child, or maternal donors, as well as for cord blood units. Recent findings indicate the existence of a microchimeric stem cell niche, in which only one dominant microchimeric cell population of only one semi-allogeneic origin persists at a time. This implies that studies regarding the impact of (maternal and fetal) microchimerism (MC) on clinical outcome of HSCT should combine analysis of NIMA and direct detection of microchimeric cells from donor and recipient on the verge of HSCT to be efficiently conclusive.

The mother-child interface: A neurobiological metamorphosis

From the start of pregnancy, mother and child induce reciprocal neurobiological changes in the brain that will prove critical for neurodevelopment and survival of both. Molecular communication between mother and fetus is constantly active and persists even after the fetus starts to synthesize its hormones in late gestation. Intriguingly, some mother and fetus exchange cells remain in the other's brain and body with long-lasting effects and memories that do not follow the laws of classical genetics but involve complex epigenetic mechanisms. After childbirth, mother and child go through a transitional phase, a sort of limbo in which both will have a peculiar functioning profile, which is adaptive for contingencies but also renders them vulnerable. The interplay between these two "limbo" states allows for an easier transition to the subsequent phases of development. In this review, we will trace mother's and child's path from pregnancy to the months following birth and, in particular, unravel i) the key features of pregnancy and brain development and the reciprocal influences; ii) how a transitory pattern of functioning characterize mother and child, moving them toward more flexible and evolved forms; and iii) how mother and fetus act during childbirth to promote neuroprotection, pain reduction, and neurophysiological changes. Therefore, this review covers a wide range of topics, integrating neuroanatomical, neurological, biochemical, neurophysiological, and psychological studies in a meaningful way, trying to integrate them in a holistic view of the mother-child interface that is usually neglected.

Human breastmilk memory T cells throughout lactation manifest activated tissue-oriented profile with prominent regulation

Breastfeeding provides important immunological benefits to the neonate, but how the different immunoactive components in breastmilk contribute to immunity remains poorly understood. Here, we characterized human breastmilk T cells using single-cell RNA-Seq and flow cytometry. Breastmilk contained predominantly memory T cells, with expression of immune signaling genes, high proliferation, and an effector Th1/cytotoxic profile with high cytokine production capacities. Elevated activation was balanced by an enriched Treg population and immune regulatory markers in conventional memory T cells. Gene and surface expression of tissue-residency markers indicate that breastmilk T cells represented tissue-adapted rather than circulatory T cells. In addition, breastmilk T cells had a broad homing profile and higher activation markers in these migratory subsets. The partly overlapping transcriptome profile between breastmilk and breast tissue T cells, particularly cytotoxic T cells, might support a role in local immune defense in the mammary gland. However, unique features of breastmilk, such as Tregs, might imply an additional role in neonatal immune support. We found some correlations between the breastmilk T cell profile and clinical parameters, most notably with maternal and household factors. Together, our data suggest that breastmilk contains an adapted T cell population that exerts their function in specific tissue sites.

A newborn's perspective on immune responses to food

In this review, we will highlight infants' immune responses to food, emphasizing the unique aspects of early-life immunity and the critical role of breast milk as a food dedicated to infants. Infants are susceptible to inflammatory responses rather than immune tolerance at the mucosal and skin barriers, necessitating strategies to promote oral tolerance that consider this susceptibility. Breast milk provides nutrients for growth and cell metabolism, including immune cells. The content of breast milk, influenced by maternal genetics and environmental exposures, prepares the infant's immune system for the outside world, including solid foods. To do this, breast milk promotes immune system development through antigen-specific and non-antigen-specific immune education by exposing the newborn to food and respiratory allergens and acting on three key targets for food allergy prevention: the gut microbiota, epithelial cells, and immune cells. Building knowledge of how the maternal exposome and human milk composition influence offspring's healthy immune development will lead to recommendations that meet the specific needs of the developing immune system and increase the chances of promoting an appropriate immune response to food in the long term.

From Womb to World: Exploring the Immunological Connections between Mother and Child

Mother and child are immunologically interconnected by mechanisms that we are only beginning to understand. During pregnancy, multiple molecular and cellular factors of maternal origin are transferred across the placenta and influence the development and function of the fetal and newborn immune system. Altered maternal immune states arising from pregnancy-associated infections or immunizations have the potential to program offspring immune function in ways that may have long-term health consequences. In this study, we review current literature on the impact of prenatal infection and vaccination on the developing immune system, highlight knowledge gaps, and look to the horizon to envision maternal interventions that could benefit both the mother and her child.

Galacto-Oligosaccharides and the Elderly Gut: Implications for Immune Restoration and Health

The increasing prevalence of noncommunicable diseases in the aging population has been correlated with a decline in innate and adaptive immune responses; hence, it is imperative to identify approaches to improve immune function, prevent related disorders, and reduce or treat age-associated health complications. Prebiotic supplementation is a promising approach to modulate the gut microbiome and immune system, offering a potential strategy to maintain the integrity of immune function in older individuals. This review summarizes the current research on prebiotic galacto-oligosaccharide (GOS) immunomodulatory mechanisms mediated by bacterial-derived metabolites, including short-chain fatty acids and secondary bile acids, to maintain immune homeostasis. The potential applications of GOS as immunotherapy for age-related disease prevention in older individuals are also highlighted. This aligns with the global shift toward proactive healthcare and emphasizes the significance of early intervention in directing an individual's health trajectory.

Maternal-Fetal Microchimerism: Impacts on Offspring's Immune Development and Transgenerational Immune Memory Transfer

Maternal-fetal microchimerism is a fascinating phenomenon in which maternal cells migrate to the tissues of the offspring during both pregnancy and breastfeeding. These cells primarily consist of leukocytes and stem cells. Remarkably, these maternal cells possess functional potential in the offspring and play a significant role in shaping their immune system development. T lymphocytes, a cell population mainly found in various tissues of the offspring, have been identified as the major cell type derived from maternal microchimerism. These T lymphocytes not only exert effector functions but also influence the development of the offspring's T lymphocytes in the thymus and the maturation of B lymphocytes in the lymph nodes. Furthermore, the migration of maternal leukocytes also facilitates the transfer of immune memory across generations. Maternal microchimerism has also been observed to address immunodeficiencies in the offspring. This review article focuses on investigating the impact of maternal cells transported within maternal microchimerism on the immune system development of the offspring, as well as elucidating the effector functions of maternal cells that migrate through the placenta and breast milk to reach the offspring.

Fused in sarcoma (FUS) inhibits milk production efficiency in mammals

Efficient milk production in mammals confers evolutionary advantages by facilitating the transmission of energy from mother to offspring. However, the regulatory mechanism responsible for the gradual establishment of milk production efficiency in mammals, from marsupials to eutherians, remains elusive. Here, we find that mammary gland of the marsupial sugar glider contained milk components during adolescence, and that mammary gland development is less dynamically cyclic compared to that in placental mammals. Furthermore, fused in sarcoma (FUS) is found to be partially responsible for this establishment of low efficiency. In mouse model, FUS inhibit mammary epithelial cell differentiation through the cyclin-dependent kinase inhibitor p57Kip2, leading to lactation failure and pup starvation. Clinically, FUS levels are negatively correlated with milk production in lactating women. Overall, our results shed light on FUS as a negative regulator of milk production, providing a potential mechanism for the establishment of milk production from marsupial to eutherian mammals.

A Systemic Review of the Difference Between Diets for Preterm Infants Containing Raw Mother's Own Milk and Frozen or Pasteurized Mother's Own Milk

BACKGROUND

Raw, never stored or pasteurized mother's own milk (MOM) is not always available to feed preterm infants; however, storage and pasteurization of MOM diminishes some bioactive components. It can be difficult to feed raw MOM to preterm infants due to transportation and storage of small volumes that might be pumped away from the infant, and a concern that they might harbor bacteria. However, the higher availability of bioactive components in raw MOM may provide benefits to preterm infants compared to frozen or pasteurized MOM.

RESEARCH AIM

To systematically review and summarize the results of studies on feeding raw MOM versus frozen or pasteurized MOM to preterm infants born at less than 37 weeks of gestation.

METHODS

Four databases were searched (Cochrane, Embase, Ovid MEDLINE, and Web of Science) for this systematic review. Of 542 studies identified, nine met inclusion criteria and were critically evaluated using the quality assessment tool for quantitative studies by the Effective Public Health Practice Project. Studies were organized using the Breastfeeding Challenges Facing Preterm Mother-Infant Dyads theoretical framework.

RESULTS

Included studies evaluated the outcomes of preterm infants fed raw versus pasteurized MOM (n = 7, 77.8%) or raw versus frozen MOM (n = 2, 22.2%). Researchers found that raw MOM did not increase infant infections and may have improved health and growth outcomes for study participants.

CONCLUSION

There is laboratory evidence supporting the safety and efficacy of the use of raw MOM for preterm infants. A raw MOM diet is recommended for preterm infants by professional organizations. Despite this, it may not be universally prioritized and could require purposeful implementation by each institution. Further research is needed to pursue the potential benefits of a raw MOM diet for preterm infants.

Protective Characteristics of Human Breast Milk on Early Childhood Otitis Media: A Narrative Review

Introduction: Human breast milk (HBM) contains a complex and dynamically changing variety of factors that contribute to the infant's developing immune system's ability to fight upper respiratory tract infections, including otitis media (OM). We sought to summarize the current evidence on the protective characteristics of HBM, through direct or donated feeding, toward early childhood OM. Methods: For this narrative review, we performed a literature search on OM in the context of HBM feeding in the PubMed, Embase, and Google Scholar databases, between January 1, 2008, and July 1, 2023. Results: Immunoglobulin A (IgA) provides a short-term immunity of 2-3 days against otopathogens causing OM. IgA-mediated immunity is effective against OM up to 7 months of age if breastfeeding continues. The role of transferred IgM and IgG in HBM is unclear. Although there is a potential protective value of microRNA, hormones, oligosaccharides, stem cells, and interleukins present in HBM, their role is unclear. Any duration of breastfeeding is superior to no breastfeeding in OM risk reduction, with a big variability among studies (odds ratio 0.23-0.81, depending on the duration). Duration of breastfeeding ≥6 months was found to be the most effective in OM risk reduction, but there was no evidence of continued benefits after 2 years of age. Expressed breastfeeding was not shown to be more beneficial. The protective values of donor HBM against OM are still undetermined. Conclusion: HBM has numerous components that contribute to protection against early childhood OM.

Pregnancy-induced transfer of pathogen-specific T cells from mother to fetus in mice

Neonatal health is determined by the transfer of maternal antibodies from the mother to the fetus. Besides antibodies, maternal cells cross the placental barrier and seed into fetal organs. Contrary to maternal antibodies, maternal microchimeric cells (MMc) show a high longevity, as they can persist in the offspring until adulthood. Recent evidence highlights that MMc leukocytes promote neonatal immunity against early-life infections in mice and humans. As shown in mice, this promotion of immunity was attributable to an improved fetal immune development. Besides this indirect effect, MMc may be pathogen-specific and thus, directly clear pathogen threats in the offspring postnatally. By using ovalbumin recombinant Listeria monocytogenes (LmOVA), we here provide evidence that OVA-specific T cells are transferred from the mother to the fetus, which is associated with increased activation of T cells and a milder course of postnatal infection in the offspring. Our data highlight that maternally-derived passive immunity of the neonate is not limited to antibodies, as MMc have the potential to transfer immune memory between generations.

First 72-hours after birth: Newborn feeding practices and neonatal mortality in India

BACKGROUND

The reductions in mortality levels among children under five years are observed in most populations, including populations that were lagging the progress in the past. However, the reduction is not uniform across ages during childhood. The mortality declines within the first month have shown relatively slow progress. Early initiation of breastfeeding and discarding pre-lacteal feed protects the newborn from acquiring infection and, thereby, reduces mortality. This paper assesses the change in the prevalence of early initiation of breastfeeding and pre-lacteal feed along with their associated factors, and their association with neonatal mortality in India.

METHODS

We used data from the three rounds of National Family Health Surveys conducted during 2005-06, 2015-16 and 2019-21 in India. We used bivariate and multivariate analyses to examine prevalence rates, risk factors, and relationships between breastfeeding practices, including early initiation of breastfeeding and pre-lacteal feed, and neonatal mortality.

RESULTS

Early initiation of breastfeeding within one hour after birth increased rapidly from 25% in 2005-06 to 42% in 2019-21, and the pre-lacteal feeding practice declined from 57% in 2005-06 to 15% in 2019-21. Pre-lacteal feed is lower in states/districts where early breastfeeding initiation is predominant and vice versa. The role of health professionals during pregnancy and the first two days after delivery significantly improved breastfeeding practice. Further, the findings suggest that an early breastfeeding initiation is associated with lower neonatal mortality, whereas pre-lacteal feed is not harmful compared to late breastfeeding initiation.

CONCLUSION

Prevalence of pre-lacteal feed reduced, and initiation of early breastfeeding increased considerably after the launch of the National Rural Health Mission in India. However, after 2015-16, early breastfeeding initiation has stagnated, and the decline in pre-lacteal feed has slowed down. The future program needs special attention to emphasize the availability and accessibility of breastfeeding advisers and observers in health facilities to help mitigate adverse neonatal outcomes.

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.

The effect of kangaroo care on cortisol levels and immune factors in breast milk

This paper investigated the effect of kangaroo mother care (KMC) in the early postpartum period on cortisol levels and immune factors in breast milk. This quasi-experimental study was conducted at the obstetrics clinic of a university hospital in western Türkiye. The sample consisted of 63 mothers and their infants. All mothers had a cesarean delivery. Participants were divided into control (n = 32) and experimental groups (n = 31). The control group received routine care at the clinic. The experimental group received KMC for the first 3 days after birth in addition to the routine care at the clinic. Milk samples were collected on the third day after delivery to examine cortisol, IgA, IgM, and IgG levels. All parameters were measured using the enzyme-linked immunosorbent assay method. The experimental group had lower cortisol levels (17.740 ± 1.438) than the control group (18.503 ± 1.449) (p < .05). This result showed that the difference between the two groups was clinically significant (effect size = .53). There was no significant difference in IgA, IgM, and IgG levels between the groups (p > .05). The experimental and control groups had similar immunological factors, but the former had lower cortisol levels than the latter. Therefore, healthcare professionals should encourage mothers to provide KMC to their infants as soon as possible.

The hormonal physiology of immune components in breast milk and their impact on the infant immune response

During pregnancy, the maternal body undergoes a considerable transformation regarding the anatomy, metabolism, and immune profile that, after delivery, allows for protection and nourishment of the offspring via lactation. Pregnancy hormones are responsible for the development and functionality of the mammary gland for breast milk production, but little is known about how hormones control its immune properties. Breast milk composition is highly dynamic, adapting to the nutritional and immunological needs that the infant requires in the first months of life and is responsible for the main immune modeling of breastfed newborns. Therefore, alterations in the mechanisms that control the endocrinology of mammary gland adaptation for lactation could disturb the properties of breast milk that prepare the neonatal immune system to respond to the first immunologic challenges. In modern life, humans are chronically exposed to endocrine disruptors (EDs), which alter the endocrine physiology of mammals, affecting the composition of breast milk and hence the neonatal immune response. In this review, we provide a landscape of the possible role of hormones in the control of passive immunity transferred by breast milk and the possible effect of maternal exposure to EDs on lactation, as well as their impacts on the development of neonatal immunity.

Patterns of Breastfeeding and Human Milk Feeding in Infants with Single-Ventricle Congenital Heart Disease: A Population Study of the National Pediatric Cardiology Quality Improvement Collaborative Registry

Introduction: Infants with single-ventricle (SV) congenital heart disease (CHD) undergo staged surgical and/or catheter-based palliation and commonly experience feeding challenges and poor growth. Little is known about human milk (HM) feeding or direct breastfeeding (BF) in this population. Aim: To determine (1) HM and BF prevalence for infants with SV CHD, and (2) whether BF at neonatal stage 1 palliation (S1P) discharge is associated with any HM at stage 2 palliation (S2P; ∼4-6 months old). Materials and Methods: Analysis of the National Pediatric Cardiology Quality Improvement Collaborative registry (2016-2021) using (1) descriptive statistics for prevalence, and (2) logistic regression adjusted for multiple variables (e.g., prematurity, insurance, length of stay) to examine early BF/later HM feeding. Results: Participants included 2,491 infants from 68 sites. HM prevalence ranged from 49.3% any/41.5% exclusive before S1P to 37.1% any/7.0% exclusive at S2P. Direct BF ranged from 16.1% any/7.9% exclusive before S1P to 9.2% any/3.2% exclusive at S2P discharge. Prevalence varied among sites; for example, 0-100% any HM before S1P. Infants BF at S1P discharge had greater odds of any HM (odds ratio = 4.11, 95% confidence interval [CI] = 2.79-6.07, p < 0.001) and exclusive HM (1.85, 95% CI 1.03-3.30, p = 0.039) at S2P. Conclusions: The prevalence of HM and BF for infants with SV CHD was low and declined over time. Direct BF at S1P discharge was associated with increased odds of any HM at S2P. Wide variation suggests that site-specific practices impact feeding outcomes. HM and BF prevalence are suboptimal in this population, and identification of supportive institutional practices is needed.

Environmental enteric dysfunction: gut and microbiota adaptation in pregnancy and infancy

Environmental enteric dysfunction (EED) is a subclinical syndrome of intestinal inflammation, malabsorption and barrier disruption that is highly prevalent in low- and middle-income countries in which poverty, food insecurity and frequent exposure to enteric pathogens impair growth, immunity and neurodevelopment in children. In this Review, we discuss advances in our understanding of EED, intestinal adaptation and the gut microbiome over the 'first 1,000 days' of life, spanning pregnancy and early childhood. Data on maternal EED are emerging, and they mirror earlier findings of increased risks for preterm birth and fetal growth restriction in mothers with either active inflammatory bowel disease or coeliac disease. The intense metabolic demands of pregnancy and lactation drive gut adaptation, including dramatic changes in the composition, function and mother-to-child transmission of the gut microbiota. We urgently need to elucidate the mechanisms by which EED undermines these critical processes so that we can improve global strategies to prevent and reverse intergenerational cycles of undernutrition.

Spike-specific T cells are enriched in breastmilk following SARS-CoV-2 mRNA vaccination

Human breastmilk is rich in T cells; however, their specificity and function are largely unknown. We compared the phenotype, diversity, and antigen specificity of T cells in breastmilk and peripheral blood of lactating individuals who received SARS-CoV-2 messenger RNA (mRNA) vaccination. Relative to blood, breastmilk contained higher frequencies of T effector and central memory populations that expressed mucosal-homing markers. T cell receptor sequence overlap was limited between blood and breastmilk. Overabundant breastmilk clones were observed in all individuals, were diverse, and contained complementarity-determining regions in three sequences with known epitope specificity, including to SARS-CoV-2 spike. SARS-CoV-2 spike-specific T cell receptors were more frequent in breastmilk compared to blood and expanded in breastmilk following a 3rd mRNA vaccine dose. Our observations indicate that the lactating breast contains a distinct T cell population that can be modulated by maternal vaccination with potential implications for passive infant protection.

Maternal immunization with pneumococcal surface protein A provides the immune memories of offspring against pneumococcal infection

Introduction

Streptococcus pneumoniae (S. pneumoniae) is one of the most widespread pathogens in the world and one of the largest infectious causes of infant mortality. Although current vaccines have various benefits, antibiotic resistance and the inability to vaccinate infants less than one year old demands the development of new protective strategies. One strategy, 'maternal immunization', is to protect infants by passive immunity from an immunized mother, although its mechanism is still not fully understood.

Materials and methods

The current study aimed to acquire immunity against S. pneumoniae in infants by maternal immunization with pneumococcal common antigen, pneumococcal surface protein A (PspA). Four-week-old female mice were immunized with recombinant PspA intranasally twice a week for three weeks. Females were mated with age-matched males after immunization, and delivered offspring.

Results

The week-old offspring derived from and fostered by immunized mothers had more anti-PspA-specific antibody producing cells in the spleen than those derived from sham-immunized mothers. The offspring were raised up to four weeks old and were subcutaneously stimulated with recombinant PspA. The levels of anti-PspA IgG in sera after stimulation were significantly higher in the offspring derived from the immunized mothers and the induced specific antibody to PspA showed protective efficacy against systemic pneumococcal infection.

Discussion

Maternal immunization is suggested to be able to provide a sustained immune memory to offspring. The current study would be a milestone in the field of maternal immunization toward a universal pneumococcal vaccine.

Spike-specific T cells are enriched in breastmilk following SARS-CoV-2 mRNA vaccination

Human breastmilk is rich in T cells; however, their specificity and function are largely unknown. We compared the phenotype, diversity, and antigen specificity of T cells in the breastmilk and peripheral blood of lactating individuals who received SARS-CoV-2 mRNA vaccination. Relative to blood, breastmilk contained higher frequencies of T effector and central memory populations that expressed mucosal-homing markers. T cell receptor (TCR) sequence overlap was limited between blood and breastmilk. Overabundan t breastmilk clones were observed in all individuals, were diverse, and contained CDR3 sequences with known epitope specificity including to SARS-CoV-2 Spike. Spike-specific TCRs were more frequent in breastmilk compared to blood and expanded in breastmilk following a third mRNA vaccine dose. Our observations indicate that the lactating breast contains a distinct T cell population that can be modulated by maternal vaccination with potential implications for infant passive protection.

One-Sentence Summary

The breastmilk T cell repertoire is distinct and enriched for SARS-CoV-2 Spike-specificity after maternal mRNA vaccination.

Durable antibody and effector memory T cell responses in breastmilk from women with SARS-CoV-2

Background

Given that only 25% of pregnant women elect to receive a COVID-19 vaccine, maternal SARS-CoV-2 infection remains an important route of conferring protective passive immunity to breastfed infants of mothers who are not vaccinated.

Methods

We enrolled 30 lactating participants between December 2020 and March 2021 who had a positive PCR-test and their first COVID-19 symptoms within the previous 21 days. Participants were asked to provide serial bilateral milk samples at 12 timepoints (~ every 3 days) over a period of 35 days. A second set of samples was collected at least four months after the beginning of the first set. Participants also were asked to provide their dried blood spots and infant stool samples. All samples were tested for receptor-binding domain (RBD)-specific immunoglobulin (Ig)A, IgG, and IgM. Milk samples were assessed for neutralizing ability against the spike protein and four SARS-CoV-2 variants: D614G, Alpha (B.1.1.7), Beta (B.1.351), and Gamma (P.1). Permeability of the breast epithelium was assessed by measuring the sodium to potassium ions (Na:K) in milk. Using flow cytometry, memory CD4 and CD8 T cells (CD45RO+ and CCR7+/-) and mucosal-homing CD4 and CD8 T cells (CD103+) were determined in cells from milk expressed at 35 days and at least 4 months after their first milk donation.

Results

Milk antibodies from SARS-CoV-2 positive participants neutralized the spike complex. Milk from 73, 90, and 53% of participants had binding reactivities to RBD-specific IgA, IgG, and IgM, respectively. In contrast to blood spots, which showed increased levels of IgG, but not IgA or IgM, the COVID-19 response in milk was associated with a robust IgA response. Twenty-seven percent of participants had increased breast-epithelium permeability, as indicated by Na:K ≥ 0.6. The percentage of CD45RO+CCR7- effector-memory T cells in the day ≥120 milk samples was significantly higher than day 35 samples (P< 0.05).

Conclusions

Antibodies in milk from participants with recent SARS-CoV-2 infection and those who recovered can neutralize the spike complex. For the first time we show that breastmilk T cells are enriched for mucosal memory T cells, further emphasizing the passive protection against SARS-CoV-2 conferred to infants via breastmilk.

Effects of Milk Replacer-Based Lactobacillus on Growth and Gut Development of Yaks' Calves: a Gut Microbiome and Metabolic Study

The gut microbiota and its metabolic activities are crucial for maintaining host homoeostasis and health, of which the role of probiotics has indeed been emphasized. The current study delves into the performance of probiotics as a beneficial managemental strategy, which further highlights their impact on growth performance, serologic investigation, gut microbiota, and metabolic profiling in yaks' calves. A field experiment was employed consisting of 2 by 3 factorial controls, including two development stages, namely, 21 and 42 days (about one and a half month), with three different feeding treatments. Results showed a positive impact of probiotic supplements on growth performance by approximately 3.16 kg (P < 0.01) compared with the blank control. Moreover, they had the potential to improve serum antioxidants and biochemical properties. We found that microorganisms that threaten health were enriched in the gut of the blank control with the depletion of beneficial bacteria, although all yaks were healthy. Additionally, the gut was colonized by a microbial succession that assembled into a more mature microbiome, driven by the probiotics strategy. The gut metabolic profiling was also changed significantly after the probiotic strategy, i.e., the concentrations of metabolites and the metabolic pattern, including enrichments in protein digestion and absorption, vitamin digestion and absorption, and biosynthesis of secondary metabolites. In summary, probiotics promoted gut microbiota/metabolites, developing precise interventions and achieving physiological benefits based on intestinal microecology. Hence, it is important to understand probiotic dietary changes to the gut microbiome, metabolome, and the host phenotype. IMPORTANCE The host microbiome is a composite of the trillion microorganisms colonizing host bodies. It can be impacted by various factors, including diet, environmental conditions, and physical activities. The yaks' calves have a pre-existing imbalance in the intestinal microbiota with an inadequate feeding strategy, resulting in poor growth performance, diarrhea, and other intestinal diseases. Hence, targeting gut microbiota might provide a new effective feeding strategy for enhancing performance and maintaining a healthy intestinal environment. Based on the current findings, milk replacer-based Lactobacillus feeding may improve growth performance and health in yaks' calves.

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 that influence MMc detection and level across infancy and the effect of MMc on T cell responses to bacillus Calmette-Guérin (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 1, 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 to 1,193/100,000 genomic equivalents and was positively impacted by absence of maternal HIV, maternal and infant HLA compatibility, infant female sex, and exclusive breastfeeding. Initiation of maternal antiretroviral therapy prior to pregnancy partially restored MMc level 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 the level of MMc, which may subsequently affect infant T cell responses.

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.

Asthma and the Missing Heritability Problem: Necessity for Multiomics Approaches in Determining Accurate Risk Profiles

Asthma is ranked among the most common chronic conditions and has become a significant public health issue due to the recent and rapid increase in its prevalence. Investigations into the underlying genetic factors predict a heritable component for its incidence, estimated between 35% and 90% of causation. Despite the application of large-scale genome-wide association studies (GWAS) and admixture mapping approaches, the proportion of variants identified accounts for less than 15% of the observed heritability of the disease. The discrepancy between the predicted heritable component of disease and the proportion of heritability mapped to the currently identified susceptibility loci has been termed the ‘missing heritability problem.’ Here, we examine recent studies involving both the analysis of genetically encoded features that contribute to asthma and also the role of non-encoded heritable characteristics, including epigenetic, environmental, and developmental aspects of disease. The importance of vertical maternal microbiome transfer and the influence of maternal immune factors on fetal conditioning in the inheritance of disease are also discussed. In order to highlight the broad array of biological inputs that contribute to the sum of heritable risk factors associated with allergic disease incidence that, together, contribute to the induction of a pro-atopic state. Currently, there is a need to develop in-depth models of asthma risk factors to overcome the limitations encountered in the interpretation of GWAS results in isolation, which have resulted in the missing heritability problem. Hence, multiomics analyses need to be established considering genetic, epigenetic, and functional data to create a true systems biology-based approach for analyzing the regulatory pathways that underlie the inheritance of asthma and to develop accurate risk profiles for disease.

Cellular and transcriptional diversity over the course of human lactation

Human breast milk (hBM) is a dynamic fluid that contains millions of cells, but their identities and phenotypic properties are poorly understood. We generated and analyzed single-cell RNA-sequencing (scRNA-seq) data to characterize the transcriptomes of cells from hBM across lactational time from 3 to 632 d postpartum in 15 donors. We found that the majority of cells in hBM are lactocytes, a specialized epithelial subset, and that cell-type frequencies shift over the course of lactation, yielding greater epithelial diversity at later points. Analysis of lactocytes reveals a continuum of cell states characterized by transcriptional changes in hormone-, growth factor-, and milk production-related pathways. Generalized additive models suggest that one subcluster, LC1 epithelial cells, increases as a function of time postpartum, daycare attendance, and the use of hormonal birth control. We identify several subclusters of macrophages in hBM that are enriched for tolerogenic functions, possibly playing a role in protecting the mammary gland during lactation. Our description of the cellular components of breast milk, their association with maternal–infant dyad metadata, and our quantification of alterations at the gene and pathway levels provide a detailed longitudinal picture of hBM cells across lactational time. This work paves the way for future investigations of how a potential division of cellular labor and differential hormone regulation might be leveraged therapeutically to support healthy lactation and potentially aid in milk production.

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.

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.

Chrononutrition and Human Milk

Background

Breastfed infants have a reduced risk of infections and allergies. The study of chrononutrition in human milk seeks to understand the circadian variation of various human milk immune factors.

Methods

Empirical studies on human milk, chrononutrition, and immune factors were searched through PUBMED, Google Scholar, and SCOPUS. Keywords included “chrononutrition,” “breastmilk composition,” “human milk,” “day-night cycles,” “sleep-wake cycles” and the names of various immune factors. After excluding duplicate articles, animal studies, studies looking at other human milk components, studies that did not collect human milk samples over a 24 hour period, and studies that were not in English, eleven studies on the topic remained and ten studies were included in the review. The excluded study had a sample size of two.

Results

This review identified the circadian variation of certain immune factors found in human milk such as antibodies, complement proteins, cytokines, by-products of phagocyte activity, nucleotides, microRNAs, and antioxidants.

Conclusion

The circadian variation observed in some human milk components highlights the unique ability of human milk to vary in composition based on the circadian rhythms of mothers and infants. The limited number of studies makes it difficult to make conclusive recommendations and creates an opportunity for further research in this growing field.

Baseline Concentrations of Various Immune Biomarkers Determine Their Increase after Consumption of a Postbiotic Based on Cow’s Milk Fermented with Lactobacillus paracasei CBA L74 in Both Newborns and Young Children

Intake of a postbiotic product can support immunity depending on specific conditions of the consumer. The present study evaluates the potential impact of baseline values on the change of various immune factors (α-defensin, β-defensin, cathelicidin, and secretory IgA) after three months of consumption of a postbiotic based on cow’s milk fermented with Lactobacillus paracasei CBA L74 in a young population. For the analysis, raw data of three studies were used in a multivariate analysis applying confounding factors. One study in newborns demonstrated that intake of the postbiotic yielded an increase in the concentrations of α-defensin and secretory IgA (at least p < 0.02), while for all factors, except β-defensin, the higher the baseline values the lower the increase (at least p < 0.002). Two combined studies in young children (aged 1–4 years) showed an increase in the concentration of all factors after intake of the postbiotic (at least p < 0.003), but now showing the higher the baseline values the higher the increase after three months (at least p < 0.02) in only the postbiotic group. It is concluded that consumption of the postbiotic leads to a baseline- and age-dependent increase in the concentrations of the immune factors under study in both newborns and young children. It is hypothesized that maturation of the immune system leads to different effects on optimizing host defense factors via this postbiotic intake.

Secretory IgA and T cells targeting SARS-CoV-2 spike protein are transferred to the breastmilk upon mRNA vaccination

In view of the scarcity of data to guide decision making, we evaluated how BNT162b2 and mRNA-1273 vaccines affect the immune response in lactating women and the protective profile of breastmilk. Compared with controls, lactating women had a higher frequency of circulating RBD memory B cells and higher anti-RBD antibody titers but similar neutralizing capacity. We show that upon vaccination, immune transfer to breastmilk occurs through a combination of anti-spike secretory IgA (SIgA) antibodies and spike-reactive T cells. Although we found that the concentration of anti-spike IgA in breastmilk might not be sufficient to directly neutralize SARS-CoV-2, our data suggest that cumulative transfer of IgA might provide the infant with effective neutralization capacity. Our findings put forward the possibility that breastmilk might convey both immediate (through anti-spike SIgA) and long-lived (via spike-reactive T cells) immune protection to the infant. Further studies are needed to address this possibility and to determine the functional profile of spike T cells.

Targeting the Toll-like receptor pathway as a therapeutic strategy for neonatal infection

Toll-like receptors (TLRs) are crucial transmembrane receptors that form part of the innate immune response. They play a role in the recognition of various microorganisms and their elimination from the host. TLRs have been proposed as vital immunomodulators in the regulation of multiple neonatal stressors that extend beyond infection such as oxidative stress and pain. The immune system is immature at birth and takes some time to become fully established. As such, babies are especially vulnerable to sepsis at this early stage of life. Findings suggest a gestational age-dependent increase in TLR expression. TLRs engage with accessory and adaptor proteins to facilitate recognition of pathogens and their activation of the receptor. TLRs are generally upregulated during infection and promote the transcription and release of proinflammatory cytokines. Several studies report that TLRs are epigenetically modulated by chromatin changes and promoter methylation upon bacterial infection that have long-term influences on immune responses. TLR activation is reported to modulate cardiorespiratory responses during infection and may play a key role in driving homeostatic instability observed during sepsis. Although complex, TLR signaling and downstream pathways are potential therapeutic targets in the treatment of neonatal diseases. By reviewing the expression and function of key Toll-like receptors, we aim to provide an important framework to understand the functional role of these receptors in response to stress and infection in premature infants.

Breastfeeding and the developmental origins of mucosal immunity: how human milk shapes the innate and adaptive mucosal immune systems

PURPOSE OF REVIEW

Breastfeeding provides passive immunity while the neonatal immune system matures, and may also protect against chronic immune-mediated conditions long after weaning. This review summarizes current knowledge and new discoveries about human milk and mucosal immunity.

RECENT FINDINGS

New data suggest that certain microbes in maternal milk may seed and shape the infant gut microbiota, which play a key role in regulating gut barrier integrity and training the developing immune system. Human milk oligosaccharides, best known for their prebiotic functions, have now been shown to directly modulate gene expression in mast and goblet cells in the gastrointestinal tract. Epidemiologic data show a reduced risk of peanut sensitization among infants breastfed by peanut-consuming mothers, suggesting a role for milk-borne food antigens in tolerance development. Cross-fostering experiments in mice suggest the soluble Toll-like receptor 2, found in human milk, may be critical in this process. Finally, interest in human milk antibodies surged during the pandemic with the identification of neutralizing severe acute respiratory syndrome coronavirus 2 antibodies in maternal milk following both natural infection and vaccination.

SUMMARY

Human milk provides critical immune protection and stimulation to breastfed infants. Understanding the underlying mechanisms could identify new therapeutic targets and strategies for disease prevention across the lifespan.

Eliminating HIV transmission through breast milk from women taking antiretroviral drugs

Ameena Goga and colleagues argue that frequent testing of maternal viral load is needed to eliminate HIV transmission through breast milk in low and middle income settings

Breastfeeding promotes early neonatal regulatory T-cell expansion and immune tolerance of non-inherited maternal antigens

BACKGROUND

Breastfeeding is associated with long-term health benefits, such as a lower incidence of childhood infections, asthma, obesity and autoimmune disorders. However, little is known regarding how the maternal and neonatal immune systems interact after parturition when the neonate receives nutrition from maternal breast milk.

METHODS

We undertook a comparative analysis of immune repertoire and function at birth and 3 weeks of age in a cohort of 38 term neonates born by caesarean section grouped according to feeding method (breast milk versus formula). We used flow cytometry to study the immune phenotype in neonatal and maternal blood samples and mixed lymphocyte reactions to establish the proliferation response of neonatal versus maternal lymphocytes and vice versa. The microbiome of neonatal stool samples was also investigated using 16S rRNA sequencing.

RESULTS

We show that the proportion of regulatory T cells (Tregs) increases in this period and is nearly twofold higher in exclusively breastfed neonates compared with those who received formula milk only. Moreover, breastfed neonates show a specific and Treg-dependent reduction in proliferative T-cell responses to non-inherited maternal antigens (NIMA), associated with a reduction in inflammatory cytokine production. We also observed the enrichment of short chain fatty acid producing taxa (Veillonella and Gemella) in stool samples of exclusively breastfed neonates.

CONCLUSIONS

These data indicate that exposure of the neonate to maternal cells through breastfeeding acts to drive the maturation of Tregs and 'tolerizes' the neonate towards NIMA.

Allergen shedding in human milk: Could it be key for immune system education and allergy prevention?

In addition to being a source of nutrients for the developing newborn, human milk contains thousands of bioactive compounds, which influence infant health in the short-term as exemplified by its major benefits on infectious disease prevention. Many of the human milk compounds also have the required characteristics to instruct immune development and guide long-term health. Prebiotics, probiotics, and varied antimicrobial molecules all have the potential to shape the composition and function of the establishing gut microbiota, which is known to be a major determinant of immune function. Another and less explored way human milk can instruct long-term immunity is through antigen shedding. Here, we will review the evidence that antigens from maternal environment and more specifically from allergen sources are found in human milk. We will discuss data from rodent models and birth cohorts showing that allergen shedding in breast milk may influence long-term allergy risk. We will uncover the variables that may underlie heterogeneity in oral tolerance induction and allergy prevention in children breast-fed by allergen-exposed mothers. We will focus on the parameters that control antigen transfer to breast milk, on the unique biological characteristics of allergens in breast milk, and on the milk bioactive compounds that were found to influence immune response in offspring. We propose this understanding is fundamental to guide maternal interventions leading to lifelong allergen tolerance.

Maternal effects in mammals: Broadening our understanding of offspring programming

The perinatal period is a sensitive time in mammalian development that can have long-lasting consequences on offspring phenotype via maternal effects. Maternal effects have been most intensively studied with respect to two major conditions: maternal diet and maternal stress. In this review, we shift the focus by discussing five major additional maternal cues and their influence on offspring phenotype: maternal androgen levels, photoperiod (melatonin), microbiome, immune regulation, and milk composition. We present the key findings for each of these topics in mammals, their mechanisms of action, and how they interact with each other and with the maternal influences of diet and stress. We explore their impacts in the contexts of both predictive adaptive responses and the developmental origins of disease, identify knowledge gaps and research opportunities in the field, and place a particular emphasis on the application and consideration of these effects in non-model species and natural ecological systems.

Revisiting Koch's postulate to determine the plausibility of viral transmission by human milk

As breastfeeding is of utmost importance for child development and survival, identifying whether breast milk is a route of transmission for human viruses is critical. Based on the principle of Koch's postulate, we propose an analytical framework to determine the plausibility of viral transmission by breast milk. This framework is based on five criteria: viral infection in children receiving breast milk from infected mothers; the presence of virus, viral antigen, or viral genome in the breast milk of infected mothers; the evidence for the virus in breast milk being infectious; the attempts to rule out other transmission modalities; and the reproduction of viral transmission by oral inoculation in an animal model. We searched for evidence in published reports to determine whether the 5 criteria are fulfilled for 16 human viruses that are suspected to be transmissible by breast milk. We considered breast milk transmission is proven if all 5 criteria are fulfilled, as probable if 4 of the 5 criteria are met, as possible if 3 of the 5 criteria are fulfilled, and as unlikely if less than 3 criteria are met. Only five viruses have proven transmission through breast milk: human T-cell lymphotropic virus 1, human immunodeficiency virus, human cytomegalovirus, dengue virus, and Zika virus. The other 11 viruses fulfilled some but not all criteria and were categorized accordingly. Our framework analysis is useful for guiding public health recommendations and for identifying knowledge gaps amenable to original experiments.

Spatial and temporal key steps in early-life intestinal immune system development and education

Education of our intestinal immune system early in life strongly influences adult health. This education strongly relies on series of events that must occur in well-defined time windows. From initial colonization by maternal-derived microbiota during delivery to dietary changes from mother's milk to solid foods at weaning, these early-life events have indeed long-standing consequences on our immunity, facilitating tolerance to environmental exposures or, on the contrary, increasing the risk of developing noncommunicable diseases such as allergies, asthma, obesity, and inflammatory bowel diseases. In this review, we provide an outline of the recent advances in our understanding of these events and how they are mechanistically related to intestinal immunity development and education. First, we review the susceptibility of neonates to infections and inflammatory diseases, related to their immune system and microbiota changes. Then, we highlight the maternal factors involved in protection and education of the mucosal immune system of the offspring, the role of the microbiota, and the nature of neonatal immune system until weaning. We also present how the development of some immune responses is intertwined in temporal and spatial windows of opportunity. Finally, we discuss pending questions regarding the neonate particular immune status and the activation of the intestinal immune system at weaning.

Neonatal Immune System Ontogeny: The Role of Maternal Microbiota and Associated Factors. How Might the Non-Human Primate Model Enlighten the Path?

Interactions between the immune system and the microbiome play a crucial role on the human health. These interactions start in the prenatal period and are critical for the maturation of the immune system in newborns and infants. Several factors influence the composition of the infant's microbiota and subsequently the development of the immune system. They include maternal infection, antibiotic treatment, environmental exposure, mode of delivery, breastfeeding, and food introduction. In this review, we focus on the ontogeny of the immune system and its association to microbial colonization from conception to food diversification. In this context, we give an overview of the mother-fetus interactions during pregnancy, the impact of the time of birth and the mode of delivery, the neonate gastrointestinal colonization and the role of breastfeeding, weaning, and food diversification. We further review the impact of the vaccination on the infant's microbiota and the reciprocal case. Finally, we discuss several potential therapeutic interventions that might help to improve the newborn and infant's health and their responses to vaccination. Throughout the review, we underline the main scientific questions that are left to be answered and how the non-human primate model could help enlighten the path.

Breast milk antibody levels in Tdap vaccinated women after preterm delivery

INTRODUCTION/BACKGROUND & AIMS

Enrichment of breast milk (BM) with immunoglobin (Ig)A and IgG, through maternal vaccination, could help young infants combat targeted pathogens. However, evidence on this effect after preterm delivery is lacking. This study investigated the total and anti-pertussis toxin (anti-PT) specific IgA and IgG production in BM after term or preterm delivery in the presence of maternal Tdap (tetanus, diphtheria, acellular pertussis) vaccination.

METHODS

Serum and BM samples of lactating women, who delivered at term or prematurely and did or did not receive Tdap vaccine (Boostrix®, GSK Biologicals) during pregnancy, were collected as part of a clinical study (N=234, NCT02511327). Anti-PT IgA/IgG (IBL®; MSD®) and Total IgA/IgG (Thermofisher®, on BM samples only) immunosorbent assays were performed on all samples collected at 72 hours, 4, 8, and 12 weeks postpartum.

RESULTS

BM after preterm delivery contained anti-PT IgA and IgG geometric mean concentrations (GMCs) comparable to those after term delivery (e.g. colostrum anti-PT IgA: 5.39 International Units per milliliter (IU/mL) vs 6.69 IU/mL, respectively). Maternal Tdap vaccination induced significantly higher anti-PT IgG GMC's in colostrum of vaccinated compared to unvaccinated women delivering at term (0.110 IU/mL vs 0.027 IU/mL, p=0.009). Compliance with postpartum vaccination led to no differences in BM after 4 weeks postpartum. Anti-PT antibodies persisted up to 12 weeks postpartum.

CONCLUSIONS

This study provides evidence that maternal Tdap vaccination induces high Ig levels in BM after both term and preterm delivery and that these antibodies remain abundantly present throughout lactation, possibly offering additional mucosal protection during the most vulnerable period in early life.

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.

Diet as a Potential Moderator for Genome Stability and Immune Response in Pediatric Leukemia

Simple Summary

Pediatric acute lymphoblastic leukemia (ALL) is the most prevalent cancer affecting children in developed societies. Here, we review the role of diet in control of the incidence and progression of childhood ALL. Prenatally, ALL risk is associated with higher birthweights of newborns, suggesting that ALL begins to evolve in-utero. Indeed, maternal diet influences the fetal genome and immune development. Postnatally, breastfeeding associates with decreased risk of ALL development. Finally, for the ALL-affected child, certain dietary regimens that impact the hormonal environment may impede disease progression. Improved understanding of the dietary regulation of hormones and immunity may inform better approaches to predict, protect, and ultimately save children afflicted with pediatric leukemia.

Abstract

Pediatric leukemias are the most prevalent cancers affecting children in developed societies, with childhood acute lymphoblastic leukemia (ALL) being the most common subtype. As diet is a likely modulator of many diseases, this review focuses on the potential for diet to influence the incidence and progression of childhood ALL. In particular, the potential effect of diets on genome stability and immunity during the prenatal and postnatal stages of early childhood development are discussed. Maternal diet plays an integral role in shaping the bodily composition of the newborn, and thus may influence fetal genome stability and immune system development. Indeed, higher birth weights of newborns are associated with increased risk of ALL, which suggests in-utero biology may shape the evolution of preleukemic clones. Postnatally, the ingestion of maternal breastmilk both nourishes the infant, and provides essential components that strengthen and educate the developing immune system. Consistently, breast-feeding associates with decreased risk of ALL development. For children already suffering from ALL, certain dietary regimens have been proposed. These regimens, which have been validated in both animals and humans, alter the internal hormonal environment. Thus, hormonal regulation by diet may shape childhood metabolism and immunity in a manner that is detrimental to the evolution or expansion of preleukemic and leukemic ALL clones.

Forever Connected: The Lifelong Biological Consequences of Fetomaternal and Maternofetal Microchimerism

BACKGROUND

Originally studied as a mechanism to understand eclampsia-related deaths during pregnancy, fetal cells in maternal blood have more recently garnered attention as a noninvasive source of fetal material for prenatal testing. In the 21st century, however, intact fetal cells have been largely supplanted by circulating cell-free placental DNA for aneuploidy screening. Instead, interest has pivoted to the ways in which fetal cells influence maternal biology. In parallel, an increasing appreciation of the consequences of maternal cells in the developing fetus has occurred.

CONTENT

In this review, we highlight the potential clinical applications and functional consequences of the bidirectional trafficking of intact cells between a pregnant woman and her fetus. Fetal cells play a potential role in the pathogenesis of maternal disease and tissue repair. Maternal cells play an essential role in educating the fetal immune system and as a factor in transplant acceptance. Naturally occurring maternal microchimerism is also being explored as a source of hematopoietic stem cells for transplant in fetal hematopoietic disorders.

SUMMARY

Future investigations in humans need to include complete pregnancy histories to understand maternal health and transplant success or failure. Animal models are useful to understand the mechanisms underlying fetal wound healing and/or repair associated with maternal injury and inflammation. The lifelong consequences of the exchange of cells between a mother and her child are profound and have many applications in development, health, and disease. This intricate exchange of genetically foreign cells creates a permanent connection that contributes to the survival of both individuals.

Effects of Holder Pasteurization on Immune Composition of Human Milk

Background: Human milk (HM) is the ideal food for newborn (NB) nutrition, it provides all macro and micronutrients for human growth and development and also contains bioactive compounds, which influence the development of the neonatal digestive and immune systems. The holder pasteurization process is essential to prevent NB infection from donated milk. Therefore, the aim of this study was to check whether or not holder pasteurization could impact the concentration of immune components in HM and the capacity to induce epithelial cell growth. Materials and Methods: The study was performed on raw and holder pasteurized (62.5°C/30 minutes) paired milk samples after submission to the freezing process in both phases. For cytokine and adipokine measurements, ELISA was performed on 40 individual samples of HM from single donors. For analyzes of epithelial cell growth, HuTu-80 cells were cultivated in Minimum Essential Eagle medium with 15% of raw or pasteurized milk, eight pairs of milk were used. Results: The results showed that no alteration was observed in the concentration of cytokine after milk holder pasteurization, and leptin concentration was reduced in holder pasteurized milk. The heat treatment also did not impact the capacity of breast milk to promote intestinal epithelial cell growth. Conclusions: The results showed that donated breast milk pasteurization has a small impact on the HM bioactive concentration compounds. This technique is important to avoid NB infection.