Infant immunity against viral infections is advanced by the placenta-dependent vertical transfer of maternal antibodies

Where Birth Month, Sex and Age Matters: The Burden of Severe Respiratory Disease in Danish Children <5 Years, 2016-2022

BACKGROUND

In light of the substantial impact that respiratory diseases in young children poses on healthcare systems globally, and in the wake of the recent COVID-19 pandemic, there is a growing urgency to obtain reliable estimates on the burden of respiratory disease.

OBJECTIVES

The aim of this study is to quantify the overall burden of respiratory disease requiring hospitalizations and explore the trends in these admissions in Danish children <5 years, January 1, 2016-October 31, 2022.

METHODS

The number of hospitalizations attributed to respiratory infections in children <5 years, was extracted from the Danish National Patient Register, and stratified into subgroups based on age, gender and birth month, and presented on a month-to-month basis.

RESULTS

A total of 48,194 children under the age of 5, were hospitalized due to respiratory infections within the study period and the annual hospitalization incidence exhibited a noteworthy variation. Risk factors associated with the highest hospitalization incidence were young age, male gender and in children under 1-year-old, birth months falling in the period of November to January. Younger age and admission during the winter months were linked to longer hospital stays. The seasonal pattern of hospitalizations and the distribution of hospitalizations across various subgroups were greatly influenced by the COVID-19 pandemic.

CONCLUSION

This study describes and quantifies the importance of factoring in specific child demographics and seasonal variations in hospitalizations when devising preventive healthcare strategies such as the use of monoclonal antibody therapy and vaccines.

Fetal lung growth predicts the risk for early-life respiratory infections and childhood asthma

BACKGROUND

Early-life respiratory infections and asthma are major health burdens during childhood. Markers predicting an increased risk for early-life respiratory diseases are sparse. Here, we identified the predictive value of ultrasound-monitored fetal lung growth for the risk of early-life respiratory infections and asthma.

METHODS

Fetal lung size was serially assessed at standardized time points by transabdominal ultrasound in pregnant women participating in a pregnancy cohort. Correlations between fetal lung growth and respiratory infections in infancy or early-onset asthma at five years were examined. Machine-learning models relying on extreme gradient boosting regressor or classifier algorithms were developed to predict respiratory infection or asthma risk based on fetal lung growth. For model development and validation, study participants were randomly divided into a training and a testing group, respectively, by the employed algorithm.

RESULTS

Enhanced fetal lung growth throughout pregnancy predicted a lower early-life respiratory infection risk. Male sex was associated with a higher risk for respiratory infections in infancy. Fetal lung growth could also predict the risk of asthma at five years of age. We designed three machine-learning models to predict the risk and number of infections in infancy as well as the risk of early-onset asthma. The models' R2 values were 0.92, 0.90 and 0.93, respectively, underscoring a high accuracy and agreement between the actual and predicted values. Influential variables included known risk factors and novel predictors, such as ultrasound-monitored fetal lung growth.

CONCLUSION

Sonographic monitoring of fetal lung growth allows to predict the risk for early-life respiratory infections and asthma.

Congenital and Postnatal Cytomegalovirus: Case Series and State of the Science for Neonatal Providers

Cytomegalovirus (CMV), a beta-herpes virus, is the most common viral infection in infants. Transmission may occur congenitally (cCMV) or postnatally (pCMV). Early detection and intervention are crucial in reducing morbidities, notable developmental delays, and sensorineural hearing loss. However, more than 90% of infants are asymptomatic at birth. Treatment involves intravenous ganciclovir or the oral prodrug, valganciclovir, drugs usually reserved for use with symptomatic infants because of the toxicity profile. Research currently supports standardized antenatal CMV screening and treatment of affected pregnant patients with hyperimmune globulin as well as vaccination against CMV in unaffected pregnant patients, although widespread adoption is lacking. Standardized postnatal CMV screening is a proven, cost-effective way to detect and diagnose CMV and optimize outcomes across the lifespan. This article presents a case series of cCMV and pCMV and a review of the state of science of CMV as well as promising scientific advances that are on the horizon.

The 'communicatome' of pregnancy: spotlight on cellular and extravesicular chimerism

Communication via biological mediators between mother and fetus are key to reproductive success and offspring's future health. The repertoire of mediators coding signals between mother and fetus is broad and includes soluble factors, membrane-bound particles and immune as well as non-immune cells. Based on the emergence of technological advancements over the last years, considerable progress has been made toward deciphering the "communicatome" between fetus and mother during pregnancy and even after birth. In this context, pregnancy-associated chimerism has sparked the attention among immunologists, since chimeric cells-although low in number-are maintained in the allogeneic host (mother or fetus) for years after birth. Other non-cellular structures of chimerism, e.g. extracellular vesicles (EVs), are increasingly recognized as modulators of pregnancy outcome and offspring's health. We here discuss the origin, distribution and function of pregnancy-acquired microchimerism and chimeric EVs in mother and offspring. We also highlight the pioneering concept of maternal microchimeric cell-derived EVs in offspring. Such insights expand the understanding of pregnancy-associated health or disease risks in mother and offspring.

Impact of Antenatal SARS-CoV-2 Exposure on SARS-CoV-2 Neutralization Potency

A pregnancy booster dose significantly reduces the risk and severity of COVID-19, and it is widely recommended. A prospective cohort study was conducted to compare the transplacental passage of maternal antibodies from vaccination or infection during three trimesters against both the vaccine-targeted Wuhan strain and the Omicron strain of SARS-CoV-2. Maternal-infant dyads from vaccinated mothers were collected between 6 June 2022 and 20 September 2022. We analyzed 38 maternal-infant dyads from mothers who had been infected with COVID-19 and 37 from mothers without any previous infection. Pregnant women who received their last COVID-19 vaccine dose in the third trimester exhibited the highest anti-spike protein antibody levels and neutralizing potency against both the Wuhan strain and Omicron BA.2 variant in their maternal and cord plasma. Both second- and third-trimester vaccination could lead to a higher level of neutralization against the Wuhan and Omicron strains. COVID-19 infection had a negative effect on the transplacental transfer ratio of SARS-CoV-2 antibodies. A booster dose during the second or third trimester is encouraged for the maximum transplacental transfer of humoral protection against COVID-19 for infants.

Differential Diagnosis and Interdisciplinary Workup of a Pediatric Patient With an Unknown Immune Condition: Chronic Respiratory Distress Secondary to Viral Illness and Developmental Consequences

We present a case of a three-year-old African American male, born at term, who initially presented with bronchiolitis at six months and has since experienced recurrent episodes of respiratory distress and hospitalizations. The patient also has severe eczema, developmental delays, and recurrent viral illnesses. Despite thorough evaluations from various specialists, such as pulmonology, allergy, and gastroenterology, the underlying cause remained elusive. The differential diagnosis for this case is as follows: severe persistent asthma with a possible link to genetic mutations such as CDHR3, hyper-IgE syndrome, atypical presentation of Wiskott-Aldrich syndrome, and severe gastroesophageal reflux disease (GERD) with aspiration pneumonitis. This patient's chronic condition has contributed to several developmental consequences, including failure to gain weight and possible hypoxic encephalopathy, leading to delays in cognitive and motor milestones and speech delays. Aggressive medical management, especially long-term systemic steroids, raises concerns about future complications. Through this case, we highlight the importance of thorough workups and an interdisciplinary approach to diagnosing and managing an unknown immune condition, as well as consistent pediatric primary care follow-up to assess development and coordinate necessary support. Here, we aim to address a gap in research on the unique presentations of pediatric respiratory distress symptoms by formulating a comprehensive differential diagnosis and exploring the various ways that chronic respiratory illness can contribute to developmental deficits such as speech and cognitive delays in pediatric patients. This study calls for further research into genetic contributions to asthma, diverse presentations of GERD, prevention of viral illnesses, alternative treatments minimizing steroid use, and an understanding of the impact of chronic respiratory distress on cognitive and language development in children. Thorough workups and interdisciplinary approaches are essential for effective diagnosis and management.

Adeno-associated virus serotype 9 antibody seroprevalence for patients in the United States with spinal muscular atrophy

Onasemnogene abeparvovec is a recombinant adeno-associated virus serotype 9 (AAV9) vector-based gene therapy for spinal muscular atrophy (SMA). Patients with elevated titers of anti-AAV9 antibodies (AAV9-Ab) should not receive onasemnogene abeparvovec because of potential safety and efficacy implications. We conducted a retrospective study to describe the seroprevalence of anti-AAV9 binding antibodies for pediatric patients with SMA in the United States. At initial testing, 13.0% (115 of 882) of patients (mean [SD] age, 26.29 [33.66] weeks) had elevated AAV9-Ab titers. The prevalence of elevated titers decreased as age increased, with 18.2% (92 of 507) of patients ≤3 months old but only 1.1% (1 of 92) of patients ≥21 months old having elevated titers. This suggests transplacental maternal transfer of antibodies. No patterns of geographic variations in AAV9-Ab prevalence were confirmed. Elevated AAV9-Ab titers in children <6 weeks old decreased in all circumstances. Lower magnitudes of elevated titers declined more rapidly than greater magnitudes. Retesting was completed at the discretion of the treating clinician, so age at testing and time between tests varied. AAV9-Ab retesting should be considered when patients have elevated titers, and elevations at a young age are not a deterrent to eventual onasemnogene abeparvovec administration. Early disease-modifying treatment for SMA leads to optimal outcomes.

The protective role of maternal genetic immunization on maternal-fetal health and welfare

Pregnancy is a critical period associated with alterations in physiologic, biologic, and immunologic processes, which can affect maternal-fetal health through development of several infectious diseases. At birth, neonates have an immature immune system that makes them more susceptible to severe viral infections and diseases. For this reason, different maternal nutritional and immunization interventions have been used to improve the immune and health status of the mother and her neonate through passive immunity. Here, we reviewed the protective role of maternal immunization with different types of vaccines, especially genetic vaccines, during pregnancy in maternal-fetal health, immune response, colostrum quality, immune response, and anti-oxidative status. For this purpose, we have used different scientific databases (PubMed and Google Scholar) and other official web pages. We customized the search period range from the year 2000 to 2023 using the key words "maternal immunization" OR "gestation period/pregnancy" OR "genetic vaccination" OR "maternal-fetal health" OR "micronutrients" OR "neonatal immunity" "oxidative stress" OR "colostrum quality". The evidence demonstrated that inactivated or killed vaccines produced significant immune protection in the mother and fetus. Furthermore, most recent studies have suggested that the use of genetic vaccines (mRNA and DNA) during pregnancy is efficient at triggering the immune response in mother and neonate without the risk of undesired pregnancy outcomes. However, factors such as maternal redox balance, nutritional status, and the timing of immunization play essential roles in regulating immune response inflammatory status, antioxidant capacity, and the welfare of both the pregnant mother and her newborn.

Trimester-specific effects of maternal exposure to single and mixed metals on cord serum inflammatory cytokines levels: A prospective birth cohort study

BACKGROUND

Cord blood inflammatory cytokines are vital in early-life programming. An increasing number of studies concern the effect of maternal exposure to different metal elements during pregnancy on inflammatory cytokines, but limited studies have explored the association between maternal exposure to mixed metals and cord blood inflammatory cytokine levels.

METHODS

We measured serum concentrations of vanadium (V), copper (Cu), arsenic (As), cadmium (Cd), and barium (Ba) in the first, second, and third trimesters and eight cord serum inflammatory cytokines (IFN-γ, IL-1β, IL-6, IL-8, IL-10, IL-12p70, IL-17A, and TNF-α) in 1436 mother-child dyads from the Ma'anshan Birth Cohort. Generalized linear models and Bayesian kernel machine regression (BKMR) were performed to assess the association of single and mixed metal exposure during each trimester with cord serum inflammatory cytokine levels, respectively.

RESULTS

Regarding metal exposure in the first trimester, V was positively associated with TNF-α (β = 0.33, 95 % CI: 0.13, 0.53); Cu was positively associated with IL-8 (β = 0.23, 95 % CI: 0.07, 0.39); Ba was positively associated with IFN-γ and IL-6; As was negatively associated with IFN-γ and IL-17A; and Cd was negatively associated with IFN-γ, IL-1β, IL-12p70, IL-17A, and TNF-α. BKMR revealed that exposure to metal mixtures in the first trimester was positively associated with IL-8 and TNF-α but negatively associated with IL-17A. Moreover, V contributed the most to these associations. Interaction effects were observed between Cd and As and between Cd and Cu with IL-8, and between Cd and V with IL-17A. Among males, As decreased inflammatory cytokines; among females, Cu increased inflammatory cytokine levels, whereas Cd decreased inflammatory cytokine concentrations.

CONCLUSIONS

Maternal exposure to metal mixtures in the first trimester interfered with cord serum inflammatory cytokine levels. The associations of maternal exposure to As, Cu and Cd with inflammatory cytokines showed sex differences. Further studies are warranted to support the findings and explore the mechanism of the susceptibility window and sex-specific disparity.

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.

Sex differences in innate and adaptive immunity impact fetal, placental, and maternal health†

The differences between males and females begin shortly after birth, continue throughout prenatal development, and eventually extend into childhood and adult life. Male embryos and fetuses prioritize proliferation and growth, often at the expense of the fetoplacental energy reserves. This singular focus on growth over adaptability leaves male fetuses and neonates vulnerable to adverse outcomes during pregnancy and birth and can have lasting impacts throughout life. Beyond this prioritization of growth, male placentas and fetuses also respond to infection and inflammation differently than female counterparts. Pregnancies carrying female fetuses have a more regulatory immune response, whereas pregnancies carrying male fetuses have a stronger inflammatory response. These differences can be seen as early as the innate immune response with differences in cytokine and chemokine signaling. The sexual dimorphism in immunity then continues into the adaptive immune response with differences in T-cell biology and antibody production and transfer. As it appears that these sex-specific differences are amplified in pathologic pregnancies, it stands to reason that differences in the placental, fetal, and maternal immune responses in pregnancy contribute to increased male perinatal morbidity and mortality. In this review, we will describe the genetic and hormonal contributions to the sexual dimorphism of fetal and placental immunity. We will also discuss current research efforts to describe the sex-specific differences of the maternal-fetal interface and how it impacts fetal and maternal health.

Serologic evolution and follow-up to IgG antibodies of infants born to mothers with gestational COVID

BACKGROUND

It is known that SARS-CoV-2 antibodies from pregnant women with SARS-CoV-2 infection during pregnancy cross the placenta but the duration and the protective effect of these antibodies in infants is scarce.

METHODS

This prospective study included mothers with SARS-COV-2 infection during pregnancy and their infants from April 2020 to March 2021. IgG antibodies to SARS-CoV-2 spike protein were performed on women and infants at birth and at two and six months during follow-up. Anthropometrical measures and physical and neurological examinations and a clinical history of symptoms and COVID-19 diagnosis were collected. Simple linear regression was performed to compare categorical and continuous variables. To compare the mother's and infant's antibody titers evolution, a mixed linear regression model was used. A predictive model of newborn antibody titers at birth has been established by means of simple stepwise linear regression.

RESULTS

51 mother-infant couples were included. 45 (90%) of the mothers and 44 (86.3%) of the newborns had a positive serology al birth. These antibodies were progressively decreasing and were positive in 34 (66.7%) and 7 (13.7%) of infants at 2 and 6 months, respectively. IgG titers of newborns at birth were related to mothers' titers, with a positive moderate correlation (Pearson's correlation coefficient: 0.82, p < 0,001). Fetal/maternal antibodies placental transference rate was 1.3 (IQR: 0.7-2.2). The maternal IgG titers at delivery and the type of maternal infection (acute, recent, or past infection) was significantly related with infants' antibody titers at birth. No other epidemiological or clinical factors were related to antibodies titers. Neurodevelopment, psychomotor development, and growth were normal in 94.2% of infants in the third follow-up visit. No infants had a COVID-19 diagnosis during the follow-up period.

CONCLUSIONS

Transplacental transfer of maternal antibodies is high in newborns from mothers with recent or past infection at delivery, but these antibodies decrease after the first months of life. Infant's IgG titers were related to maternal IgG titers at delivery. Further studies are needed to learn about the protective role of maternal antibodies in infants.

In utero priming of fetal immune activation: Myths and mechanisms

Mechanisms of fetal immune system development in utero remain incompletely elucidated. Protective immunity, the arm of reproductive immunology concerned with the progressive education of the fetal immune system as pregnancy advances, allows for programming of the immune system and immune maturation in utero and provides a responsive system to respond to rapid microbial and other antigenic exposure ex utero. Challenges in studying fetal tissues, immune system development, and the contributions of various endogenous and exogenous factors to this process are difficult to study as a progressive sampling of fetal biological samples is impractical during pregnancy, and animal models are limited. This review provides a summary of mechanisms of protective immunity and how it has been shaped, from transplacental transfer of immunoglobulins, cytokines, metabolites, as well as antigenic microchimeric cells to perhaps more controversial notions of materno-fetal transfer of bacteria that subsequently organize into microbiomes within the fetal tissues. This review will also provide a quick overview of future direction in the area of research on fetal immune system development and discusses methods to visualize fetal immune populations and determine fetal immune functions, as well as a quick look into appropriate models for studying fetal immunity.

Vertical Transfer of Humoral Immunity against Nipah Virus: A Novel Evidence from Bangladesh

A major obstacle to in-depth investigation of the immune response against Nipah virus (NiV) infection is its rapid progression and high mortality rate. This paper described novel information on the vertical transfer of immune properties. In January 2020, a female aged below five years and her mother from Faridpur district of Bangladesh were infected. Both had a history of raw date palm sap consumption and were diagnosed as confirmed NiV cases. The daughter passed away, and the mother survived with significant residual neurological impairment. She conceived one and a half year later and was under thorough antenatal follow-up by the surveillance authority. A healthy male baby was born. As part of routine survivor follow-up, specimens were collected from the newborn and tested for NiV infection at the reference laboratory to exclude vertical transmission. Although testing negative for anti-Nipah IgM and PCR for NiV, a high titre of anti-Nipah IgG was observed. The transfer of humoral immunity against NiV from mother to neonate was confirmed for the first time. The article will serve as a reference for further exploration regarding NiV-specific antibodies that are transferred through the placenta, their potential to protect newborns, and how this may influence vaccine recommendations.

Einmalige Möglichkeit für doppelten Nutzen: Impfungen in der Schwangerschaft

Impfungen sind eine der größten Errungenschaften zum Schutz der öffentlichen Gesundheit. Impfstoffe, die schwangeren Frauen verabreicht werden, schützen dabei nicht nur die Schwangere selbst, sondern auch das Neugeborene. Schwangere Frauen sind von Infektionen unverhältnismäßig stark beeinträchtigt. Die widersprüchlichen Anforderungen an das mütterliche Immunsystem während der Schwangerschaft, mit dem Ziel, die fetale Immuntoleranz aufrechtzuerhalten, erschweren eine schnelle und effektive Immunantwort gegen Krankheitserreger. Dieser dynamische Zustand der Immunadaptation prädisponiert Schwangere für schwerere Krankheitsverläufe. Durch eine Impfung kann einer Infektion oder einem schweren Krankheitsverlauf vorgebeugt werden. In der Folge sinkt auch das Risiko einer Frühgeburt und anderer schwerer Schwangerschaftskomplikationen, die lebenslange Folgen für Mutter und Kind haben können. Nach der Geburt muss das Neugeborene zunächst ein adaptives Gedächtnis für eine bis dahin unbekannte, antigenreiche Umgebung entwickeln; es ist für Infektionen und die daraus resultierenden Komplikationen besonders vulnerabel. Durch den Transfer maternaler Antikörper über die Plazenta werden Säuglinge geschützt, die zu jung sind, um geimpft zu werden. Beim Stillen setzt sich dies durch die Muttermilch fort. Für die von der Ständigen Impfkommission (STIKO) empfohlenen Impfungen in der Schwangerschaft (Influenza, Pertussis, COVID[„coronavirus disease“]-19), gibt es eindeutige Hinweise aus verschiedenen prospektiven und observationellen Studien, dass sie Mutter und Kind entweder vor einer Infektion oder einem schweren Krankheitsverlauf effektiv schützen. Im Beitrag geben wir einen Überblick über die Impfstrategie rund um die Schwangerschaft und fassen die wissenschaftlichen Daten zur Wirksamkeit der empfohlenen Impfungen zusammen.

Racial concentration and dynamics of COVID-19 vaccination in the United States

This article considers how county-level concentrations of Asians, Blacks, Hispanics, and Whites are associated with COVID-19 vaccination differently. I argue that racially specific mechanisms-differential concentrations of social vulnerability and political ideology by race-are likely to create diverse associations between racial concentration and COVID-19 vaccination not only across racial groups but also within racial groups over time from early rollout to the time after COVID-19 vaccines became widely available. I test this argument by drawing on data from multiple sources that include county-level information on COVID-19 vaccination rates, racial population make-ups, and measures of political ideology and community vulnerability. Results show that the association between racial concentration and COVID-19 vaccination changes substantially across and within racial groups over time. Counties with higher percent of Asians and percent of Whites have higher vaccination rates at earlier time intervals whereas counties with higher percent of Latinos and percent of Blacks show lower vaccination rates. This trend flips at later dates for percent of Blacks, percent of Latinos, and percent of Whites. Results from multilevel regression models and mediation analysis controlling for vaccine hesitancy show that social vulnerability and political ideology are the underlying factors and their differential associations with diverse racial concentrations help create the racially specific and time-varying patterns.

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Racial concentration and COVID-19 vaccination are associated differently across race groups.

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Racial concentration and COVID-19 vaccination are associated differently within race groups over time .

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Social vulnerability and political dynamics are the underlying factors for the racially specific and time varying patterns.

Placental Injury and Antibody Transfer Following COVID-19 Disease in Pregnancy

We examined the relationship between placental histopathology and transplacental antibody transfer in pregnant patients following SARS-CoV-2 infection. Differences in plasma concentrations of anti-Receptor Biding Domain (RBD) Immunoglobulin (Ig) G antibodies in maternal and cord blood were analyzed according to presence of placental injury. Median [IQR] anti-RBD IgG concentrations in cord blood with placental injury (n = 7) did not differ significantly from those without injury (n= 16) [(2.7 [1.8,3.6] vs 2.7[2.4, 2.9], p= 0.59). However, they were associated with lower transfer ratios (median [IQR] 0.77[0.61, 0.97] vs. 0.97[0.80, 1.01], p = 0.05) suggesting that SARS-CoV-2 placental injury mediates reduced maternal-fetal antibody transfer.

Vaccines, Adjuvants and Key Factors for Mucosal Immune Response

Vaccines are the most effective tool to control infectious diseases, which provoke significant morbidity and mortality. Most vaccines are administered through the parenteral route and can elicit a robust systemic humoral response, but they induce a weak T-cell-mediated immunity and are poor inducers of mucosal protection. Considering that most pathogens enter the body through mucosal surfaces, a vaccine that elicits protection in the first site of contact between the host and the pathogen is promising. However, despite the advantages of mucosal vaccines as good options to confer protection on the mucosal surface, only a few mucosal vaccines are currently approved. In this review, we discuss the impact of vaccine administration in different mucosal surfaces; how appropriate adjuvants enhance the induction of protective mucosal immunity and other factors that can influence the mucosal immune response to vaccines. This article is protected by copyright. All rights reserved.

Maternal immune protection against infectious diseases

The maternal immune system protects developing offspring against pathogens before birth via transplacental transfer and after birth through secreted milk. This transferred maternal immunity influences each generation's susceptibility to infections and responsiveness to immunization. Thus, boosting immunity in the maternal-neonatal dyad is a potentially valuable public health strategy. Additionally, at critical times during fetal and postnatal development, environmental factors and immune stimuli influence immune development. These "windows of opportunity" offer a chance to identify both risk and protective factors that promote long-term health and limit disease. Here, we review pre- and postpartum maternal immune factors that protect against infectious agents in offspring and how they may shape the infant's immune landscape over time. Additionally, we discuss the influence of maternal immunity on the responsiveness to immunization in early life. Lastly, when maternal factors are insufficient to prevent neonatal infectious diseases, we discuss pre- and postnatal therapeutic strategies for the maternal-neonatal dyad.

Vertically transferred maternal immune cells promote neonatal immunity against early life infections

During mammalian pregnancy, immune cells are vertically transferred from mother to fetus. The functional role of these maternal microchimeric cells (MMc) in the offspring is mostly unknown. Here we show a mouse model in which MMc numbers are either normal or low, which enables functional assessment of MMc. We report a functional role of MMc in promoting fetal immune development. MMc induces preferential differentiation of hematopoietic stem cells in fetal bone marrow towards monocytes within the myeloid compartment. Neonatal mice with higher numbers of MMc and monocytes show enhanced resilience against cytomegalovirus infection. Similarly, higher numbers of MMc in human cord blood are linked to a lower number of respiratory infections during the first year of life. Our data highlight the importance of MMc in promoting fetal immune development, potentially averting the threats caused by early life exposure to pathogens.

Maternal immune cells seed into the foetus during mammalian pregnancy, yet the functional role of these cells is unclear. Here the authors show that maternal immune cells in foetal bone marrow stimulate immune development, subsequently reducing the risk or severity of infections in newborns.

Pertussis immunisation during pregnancy: Antibody levels and the impact of booster vaccine

Pertussis (whooping cough) is a highly infectious disease caused by Bordetella pertussis. Mothers lacking adequate immunity and contracting the disease represent the biggest risk of transmission to new-borns, for which the disease is often a threat. The aim of the study was to estimate the frequency of pertussis susceptibility among pregnant women, in order to point out the need for a vaccine recall during pregnancy, and to evaluate the antibody response in already vaccinated women. A cross-sectional observational study was conducted in the blood test centre of "St. Anna" Obstetrics and Gynaecology Hospital in Turin (Piedmont, Italy). Eligibility criteria included pregnant women coming to the centre for any blood test, aged 18 or above and with gestational age between 33 and 37 weeks at the moment of the blood draw. The data collection was carried out from May 2019 to January 2020 and the concentration of anti-Pertussis Toxin (anti-PT) IgG was measured through the Enzyme-Linked Immunosorbent Assay (ELISA) technique. Two-hundred women (median age 35) were enrolled: 132 (66%) had received at least one dose of pertussis vaccine, 82 of which during pregnancy. Recently vaccinated women had significantly higher antibody titres (even 12-15 times as high) compared to those vaccinated more than 5 years before or never vaccinated at all (p < 0.0001). Moreover, 95.1% of recently vaccinated women had anti-PT IgG levels above 10 IU/ml, and 85.4% above 20 IU/ml, while the same proportions were as low as 37% and 21% (respectively) in the group of women not vaccinated in pregnancy. This study confirmed that the vaccination is greatly effective in ensuring high antibody titres in the first months after the booster vaccine, with considerable differences in anti-PT IgG compared to women vaccinated earlier or never vaccinated at all, and therefore vaccinating pregnant women against pertussis still represents a valuable strategy.

Inefficient Placental Virus Replication and Absence of Neonatal Cell-Specific Immunity Upon Sars-CoV-2 Infection During Pregnancy

Pregnant women have been carefully observed during the COVID-19 pandemic, as the pregnancy-specific immune adaptation is known to increase the risk for infections. Recent evidence indicates that even though most pregnant have a mild or asymptomatic course, a severe course of COVID-19 and a higher risk of progression to diseases have also been described, along with a heightened risk for pregnancy complications. Yet, vertical transmission of the virus is rare and the possibility of placental SARS-CoV-2 infection as a prerequisite for vertical transmission requires further studies. We here assessed the severity of COVID-19 and onset of neonatal infections in an observational study of women infected with SARS-CoV-2 during pregnancy. Our placental analyses showed a paucity of SARS-CoV-2 viral expression ex vivo in term placentae under acute infection. No viral placental expression was detectable in convalescent pregnant women. Inoculation of placental explants generated from placentas of non-infected women at birth with SARS-CoV-2 in vitro revealed inefficient SARS-CoV-2 replication in different types of placental tissues, which provides a rationale for the low ex vivo viral expression. We further detected specific SARS-CoV-2 T cell responses in pregnant women within a few days upon infection, which was undetectable in cord blood. Our present findings confirm that vertical transmission of SARS-CoV-2 is rare, likely due to the inefficient virus replication in placental tissues. Despite the predominantly benign course of infection in most mothers and negligible risk of vertical transmission, continuous vigilance on the consequences of COVID-19 during pregnancy is required, since the maternal immune activation in response to the SARS-CoV2 infection may have long-term consequences for children’s health.