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

Assessment of Cell Isolation From Human Milk Using Immunomagnetic Beads

BACKGROUND

There is increasing interest in better understanding the immune cell composition of human milk and how these cells interact with neonatal immune development. However, consistent methods for immune cell isolation from human milk are lacking.

RESEARCH AIM

Our aim was to systematically compare available cell isolation techniques to isolate T lymphocytes from human milk samples.

METHODS

This repeated measures study design compared three cell isolation methods using human milk samples: (1) centrifugation, (2) immunomagnetic bead isolation, and (3) a combination of both methods. We assessed the proportion and viability of CD3+, CD4+, CD25+ and regulatory T cells using flow cytometry in isolated cells to compare the performance of these isolation methods.

RESULTS

Immunomagnetic separation is a feasible method to isolate T lymphocytes in human milk, similar to blood. It improves target cell enrichment and cell viability compared to centrifugation, which may be an advantage when the goal is to characterize rare cell types or when cells are further used in functional assays. No excess cell activation (CD25 positivity) was observed with the use of magnetic beads.

CONCLUSION

Immunomagnetic separation of human milk T lymphocytes may have advantages over centrifugation depending on the intended downstream use of cells.

Infant CD4 T-cell response to SARS-CoV-2 mRNA vaccination is restricted in cytokine production and modified by vaccine manufacturer

Safe and effective vaccines are a key preventative measure to protect infants from SARS-CoV-2 infection and disease. Although mRNA vaccines induce robust antibody titers in infants, little is known about the quality of CD4 T-cell responses induced by vaccination. CD4 T-cell responses are important in orchestrating coordinated immune responses during infection and may help to limit disease severity.

METHODS

To characterize the CD4 T-cell response to SARS-CoV-2 mRNA vaccination in infants, we sampled blood from 13 infants before and after primary SARS-CoV-2 mRNA vaccine series; samples from 12 historical vaccinated adults were used for comparisons. PBMC were stimulated with Spike peptide pools and the ability of CD4 T-cells to secrete Th1, Th2, and Th17 cytokines was quantified. A measure of polyfunctionality was generated using the COMPASS algorithm.

RESULTS

We observed a significant increase in CD4 T-cells producing IL-2 (0.01% vs. 0.08%, p=0.04) and TNF-α (0.007% vs. 0.07%, p=0.007) following vaccination in infants but a more muted induction of IFN-γ production (0.01% vs 0.04%, p=0.08). This contrasted with adults, in whom vaccination induced robust production of IFN-γ, IL-2, and TNF-α. Th2 and Th17 responses were limited in both infants and adults. In infants, CD4 T-cell responses post-vaccination were greater in those who received mRNA-1273 versus BNT162b. In contrast to CD4 T-cell responses, Spike-specific IgG titers were similar in infants and adults.

CONCLUSIONS

These data suggest that infants have restricted induction of cytokine producing CD4 T-cells following SARS-CoV-2 mRNA vaccination relative to adults.

Safety and Efficacy of Vaccination During Lactation: A Comprehensive Review of Vaccines for Maternal and Infant Health Utilizing a Large Language Model Citation Screening System

Newborns are born with an immature immune system, making them susceptible to infections early in life. Human milk provides essential nutrients and immunological factors that support infant immunity. Maternal vaccination during lactation has the potential to enhance these benefits by triggering an immune response in the mother, potentially extending protection to her child. However, lactating individuals are often excluded from vaccine trials, leading to uncertainties about vaccine safety and efficacy during the postpartum period. This study critically evaluates the effectiveness of vaccines in enhancing the immune-supporting properties of human milk and assesses their safety and efficacy for lactating mothers and their infants. By examining potential benefits alongside safety concerns, we aim to provide a comprehensive understanding of postpartum vaccination's impact on maternal and infant health. We utilized large-language models (LLMs) to enhance the review process and performed a structured literature search across Ovid/Medline, Embase, and Clarivate Analytics using terms like "breastfeeding", "postpartum", and "vaccination". A three-stage screening process involving human and LLM-assisted evaluation focused on postpartum vaccines and their implications for maternal and infant health. We identified 73 studies covering vaccines against COVID-19, cholera, influenza, pertussis, pneumococcal, rabies, polio, rotavirus, rubella, varicella, typhoid, smallpox, and yellow fever. Most vaccines, such as those for COVID-19 and influenza, appear safe and effective for postpartum use without requiring precautionary measures. However, caution is advised with vaccines such as the yellow fever vaccine, where temporary breastfeeding cessation is recommended. Overall, this review underscores the compatibility of most vaccines with lactation and suggests its benefits for both mother and 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.

Prenatal SARS-CoV-2 Infection Alters Human Milk-Derived Extracellular Vesicles

Human milk-derived extracellular vesicles (HMEVs) are key components in breast milk, promoting infant health and development. Maternal conditions could affect HMEV cargo; however, the impact of SARS-CoV-2 infection on HMEVs remains unknown. This study investigated the influence of SARS-CoV-2 infection during pregnancy on postpartum HMEV molecules. The median duration from SARS-CoV-2 test positivity to milk collection was 3 months. After defatting and casein micelle disaggregation, HMEVs were isolated from milk samples of nine mothers with prenatal SARS-CoV-2 and six controls by sequential centrifugation, ultrafiltration, and qEV-size exclusion chromatography. The presence of HMEV was confirmed via transmission electron microscopy. Nanoparticle tracking analysis demonstrated particle diameters of <200 nm and yields of >1 × 1011 particles per mL of milk. Western immunoblots detected ALIX, CD9, and HSP70, supporting the presence of HMEVs in the isolates. Cargo from thousands of HMEVs were analyzed using a multi-omics approach, including proteomics and microRNA sequencing, and predicted that mothers with prenatal SARS-CoV-2 infection produced HMEVs with enhanced functionalities involving metabolic reprogramming, mucosal tissue development, and immunomodulation. Our findings suggest that SARS-CoV-2 infection during pregnancy boosts mucosal site-specific functions of HMEVs, potentially protecting infants against viral infections. Further prospective studies should be pursued to reevaluate the short- and long-term benefits of breastfeeding in the post-COVID era.

The characteristics of TCR CDR3 repertoire in COVID-19 patients and SARS-CoV-2 vaccine recipients

The COVID-19 pandemic and large-scale administration of multiple SARS-CoV-2 vaccines have attracted global attention to the short-term and long-term effects on the human immune system. An analysis of the "traces" left by the body's T-cell immune response is needed, especially for the prevention and treatment of breakthrough infections and long COVID-19 and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant infections. T-cell receptor complementarity determining region 3 (TCR CDR3) repertoire serves as a target molecule for monitoring the effects, mechanisms, and memory of the T-cell response. Furthermore, it has been extensively applied in the elucidation of the infectious mechanism and vaccine refinement of hepatitis B virus (HBV), influenza virus, human immunodeficiency virus (HIV), and SARS-CoV. Laboratories worldwide have utilized high-throughput sequencing (HTS) and scTCR-seq to characterize, share, and apply the TCR CDR3 repertoire in COVID-19 patients and SARS-CoV-2 vaccine recipients. This article focuses on the comparative analysis of the diversity, clonality, V&J gene usage and pairing, CDR3 length, shared CDR3 sequences or motifs, and other characteristics of TCR CDR3 repertoire. These findings provide molecular targets for evaluating T-cell response effects and short-term and long-term impacts on the adaptive immune system following SARS-CoV-2 infection or vaccination and establish a comparative archive of T-cell response "traces."

Mechanisms and risk factors for perinatal allergic disease

Allergies are among the top causes of chronic disease in children. Their pathogenesis classically involves T helper 2 (Th2)-type inflammation driven by IgE-mediated allergen sensing. Triggers influencing allergic disease occur early in life, including before birth. The immature fetal immune system and mucosal barriers undergo periods of plasticity that are open to longitudinal programming by maternal influence. Evidence supports the importance of the maternal immune system in shaping perinatal immunity, as the transfer of cytokines, antibodies, and cells promotes offspring protection from pathogens. However, the same components may lead to allergic predisposition. Maternal-fetal interactions are further modified by epigenetic, metabolic, dietary, and microbiome-mediated effects. Here, we review how diverse maternal exposures and mediators signal across the placenta and through nursing perinatally to promote future tolerance or enhance reactivity against allergens. Improved understanding of the mechanisms predisposing for allergic disease in early life can guide the development of new therapeutics and preventative lifestyle modifications.

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 non-invasive method to sample immune cells in the lower female genital tract using menstrual discs

T cells in the human female genital tract (FGT) 2 are key mediators of susceptibility to and protection from infection, including HIV and other sexually transmitted infections. There is a critical need for increased understanding of the distribution and activation of T cell populations in the FGT, but current sampling methods require a healthcare provider and are expensive, limiting the ability to study these populations longitudinally. To address these challenges, we have developed a method to sample immune cells from the FGT utilizing disposable menstrual discs which are non-invasive, self-applied, and low-cost. To demonstrate reproducibility, we sampled the cervicovaginal fluid (CVF) 3 of healthy, reproductive-aged individuals using menstrual discs over three sequential days. CVF was processed for cervicovaginal cells, and high parameter flow cytometry was used to characterize immune populations. We identified large numbers of live, CD45+ leukocytes, as well as distinct populations of T cells and B cells. Within the T cell compartment, activation and suppression status of T cell subsets were consistent with previous studies of the FGT utilizing current approaches, including identification of both tissue resident and migratory populations. In addition, the T cell population structure was highly conserved across days within individuals but divergent across individuals. Our approach to sample immune cells in the FGT with menstrual discs will decrease barriers to participation and empower longitudinal sampling in future research studies.

A Noninvasive Method to Sample Immune Cells in the Lower Female Genital Tract Using Menstrual Discs

T cells in the human female genital tract (FGT) are key mediators of susceptibility to and protection from infection, including HIV and other sexually transmitted infections. There is a critical need for increased understanding of the distribution and activation of T cell populations in the FGT, but current sampling methods require a healthcare provider and are expensive, limiting the ability to study these populations longitudinally. To address these challenges, we have developed a method to sample immune cells from the FGT utilizing disposable menstrual discs which are noninvasive, self-applied, and low in cost. To demonstrate reproducibility, we sampled the cervicovaginal fluid of healthy, reproductive-aged individuals using menstrual discs across 3 sequential days. Cervicovaginal fluid was processed for cervicovaginal cells, and high-parameter flow cytometry was used to characterize immune populations. We identified large numbers of live, CD45+ leukocytes, as well as distinct populations of T cells and B cells. Within the T cell compartment, activation and suppression status of T cell subsets were consistent with previous studies of the FGT utilizing current approaches, including identification of both tissue-resident and migratory populations. In addition, the T cell population structure was highly conserved across days within individuals but divergent across individuals. Our approach to sample immune cells in the FGT with menstrual discs will decrease barriers to participation and empower longitudinal sampling in future research studies.

The importance of COVID-19 vaccination during lactation

The World Health Organization strongly supports breastfeeding as the main source of infant feeding to ensure maternal and child health. Since its emergence, COVID-19 has become a disease affecting the health of the world's population, and vaccines have been developed to prevent it. However, the decision to license COVID-19 vaccines for infants under 6 months of age has been delayed. Different studies have shown that during the breastfeeding period, the benefit-risk balance is much higher in favor of the benefit, at the immunological level for the infant, due to its low perception of adverse effects and the low transmission of products such as mRNA from the mother to the child. Different organizations and societies recommend vaccination in breastfeeding women. COVID-19 vaccines have been shown to be safe and effective.

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.

Prenatal SARS-CoV-2 infection alters postpartum human milk-derived extracellular vesicles

Human milk-derived extracellular vesicles (HMEVs) are crucial functional components in breast milk, contributing to infant health and development. Maternal conditions could affect HMEV cargos; however, the impact of SARS-CoV-2 infection on HMEVs remains unknown. This study evaluated the influence of SARS-CoV-2 infection during pregnancy on postpartum HMEV molecules. Milk samples (9 prenatal SARS-CoV-2 vs. 9 controls) were retrieved from the IMPRINT birth cohort. After defatting and casein micelle disaggregation, 1 mL milk was subjected to a sequential process of centrifugation, ultrafiltration, and qEV-size exclusion chromatography. Particle and protein characterizations were performed following the MISEV2018 guidelines. EV lysates were analyzed through proteomics and miRNA sequencing, while the intact EVs were biotinylated for surfaceomic analysis. Multi-Omics was employed to predict HMEV functions associated with prenatal SARS-CoV-2 infection. Demographic data between the prenatal SARS-CoV-2 and control groups were similar. The median duration from maternal SARS-CoV-2 test positivity to milk collection was 3 months (range: 1-6 months). Transmission electron microscopy showed the cup-shaped nanoparticles. Nanoparticle tracking analysis demonstrated particle diameters of <200 nm and yields of >1e11 particles from 1 mL milk. Western immunoblots detected ALIX, CD9 and HSP70, supporting the presence of HMEVs in the isolates. Thousands of HMEV cargos and hundreds of surface proteins were identified and compared. Multi-Omics predicted that mothers with prenatal SARS-CoV-2 infection produced HMEVs with enhanced functionalities involving metabolic reprogramming and mucosal tissue development, while mitigating inflammation and lower EV transmigration potential. Our findings suggest that SARS-CoV-2 infection during pregnancy boosts mucosal site-specific functions of HMEVs, potentially protecting infants against viral infections. Further prospective studies should be pursued to reevaluate the short- and long-term benefits of breastfeeding in the post-COVID era.

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.