Influenza vaccine format mediates distinct cellular and antibody responses in human immune organoids.

Highly effective vaccines elicit specific, robust, and durable adaptive immune responses. To advance informed vaccine design, it is critical that we understand the cellular dynamics underlying responses to different antigen formats. Here, we sought to understand how antigen-specific B and T cells were activated and participated in adaptive immune responses within the mucosal site. Using a human tonsil organoid model, we tracked the differentiation and kinetics of the adaptive immune response to influenza vaccine and virus modalities. Each antigen format elicited distinct B and T cell responses, including differences in their magnitude, diversity, phenotype, function, and breadth. These differences culminated in substantial changes in the corresponding antibody response. A major source of antigen format-related variability was the ability to recruit naive vs. memory B and T cells to the response. These findings have important implications for vaccine design and the generation of protective immune responses in the upper respiratory tract.

Leveraging human immune organoids for rational vaccine design.

Current influenza A and B virus (IABV) vaccines provide suboptimal protection and efforts are underway to develop a universal IABV vaccine. Blood neutralizing antibodies are the current gold standard for protection, but many processes that regulate human IABV-specific immunity occur in mucosal and lymphoid tissues. We need an improved mechanistic understanding of how immune cells respond within these tissues to advance our current (slow and expensive) vaccine testing model. We posit that advanced in vitro models of human adaptive immunity can bridge some of the gaps between vaccine design, animal models, and human clinical trials. Here, we highlight how they can be integrated into current practices and play a role in reverse translating the defined features of protective vaccines to rationally design new candidates.

Monocytes and macrophages in pregnancy: The good, the bad, and the ugly.

A successful human pregnancy requires precisely timed adaptations by the maternal immune system to support fetal growth while simultaneously protecting mother and fetus against microbial challenges. The first trimester of pregnancy is characterized by a robust increase in innate immune activity that promotes successful implantation of the blastocyst and placental development. Moreover, early pregnancy is also a state of increased vulnerability to vertically transmitted pathogens notably, human immunodeficiency virus (HIV), Zika virus (ZIKV), SARS-CoV-2, and Listeria monocytogenes. As gestation progresses, the second trimester is marked by the establishment of an immunosuppressive environment that promotes fetal tolerance and growth while preventing preterm birth, spontaneous abortion, and other gestational complications. Finally, the period leading up to labor and parturition is characterized by the reinstatement of an inflammatory milieu triggering childbirth. These dynamic waves of carefully orchestrated changes have been dubbed the "immune clock of pregnancy." Monocytes in maternal circulation and tissue-resident macrophages at the maternal-fetal interface play a critical role in this delicate balance. This review will summarize the current data describing the longitudinal changes in the phenotype and function of monocyte and macrophage populations in healthy and complicated pregnancies.

Ovol1/2 loss-induced epidermal defects elicit skin immune activation and alter global metabolism.

Skin epidermis constitutes the outer permeability barrier that protects the body from dehydration, heat loss, and myriad external assaults. Mechanisms that maintain barrier integrity in constantly challenged adult skin and how epidermal dysregulation shapes the local immune microenvironment and whole-body metabolism remain poorly understood. Here, we demonstrate that inducible and simultaneous ablation of transcription factor-encoding Ovol1 and Ovol2 in adult epidermis results in barrier dysregulation through impacting epithelial-mesenchymal plasticity and inflammatory gene expression. We find that aberrant skin immune activation then ensues, featuring Langerhans cell mobilization and T cell responses, and leading to elevated levels of secreted inflammatory factors in circulation. Finally, we identify failure to gain body weight and accumulate body fat as long-term consequences of epidermal-specific Ovol1/2 loss and show that these global metabolic changes along with the skin barrier/immune defects are partially rescued by immunosuppressant dexamethasone. Collectively, our study reveals key regulators of adult barrier maintenance and suggests a causal connection between epidermal dysregulation and whole-body metabolism that is in part mediated through aberrant immune activation.

Ethanol Consumption Induces Nonspecific Inflammation and Functional Defects in Alveolar Macrophages.

Chronic alcohol drinking is associated with increased susceptibility to viral and bacterial respiratory pathogens. In this study, we use a rhesus macaque model of voluntary ethanol self-administration to study the effects of long-term alcohol drinking on the immunological landscape of the lung. We report a heightened inflammatory state in alveolar macrophages (AMs) obtained from ethanol (EtOH)-drinking animals that is accompanied by increased chromatin accessibility in intergenic regions that regulate inflammatory genes and contain binding motifs for transcription factors AP-1, IRF8, and NFKB p-65. In line with these transcriptional and epigenetic changes at the basal state, AMs from EtOH-drinking animals generate elevated inflammatory mediator responses to lipopolysaccharides and respiratory syncytial virus. However, the transcriptional analysis revealed an inefficient induction of interferon-stimulated genes with EtOH in response to the respiratory syncytial virus, suggesting disruption of antimicrobial defenses. Correspondingly, AMs from EtOH-drinking animals exhibited transcriptional shifts indicative of increased oxidative stress and oxidative phosphorylation, which was coupled with higher cytosolic reactive oxygen species and mitochondrial potential. This heightened oxidative stress state was accompanied by decreased ability to phagocytose bacteria. Bulk RNA and assay for transposase-accessible chromatin sequencing data further revealed reduced expression and chromatin accessibility of loci associated with tissue repair and maintenance with chronic EtOH drinking. Similarly, analysis of single-cell RNA sequencing data revealed shifts in cell states from tissue maintenance to inflammatory responses with EtOH. Collectively, these data provide novel insight into mechanisms by which chronic EtOH drinking increases susceptibility to infection in patients with alcohol use disorders.

Importance of sex and trauma context on circulating cytokines and amygdalar GABAergic signaling in a comorbid model of posttraumatic stress and alcohol use disorders.

Alcohol use disorder (AUD) and anxiety disorders are frequently comorbid and share mechanisms that could be therapeutic targets. To facilitate mechanistic studies, we adapted an inhibitory avoidance-based "2-hit" rat model of posttraumatic stress disorder (PTSD) and identified predictors and biomarkers of comorbid alcohol (ethanol)/PTSD-like symptoms in these animals. Stressed Wistar rats received a single footshock on two occasions. The first footshock occurred when rats crossed into the dark chamber of a shuttle box. Forty-eight hours later, rats received the second footshock in a familiar (FAM) or novel (NOV) context. Rats then received 4 weeks of two-bottle choice (2BC) ethanol access. During subsequent abstinence, PTSD-like behavior responses, GABAergic synaptic transmission in the central amygdala (CeA), and circulating cytokine levels were measured. FAM and NOV stress more effectively increased 2BC drinking in males and females, respectively. Stressed male rats, especially drinking-vulnerable individuals (≥0.8 g/kg average 2-h ethanol intake with >50% ethanol preference), showed higher fear overgeneralization in novel contexts, increased GABAergic transmission in the CeA, and a profile of increased G-CSF, GM-CSF, IL-13, IL-6, IL-17a, leptin, and IL-4 that discriminated between stress context (NOV > FAM > Control). However, drinking-resilient males showed the highest G-CSF, IL-13, and leptin levels. Stressed females showed increased acoustic startle and decreased sleep maintenance, indicative of hyperarousal, with increased CeA GABAergic transmission in NOV females. This paradigm promotes key features of PTSD, including hyperarousal, fear generalization, avoidance, and sleep disturbance, with comorbid ethanol intake, in a sex-specific fashion that approximates clinical comorbidities better than existing models, and identifies increased CeA GABAergic signaling and a distinct pro-hematopoietic, proinflammatory, and pro-atopic cytokine profile that may aid in treatment.

Profiling of extracellular vesicle-bound miRNA to identify candidate biomarkers of chronic alcohol drinking in nonhuman primates.

BACKGROUND: Long-term alcohol drinking is associated with numerous health complications including susceptibility to infection, cancer, and organ damage. However, due to the complex nature of human drinking behavior, it has been challenging to identify reliable biomarkers of alcohol drinking behavior prior to signs of overt organ damage. Recently, extracellular vesicle-bound microRNAs (EV-miRNAs) have been found to be consistent biomarkers of conditions that include cancer and liver disease. METHODS: In this study, we profiled the plasma EV-miRNA content by miRNA-Seq from 80 nonhuman primates after 12 months of voluntary alcohol drinking. RESULTS: We identified a list of up- and downregulated EV-miRNA candidate biomarkers of heavy drinking and those positively correlated with ethanol dose. We overexpressed these candidate miRNAs in control primary peripheral immune cells to assess their potential functional mechanisms. We found that overexpression of miR-155, miR-154, miR-34c, miR-450a, and miR-204 led to increased production of the inflammatory cytokines TNFα or IL-6 in peripheral blood mononuclear cells after stimulation. CONCLUSION: This exploratory study identified several EV-miRNAs that could serve as biomarkers of long-term alcohol drinking and provide a mechanism to explain alcohol-induced peripheral inflammation.

Sex and context differences in the effects of trauma on comorbid alcohol use and post-traumatic stress phenotypes in actively drinking rats.

Alcohol use disorder (AUD) and affective disorders are frequently comorbid and share underlying mechanisms that could be targets for comprehensive treatment. Post-traumatic stress disorder (PTSD) has high comorbidity with AUD, but comprehensive models of this overlap are nascent. We recently characterized a model of comorbid AUD and PTSD-like symptoms, wherein stressed rats receive an inhibitory avoidance (IA)-related footshock on two occasions followed by two-bottle choice (2BC) voluntary alcohol drinking. Stressed rats received the second footshock in a familiar (FAM, same IA box as the first footshock) or novel context (NOV, single-chambered apparatus); the FAM paradigm more effectively increased alcohol drinking in males and the NOV paradigm in females. During abstinence, stressed males displayed avoidance-like PTSD symptoms, and females showed hyperarousal-like PTSD symptoms. Rats in the model had altered spontaneous action potential-independent GABAergic transmission in the central amygdala (CeA), a brain region key in alcohol dependence and stress-related signaling. However, PTSD sufferers may have alcohol experience prior to their trauma. Here, we therefore modified our AUD/PTSD comorbidity model to provide 3 weeks of intermittent extended alcohol access before footshock and then studied the effects of NOV and FAM stress on drinking and PTSD phenotypes. NOV stress suppressed the escalation of alcohol intake and preference seen in male controls, but no stress effects were seen on drinking in females. Additionally, NOV males had decreased action potential-independent presynaptic GABA release and delayed postsynaptic GABAA receptor kinetics in the CeA compared to control and FAM males. Despite these changes to alcohol intake and CeA GABA signaling, stressed rats showed broadly similar anxiogenic-like behaviors to our previous comorbid model, suggesting decoupling of the PTSD symptoms from the AUD vulnerability for some of these animals. The collective results show the importance of alcohol history and trauma context in vulnerability to comorbid AUD/PTSD-like symptoms.

Impaired hypothalamic feedback dysregulates brain glucocorticoid signaling in genetically-selected Marchigian Sardinian alcohol-preferring rats.

Genetically-selected Marchigian Sardinian alcohol-preferring (msP) rats display comorbid symptoms of increased alcohol preference and elevated anxiety-like behavior. Heightened stress sensitivity in msPs is influenced by genetic polymorphisms of the corticotropin-releasing factor receptor in the central nucleus of the amygdala (CeA), as well as reduced influence of anti-stress mechanisms that normally constrain the stress response. Given this propensity for stress dysregulation, in this study, we expand on the possibility that msPs may display differences in neuroendocrine processes that normally terminate the stress response. We utilized behavioral, biochemical, and molecular assays to compare basal and restraint stress-induced changes in the hypothalamic-pituitary-adrenal (HPA) axis of male and female msPs relative to their nonselected Wistar counterparts. The results showed that msPs display deficits in marble-burying behavior influenced by environmental factors and procedures that modulate arousal states in a sex-dependent manner. Whereas male msPs display evidence of dysregulated neuroendocrine function (higher adrenocorticotropic hormone levels and subthreshold reductions in corticosterone), females display restraint-induced elevations in corticosterone levels that were persistently higher in msPs. A dexamethasone challenge reduced the circulation of these stress hormones, although the reduction in corticosterone was generally attenuated in msP versus Wistar rats. Finally, we found evidence of diminished stress-induced glucocorticoid receptor (GR) phosphorylation in the hypothalamic paraventricular nucleus of msPs, as well as innate increases in phosphorylated GR levels in the CeA of male msPs. Collectively, these findings suggest that negative feedback processes regulating HPA responsiveness are diminished in msP rats, possibly underlying differences in the expression of anxiety-like behaviors.

Chronic ethanol consumption alters lamina propria leukocyte response to stimulation in a region-dependent manner.

Chronic heavy alcohol consumption, also referred to as chronic heavy drinking (CHD), results in intestinal injury characterized by increased permeability, dysbiosis, nutrient malabsorption, potentially higher susceptibility to infection, and increased risk of colorectal cancer. However, our understanding of the mechanisms by which CHD results in intestinal damage remains incomplete. Here, we investigated the impact of chronic drinking on transcriptional and functional responses of lamina propria leukocytes (LPLs) isolated from the 4 major gut sections. Although no significant differences were detected between LPLs isolated from the ethanol and control groups at resting state within each major gut section, our analysis uncovered key regional differences in composition and function of LPLs independent of alcohol consumption. However, in response to phorbol myristate acetate and ionomycin, duodenal LPLs from ethanol-drinking animals generated a dampened response, whereas jejunal and ileal LPLs from ethanol-drinking animals produced a heightened response. Transcriptional responses following stimulation were pronounced in ileal and duodenal LPLs from the ethanol-drinking group but less evident in jejunal and colonic LPLs compared with controls, suggesting a more significant impact of alcohol on these gut regions. The altered intestinal LPL function detected in our study reveals remarkable region specificity and novel insight into potential mechanisms of intestinal injury associated with CHD.-Barr, T., Lewis, S. A., Sureshchandra, S., Doratt, B., Grant, K. A., Messaoudi, I. Chronic ethanol consumption alters lamina propria leukocyte response to stimulation in a region-dependent manner.

Maternal Pregravid Obesity Remodels the DNA Methylation Landscape of Cord Blood Monocytes Disrupting Their Inflammatory Program.

Prepregnancy maternal obesity is associated with adverse outcomes for the offspring, including increased incidence of neonatal bacterial sepsis and necrotizing enterocolitis. We recently reported that umbilical cord blood (UCB) monocytes from babies born to obese mothers generate a reduced IL-6/TNF-α response to TLR 1/2 and 4 ligands compared to those collected from lean mothers. These observations suggest altered development of the offspring's immune system, which in turn results in dysregulated function. We therefore investigated transcriptional and epigenetic differences within UCB monocytes stratified by prepregnancy maternal body mass index. We show that UCB monocytes from babies born to obese mothers generate a dampened response to LPS stimulation compared with those born to lean mothers, at the level of secreted immune mediators and transcription. Because gene expression profiles of resting UCB monocytes from both groups were comparable, we next investigated the role of epigenetic differences. Indeed, we detected stark differences in methylation levels within promoters and regulatory regions of genes involved in TLR signaling in resting UCB monocytes. Interestingly, the DNA methylation status of resting cells was highly predictive of transcriptional changes post-LPS stimulation, suggesting that cytosine methylation is one of the dominant mechanisms driving functional inadequacy in UCB monocytes obtained from babies born to obese mothers. These data highlight a potentially critical role of maternal pregravid obesity-associated epigenetic changes in influencing the function of an offspring's monocytes at birth. These findings further our understanding of mechanisms that explain the increased risk of infection in neonates born to mothers with high prepregnancy body mass index.

Alcohol Consumption Modulates Host Defense in Rhesus Macaques by Altering Gene Expression in Circulating Leukocytes.

Several lines of evidence indicate that chronic alcohol use disorder leads to increased susceptibility to several viral and bacterial infections, whereas moderate alcohol consumption decreases the incidence of colds and improves immune responses to some pathogens. In line with these observations, we recently showed that heavy ethanol intake (average blood ethanol concentrations > 80 mg/dl) suppressed, whereas moderate alcohol consumption (blood ethanol concentrations < 50 mg/dl) enhanced, T and B cell responses to modified vaccinia Ankara vaccination in a nonhuman primate model of voluntary ethanol consumption. To uncover the molecular basis for impaired immunity with heavy alcohol consumption and enhanced immune response with moderate alcohol consumption, we performed a transcriptome analysis using PBMCs isolated on day 7 post-modified vaccinia Ankara vaccination, the earliest time point at which we detected differences in T cell and Ab responses. Overall, chronic heavy alcohol consumption reduced the expression of immune genes involved in response to infection and wound healing and increased the expression of genes associated with the development of lung inflammatory disease and cancer. In contrast, chronic moderate alcohol consumption upregulated the expression of genes involved in immune response and reduced the expression of genes involved in cancer. To uncover mechanisms underlying the alterations in PBMC transcriptomes, we profiled the expression of microRNAs within the same samples. Chronic heavy ethanol consumption altered the levels of several microRNAs involved in cancer and immunity and known to regulate the expression of mRNAs differentially expressed in our data set.

Long-lasting effect of obesity on skeletal muscle transcriptome.

BACKGROUND: Reduced physical activity and increased intake of calorically-dense diets are the main risk factors for obesity, glucose intolerance, and type 2 diabetes. Chronic overnutrition and hyperglycemia can alter gene expression, contributing to long-term obesity complications. While caloric restriction can reduce obesity and glucose intolerance, it is currently unknown whether it can effectively reprogram transcriptome to a pre-obesity level. The present study addressed this question by the preliminary examination of the transcriptional dynamics in skeletal muscle after exposure to overnutrition and following caloric restriction. RESULTS: Six male rhesus macaques of 12-13 years of age consumed a high-fat western-style diet for 6 months and then were calorically restricted for 4 months without exercise. Skeletal muscle biopsies were subjected to longitudinal gene expression analysis using next-generation whole-genome RNA sequencing. In spite of significant weight loss and normalized insulin sensitivity, the majority of WSD-induced (n = 457) and WSD-suppressed (n = 47) genes remained significantly dysregulated after caloric restriction (FDR ≤0.05). The MetacoreTM pathway analysis reveals that western-style diet induced the sustained activation of the transforming growth factor-ß gene network, associated with extracellular matrix remodeling, and the downregulation of genes involved in muscle structure development and nutritional processes. CONCLUSIONS: Western-style diet, in the absence of exercise, induced skeletal muscle transcriptional programing, which persisted even after insulin resistance and glucose intolerance were completely reversed with caloric restriction.

Acute Simian Varicella Virus Infection Causes Robust and Sustained Changes in Gene Expression in the Sensory Ganglia.

Primary infection with varicella-zoster virus (VZV), a neurotropic alphaherpesvirus, results in varicella. VZV establishes latency in the sensory ganglia and can reactivate later in life to cause herpes zoster. The relationship between VZV and its host during acute infection in the sensory ganglia is not well understood due to limited access to clinical specimens. Intrabronchial inoculation of rhesus macaques with simian varicella virus (SVV) recapitulates the hallmarks of VZV infection in humans. We leveraged this animal model to characterize the host-pathogen interactions in the ganglia during both acute and latent infection by measuring both viral and host transcriptomes on days postinfection (dpi) 3, 7, 10, 14, and 100. SVV DNA and transcripts were detected in sensory ganglia 3 dpi, before the appearance of rash. CD4 and CD8 T cells were also detected in the sensory ganglia 3 dpi. Moreover, lung-resident T cells isolated from the same animals 3 dpi also harbored SVV DNA and transcripts, suggesting that T cells may be responsible for trafficking SVV to the ganglia. Transcriptome sequencing (RNA-Seq) analysis showed that cessation of viral transcription 7 dpi coincides with a robust antiviral innate immune response in the ganglia. Interestingly, a significant number of genes that play a critical role in nervous system development and function remained downregulated into latency. These studies provide novel insights into host-pathogen interactions in the sensory ganglia during acute varicella and demonstrate that SVV infection results in profound and sustained changes in neuronal gene expression. IMPORTANCE: Many aspects of VZV infection of sensory ganglia remain poorly understood, due to limited access to human specimens and the fact that VZV is strictly a human virus. Infection of rhesus macaques with simian varicella virus (SVV), a homolog of VZV, provides a robust model of the human disease. Using this model, we show that SVV reaches the ganglia early after infection, most likely by T cells, and that the induction of a robust innate immune response correlates with cessation of virus transcription. We also report significant changes in the expression of genes that play an important role in neuronal function. Importantly, these changes persist long after viral replication ceases. Given the homology between SVV and VZV, and the genetic and physiological similarities between rhesus macaques and humans, our results provide novel insight into the interactions between VZV and its human host and explain some of the neurological consequences of VZV infection.

Tissue-specific sex differences in pediatric and adult immune cell composition and function.

Sex-based differences in immune cell composition and function can contribute to distinct adaptive immune responses. Prior work has quantified these differences in peripheral blood, but little is known about sex differences within human lymphoid tissues. Here, we characterized the composition and phenotypes of adaptive immune cells from male and female ex vivo tonsils and evaluated their responses to influenza antigens using an immune organoid approach. In a pediatric cohort, female tonsils had more memory B cells compared to male tonsils direct ex vivo and after stimulation with live-attenuated but not inactivated vaccine, produced higher influenza-specific antibody responses. Sex biases were also observed in adult tonsils but were different from those measured in children. Analysis of peripheral blood immune cells from in vivo vaccinated adults also showed higher frequencies of tissue homing CD4 T cells in female participants. Together, our data demonstrate that distinct memory B and T cell profiles are present in male vs. female lymphoid tissues and peripheral blood respectively and suggest that these differences may in part explain sex biases in response to vaccines and viruses.

A human lymphoma organoid model for evaluating and targeting the follicular lymphoma tumor immune microenvironment.

Heterogeneity in the tumor microenvironment (TME) of follicular lymphomas (FLs) can affect clinical outcomes. Current immunotherapeutic strategies, including antibody- and cell-based therapies, variably overcome pro-tumorigenic mechanisms for sustained disease control. Modeling the intact FL TME, with its native, syngeneic tumor-infiltrating leukocytes, is a major challenge. Here, we describe an organoid culture method for cultivating patient-derived lymphoma organoids (PDLOs), which include cells from the native FL TME. We define the robustness of this method by successfully culturing cryopreserved FL specimens from diverse patients and demonstrate the stability of TME cellular composition, tumor somatic mutations, gene expression profiles, and B/T cell receptor dynamics over 3 weeks. PDLOs treated with CD3:CD19 and CD3:CD20 therapeutic bispecific antibodies showed B cell killing and T cell activation. This stable system offers a robust platform for advancing precision medicine efforts in FL through patient-specific modeling, high-throughput screening, TME signature identification, and treatment response evaluation.

Tissue determinants of the human T cell receptor repertoire.

98% of T cells reside in tissues, yet nearly all human T cell analyses are performed from peripheral blood. We single-cell sequenced 5.7 million T cells from ten donors' autologous blood and tonsils and sought to answer key questions about T cell receptor biology previously unanswerable by smaller-scale experiments. We identified distinct clonal expansions and distributions in blood compared to tonsils, with surprisingly low (1-7%) clonal sharing. These few shared clones exhibited divergent phenotypes across bodily sites. Analysis of antigen-specific CD8 T cells revealed location as a main determinant of frequency, phenotype, and immunodominance. Finally, diversity estimates from the tissue recalibrates current repertoire diversity estimates, and we provide a refined estimate of whole-body repertoire. Given the tissue-restricted nature of T cell phenotypes, functions, differentiation, and clonality revealed by this dataset, we conclude that tissue analyses are crucial for accurate repertoire analysis and monitoring changes after perturbing therapies.

Multimodal profiling of term human decidua demonstrates immune adaptations with pregravid obesity.

Leukocyte diversity of the first-trimester maternal-fetal interface has been extensively described; however, the immunological landscape of the term decidua remains poorly understood. We therefore profiled human leukocytes from term decidua collected via scheduled cesarean delivery. Relative to the first trimester, our analyses show a shift from NK cells and macrophages to T cells and enhanced immune activation. Although circulating and decidual T cells are phenotypically distinct, they demonstrate significant clonotype sharing. We also report significant diversity within decidual macrophages, the frequency of which positively correlates with pregravid maternal body mass index. Interestingly, the ability of decidual macrophages to respond to bacterial ligands is reduced with pregravid obesity, suggestive of skewing toward immunoregulation as a possible mechanism to safeguard the fetus against excessive maternal inflammation. These findings are a resource for future studies investigating pathological conditions that compromise fetal health and reproductive success.

Mild/asymptomatic COVID-19 in unvaccinated pregnant mothers impairs neonatal immune responses.

Maternal SARS-CoV-2 infection triggers placental inflammation and alters cord blood immune cell composition. However, most studies focus on outcomes of severe maternal infection. Therefore, we analyzed cord blood and chorionic villi from newborns of unvaccinated mothers who experienced mild/asymptomatic SARS-CoV-2 infection during pregnancy. We investigated immune cell rewiring using flow cytometry, single-cell RNA sequencing, and functional readouts using ex vivo stimulation with TLR agonists and pathogens. Maternal infection was associated with increased frequency of memory T and B cells and nonclassical monocytes in cord blood. Ex vivo T and B cell responses to stimulation were attenuated, suggesting a tolerogenic state. Maladaptive responses were also observed in cord blood monocytes, where antiviral responses were dampened but responses to bacterial TLRs were increased. Maternal infection was also associated with expansion and activation of placental Hofbauer cells, secreting elevated levels of myeloid cell-recruiting chemokines. Moreover, we reported increased activation of maternally derived monocytes/macrophages in the fetal placenta that were transcriptionally primed for antiviral responses. Our data indicate that even in the absence of vertical transmission or symptoms in the neonate, mild/asymptomatic maternal COVID-19 altered the transcriptional and functional state in fetal immune cells in circulation and in the placenta.

Mild/Asymptomatic Maternal SARS-CoV-2 Infection Leads to Immune Paralysis in Fetal Circulation and Immune Dysregulation in Fetal-Placental Tissues.

Few studies have addressed the impact of maternal mild/asymptomatic SARS-CoV-2 infection on the developing neonatal immune system. In this study, we analyzed umbilical cord blood and placental chorionic villi from newborns of unvaccinated mothers with mild/asymptomatic SARSCoV-2 infection during pregnancy using flow cytometry, single-cell transcriptomics, and functional assays. Despite the lack of vertical transmission, levels of inflammatory mediators were altered in cord blood. Maternal infection was also associated with increased memory T, B cells, and non-classical monocytes as well as increased activation. However, ex vivo responses to stimulation were attenuated. Finally, within the placental villi, we report an expansion of fetal Hofbauer cells and infiltrating maternal macrophages and rewiring towards a heightened inflammatory state. In contrast to cord blood monocytes, placental myeloid cells were primed for heightened antiviral responses. Taken together, this study highlights dysregulated fetal immune cell responses in response to mild maternal SARS-CoV-2 infection during pregnancy.