Investigating the Impact of Maternal Antiviral Responses on Pregnancy and Fetal Development

The maternal-fetal interface during pregnancy is an underexplored environment rich in immunological factors that must propel developmental processes while simultaneously providing protection from invading pathogens such as viruses. Almost half of all cells in the maternal decidua in pregnancy are leukocytes, which are required for successful pregnancy, and the placenta has increasingly become recognized as an immunological organ. Viral infections during pregnancy are associated with significant mortality and morbidity, both for the pregnant female and the developing fetus. Notably, impacts on fetal development have typically been attributed to direct viral damage to cells and tissues during the course of infection, without a deep consideration of the potential collateral damage incurred upon the activation of antiviral immune responses. In this dissertation, I characterize the contribution of the immune system and antiviral responses to pathologies of pregnancy and fetal development, using both mouse models of maternal immune activation and human studies of viral infection and immunization during the coronavirus disease 2019 (COVID-19) pandemic. First, I establish and characterize a novel model of maternal immune activation (MIA) in early pregnancy that leads to a high rate of neural tube defects (NTDs) and craniofacial abnormalities in the affected offspring. Using systemic administration of the double-stranded RNA mimic poly(I:C) to pregnant mice, I demonstrate that the activation of antiviral immune responses alone is capable of driving fetal birth defects. These phenotypes mirror human NTDs, among the most common birth defects seen worldwide. I identify key immunological pathways and factors driving pathogenesis, which is TLR3- and STAT1-dependent. Strikingly, mice deficient in γδ T cells are protected from the development of MIA-induced NTDs. Together with collaborators, I use immunofluorescence imaging and a spatial gene expression approach to show that γδ T cells are associated with laminin loss at the ectoplacental cone of the primitive placenta. I demonstrate that these changes at the maternal-fetal interface are associated with decreased proliferation of neural progenitors in the developing fetus, resulting in the failure of neural tube closure. We thus uncover a previously unrecognized role for γδ T cells at the maternal-fetal interface and novel mechanism underlying NTD pathogenesis. Next, I interrogate the impact of antiviral responses on outcomes in human pregnancy. The emergence of SARS-CoV-2 and the ongoing COVID-19 pandemic has highlighted the importance of studying the unique consequences of viral infections during pregnancy, as pregnant individuals are at much greater risk for severe COVID-19 disease than nonpregnant individuals. Working with a multidisciplinary team, I help to identify one of the first reports worldwide showing that SARS-CoV-2 is capable of infecting the placenta. I discover that SARS-CoV-2 is capable of infecting the placenta at the syncytiotrophoblast layer, the multinucleated layer of trophoblast derived from stem cell cytotrophoblasts, and that infection, while rare, is restricted to this region of the maternal-fetal interface. In pregnancies affected by asymptomatic SARS-CoV-2, the vast majority of placentas are not infected due to a robust antiviral response at the maternal-fetal interface. However, I find that this powerful antiviral defense includes a distinct inflammatory profile at the placenta that is directly associated with preeclampsia and other inflammatory disorders of pregnancy, suggesting that antiviral immunity mounted to effectively shield the fetus from viral infection may come at the price of dysregulation of the maternal-fetal interface. This observation lends insight as to why pathogens typically are not able to invade the placenta during pregnancy and how even asymptomatic or mild infections limited to the respiratory tract can lead to severe maternal outcomes at a distant organ site. Finally, I directly address some of the most prevalent vaccine misinformation encountered by the public today, including false theories that the COVID-19 mRNA vaccines cause infertility and harm developing fetuses in utero when administered in pregnancy. With a mouse model of vaccination during early pregnancy, I show that administration of the mRNA-1273 vaccine has no impact on fetal size at term and does not lead to birth defects. In contrast, poly(I:C) administration, which unlike the mRNA vaccines activates TLR3 pathways, significantly reduces crown-rump length and weight at term. I further demonstrate that mRNA-1273 vaccination even in the earliest stages of pregnancy, prior to formation of the definitive placenta, leads to high levels of protective antibodies in fetuses at term. In a large study of human volunteers, we challenge a common infertility myth by providing direct evidence that COVID-19 vaccination with either mRNA-1273 or BNT162b2 does not lead to an increase in circulating anti-syncytin-1 antibodies. Together, these contributions dispel a number of the most common vaccine rumors fueling vaccine hesitancy worldwide

A unique maternal and placental galectin signature upon SARS-CoV-2 infection suggests galectin-1 as a key alarmin at the maternal–fetal interface

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic imposed a risk of infection and disease in pregnant women and neonates. Successful pregnancy requires a fine-tuned regulation of the maternal immune system to accommodate the growing fetus and to protect the mother from infection. Galectins, a family of β-galactoside–binding proteins, modulate immune and inflammatory processes and have been recognized as critical factors in reproductive orchestration, including maternal immune adaptation in pregnancy. Pregnancy-specific glycoprotein 1 (PSG1) is a recently identified gal-1 ligand at the maternal–fetal interface, which may facilitate a successful pregnancy. Several studies suggest that galectins are involved in the immune response in SARS-CoV-2–infected patients. However, the galectins and PSG1 signature upon SARS-CoV-2 infection and vaccination during pregnancy remain unclear. In the present study, we examined the maternal circulating levels of galectins (gal-1, gal-3, gal-7, and gal-9) and PSG1 in pregnant women infected with SARS-CoV-2 before vaccination or uninfected women who were vaccinated against SARS-CoV-2 and correlated their expression with different pregnancy parameters. SARS-CoV-2 infection or vaccination during pregnancy provoked an increase in maternal gal-1 circulating levels. On the other hand, levels of PSG1 were only augmented upon SARS-CoV-2 infection. A healthy pregnancy is associated with a positive correlation between gal-1 concentrations and gal-3 or gal-9; however, no correlation was observed between these lectins during SARS-CoV-2 infection. Transcriptome analysis of the placenta showed that gal-1, gal-3, and several PSG and glycoenzymes responsible for the synthesis of gal-1-binding glycotopes (such as linkage-specific N-acetyl-glucosaminyltransferases (MGATs)) are upregulated in pregnant women infected with SARS-CoV-2. Collectively, our findings identify a dynamically regulated “galectin-specific signature” that accompanies the SARS-CoV-2 infection and vaccination in pregnancy, and they highlight a potentially significant role for gal-1 as a key pregnancy protective alarmin during virus infection

Tracking smell loss to identify healthcare workers with SARS-CoV-2 infection

Introduction Healthcare workers (HCW) treating COVID-19 patients are at high risk for infection and may also spread infection through their contact with vulnerable patients. Smell loss has been associated with SARS-CoV-2 infection, but it is unknown whether monitoring for smell loss can be used to identify asymptomatic infection among high risk individuals. In this study we sought to determine if tracking smell sensitivity and loss using an at-home assessment could identify SARS-CoV-2 infection in HCW. Methods and findings We performed a prospective cohort study tracking 473 HCW across three months to determine if smell loss could predict SARS-CoV-2 infection in this high-risk group. HCW subjects completed a longitudinal, behavioral at-home assessment of olfaction with household items, as well as detailed symptom surveys that included a parosmia screening questionnaire, and real-time quantitative polymerase chain reaction testing to identify SARS-CoV-2 infection. Our main measures were the prevalence of smell loss in SARS-CoV-2-positive HCW versus SARS-CoV- 2-negative HCW, and timing of smell loss relative to SARS-CoV-2 test positivity. SARS-CoV-2 was identified in 17 (3.6%) of 473 HCW. HCW with SARS-CoV-2 infection were more likely to report smell loss than SARS-CoV-2-negative HCW on both the at-home assessment and the screening questionnaire (9/17, 53% vs 105/456, 23%, P < .01). 6/9 (67%) of SARS-CoV-2-positive HCW reporting smell loss reported smell loss prior to having a positive SARS-CoV-2 test, and smell loss was reported a median of two days before testing positive. Neurological symptoms were reported more frequently among SARS-CoV-2-positive HCW who reported smell loss compared to those without smell loss (9/9, 100% vs 3/8, 38%, P < .01). Conclusions In this prospective study of HCW, self-reported changes in smell using two different measures were predictive of SARS-CoV-2 infection. Smell loss frequently preceded a positive test and was associated with neurological symptoms

Gut Microbiome Dysbiosis in Antibiotic-Treated COVID-19 Patients is Associated with Microbial Translocation and Bacteremia

Although microbial populations in the gut microbiome are associated with COVID-19 severity, a causal impact on patient health has not been established. Here we provide evidence that gut microbiome dysbiosis is associated with translocation of bacteria into the blood during COVID-19, causing life-threatening secondary infections. We first demonstrate SARS-CoV-2 infection induces gut microbiome dysbiosis in mice, which correlated with alterations to Paneth cells and goblet cells, and markers of barrier permeability. Samples collected from 96 COVID-19 patients at two different clinical sites also revealed substantial gut microbiome dysbiosis, including blooms of opportunistic pathogenic bacterial genera known to include antimicrobial-resistant species. Analysis of blood culture results testing for secondary microbial bloodstream infections with paired microbiome data indicates that bacteria may translocate from the gut into the systemic circulation of COVID-19 patients. These results are consistent with a direct role for gut microbiome dysbiosis in enabling dangerous secondary infections during COVID-19

Sex differences in immune responses that underlie COVID-19 disease outcomes

There is increasing evidence that coronavirus disease 2019 (COVID-19) produces more severe symptoms and higher mortality among men than among women1,2,3,4,5. However, whether immune responses against severe acute respiratory syndrome coronavirus (SARS-CoV-2) differ between sexes, and whether such differences correlate with the sex difference in the disease course of COVID-19, is currently unknown. Here we examined sex differences in viral loads, SARS-CoV-2-specific antibody titres, plasma cytokines and blood-cell phenotyping in patients with moderate COVID-19 who had not received immunomodulatory medications. Male patients had higher plasma levels of innate immune cytokines such as IL-8 and IL-18 along with more robust induction of non-classical monocytes. By contrast, female patients had more robust T cell activation than male patients during SARS-CoV-2 infection. Notably, we found that a poor T cell response negatively correlated with patients’ age and was associated with worse disease outcome in male patients, but not in female patients. By contrast, higher levels of innate immune cytokines were associated with worse disease progression in female patients, but not in male patients. These findings provide a possible explanation for the observed sex biases in COVID-19, and provide an important basis for the development of a sex-based approach to the treatment and care of male and female patients with COVID-19