The availability of three COVID-19 vaccines in the United States provides an unprecedented opportunity to examine how vaccine platforms and timing of vaccination in pregnancy impact maternal and neonatal immunity. Here, we characterize the antibody profile after Ad26.COV2.S, mRNA-1273 or BNT162b2 vaccination in 158 pregnant individuals and evaluate transplacental antibody transfer by profiling maternal and umbilical cord blood in 175 maternal-neonatal dyads. These analyses reveal lower vaccine-induced functions and Fc receptor-binding after Ad26.COV2.S compared to mRNA vaccination and subtle advantages in titer and function with mRNA-1273 versus BN162b2. mRNA vaccines have higher titers and functions against SARS-CoV-2 variants of concern. First and third trimester vaccination results in enhanced maternal antibody-dependent NK-cell activation, cellular and neutrophil phagocytosis, and complement deposition relative to second trimester. Higher transplacental transfer ratios following first and second trimester vaccination may reflect placental compensation for waning maternal titers. These results provide novel insight into the impact of platform and trimester of vaccination on maternal humoral immune response and transplacental antibody transfer.

The SARS-CoV-2 virus activates maternal and placental immune responses, which in the setting of other infections occurring during pregnancy are known to impact fetal brain development. The effects of maternal immune activation on neurodevelopment are mediated at least in part by fetal brain microglia. However, microglia are inaccessible for direct analysis, and there are no validated non-invasive surrogate models to evaluate in utero microglial priming and function. We have previously demonstrated shared transcriptional programs between microglia and Hofbauer cells (HBCs, or fetal placental macrophages) in mouse models. Here, we assessed the impact of maternal SARS-CoV-2 on HBCs isolated from term placentas using single-cell RNA-sequencing. We demonstrated that HBC subpopulations exhibit distinct cellular programs, with specific subpopulations differentially impacted by SARS-CoV-2. Assessment of differentially expressed genes implied impaired phagocytosis, a key function of both HBCs and microglia, in some subclusters. Leveraging previously validated models of microglial synaptic pruning, we showed that HBCs isolated from placentas of SARS-CoV-2 positive pregnancies can be transdifferentiated into microglia-like cells, with altered morphology and impaired synaptic pruning behavior compared to HBC models from negative controls. These findings suggest that HBCs isolated at birth can be used to create personalized cellular models of offspring microglial programming.

Cited2 is a transcriptional regulator essential for embryonic development and cellular homeostasis. Studies in vertebrate models highlight its critical roles in heart, placental, neural tube, and hematopoietic development. In humans, CITED2 variants are associated with congenital heart disease. Functionally, Cited2 interacts with the transcriptional co-regulators p300/CBP and modulates the activity of multiple transcription factors. In embryonic stem cells (ESC), Cited2 supports pluripotency, self-renewal, and differentiation potential. Here, we performed comparative transcriptomic analysis after acute Cited2 depletion in mouse ESC to define its role in maintaining self-renewal, lineage competence, and cell survival. Loss of Cited2 rapidly destabilized the pluripotency network and induced aberrant activation of developmental gene programs. Nodal/Activin pathway targets, including key regulators of mesoderm, cardiac, and neural development, were markedly downregulated, consistent with Cited2-null embryonic phenotypes. Cited2 depletion also altered the expression of genes involved in DNA damage response, immune signaling, and apoptosis, correlating with the increased γH2AX accumulation and decreased cell viability at least in part involving p53. Comparison with p300-, CBP-, and Cited2-depletion datasets revealed only partial overlap between affected gene sets. These results position Cited2 as a core regulator preserving ESC identity, genomic stability, and proper lineage engagement during early differentiation.