Single-cell immunophenotyping of the fetal immune response to maternal SARS-CoV-2 infection

During the COVID-19 pandemic, thousands of pregnant women have been infected with SARS-CoV-2 worldwide. The short- and long-term implications of maternal SARS-CoV-2 infection on fetal and childhood well-being are unknown. To characterize the fetal immune response to maternal SARS-CoV-2 infection, we performed single-cell RNA sequencing and T cell receptor sequencing on cord blood mononuclear cells from infants born to mothers infected with SARS-CoV-2 in the third trimester. We identified widespread gene expression changes in cord blood leukocytes, including upregulation of interferon-stimulated genes (ISG) and of HLA genes in CD14+ monocytes; decreased activation of CD16+ monocytes; activation of plasmacytoid dendritic cells; and activation and exhaustion of NK cells and T CD8+ cells in the cord blood of infants born to SARS-CoV-2+ mothers.  Lastly, we observed fetal TCR repertoire clonal expansion in cord blood T cells from pregnancies complicated by maternal SARS-CoV-2 infection. Our results suggest that even in the absence of vertical transmission, SARS-CoV-2 maternal infection in the third trimester modulates the fetal immune system. Single-cell RNA-seq of cord blood mononuclearcells from COVID-positive and COVID-negative pregnancies, as well as T-cell receptor repertoire sequencing from the same samples