Human placental cells are resistant to SARS-CoV-2 infection and replication

Abstract

Background Infection during pregnancy with SARS-CoV-2 can have a serious impact on both maternal and foetal health. Clinical studies have shown that SARS-CoV-2 transmission from the mother to the foetus typically does not occur. However, there is evidence that SARS-CoV-2 can infect the placenta in utero. Here we sought to quantify the permissiveness of placental cells to SARS-CoV-2 infection and to determine if they support viral release. Methods By using publicly available single-cell RNA sequencing (scRNAseq) data sets and confocal microscopy we compared ACE2 transcript and protein expression across human first trimester and term placental cells. ACE2 transcripts are found in a range of placental cell types across gestation, including trophoblast. However, ACE2 protein expression does not significantly change across placental cell types from first trimester to term. Results Using in vitro infection assays, we demonstrate that 0.5±0.15 % of term trophoblast cells can be infected with SARS-CoV-2 while primary placental fibroblasts and macrophages, and JEG-3, JAR and HUVEC cell lines are resistant to infection. Furthermore, primary trophoblast cells poorly support viral release while JEG-3 cells allow relatively high levels of viral release. Conclusions The low level of viral release by primary placental cells provides insight into how the virus is impaired from crossing the placenta to the foetus.