COVID-19 and Vertical Transmission: Assessing the Expression of ACE2 / TMPRSS2 in the Human Fetus and Placenta to Assess the Risk of SARS-CoV-2 Infection

Background: While pregnant women have been identified as a potentially at-risk group concerning COVID-19 infection, little is known regarding the susceptibility of the fetus to infection. Co-expression of ACE2 and TMPRSS2 has been identified as a pre-requisite for infection, and expression across different tissues is known to vary between children and adults. However, the expression of these proteins in the fetus is unknown.Methods: We performed a retrospective analysis of single cell data repositories. This data was then validated at both gene and protein level by performing qRT-PCR and two-colour immunohistochemistry on a library of second-trimester human fetal tissues.Findings: TMPRSS2 is present at both gene and protein level in the predominantly epithelial fetal tissues analysed. ACE2 is present at significant levels, only in the fetal intestine and kidney and is not expressed in the fetal lung. The placenta is also negative for the two proteins both during development and at term.Interpretation: This dataset indicates that the lungs are unlikely to be a viable route of SARS-CoV2 fetal infection. The fetal kidney, despite presenting both the proteins required for the infection, is anatomically protected from the exposure to the virus. However, the GI tract is likely to be susceptible to infection due to its high co-expression of both proteins, as well as its exposure to potentially infected amniotic fluid.Funding Information: This work was made possible by an MRC / UKRI COVID-19 Rapid response initiative grant (MR/V028480/1).Declaration of Interests: The authors declare no conflicts of interest related to this work or its developments. DC is founder, shareholder, and consultant of Next Generation Diagnostic SRL.Ethics Approval Statement: Human fetal tissues were obtained with consent through the Human Developmental Biology Resource (HDBR; REC 18/LO/0822 – IRAS 244325; Project ID 2000478). Placental samples were obtained at delivery of an uncomplicated, full-term pregnancy (median 39 weeks PCW [Range 38+1 -39+4] for 6 patients recruited through the EVERREST Prospective Study as normal controls (National Research Ethics reference 13/LO/1254), NCT02097667 registered 31st October 2013[10].