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
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: This work was made
possible by an MRC / UKRI COVID-19 Rapid response initiative grant