Coronavirus disease 2019 (COVID-19) is an illness caused by a novel coronavirus, now called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Such virus canonically utilizes the angiotensin-converting enzyme 2 (ACE2) receptor and the serine protease TMPRSS2 for cell entry. Therefore, cells that co-express ACE2 and TMPRSS2 (such as those found in the lungs) are particularly vulnerable to infection.
PRB researchers employed single-cell genomics to investigate the expression of ACE2 and TMPRSS2 throughout pregnancy in the placenta, as well as in third trimester chorioamniotic membranes. The team reported that co-transcription of ACE2 and TMPRSS2 is negligible in the placenta, thus not a likely path of vertical transmission for SARS-CoV-2 from mother to fetus. In contrast, receptors for Zika virus and cytomegalovirus (both of which cause congenital infections) are highly expressed by placental cell types. The team also showed that SARS-CoV-2 receptors are not expressed by the chorioamniotic membranes in the third trimester. While the study allows the possibility that SARS-CoV-2 could infect the placenta via alternate entry routes while interacting with other proteins, the findings provide strong evidence that it is unlikely to infect the placenta and fetus through the traditional cell entry mediators.