Is There an Effect of Fetal Mesenchymal Stem Cells in the Mother–Fetus Dyad in COVID-19 Pregnancies and Vertical Transmission?
Because of the polysystemic nature of coronavirus disease 2019 (COVID-19), during the present pandemic, there have been serious concerns regarding pregnancy, vertical transmission, and intrapartum risk. The majority of pregnant patients with COVID-19 infection present with mild or asymptomatic course of the disease. Some cases were hospitalized, and few needed intensive care unit admission, or mechanical ventilation.
There have also been scarce case reports where neonates required mechanical ventilation post COVID-19 pregnancies. Without approved therapies other than dexamethasone, advanced mesenchymal cell therapy is one immunomodulatory therapeutic approach that is currently explored and might hold great promise. We suggest that the circulating fetal stem cells might have an immune-protective effect to mothers and contribute to the often mild and even asymptomatic post-COVID-19 pregnancies. Thus, COVID-19 pregnancies come forth as a paradigm to be further and more comprehensively approached, to understand both the mechanism and action of circulating stem cells in immunoprotection and hypoxia in microcirculation.
Maternal–fetal transmission of viral diseases may occur transvaginally or through the hematogenic, i.e., the transplacental transmission pathway. In the latter, the virus circulating in the maternal blood vessels may reach and enter the placenta across chorionic villous and non-villous structures fetal blood vessels and be transmitted to the fetus. This mechanism of vertical transmission was not reported after the infection of pregnant women with the coronaviruses, severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1) and Middle East respiratory syndrome coronavirus (MERS-CoV). Despite the fact that pregnant women may be infected by these coronaviruses other than severe pneumonia, they may face complications such as early pregnancy loss or even death (Schwartz and Graham, 2020).
The uterine enlargement during pregnancy is known to bring major changes in maternal physiology. These can be both mechanical, such as reduced functional residual volumes and diaphragm elevation, and cellular, such as altered cellular immunity. The maternal immune system may tolerate fetal antigens suppressing cell-mediated immunity while retaining normal humoral immunity, changes known to occur locally at the maternal–fetal interface, which could affect systemic immune responses to infection (Jamieson et al., 2006). This may render pregnant women more vulnerable to viral infections, especially in cases where the infections may have an effect on the cardiorespiratory system during pregnancy and could enhance progression to respiratory failure (Dashraath et al., 2020). The ability to increase ventilation is reduced, when pregnant. Therefore, there is an increased risk of inadequate response to environmental stressors such as upper/lower respiratory tract infections and hypoxic and hypercapnic respiratory failure (Lapinsky et al., 2014). During the SARS epidemic, up to 35% of the infected pregnant patients required mechanical ventilation, and mortality rates reached 18%; in the case of MERS, the numbers reached 41 and 25%, respectively (Dashraath et al., 2020; Liu et al., 2020; Schwartz and Graham, 2020).