Funding for this research was provided by:
National Research Foundation of Korea (2020R1I1A1A01063168)
Received: 14 February 2021
Accepted: 22 April 2021
First Online: 6 May 2021
: Human placentas were obtained from two donors with approval from the Institutional Review Board (KUGH14239–002) of Korea University Guro Hospital, South Korea.
: Not applicable.
: The authors declare that they have no competing interests.