1 14-02-2020; 20-02-2020 to 20-02-2021 0Not recruiting ChiCTR2000029812;http://www.chictr.org.cn/showproj.aspx?proj=49374 Clinical study for umbilical cord blood mononuclear cells in the treatment of acute novel coronavirus pneumonia (COVID-19) UCBMCs 60 Experimental group: conventional treatment followed by i.v. UCBMC preparationsControl group: conventional treatment