Low immunogenicity of allogeneic human umbilical cord blood-derived mesenchymal stem cells in vitro and in vivo.

•hUCB-MSCs maintained low immunogenicity even after immune challenge in vitro.•Humanized NSG mice were established using human UCB CD34+ cells.•Repeated intravenous hUCB-MSC injection into mice did not lead to immune responses and adverse events.•Allogeneic hUCB-MSCs maintained low immunogenicity in vitro and in vivo.