CD34 and breast cancer: PD-L1 expression was immunohistochemically analyzed in an in vivo model based on NOD-scid IL2Rγnull (NSG) mice that were transplanted with human BC cell lines (MDA-MB-231, BT-474, SK-BR-3, and JIMT-1) with or without a simultaneous intrahepatic transplantation of CD34+ hematopoietic stem cells.