Here we describe the specific steps used on PDX-ALL cells in co-culture with human MSC (CD105+CD90+CD73+CD45- MSCs, that can differentiate into osteoblasts, adipocytes and chondrocytes), and label PDX-ALL cells in vitro with CellTrace Violet, and Hoechst-33342 and Pyronin Y staining to determine cell cycling and quiescence. Here, THY1 is linked to acute lymphoblastic leukemia.