We tested 12 patient-derived xenografts (PDX) obtained from four human T-ALL samples and found that leukemic cells carry the CD44 standard isoform (Supplementary Fig. 5A), which is expressed at higher levels in cells from BMAT-rich/tail vertebrae compared with BMAT-poor BM (Fig. 2E). Here, CD44 is linked to acute lymphoblastic leukemia.