BM-stromal (BM-S) myofibroblasts support leukemia cell functions[2], [3] and tumor-stimulated BM endothelium (BM-EC) promotes the survival of primary leukemia cells,[6] with BM endothelial microdomains functioning as niches for leukemia cell maintenance.[33] Since BAFF and APRIL can promote malignant cell survival and proliferation in mature B-cell tumors developing in the BM,[31] we investigated the expression of BAFF-system transcripts in BM-EC (n = 5), mesenchymal stem cells (MSC; n = 4) and BM-S (n = 5). Here, TNFSF13 is linked to leukemia.