Melphalan and bortezomib affect the hematopoietic, but not the stromal, compartment of rBM. (A-D) MM BMCs were grown in 3-D for 14 days and treated with melphalan or bortezomib (“Preclinical drug treatment studies”). (A) The reduction of the clonal cells was measured by RQ-PCR with patient specific primers (melphalan, P = .016; bortezomib, P = .033; n = 5 individually analyzed patients). (B) Apoptosis within rBM was assessed by flow cytometry measuring annexin V reactivity after treatment with melphalan (left panel) or bor-tezomib (middle panel). MM specific cell killing by bor-tezomib was monitored in the CD138⁺/CD56⁺ population by annexin V reactivity (right panel; n = 5 individually analyzed patients). Error bars represent SEM. (C) rBM was grown and treated with melphalan as in panel A. Cell kill was monitored by brightfield microscopy (original magnification 200×; see “Microscopy”). Representative images from 5 individually analyzed patients. (D) The rBM layer was removed, and the cells at rEnd were stained with TRAP (osteoclasts), Oil Red (adipocytes), and ALP (osteoblasts). Brightfield microscopy (original magnification 200×; see “Immunohistochemistry”). Representative images from 5 individually analyzed patients.