Human Placenta-Derived Adherent Stem Cells Prevent Bone Loss and Stimulate Bone Formation in Myelomatous Bones, and Suppress Growth of Primary Multiple Myeloma
Authors: Li Xin , Ling Wen , Pennisi Angela , Chen Jianmei , Khan Sharmin , Heidaran Mohammad , Faleck Herbert , Hariri Robert , Shaughnessy John , van Rhee Frits , Epstein Joshua , Barlogie Bart , Yaccoby Shmuel 
Published: October 2019

Abstract
Induction of osteolytic bone disease in multiple myeloma (MM) is caused by activation of osteoclastogenesis and suppression of osteoblastogenesis. Bone formation is reduced mainly through production of inhibitors of osteoblast differentiation by MM cells and by impaired osteogenic differentiation of endogenous mesenchymal stem cells (MSCs). Recently, human placenta has emerged as a potentially valuable source of progenitor cells for multiple therapeutic purposes, including bone repair and cancer (Parolini et al., Stem Cells26:300–311, 2008). The aim of the study was to investigate the effects of human placenta-derived adherent cells (PDAC™) on MM bone disease and tumor growth in the SCID-rab mouse model for MM. PDAC™ are mesenchymal like adherent cells isolated from postpartum human placenta and capable of supporting bone formation in vivo. Bone disease was evaluated by measurements of bone mineral density (BMD) and visualized by X-rays. MM growth was determined by human immunoglobulin (hIg) ELISA and live animal imaging. For in vivo tracking PDAC™ or our stroma-dependent BN MM cell line was transduced with a luciferase/GFP reporter in a lentiviral vector. In the first in vivo experiment, 10 SCID-rab mice were engrafted with a patient’s MM cells. Following establishment of MM and detection of bone disease, luciferase-expressing PDAC™ (1×106 cells/bone) or phosphate-buffered saline (PBS) were injected directly into implanted myelomatous bones in SCID-rab mice (5 mice/group). At experiment’s end (5 wk after cytotherapy) PDAC™ could be detected in mice by live animal imaging. Whereas in control mice, BMD of the implanted bone was reduced from pretreatment levels by 8±4%, administration of PDAC™ resulted in increased BMD of the implanted bone in all mice by 132±20% from pretreatment levels (p<0.0006). Levels of hIg in mice sera (tumor burden) at experiment’s end were 202±56 μg/ml and 12±4 μg/ml in PBS- and PDAC™ -treated hosts, respectively (p<0.007). In the second in vivo experiment hosts engrafted with our luciferase-expressing BN MM line (Li et al., BJH 2007) were similarly injected with PDAC™ or PBS (8 mice/group). Six wk following treatment the BMD of the implanted bone in the control PBS group was reduced by 31±33% (p<0.0009) from pretreatment levels while in PDAC™ –treated group it was slightly reduced by 2±6% from pretreatment levels. Treatment with PDAC™ had no effect on in vivo growth of the BN MM cell line, indicating that prevention of bone disease by PDAC™ was not a consequence of reduced MM. In contrast to fetal MSCs, PDAC™ expressed high levels of OPG (>30 fold) and low levels of RANKL (<5 fold) as determined by qRT-PCR. Differentiation of osteoclast precursors in media supplemented with RANKL and M-CSF was reduced in the presence of PDAC™ or their conditioned media by 60±6% (p<0.004), an effect that was partially blocked by OPG neutralizing antibody (p<0.04). PDAC™ also induced apoptosis of osteoclast precursors as determined by annexin V/PI staining. We conclude that PDAC™ prevent bone loss and promote bone formation in myelomatous bone through simultaneous inhibition of osteoclastogenesis and stimulation of osteoblastogenesis, and that engraftment of PDAC™ inhibits growth of primary MM in vivo.