Mesenchymal Stem Cell Deficiencies in Myeloma Patients.

Progression of Multiple Myeloma (MM) is associated with disrupted bone remodelling resulting from increased osteoclast activity and reduced osteoblast number in involved bones. The aim of this study was to investigate Mesenchymal Stem Cells (MSCs) properties in MM patients to find out whether disorders exist within the Bone Marrow (BM) microenvironment and during disease progression. We examined MSCs derived from 6 MM patients at diagnosis, 3 patients with Bone Lesions (BL-MSCs) and 3 patients Without Lesions (WL-MSCs), and 3 Normal Donors (ND-MSCs). We focused on mesenchymal phenotype, clonogenic and proliferative capacities, Growth Factor Receptors (GF-R) expression, as well as osteogenic differentiation. BM adherent mononuclear cells were used to initiate MSC cultures and 2 passages were performed when confluency was reached. Adherent MSCs were numbered after each passage and CFU-F was counted (at 11 day culture). Analysis of MSC immunophenotype and GF-R expression were performed by flow cytometry. Osteoblastic differentiation assay was performed in inducible specific medium by analysing alkaline phosphatase activity and matrix mineralisation deposition (Von Kossa method). MSCs represented 0.1 to 1% of BM nuclear cells from all sources. The characteristic MSC phenotype (CD45⁻/CD90⁺/CD73⁺/CD105⁺) was observed in all sources of cells (MM- and ND-MSCs). The clonogenic capacity of BL-MSCs was 2 fold lower than that of WL-MSCs (44 ± 21 vs 89 ± 23, p = 0.05) and their proliferative capacity was 7.5 fold decreased (16,5 x 10⁶ ± 15 vs 124 x 10⁶ ± 68, p = 0.02, total cells after 2 passages). Expression level of PDGFa & b, IGF-1, EGF and NGF Receptors was lower in MM-MSCs than in ND-MSCs (185 ± 39 vs 413 ± 50 UA, p = 0.0004, 212 ± 63 vs 383 ± 143 UA, p = 0.01, 227 ± 50 vs 534 ± 67 UA, p = 0.0007, 229 ± 34 vs 535 ± 84 UA, p = 0.0001 and 179 ± 26 vs 441 ± 98 UA, p = 0.001, respectively), while the percentage of FGF receptor-expressing cells was dramatically decreased in MM as compared to ND (59 ± 31.5 vs 90 ± 6 %, p = 0.01). Interestingly, the osteogenic differentiation capacity of MSCs was maintained in MM-MSCs whatever the progression status of the disease. This study demonstrates that impaired bone formation in MM could be related to a deficient proliferation capacity of MSCs associated with a low growth factor receptors expression. The lack of expansion capacity increases with disease progression. Therapeutic approaches using normal expanded MSCs grafts may improve bone reconstruction in myeloma patients.