No abstract

Multiple Myeloma (MM) is a systemic hematologic disease due to uncontrolled proliferation of monoclonal plasma cells (PC) in bone marrow (BM). Emerging in other solid and liquid cancers, the host immune system and the microenvironment have a pivotal role for PC growth, proliferation, survival, migration, and resistance to drugs and are responsible for some clinical manifestations of MM. In MM, microenvironment is represented by the cellular component of a normal bone marrow together with extracellular matrix proteins, adhesion molecules, cytokines, and growth factors produced by both stromal cells and PC themselves. All these components are able to protect PC from cytotoxic effect of chemo- and radiotherapy. This review is focused on the role of immunome to sustain MM progression, the emerging role of myeloid derived suppressor cells, and their potential clinical implications as novel therapeutic target.

Human bone marrow mesenchymal stem cells (MSCs) are pleiotrophic cells that differentiate to either adipocytes or osteoblasts as a result of crosstalk by specific signaling pathways including heme oxygenase (HO)-1/-2 expression. We examined the effect of inducers of HO-1 expression and inhibitors of HO activity on MSC differentiation to the osteoblast and following high glucose exposure. MSC cultured in osteogenic medium increased expression of osteonectin, Runt-related transcription factor 2 (RUNX-2), osteocalcin, and alkaline phosphatase. HO-1 expression during differentiation was initially decreased and then followed by a rebound increase after 15 days of culture. Additionally, the effect of HO-1 on osteoblasts appears different to that seen in adipocyte stem cells. On addition of a cobalt compound, the resultant induction of HO-1 decreases adipogenesis. Moreover, glucose (30 mM) inhibited osteoblast differentiation, as evidenced by decreased bone morphogenetic protein (BMP)-2, osteonectin, osteocalcin, and osteoprotegerin (OPG). In contrast, MSC-derived adipocytes were increased by glucose. Increased HO-1 expression increased the levels of osteonectin, OPG, and BMP-2. Inhibition of HO activity prevented the increase in osteonectin and potentiated the decrease of osteocalcin and OPG in cells exposed to high glucose levels. Furthermore, targeting HO-1 expression increased pAMPK and endothelial nitric oxide synthase (eNOS) and restored osteoblastic markers. Our findings suggest that targeting HO-1 gene expression attenuates the hyperglycemia-mediated decrease in MSC-derived osteoblast differentiation. Finally, the mechanism underlying the HO-1-specific cell effect on osteoblasts and adipocytes is yet to be explored. Thus, the targeting of HO-1 gene expression presents a portal to increase osteoblast function and differentiation and attenuate osteoporosis by promoting bone formation.

SummaryIn the attempt to find a peripheral blood biological marker that could mirror the dysregulated microenvironment of Hodgkin Lymphoma (HL), we analysed the amount of myeloid-derived suppressor cells (MDSC), including the three main sub-types (monocytic, granulocytic and CD34 + fraction). The absolute MDSC count was investigated in 60 consecutive newly diagnosed HL patients and correlated with clinical variables at diagnosis and outcome. Patients received standard-of-care chemotherapy with the exception of interim fluorodeoxyglucose positron emission tomography (PET-2)-positive patients, who were switched early to a salvage regimen. All MDSC subsets were increased in HL patients compared to normal subjects (P < 0Á0001) and were higher in non-responders. However, a strong prognostic significance was limited to immature (CD34 + ) MDSC. A cut-off level of 0Á0045 9 10 9 /l for CD34 + MDSC resulted in 89% (95% confidence interval [CI] 52-99%) sensitivity and 92% (95% CI 81-98%) specificity. The positive predictive value to predict progression-free survival was 0Á90 for PET-2 and 0Á98 for CD34 + MDSC count; the negative predictive value was 0Á57 for PET-2 and 0Á73 for CD34 + MDSC. PFS was significantly shorter in patients with more than 0Á0045 9 10 9 CD34 + MDSC cells/l at diagnosis and/or PET-2 positivity (P < 0Á0001). In conclusion, all circulating MDSC subsets are increased in HL; CD34 + MDSC predict short PFS, similarly to PET-2 but with the advantage of being available at diagnosis.

Granulocytic-Myeloid-derived suppressor cells (G-MDSC) are increased in Multiple Myeloma (MM) patients but the mechanisms of G-MDSC generation are still unknown. There are many evidences of the role of mesenchymal stem cells (MSC) in promoting MM cell growth, survival and drug-resistance. We here used a specific experimental model in vitro to evaluate the ability of MSC to induce G-MDSC. We found that although MSC derived from healthy donors (HD), MGUS and MM were able to generate the same amount of MDSC, only MM-MSC-educated G-MDSC exhibited suppressive ability. In addition, in comparison with MSC derived from HD, MM-MSC produce higher amount of immune-modulatory factors that could be involved in MDSC induction. Compared to G-MDSC obtained from co-culture models with MSC from healthy subjects, both MGUS and MM-MSC-educated G-MDSC showed increase of immune-modulatory factors. However, only MM-MSC educated G-MDSC 1) up-regulated immune-suppressive factors as ARG1 and TNFα, 2) expressed higher levels of PROK2, important in angiogenesis and inflammatory process, and 3) showed ability to digest bone matrix.Our data demonstrate that MM-MSC are functionally different from healthy subjects and MGUS-MSC, supporting an evolving concept regarding the contribution of MM-MSC to tumor development and progression.

Tumor immune tolerance can derive from the recruitment of suppressor cell population, including myeloid derived suppressor cells (MDSCs), able to inhibit T cells activity. We identified a significantly expanded MDSCs population in chronic myeloid leukemia (CML) patients at diagnosis that decreased to normal levels after imatinib therapy. In addition, expression of arginase 1 (Arg1) that depletes microenvironment of arginine, an essential aminoacid for T cell function, resulted in an increase in patients at diagnosis. Purified CML CD11b+CD33+CD14-HLADR- cells markedly suppressed normal donor T cell proliferation in vitro. Comparing CML Gr-MDSCs to autologous polymorphonuclear leukocytes (PMNs) we observed a higher Arg1 expression and activity in PMNs, together with an inhibitory effect on T cells in vitro. Our data indicate that CML cells create an immuno-tolerant environment associated to MDSCs expansion with immunosuppressive capacity mediated by Arg1. In addition, we demonstrated for the first time also an immunosuppressive activity of CML PMNs, suggesting a strong potential immune escape mechanism created by CML cells, which control the anti-tumor reactive T cells. MDSCs should be monitored in imatinib discontinuation trials to understand their importance in relapsing patients.

Identification of imatinib mesylate as a potent inhibitor of the Abl kinase and the subsequent findings that this compound displays growth inhibitory and pro-apoptotic effects in Bcr-Abl+ cells, has deeply conditioned CML treatment. Unfortunately the initial striking efficacy of this drug has been overshadowed by the development of clinical resistance. A wide variety of molecular mechanisms can underlie such resistance mechanisms. In the recent years, heme oxygenase-1 (HO-1) expression has been reported as an important protective endogenous mechanism against physical, chemical and biological stress and this cytoprotective role has already been demonstrated for several solid tumors and acute leukemias. The aim of the present study was to investigate the effect of HO-1 expression on cell proliferation and apoptosis in chronic myeloid leukemia cells, K562 and LAMA-84 cell lines following imatinib treatment. Cells were incubated for 24h with Imatinib (1 μM) alone or in combination with Hemin (10μM), an inducer of HO-1. In addition, cells were also treated with HO byproducts, bilirubin and carbon monoxide (CO), or with a protease inhibitor (Ed64) to inhibit HO-1 nuclear translocation. Pharmacological induction of HO-1 was able to overcome the effect of imatinib. The cytoprotective effect of HO-1 was further confirmed after silencing HO-1 by siRNA. Interestingly, neither bilirubin nor CO was able to protect cells from Imatinib-induced toxicity. By contrast, the protective effect of HO-1 was mitigated by the addition of E64d, preventing HO-1 nuclear translocation. Finally, imatinib was able to increase the formation of cellular reactive oxygen species (ROS) and this effect was reversed by HO-1 induction or the addition of N-acetylcisteine (NAC). In conclusion, the protective effect of HO-1 on imatinib-induced cytotoxicity does not involve its enzymatic byproducts, but rather the nuclear translocation of HO-1 following proteolytic cleavage.

The Low-Affinity Nerve Growth Factor Receptor (LNGFR), also known as CD271, is a member of the tumor necrosis factor receptor superfamily. The CD271 cell surface marker defines a subset of multipotential mesenchymal stromal cells and may be used to isolate and enrich cells derived from bone marrow aspirate. In this study, we compare the proliferative and differentiation potentials of CD271+ and CD271− mesenchymal stromal cells. Mesenchymal stromal cells were isolated from bone marrow aspirate and adipose tissue by plastic adherence and positive selection. The proliferation and differentiation potentials of CD271+ and CD271− mesenchymal stromal cells were assessed by inducing osteogenic, adipogenic and chondrogenic in vitro differentiation. Compared to CD271+, CD271− mesenchymal stromal cells showed a lower proliferation rate and a decreased ability to give rise to osteocytes, adipocytes and chondrocytes. Furthermore, we observed that CD271+ mesenchymal stromal cells isolated from adipose tissue displayed a higher efficiency of proliferation and trilineage differentiation compared to CD271+ mesenchymal stromal cells isolated from bone marrow samples, although the CD271 expression levels were comparable. In conclusion, these data show that both the presence of CD271 antigen and the source of mesenchymal stromal cells represent important factors in determining the ability of the cells to proliferate and differentiate.