Adipose stromal cells mediated switching of the pro-inflammatory profile of M1-like macrophages is facilitated by PGE2: in vitro evaluation.

OBJECTIVE: To define if adipose mesenchymal stromal cell (ASC) treatment mediated switching of the pro-inflammatory profile of M1-like macrophages as a means to develop a tailored in vitro efficacy/potency test. DESIGN: We firstly performed immunohistochemical analysis of CD68, CD80 (M1-like) and CD206 (M2-like) macrophages in osteoarthritic (OA) synovial tissue. ASC were co-cultured in contact and in transwell with activated (GM-CSF + IFNγ)-M1 macrophages. We analyzed IL1ß, TNFα, IL6, MIP1α/CCL3, S100A8, S100A9, IL10, CD163 and CD206 by qRT-PCR or immunoassays. Prostaglandin E2 (PGE2) blocking experiments were performed using PGE2 receptor antagonist. RESULTS: In moderate grade OA synovium we did not always find a higher percentage of CD80 with respect to CD206. M1-like-activated macrophage factors IL1ß, TNFα, IL6, MIP1α/CCL3, S100A8 and S100A9 were down-modulated both in contact and in transwell by ASC. However, in both systems ASC induced the typical M2-like macrophage markers IL10, CD163 and CD206. Activated-M1-like macrophages pre-treated with PGE2 receptor antagonist failed to decrease secretion of TNFα, IL6 and to increase that of IL10, CD163 and CD206 when co-cultured with ASC confirming a PGE2 specific role. CONCLUSIONS: We demonstrated that ASC are responsible for the switching of activated-M1-like inflammatory macrophages to a M2-like phenotype, mainly through PGE2. This evidenced that activated-M1-like macrophages may represent a relevant cell model to test the efficacy/potency of ASC and suggests a specific role of ASC as important determinants in therapeutic dampening of synovial inflammation in OA.

Lack of anti-inflammatory and anti-catabolic effects on basal inflamed osteoarthritic chondrocytes or synoviocytes by adipose stem cell-conditioned medium.

OBJECTIVE: To define whether good manufacturing practice (GMP)-clinical grade adipose stem cell (ASC)-derived conditioned medium (CM) is as effective as GMP-ASC in modulating inflammatory and catabolic factors released by both osteoarthritis (OA) chondrocytes or synoviocytes. METHODS: OA chondrocytes and synoviocytes were treated with ASC-CM or co-cultured with ASC. Inflammatory factors (IL6, CXCL1/GROα,CXCL8/IL8, CCL2/MCP-1, CCL3/MIP-1α and CCL5/RANTES) and proteinases, such as metalloproteinase (MMP13), a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS4, ADAMTS5) and their tissue metalloproteinase inhibitors (TIMP1, TIMP3) were evaluated by qRT-PCR or immunoassays. The involvement of prostaglandin E2 (PGE2) was also analyzed. RESULTS: Most ASC-CM ratios tested did not decrease IL6, CCL2/MCP-1, CCL3/MIP1-α, CCL5/RANTES on basal inflamed chondrocytes or synoviocytes in contrast to what we found using ASC in co-culture. CXCL8/IL8 and CXCL1/GROα were not decreased by ASC-CM on synoviocytes but were only partially reduced on chondrocytes. Moreover, ASC-CM was less efficient both on basal inflamed OA chondrocytes and synoviocytes in reducing proteinases, such as MMP13, ADAMTS4, ADAMTS5 and increasing TIMP1 and TIMP3 compared to ASC in co-culture. The different ratios of ASC-CM contain lower amounts of PGE2 which were not sufficient to reduce inflammatory factors. CONCLUSIONS: These data show that ASC-CM has a limited ability to decrease inflammatory and proteinases factors produced by OA chondrocytes or synoviocytes. ASC-CM is not sufficient to recapitulate the beneficial effect demonstrated using ASC in co-culture with inflamed OA chondrocytes and synoviocytes and shows that their use in clinical trials is fundamental to counteract OA progression.

Slug transcription factor and nuclear Lamin B1 are upregulated in osteoarthritic chondrocytes.

OBJECTIVE: To contribute to clarify molecular mechanisms supporting senescence and de-differentiation of chondrocytes in chondrocyte pathologies such as osteoarthritis (OA). Specifically, we investigated the relationship between the nuclear lamina protein Lamin B1 and the negative regulator of chondrogenesis Slug transcription factor in osteoarthritic chondrocytes. METHODS: Lamin B1 and Slug proteins were analyzed in cartilage explants from normal subjects and OA patients by immunohistochemical technique. Their expression was confirmed on isolated chondrocytes both at passage 0 and passage 2 (de-differentiated chondrocytes) by immunofluorescence and western blot. Subsequently, we explored the "in vivo" binding of Slug on LMNB1 promoter by chromatin immunoprecipitation assay (ChIP). RESULTS: In this study we demonstrated that nuclear lamina protein Lamin B1 and anti-chondrogenic Slug transcription factor are upregulated in cartilage and OA chondrocytes. Furthermore, we found that Slug is "in vivo" recruited by LMNB1 gene promoter mostly when chondrocytes undergo de-differentiation or OA degeneration. CONCLUSIONS: We described for the first time a potential regulatory role of Slug on the LMNB1 gene expression in OA chondrocytes. These findings may have important implications for the study of premature senescence, and degeneration of cartilage, and may contribute to develop effective therapeutic strategies against signals supporting cartilage damage in different subsets of patients.

Design, Development and Validation of a Knee Brace to Standardize the US Imaging Evaluation of Knee Osteoarthritis.

OBJECTIVE: A repeatable and reliable follow-up of knee injuries would be desirable to prevent delayed diagnosis and to monitor the efficacy of the applied treatment over time. Ultrasound (US) techniques are an attractive option to this purpose, since they are safe, low-cost and non-invasive. However, its use in the clinical practice is limited by the high dependency on the operator's experience. Hence, the objective of this study is to provide a standardization of the US image acquisition process for knee osteoarthritis (OA) allowing an extended clinical use of US technologies in this domain. METHODS: Clinical specifications were provided by expert musculoskeletal radiologists thus identifying the subject poses and the US probe positions needed to evaluate the cartilage structure, signs of synovitis and joint effusion. Such considerations were used to derive the technical requirements needed for the development of a wearable brace equipped with specific openings to guide the correct placement of the probe. The feasibility of the developed wearable brace was tested on three healthy volunteers, which were asked to acquire informative US images, similar to the reference images performed by the musculoskeletal radiologist. RESULTS: Thanks to the knee brace, the untrained subjects were able to self-acquire informative B-mode images comparable to the corresponding images acquired by an expert clinician. DISCUSSION/CONCLUSION: The use of a knee brace intended for knee OA US diagnosis demonstrated the possibility to standardize the acquisition protocol and make its application achievable also for untrained subjects, representing a key step toward tele-ultrasonography.

Chemical-physical properties and in vitro cell culturing of a novel biphasic bio-mimetic scaffold for osteo-chondral tissue regeneration.

The requirements for a successful regeneration of an osteo-chondral defect could effectively be met by using a bi-layered composite scaffold, able to support proliferation and differentiation of mesenchymal stem cells, while providing a biochemical environment promoting the formations of the two distinct tissues. The novel strategy here presented consists of developing a bio-mimetic scaffolds obtained by the combination of two integrated organic compounds (type I collagen and chitosan) with or without bioactive Mg-doped hydroxyapatite (Mg-HA) nanocrystals, depending on the specific layer, reproducing cartilaginous or subchondral bone tissue. An innovative patented methodology for scaffolds production, called - pH-dependent 3-phasic assembling -, allowed to development of a highly homogenous and chemically stable scaffold, presenting a very good integration among all three components, as confirmed by extensive SEM and thermogravimetric analyses. A preliminary in vitro evaluation was also carried out by seeding bi-layered scaffold with human bone marrow stromal cells (h-MSCs), by giving particular emphasis to cell viability and distribution at day 0, 7 and 14. Cells were viable and uniformly colonized the whole scaffold until day 14, indicating that the scaffold contributed to the maintenance of cell behaviour.

Development and validation of low-intensity pulsed ultrasound systems for highly controlled in vitro cell stimulation.

This work aims to describe the development and validation of two low-intensity pulsed ultrasound stimulation systems able to control the dose delivered to the biological target. Transducer characterization was performed in terms of pressure field shape and intensity, for a high-frequency range (500 kHz to 5 MHz) and for a low-frequency value (38 kHz). This allowed defining the distance, on the beam axis, at which biological samples should be placed during stimulation and to exactly know the intensity at the target. Carefully designed retaining systems were developed, for hosting biological samples. Sealing tests proved their impermeability to external contaminants. The assembly/de-assembly time of the systems resulted ~3 min. Time-domain acoustic simulations allowed to precisely estimate the ultrasound beam within the biological sample chamber, thus enabling the possibility to precisely control the pressure to be transmitted to the biological target, by modulating the transducer's input voltage. Biological in vitro tests were also carried out, demonstrating the sterility of the system and the absence of toxic and inflammatory effects on growing cells after multiple immersions in water, over seven days.

Specific inductive potential of a novel nanocomposite biomimetic biomaterial for osteochondral tissue regeneration.

Osteochondral lesions require treatment to restore the biology and functionality of the joint. A novel nanostructured biomimetic gradient scaffold was developed to mimic the biochemical and biophysical properties of the different layers of native osteochondral structure. The present results show that the scaffold presents important physicochemical characteristics and can support the growth and differentiation of mesenchymal stromal cells (h-MSCs), which adhere and penetrate into the cartilaginous and bony layers. H-MSCs grown in chondrogenic or osteogenic medium decreased their proliferation during days 14-52 on both scaffold layers and in medium without inducing factors used as controls. Both chondrogenic and osteogenic differentiation of h-MSCs occurred from day 28 and were increased on day 52, but not in the control medium. Safranin O staining and collagen type II and proteoglycans immunostaining confirmed that chondrogenic differentiation was specifically induced only in the cartilaginous layer. Conversely, von Kossa staining, osteocalcin and osteopontin immunostaining confirmed that osteogenic differentiation occurred on both layers. This study shows the specific potential of each layer of the biomimetic scaffold to induce chondrogenic or osteogenic differentiation of h-MSCs. These processes depended mainly on the media used but not the biomaterial itself, suggesting that the local milieu is fundamental for guiding cell differentiation. Copyright © 2013 John Wiley & Sons, Ltd.

Analysis of mesenchymal stem cells grown on a three-dimensional HYAFF 11-based prototype ligament scaffold.

Ligaments are complex structures that maintain the mechanical stability of the joint. Healing of injured ligaments involves the interactions of different cell types, local cellular environment, and the use of devices. To gain new information on the complex interactions between mesenchymal stem cells (MSCs) and a specific hyaluronan-based prototype scaffold (HYAFF, useful for ligament tissue engineering, short time-course experiments were performed to analyze the proliferation, vitality, and phenotype of MSCs grown on the scaffold. MSC proliferation was analyzed using the MTT test, during the early time points (2, 4, 6, days). Viability was assessed using calcein/acetyloxymethylester immunofluorescence dye and confocal microscopy analysis. Hyaluronic acid receptor (CD44), typical matrix ligament proteins (collagen type I, type III, laminin, fibronectin, actin), and chondrogenic/osteogenic markers (collagen type II and bone sialoprotein) were evaluated by immunohistochemistry. Our data demonstrated that MSC growth and viability were cell density-dependent. MSCs completely wrapped the fibers of the scaffold, expressed CD44, collagen type I, type III, laminin, fibronectin, and actin, and were negative to collagen type II and bone sialoprotein. These data demonstrate that MSCs survive well in the hyaluronan-based prototype ligament scaffold, as assessed after 2 days from seeding, and express CD44, a receptor important for scaffold interaction, and proteins responsible for the functional characteristics of the ligaments.

A fluorescent in situ hybridization method in flow cytometry to detect HIV-1 specific RNA.

In HIV+ patients, the presence of HIV-RNA in plasma and circulating cells has been reported to be a marker of progression but the percentage of transcriptionally active infected cells remains unclear. We have developed a reliable fluorescent in situ hybridization method for the detection of HIV specific RNA by flow cytometry. The procedure was applied to a panel of chronically infected cell lines and to an acutely infected cell line mimicking normal peripheral blood lymphocytes in susceptibility to HIV-1. The cells were fixed in suspension and hybridized by means of an HIV-1 genomic probe labeled with digoxigenin-11-dUTP. An FITC-labeled anti-digoxigenin antiserum was then applied and the resulting fluorescence signals were analyzed both by flow cytometry and confocal microscopy. Different procedures for double staining HIV-RNA together with virus induced proteins or surface markers were also developed. Flow cytometric detection of in situ hybridization offers the possibility of analyzing thousands of cells in a few seconds and of collecting multiparametric information at the single cell level, thus providing a potential tool for detecting the rare HIV-RNA expressing cells in peripheral blood samples.

Transfer of HIV-1 to human tonsillar stromal cells following cocultivation with infected lymphocytes.

The susceptibility of normal human tonsillar stromal cells (HTSCs) to infection by HIV-1 was assessed using transmission electron microscopy (TEM), immunocytochemistry, and HIV-1-specific PCR analyses. Our results demonstrate that HTSCs are efficiently infected following cocultivation with the HIV-1-infected lymphoblastoid cell line GY1. Infected stromal cells contain intracellular viral particles present as free virus or associated with phagocytic vesicles. These particles express the HIV-1-specific p24 antigen as assessed by immunocytochemical analyses using an HIV-specific anti-p24 monoclonal antibody. Moreover, PCR analysis of genomic DNA isolated from particle-bearing tonsillar stromal cells identified HIV-1-specific sequences not present in either uninfected stromal cells or parental GY1 uninfected cells. The mechanism by which HIV-1 infects HTSCs does not appear to be CD4 mediated, as none of the human tonsillar stromal cell lines express CD4 as assessed by flow cytometry, immunohistochemistry, and PCR analysis. Taken together, these results demonstrate that human tonsillar stromal cells can be infected by HIV-1, and that subsequent to infection the viral genome is reverse transcribed, and integrated into the stromal cell DNA. The infection of HTSCs may contribute to HIV-1-mediated pathogenesis indirectly as a viral reservoir or directly by structural and functional modification of the lymphoid microenvironment.

Different expression pattern of cytokine receptors by human osteosarcoma cell lines.

Cytokine receptor expression in human osteosarcoma cell lines (U2-OS, Saos-2, MG-63) was analyzed by flow cytometry to identify receptors which may interact with osteosarcoma cell growth and that should not be used in a clinical setting. U2-OS, Saos-2, MG-63 and bone marrow stromal cells, that were used as normal controls, constitutively express the FAS and SCFR surface molecules. GM-CSFR is expressed only by U2-OS and Saos-2 cell lines, that are phenotypically less differentiated than MG-63. Different gp130 clones were express ed only by Saos-2 and MG-63 cell lines. IL-2Rgamma,IL-7R and 4-1BB were expressed only by Saos-2 cell line. These data add new evidence of receptors that may be activated by autocrine or paracrine cytokines that could induce osteosarcoma cell growth.

Osteogenesis of large segmental radius defects enhanced by basic fibroblast growth factor activated bone marrow stromal cells grown on non-woven hyaluronic acid-based polymer scaffold.

Osteogenesis of large segmental radius defects in a rat model was studied by implanting a biodegradable non-woven hyaluronic acid-based polymer scaffold (Hyaff 11) alone or in combination with bone marrow stromal cells (BMSCs). These cells had been previously grown in vitro in mineralising medium either supplemented with basic fibroblast growth factor (bFGF) or unsupplemented. The healing of bone defects was evaluated at 40, 80, 160 and 200 days and the repair process investigated by radiographic, histomorphometric (assessment of new bone growth and lamellar bone) and histological analyses (toluidine blue and von Kossa staining). Mineralisation of bone defects occurred in the presence of the Hyaff 11 scaffold alone or when combined with BMSCs grown with or without bFGF, but each process had a different timing. In particular, bFGF significantly induced mineralisation from day 40, whereas 160 days were necessary for direct evidence that a similar process was developing under the other two conditions tested (scaffold alone or with BMSCs). Radiographic score, new bone growth and lamellar bone percentage were highly correlated. The present outcomes were further confirmed by toluidine blue and von Kossa staining. According to these in vivo findings, the Hyaff 11 scaffold is an appropriate carrier vehicle for the repair of bone defects; additionally, it can significantly accelerate bone mineralisation in combination with BMSCs and bFGF.

Basic fibroblast growth factor enhances in vitro mineralization of rat bone marrow stromal cells grown on non-woven hyaluronic acid based polymer scaffold.

A biodegradable non-woven hyaluronic acid polymer scaffold (Hyaff 11) was analysed in vitro as a carrier vehicle for differentiation and mineralization of rat bone marrow stromal cells (BMSC). BMSC were grown on Hyaff 11 in a mineralizing medium in the presence/absence of basic fibroblast growth factor (bFGF). Osteoblastic differentiation was investigated by light and electron microscopy analysing the expression of osteogenic markers: calcium, alkaline phosphatase (AP), osteopontin (OP), bone sialoprotein (BSP) and collagen type 1. We also measured proliferation, AP activity and mRNA expression of AP and osteocalcin (OC). Electron microscopy and Toluidine-blue staining demonstrated that bFGF accelerated (day 20 vs. day 40) and increased mineralization. With bFGF, calcium, OP and BSP were strongly enhanced at day 40, whereas AP decreased. Our in vitro results demonstrate that Hyaff 11 is a useful vehicle for growth, differentiation and mineralization of rat BMSC, and that it permits bone development.

Copper/zinc superoxide dismutase expression by different human osteosarcoma cell lines.

Oxidative stress has been frequently implicated in the initiation and promotion phases of carcinogenesis. Antioxidant enzymes, which can antagonize this process, are lowered in a number of malignancies even though different findings have been reported in the literature. It has been shown that tumors have less copper/zinc superoxide dismutase (Cu/Zn SOD) in comparison with the more metabolically active tissues, but there is a large overlap between normal and tumor tissue. In order to examine the relationship between osteosarcoma at different degrees of proliferation and differentiation and Cu/Zn SOD levels, four different human ostosarcoma cell lines: HOS, U-2 OS, MG63, Saos-2 were studied for their production and release of Cu/Zn SOD. A normal human stromal cell line was used as control. Osteosarcoma cells were stimulated with TNF alpha, a cytokine previously shown to have antiproliferative activity. The release of Cu/Zn SOD into the supernatant was higher for the HOS and U-2 OS lines when compared to the other cell lines evaluated both in basal condition and after incubation with TNF alpha. Elevated intracellular levels of Cu/Zn SOD were shown except for the HOS and U-2 OS which possess high concentrations of the enzyme at 24 hours declining during the other incubation periods. These concentrations were increased after TNF alpha treatment. The different behaviour of the four cell lines evaluated might be explained by their degree of differentiation.

Expression of different chemokines by human osteosarcoma cells in response to tumor necrosis factor-alpha.

We investigated the expression of different chemokines in the surnatants and inside the cells of four human osteosarcoma cell lines. HOS, U-2 OS, MG63 and Saos-2 cells were cultured for 24, 48, 72 hours both in basal conditions and after stimulus with TNF alpha. Human stromal cells were used as control. IL-8 and MCP-1 are present in higher concentration in the surnatants in contrast to RANTES which is present primarily inside the cells. IL-8 and MCP-1 are not totally expressed by all the human osteosarcoma cell lines in unstimulated conditions, but became detectable after TNF alpha treatment. In general, this cytokine stimulated the production and release of the three chemokines.

Cell cycle synchronization of FRTL5 cells. A physiological model system.

We describe a "physiological" cell cycle synchronization model system. FRTL5 cells, TSH-dependent for proliferation, were starved from TSH. The cell cycle phases and the expression of markers associated to different cycle phases were evaluated. TSH starvation blocks proliferation without provoking death and induces virtually all the cells to accumulate in G0/G1 phase. TSH readdition allows 30% of these cells to enter the S phase. DNA topoisomerase II 170-kDa isoform is not expressed in G0/G1 synchronized cells while it is expressed in logarithmic growing cells. The 180-kDa isoform is not expressed in G0/G1 synchronized cells while it is expressed in 20% of logarithmic growing cells regardless of the cycle phase. c-myc mRNA is not expressed in G0/G1 synchronized cells while it is detectable upon TSH readdition. This system provides a tool for the analysis of events associated with the G0/G1 phase and the transition from G0/G1 to S phase.

Tissue engineering for cartilage repair: in vitro properties of a hyaluronan-derivative.

Association of biomaterials with autologous cells can provide a new generation of implantable devices for cartilage and bone repair. Such scaffolds should provide a performed three-dimensional shape, prevent cells from floating out of the defect, have sufficient mechanical strength, facilitate uniform spread of cells, and stimulate the phenotype of transplanted cells. Hyaff-11 is a recently developed hyaluronic-acid based biodegradable polymer, that has been shown to provide successful cell scaffolds for tissue-engineered repair. The aim of this study was to evaluate in vitro the potential of Hyaff-11 to support the growth of human chondrocytes and to maintain their original phenotype. Our data indicate that human chondrocytes seeded on Hyaff-11 express and produce collagen type II and aggrecan and downregulate the production of collagen type I. These results provide an in vitro demonstration of therapeutic potential of Hyaff-11 as a delivery vehicle in tissue-engineered repair of articular cartilage defects.

Hyaluronan-based biomaterial (Hyaff-11) as scaffold to support mineralization of bone marrow stromal cells.

Various techniques are widely used to repair bone defects, association of hyaluronan-based biodegradable polymers (Hyaff-11) with bone marrow stromal cells (BMSC) promises to provide successful cell scaffolds for tissue-engineered repair of bone tissue. We evaluate in vitro and in vivo the potential of Hyaff-11 to facilitate mineralization of BMSC. Rat BMSC were seeded on Hyaff-11 and their differentiation were assessed at different time points. Osteogenic differentiation was investigated in vitro analysing the expression of alkaline phosphatase and osteocalcin. Mineralization of bone defects was evaluated also in vivo implanting Hyaff-11 scaffold combined with BMSC in large segmental radius defects. In vitro, we found a decrease expression of alkaline phosphatase and an increase of osteocalcin. In vivo, our data showed that mineralization was induced and basic fibroblast growth factor contributed to this process. These results provide a demonstration to therapeutic potential of Hyaff-11 as appropriate carrier vehicle for differentiation and mineralization of BMSC and for the repair of bone defects.

Myeloma cells inhibit non-canonical wnt co-receptor ror2 expression in human bone marrow osteoprogenitor cells: effect of wnt5a/ror2 pathway activation on the osteogenic differentiation impairment induced by myeloma cells.

Multiple myeloma (MM) is characterized by the impaired osteogenic differentiation of human mesenchymal stromal cells (hMSCs). Canonical Wnt signaling is critical for the regulation of bone formation, however, recent evidence suggests that the non-canonical Wnt agonist Wnt5a stimulates human osteoblastogenesis through its co-receptor Ror2. The effects of MM cells on non-canonical Wnt signaling and the effect of the activation of this pathway on MM-induced osteoblast exhaustion are not known and were investigated in this study. We found that the osteogenic differentiation of bone marrow hMSCs toward osteoprogenitor cells (PreOB) significantly increased Ror2 expression, and that MM cells inhibit Ror2 expression by PreOB in co-culture by inhibiting the non-canonical Wnt5a signaling. The activation of the non-canonical Wnt pathway in hMSCs by means of Wnt5a treatment and the overexpression of Wnt5 or Ror2 by lentiviral vectors increased the osteogenic differentiation of hMSCs and blunted the inhibitory effect of MM in co-culture. Consistently, Wnt5a inhibition by specific small interfering RNA reduced the hMSC expression of osteogenic markers. Our findings demonstrate that the Wnt5a/Ror2 pathway is involved in the pathophysiology of MM-induced bone disease and that the activation of the non-canonical Wnt5a/Ror2 pathway in hMSCs increases osteogenic differentiation and may counterbalance the inhibitory effect of MM cells.

HOXB7 expression by myeloma cells regulates their pro-angiogenic properties in multiple myeloma patients.

The deregulation of the homeobox genes as homeoboxB (HOXB)-7 has been previously associated to tumor progression and angiogenesis; here we investigated the potential role of HOXB7 in the pro-angiogenic properties of multiple myeloma (MM) cells. We found that HOXB7 was expressed in 10 out of 22 MM patients analyzed at the diagnosis related to high bone marrow angiogenesis and overexpressed in about 40% of myeloma cell lines compared with normal plasma cells. Enforced HOXB7 expression in MM cells by a lentiviral vector significantly modified their transcriptional and angiogenic profile, checked by combined microarray and angiogenesis PCR analyses, upregulating VEGFA, FGF2, MMP2, WNT5a and PDGFA and downregulating thrombospoindin-2. The pro- and anti-angiogenic HOXB7-related gene signature was also validated in a large independent dataset of MM patients. Accordingly, MM-induced vessel formation was significantly increased by HOXB7 overexpression both in vitro angiogenic and chorioallantoic membrane assays, as well as the HOXB7 silencing by small interfering RNA inhibited the production of angiogenic factors, and the pro-angiogenic properties of MM cells. Finally, in SCID-NOD mice we confirmed that HOXB7 overexpression by MM cells stimulated tumor growth, increased MM-associated angiogenesis and the expression of pro-angiogenic genes by microarray analysis supporting the critical role of HOXB7 in the angiogenic switch in MM.