Rapid innervation and physiological epidermal regeneration by bioengineered dermis implanted in mouse

Tissue-engineered skin substitutes are promising tools to cover large and deep skin defects. However, the lack of a synergic and fast regeneration of the vascular network, nerves, and skin appendages limits complete skin healing and impairs functional recovery. It has been highlighted that an ideal skin substitute should mimic the structure of the native tissue to enhance clinical effectiveness. Here, we produced a pre-vascularized dermis (PVD) comprised of fibroblasts embedded in their own extracellular matrix (ECM) and a capillary-like network. Upon implantation in a mouse full-thickness skin defect model, we observed a very early innervation of the graft in 2 weeks. In addition, mouse capillaries and complete epithelialization were detectable as early as 1 week after implantation and, skin appendages developed in 2 weeks. These anatomical features underlie the interaction with the skin nerves, thus providing a further cue for reinnervation guidance. Further, the graft displays mechanical properties, collagen density, and assembly features very similar to the host tissue. Taken together our data show that the pre-existing ECM components of the PVD, physiologically organized and assembled similarly to the native tissue, support a rapid regeneration of dermal tissue. Therefore, our results suggest a promising potential for PVD in skin regeneration.

In Vitro Mineralisation of Tissue-Engineered Cartilage Reduces Endothelial Cell Migration, Proliferation and Tube Formation

Tissue engineering bone via endochondral ossification requires the generation of a cartilage template which undergoes vascularisation and remodelling. While this is a promising route for bone repair, achieving effective cartilage vascularisation remains a challenge. Here, we investigated how mineralisation of tissue-engineered cartilage affects its pro-angiogenic potential. To generate in vitro mineralised cartilage, human mesenchymal stromal cell (hMSC)-derived chondrogenic pellets were treated with β-glycerophosphate (BGP). After optimising this approach, we characterised the changes in matrix components and pro-angiogenic factors by gene expression analysis, histology and ELISA. Human umbilical vein endothelial cells (HUVECs) were exposed to pellet-derived conditioned media, and migration, proliferation and tube formation were assessed. We established a reliable strategy to induce in vitro cartilage mineralisation, whereby hMSC pellets are chondrogenically primed with TGF-β for 2 weeks and BGP is added from week 2 of culture. Cartilage mineralisation determines loss of glycosaminoglycans, reduced expression but not protein abundance of collagen II and X, and decreased VEGFA production. Finally, the conditioned medium from mineralised pellets showed a reduced ability to stimulate endothelial cell migration, proliferation and tube formation. The pro-angiogenic potential of transient cartilage is thus stage-dependent, and this aspect must be carefully considered in the design of bone tissue engineering strategies.

VEGF dose controls the coupling of angiogenesis and osteogenesis in engineered bone

Vascular endothelial growth factor-A (VEGF) physiologically regulates both angiogenesis and osteogenesis, but its application in bone tissue engineering led to contradictory outcomes. A poorly understood aspect is how VEGF dose impacts the coordination between these two processes. Taking advantage of a unique and highly tunable platform, here we dissected the effects of VEGF dose over a 1,000-fold range in the context of tissue-engineered osteogenic grafts. We found that osteo-angiogenic coupling is exquisitely dependent on VEGF dose and that only a tightly defined dose range could stimulate both vascular invasion and osteogenic commitment of progenitors, with significant improvement in bone formation. Further, VEGF dose regulated Notch1 activation and the induction of a specific pro-osteogenic endothelial phenotype, independently of the promotion of vascular invasion. Therefore, in a therapeutic perspective, fine-tuning of VEGF dose in the signaling microenvironment is key to ensure physiological coupling of accelerated vascular invasion and improved bone formation.

The osteo-angiogenic signaling crosstalk for bone regeneration: harmony out of complexity

In recent years it has been increasingly appreciated that blood vessels are not simply suppliers of nutrients and oxygen, but actually play an exquisite regulatory role in bone development and repair. A specialized kind of endothelium, named type H because of its high expression of CD31 and Endomucin, constitutes anatomically defined vessels in proximity of the epiphyseal growth plate. Type H endothelium regulates the proliferation and differentiation of both osteoblasts and osteoclasts through the secretion of angiocrine signals and is a hub for the bidirectional molecular crosstalk between the different cell populations of the osteogenic microenvironment. Type H vessels are a key target for current translational approaches aiming at coupling angiogenesis and osteogenesis for bone repair. Open questions remain about their presence and features in notstereotyped tissues, like engineered osteogenic grafts, and the opportunities for their clinical stimulation by pharmacological treatments.

Robust coupling of angiogenesis and osteogenesis by VEGF-decorated matrices for bone regeneration

Rapid vascularization of clinical-size bone grafts is an unsolved challenge in regenerative medicine. Vascular endothelial growth factor-A (VEGF) is the master regulator of angiogenesis. Its over-expression by genetically modified human osteoprogenitors has been previously evaluated to drive vascularization in osteogenic grafts, but has been observed to cause paradoxical bone loss through excessive osteoclast recruitment. However, during bone development angiogenesis and osteogenesis are physiologically coupled by VEGF expression. Here we investigated whether the mode of VEGF delivery may be a key to recapitulate its physiological function. VEGF activity requires binding to the extracellular matrix, and heterogeneous levels of expression lead to localized microenvironments of excessive dose. Therefore we hypothesized that a homogeneous distribution of matrix-associated factor in the microenvironment may enable efficient coupling of angiogenesis and bone formation. This was achieved by decorating fibrin matrices with a cross-linkable engineered version of VEGF (TG-VEGF) that is released only by enzymatic cleavage by invading cells. In ectopic grafts, both TG-VEGF and VEGF-expressing progenitors similarly improved vascularization within the first week, but efficient bone formation was possible only in the factor-decorated matrices, whereas heterogenous, cell-based VEGF expression caused significant bone loss. In critical-size orthotopic calvaria defects, TG-VEGF effectively improved early vascular invasion, osteoprogenitor survival and differentiation, as well as bone repair compared to both controls and VEGF-expressing progenitors. In conclusion, homogenous distribution of matrix-associated VEGF protein preserves the physiological coupling of angiogenesis and osteogenesis, providing an attractive and clinically applicable strategy to engineer vascularized bone. STATEMENT OF SIGNIFICANCE: The therapeutic regeneration of vascularized bone is an unsolved challenge in regenerative medicine. Stimulation of blood vessel growth by over-expression of VEGF has been associated with paradoxical bone loss, whereas angiogenesis and osteogenesis are physiologically coupled by VEGF during development. Here we found that controlling the distribution of VEGF dose in an osteogenic graft is key to recapitulate its physiological function. In fact, homogeneous decoration of fibrin matrices with engineered VEGF could improve both vascularization and bone formation in orthotopic critical-size defects, dispensing with the need for combined osteogenic factor delivery. VEGF-decorated fibrin matrices provide a readily translatable platform for engineering a controlled microenvironment for bone regeneration.

Therapeutic arteriogenesis by factor-decorated fibrin matrices promotes wound healing in diabetic mice

Chronic wounds in type-2 diabetic patients present areas of severe local skin ischemia despite mostly normal blood flow in deeper large arteries. Therefore, restoration of blood perfusion requires the opening of arterial connections from the deep vessels to the superficial skin layer, that is, arteriogenesis. Arteriogenesis is regulated differently from microvascular angiogenesis and is optimally stimulated by high doses of Vascular Endothelial Growth Factor-A (VEGF) together with Platelet-Derived Growth Factor-BB (PDGF-BB). Here we found that fibrin hydrogels decorated with engineered versions of VEGF and PDGF-BB proteins, to ensure protection from degradation and controlled delivery, efficiently accelerated wound closure in diabetic and obese db/db mice, promoting robust microvascular growth and a marked increase in feeding arterioles. Notably, targeting the arteriogenic factors to the intact arterio-venous networks in the dermis around the wound was more effective than the routine treatment of the inflamed wound bed. This approach is readily translatable to a clinical setting.

Robust Angiogenesis and Arteriogenesis in the Skin of Diabetic Mice by Transient Delivery of Engineered VEGF and PDGF-BB Proteins in Fibrin Hydrogels

Non-healing ulcers are a serious complication of diabetes mellitus and a major unmet medical need. A major cause for the lack of healing is the impairment of spontaneous vascularization in the skin, despite mostly normal blood flow in deeper large vessels. Therefore, pro-angiogenic treatments are needed to increase therapeutic perfusion by recruiting new arterial connections (therapeutic arteriogenesis). Vascular endothelial growth factor (VEGF) is the master regulator of angiogenesis in physiology and disease, but exploitation of its therapeutic potential requires careful control of its dose distribution in tissue. Co-delivery of platelet derived growth factor-BB (PDGF-BB) has been shown to expand the therapeutic window of VEGF and also improve associated arteriogenesis. We used a highly controlled protein delivery system, based on a clinically applicable fibrin-based platform, to investigate the angiogenic and arteriogenic potential of engineered versions (TG-) of VEGF and PDGF-BB proteins in the skin of diabetic and obese db/db mice. Intradermal delivery of therapeutically relevant doses of TG-VEGF and TG-PDGF-BB induced robust growth of new microvascular networks with similar efficacy as in normal littermate control mice. Further, TG-PDGF-BB prevented the formation of aberrant vascular enlargements by high TG-VEGF levels. As fibrin was degraded after the first week, the induced angiogenesis mostly regressed by 4 weeks, but it promoted effective arteriogenesis in the dermal layer. Therefore, controlled co-delivery of TG-VEGF and TG-PDGF-BB recombinant proteins is effective to induce angiogenesis and arteriogenesis in diabetic mouse skin and should be further investigated to promote diabetic wound healing.

Hypoxia Triggers the Intravasation of Clustered Circulating Tumor Cells

Circulating tumor cells (CTCs) are shed from solid cancers in the form of single or clustered cells, and the latter display an extraordinary ability to initiate metastasis. Yet, the biological phenomena that trigger the shedding of CTC clusters from a primary cancerous lesion are poorly understood. Here, when dynamically labeling breast cancer cells along cancer progression, we observe that the majority of CTC clusters are undergoing hypoxia, while single CTCs are largely normoxic. Strikingly, we find that vascular endothelial growth factor (VEGF) targeting leads to primary tumor shrinkage, but it increases intra-tumor hypoxia, resulting in a higher CTC cluster shedding rate and metastasis formation. Conversely, pro-angiogenic treatment increases primary tumor size, yet it dramatically suppresses the formation of CTC clusters and metastasis. Thus, intra-tumor hypoxia leads to the formation of clustered CTCs with high metastatic ability, and a pro-angiogenic therapy suppresses metastasis formation through prevention of CTC cluster generation.

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Hypoxia leads to cell-cell junction upregulation and intravasation of CTC clusters

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Hypoxic CTC clusters are highly metastatic compared to normoxic CTCs

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Increase in intra-tumor hypoxia leads to accelerated metastasis

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Treatment with EpB2 reduces hypoxia and prevents CTC cluster formation

The NFIB-ERO1A axis promotes breast cancer metastatic colonization of disseminated tumour cells

Metastasis is the main cause of deaths related to solid cancers. Active transcriptional programmes are known to regulate the metastatic cascade but the molecular determinants of metastatic colonization remain elusive. Using an inducible piggyBac (PB) transposon mutagenesis screen, we have shown that overexpression of the transcription factor nuclear factor IB (NFIB) alone is sufficient to enhance primary mammary tumour growth and lung metastatic colonization. Mechanistically and functionally, NFIB directly increases expression of the oxidoreductase ERO1A, which enhances HIF1α-VEGFA-mediated angiogenesis and colonization, the last and fatal step of the metastatic cascade. NFIB is thus clinically relevant: it is preferentially expressed in the poor-prognostic group of basal-like breast cancers, and high expression of the NFIB/ERO1A/VEGFA pathway correlates with reduced breast cancer patient survival.

Strategies for re-vascularization and promotion of angiogenesis in trauma and disease

The maintenance of a healthy vascular system is essential to ensure the proper function of all organs of the human body. While macrovessels have the main role of blood transportation from the heart to all tissues, microvessels, in particular capillaries, are responsible for maintaining tissues' functionality by providing oxygen, nutrients and waste exchanges. Occlusion of blood vessels due to atherosclerotic plaque accumulation remains the leading cause of mortality across the world. Autologous vein and artery grafts bypassing are the current gold standard surgical procedures to substitute primarily obstructed vascular structures. Ischemic scenarios that condition blood supply in downstream tissues may arise from blockage phenomena, as well as from other disease or events leading to trauma. The (i) great demand for new vascular substitutes, arising from both the limited availability of healthy autologous vessels, as well as the shortcomings associated with small-diameter synthetic vascular grafts, and (ii) the challenging induction of the formation of adequate and stable microvasculature are current driving forces for the growing interest in the development of bioinspired strategies to ensure the proper function of vasculature in all its dimensional scales. Here, a critical review of well-established technologies and recent biotechnological advances to substitute or regenerate the vascular system is provided.

Fibrin hydrogels promote scar formation and prevent therapeutic angiogenesis in the heart

Therapeutic angiogenesis is the delivery of factors to promote vascular growth and holds promise for the treatment of ischemic heart conditions. Recombinant protein delivery to the myocardium by factor-decorated fibrin matrices is an attractive approach, thanks to the ability to precisely control both dose and duration of the treatment, the use of a clinically approved material like fibrin, and the avoidance of genetic modification. Here, we investigated the feasibility of inducing therapeutic angiogenesis in the rat myocardium by a state-of-the-art fibrin-based delivery platform that we previously optimized. Engineered versions of murine vascular endothelial growth factor A (VEGF₁₆₄ ) and platelet-derived growth factor BB (PDGF-BB) were fused with an octapeptide substrate of the transglutaminase coagulation factor fXIIIa (TG) to allow their covalent cross-linking into fibrin hydrogels and release by enzymatic cleavage. Hydrogels containing either 100 μg/mL TG-VEGF alone or in combination with 10 μg/mL TG-PDGF-BB or no factor were injected into rat myocardium. Surprisingly, vascular density was severely reduced in all conditions, both in and around the injection site, where large fibrotic scars were formed. Scar formation was not due to the presence of growth factors, adaptive immunity to human proteins, damage from injection, nor to mechanical trauma from the hydrogel stiffness or volume. Rather scar was induced directly by fibrin and persisted despite hydrogel degradation within 1 week. These results caution against the suitability of fibrin-based platforms for myocardial growth factor delivery, despite their efficacy in other tissues, like skeletal muscle. The underlying molecular mechanisms must be further investigated in order to identify rational targets to prevent this serious side effect.

VEGF Over-Expression by Engineered BMSC Accelerates Functional Perfusion, Improving Tissue Density and In-Growth in Clinical-Size Osteogenic Grafts

The first choice for reconstruction of clinical-size bone defects consists of autologous bone flaps, which often lack the required mechanical strength and cause significant donor-site morbidity. We have previously developed biological substitutes in a rabbit model by combining bone tissue engineering and flap pre-fabrication. However, spontaneous vascularization was insufficient to ensure progenitor survival in the core of the constructs. Here, we hypothesized that increased angiogenic stimulation within constructs by exogenous VEGF can significantly accelerate early vascularization and tissue in-growth. Bone marrow stromal cells from NZW rabbits (rBMSC) were transduced with a retroviral vector to express rabbit VEGF linked to a truncated version of rabbit CD4 as a cell-surface marker. Autologous cells were seeded in clinical-size 5.5 cm³ HA scaffolds wrapped in a panniculus carnosus flap to provide an ample vascular supply, and implanted ectopically. Constructs seeded with VEGF-expressing rBMSC showed significantly increased progenitor survivival, depth of tissue ingrowth and amount of mineralized tissue. Contrast-enhanced MRI after 1 week in vivo showed significantly improved tissue perfusion in the inner layer of the grafts compared to controls. Interestingly, grafts containing VEGF-expressing rBMSC displayed a hierarchically organized functional vascular tree, composed of dense capillary networks in the inner layers connected to large-caliber feeding vessels entering the constructs at the periphery. These data constitute proof of principle that providing sustained VEGF signaling, independently of cells experiencing hypoxia, is effective to drive rapid vascularization and increase early perfusion in clinical-size osteogenic grafts, leading to improved tissue formation deeper in the constructs.

Balanced single-vector co-delivery of VEGF/PDGF-BB improves functional collateralization in chronic cerebral ischemia

The myoblast-mediated delivery of angiogenic genes represents a cell-based approach for targeted induction of therapeutic collateralization. Here, we tested the superiority of myoblast-mediated co-delivery of vascular endothelial growth factor-A (VEGF) together with platelet-derived growth factor-BB (PDGF-BB) on transpial collateralization of an indirect encephalomyosynangiosis (EMS) in a model of chronic cerebral ischemia. Mouse myoblasts expressing a reporter gene alone (empty vector), VEGF, PDGF-BB or VEGF and PDGF-BB through a single bi-cistronic vector (VIP) were implanted into the temporalis muscle of an EMS following permanent ipsilateral internal carotid artery occlusion in adult, male C57BL/6N mice. Over 84 days, myoblast engraftment and gene product expression, hemodynamic impairment, transpial collateralization, angiogenesis, pericyte recruitment and post-ischemic neuroprotection were assessed. By day 42, animals that received PDGF-BB in combination with VEGF (VIP) showed superior hemodynamic recovery, EMS collateralization and ischemic protection with improved pericyte recruitment around the parenchymal vessels and EMS collaterals. Also, supplementation of PDGF-BB resulted in a striking astrocytic activation with intrinsic VEGF mobilization in the cortex below the EMS. Our findings suggest that EMS surgery together with myoblast-mediated co-delivery of VEGF/PDGF-BB may have the potential to serve as a novel treatment strategy for augmentation of collateral flow in the chronically hypoperfused brain.

Therapeutic vascularization in regenerative medicine

Therapeutic angiogenesis, that is, the generation of new vessels by delivery of specific factors, is required both for rapid vascularization of tissue‐engineered constructs and to treat ischemic conditions. Vascular endothelial growth factor (VEGF) is the master regulator of angiogenesis. However, uncontrolled expression can lead to aberrant vascular growth and vascular tumors (angiomas). Major challenges to fully exploit VEGF potency for therapy include the need to precisely control in vivo distribution of growth factor dose and duration of expression. In fact, the therapeutic window of VEGF delivery depends on its amount in the microenvironment around each producing cell rather than on the total dose, since VEGF remains tightly bound to extracellular matrix (ECM). On the other hand, short‐term expression of less than about 4 weeks leads to unstable vessels, which promptly regress following cessation of the angiogenic stimulus. Here, we will briefly overview some key aspects of the biology of VEGF and angiogenesis and discuss their therapeutic implications with a particular focus on approaches using gene therapy, genetically modified progenitors, and ECM engineering with recombinant factors. Lastly, we will present recent insights into the mechanisms that regulate vessel stabilization and the switch between normal and aberrant vascular growth after VEGF delivery, to identify novel molecular targets that may improve both safety and efficacy of therapeutic angiogenesis.

Mechanically Defined Microenvironment Promotes Stabilization of Microvasculature, Which Correlates with the Enrichment of a Novel Piezo-1+ Population of Circulating CD11b+ /CD115+ Monocytes

Vascularization is a critical step in the restoration of cellular homeostasis. Several strategies including localized growth factor delivery, endothelial progenitor cells, genetically engineered cells, gene therapy, and prevascularized implants have been explored to promote revascularization. But, long-term stabilization of newly induced vessels remains a challenge. It has been shown that fibroblasts and mesenchymal stem cells can stabilize newly induced vessels. However, whether an injected biomaterial alone can serve as an instructive environment for angiogenesis remains to be elucidated. It is reported here that appropriate vascular branching, and long-term stabilization can be promoted simply by implanting a hydrogel with stiffness matching that of fibrin clot. A unique subpopulation of circulating CD11b⁺ myeloid and CD11b⁺ /CD115⁺ monocytes that express the stretch activated cation channel Piezo-1, which is enriched prominently in the clot-like hydrogel, is identified. These findings offer evidence for a mechanobiology paradigm in angiogenesis involving an interplay between mechanosensitive circulating cells and mechanics of tissue microenvironment.

Vascular endothelial growth factor biology for regenerative angiogenesis

Despite major advances in medical, catheter-based or surgical treatment, cardiovascular diseases such as peripheral artery disease and coronary artery disease still cause significant morbidity and mortality. Furthermore, many patients do not qualify for catheter-based treatment or bypass surgery because of advanced disease or surgical risk. There is therefore an urgent need for novel treatment strategies. Therapeutic angiogenesis aims to restore blood flow to ischaemic tissue by stimulating the growth of new blood vessels through the local delivery of angiogenic factors, and may thus be an attractive treatment alternative for these patients. Angiogenesis is a complex process and the growth of normal, stable and functional vasculature depends on the coordinated interplay of different cell types and growth factors. Vascular endothelial growth factor-A (VEGF) is the fundamental regulator of vascular growth and the key target of therapeutic angiogenesis approaches. However, first-generation clinical trials of VEGF gene therapy have been disappointing, and a clear clinical benefit has yet to be established. In particular, VEGF delivery (a) appears to have a very limited therapeutic window in vivo: low doses are safe but mostly inefficient, whereas higher doses become rapidly unsafe; and (b) requires a sustained expression in vivo of at least about four weeks to achieve stable vessels that persist after cessation of the angiogenic stimulus. Here we will review the current understanding of how VEGF induces the growth of normal or pathological blood vessels, what limitations for the controlled induction of safe and efficient angiogenesis are intrinsically linked to the biological properties of VEGF, and how this knowledge can guide the design of more effective strategies for therapeutic angiogenesis.

PDGF-BB regulates splitting angiogenesis in skeletal muscle by limiting VEGF-induced endothelial proliferation

VEGF induces normal or aberrant angiogenesis depending on its dose in the microenvironment around each producing cell in vivo. This transition depends on the balance between VEGF-induced endothelial stimulation and PDGF-BB-mediated pericyte recruitment, and co-expression of PDGF-BB normalizes aberrant angiogenesis despite high VEGF doses. We recently found that VEGF over-expression induces angiogenesis in skeletal muscle through an initial circumferential vascular enlargement followed by longitudinal splitting, rather than sprouting. Here we investigated the cellular mechanism by which PDGF-BB co-expression normalizes VEGF-induced aberrant angiogenesis. Monoclonal populations of transduced myoblasts, expressing similarly high levels of VEGF alone or with PDGF-BB, were implanted in mouse skeletal muscles. PDGF-BB co-expression did not promote sprouting and angiogenesis that occurred through vascular enlargement and splitting. However, enlargements were significantly smaller in diameter, due to a significant reduction in endothelial proliferation, and retained pericytes, which were otherwise lost with high VEGF alone. A time-course of histological analyses and repetitive intravital imaging showed that PDGF-BB co-expression anticipated the initiation of vascular enlargement and markedly accelerated the splitting process. Interestingly, quantification during in vivo imaging suggested that a global reduction in shear stress favored the initiation of transluminal pillar formation during VEGF-induced splitting angiogenesis. Quantification of target gene expression showed that VEGF-R2 signaling output was significantly reduced by PDGF-BB co-expression compared to VEGF alone. In conclusion, PDGF-BB co-expression prevents VEGF-induced aberrant angiogenesis by modulating VEGF-R2 signaling and endothelial proliferation, thereby limiting the degree of circumferential enlargement and enabling efficient completion of vascular splitting into normal capillary networks despite high VEGF doses.

Bone and Soft Tissue Sarcomas in the Follow-Up of Hodgkin's Disease

Prolonged follow-up of large series of patients treated for Hodgkin's disease with an intensive therapeutic approach has demonstrated an incidence of second tumors of around 5–10%. Acute leukemia is the most frequent second neoplasia, and treatments including alkylating agents and radiotherapy seem to be correlated with a higher risk of this fatal complication. Bone and soft tissue sarcomas have rarely been observed after treatment of Hodgkin's disease, and only a few cases are described in the literature. Four cases observed at the Istituto Nazionale Tumori of Milano in a large series of nearly 800 patients treated over the last two decades with different modalities are presented. One case of chondrosarcoma and 3 cases of soft tissue sarcomas were diagnosed after a median and mean interval of 50 and 70 months, respectively (range 49–96). Three patients had been treated with radiotherapy plus chemotherapy (MOPP, 2 cases; ABVD, 1 case), and one with radiotherapy alone. The site of the second tumor was always within an irradiated area, which had received a dose ranging from 10 to 43 Gy. Prognosis of secondary bone and soft tissue sarcomas is very poor. Three of our cases died 14, 15 and 19 months after diagnosis; only one patient is alive, 3 months after diagnosis of a chondrosarcoma. The problem of second tumors in patients treated for Hodgkin's disease requires a careful evaluation of aggressive treatment modalities to minimize the risks of this severe complication.

Indications and Results of Telecobalt Therapy in Epithelial Tumors of the Oral Cavity

A report of the results obtained in 194 cases of epithelial tumors of the oral cavity subjected to telecobalt therapy between June 1958 and December 1964 at the Institute of Radiology, University of Milan, and the Radiology Division of the National Cancer Institute. The criteria for establishing whether the treatment was indicated and the principles of selection of cases are specified. In the majority of cases the tumors were no longer circumscribed (T3-T4) and in over half the cases regional lymph node metastases were present when treatment commenced. Thirty-six patients had previously been subjected to radiotherapy or surgery. Telecobalt therapy was given almost exclusively to stationary fields using one or two portals of entry. Tumors of the floor of the mouth were often irradiated through wedges of lead. In 80% of the cases a tumor-dose of between 5000 and 6000 r was given over 6–8 weeks. At the end of treatment the tumor had completely disappeared in 22.7% of the patients, regressed to some extent in 40.6% and was unchanged or had deteriorated in 36.7%. The survival curves show that 2/3 of the patients died within two years of starting treatment; the five-year survival rate was 10.9%. This case-series confirmed that the prognosis is poorer in cases with regional lymph node metastases at the start of treatment and in patients subjected to telecobalt therapy for relapse after radiotherapy or surgery. The results obtained with telecobalt therapy proved to be considerably inferior to those obtained with curietherapy and so the latter is recommended in cancers of the oral cavity whenever it is feasible. Telecobalt therapy may be indicated, mainly as a symptomatic palliative, in very extensive infiltrating tumors adhering to the bone structures and in patients with inoperable lymph node metastases.

Lymphographic Evaluation in Ovarian Carcinoma of Epithelial Origin

From January 1973 to May 1974, 117 patients with ovarian carcinomas were evaluated with lymphography. The tumors were staged and classified histopathologically according to FIGO (1971). Considering all cases, lymphography showed nodal metastases in 44 patients (38%). Lymphography was positive in 36% of serous cystoadenocarcinomas, in 26 % of mucinous cystoadenocarcinomas, in 48 % of endometrioid carcinomas and in 36 % of unclassified carcinomas. Of the 10 cases not identified by cell type, lymphography was positive in 40 % of cases. In 68 % of cases bilateral involvement was found. The site of metastatic nodes was in 32 % of cases only in the iliac chains were both involved. Considering the single node chains we found 36 % of para-aortic, 27 % of common iliac, 35 % of external iliac and 2 % of inguinal involvement. Metastases were observed, regardless of histological type, in 25 % of cases in stage III, 62 % in stage IV, 54 % in recurrences and only in 5 % of cases in stage I. Therefore the lymphatic spread seems to occur in more advanced stages and in recurrences. In 28 of 117 patients node biopsy was performed. Histological-lymphographic correlation was correct in 7/7 positive cases and in 19/21 negative cases (93 %). These results show that lymphography is a reliable tool in the evaluation of ovarian cancer.

Clinical Staging and Treatment of Lymphosarcoma and Reticulum Cell Sarcoma

The Committee for the Study of Malignant Lymphomas of the National Cancer Institute of Milano in cooperation with the Institute of Radiology, University of Milano presents a new clinical classification for lymphosarcoma and reticulum cell sarcoma as well as the method of treatment adopted in these Institutes. For primary lymph node lesions the staging is identical to that already proposed for Hodgkin's disease. Stage I: disease limited to a single peripheric lymphatic region. Within this stage two groups can he distinguished: a) involvement of one single lymph node or few nodes limited to a small area of the region (unifocal lesions); b) involvement of many nodes spread throughout the region (uniregional lesions). Stage II: disease limited to two contiguous peripheric lymphatic regions, or to few deep nodes (mediastinal, retroperitoneal). Stage III: disease limited to two non contiguous peripheric lymphatic regions, or to many peripheric and/or deep (mediastinal, retroperitoneal) regions, provided the involvement is either above or below the diaphragm. Stage IV: generalized disease with involvement of lymph nodes above and below the diaphragm, or involvement of one or more lymphatic regions with concomitant involvement of visceral organs, bones, marrow, nervous system and skin. For primary pharyngeal lesions the T.N.M. nomenclature has been adopted. T1: unifocal lesion (e.g. nasopharynx, tonsil, uvula); T2: multifocal lesions (e. g. nasopharynx and tonsil, tonsils, tonsil and base of the tongue); T3: unifocal lesion with extension beyond the anatomical confine of the site of origin (e. g. base of the skull, paranasal sinuses, jaw, orbit); T4: multifocal lesions with extension beyond the anatomical confine of the site of origin. N0: no adenopathy; N1: ipsilateral contiguous adenopathy (submental and/or cervical); N2: bilateral contiguous adenopathy; N3: bilateral contiguous and/or supravicular adenopathy (unilateral or bilateral); N4: distant adenopathy. M–-: absence of metastases; M+: presence of metastases (visceral, osseous, nervous, cutaneous). The remaining primary extranodal lesions (visceral, osseous, cutaneous, etc.) are classified as local, regional and diffuse. Systemic symptoms and signs (fatigue, fever, night sweats, more than 10% weight loss, itching, anemia, leukocytosis, lymphocytopenia, high erythrosedimentation rate) must be recorded in each case to evaluate prognosis and proper treatment but are not important for staging the disease. In all stages with primary lymph node lesions endolymphatic radiotherapy with Lipiodol F I131 is indicated (10 ml in each foot with 2–5 mc/ml giving a tissue-dose of 15-20,000 rads). This is considered as radical as well as prophylactic treatment for those lymph nodes adequatelly filled with the contrast medium. In case of non filling or incomplete filling of part of the lymph node chains, treatment will be completed with external radiation therapy. Stage I and II are treated with radical radiation therapy. No prophylactic radiotherapy is given. If systemic symptoms and signs are still present after radiotherapy a course with anticancer drugs will be administered. Radiation therapy is given with high voltage or Co60 units. In radical treatments tumor doses of at least 3,000 rads within 3–4 weeks are administered to all involved lymphatic regions. In stage III radical radiotherapy follows a course of chemotherapy. In stage IV chemotherapy is the treatment of choice. Palliative radiotherapy is given to any bulk of tumors, wherever the location, when specific symptoms can be attributed to the masses. For primary pharyngeal lesions the primary focus (T1, T2, T3, T4) is always treated with radical radiation therapy (Co60 unit) which includes in the whole Waldeyer's ring. Prophylactic radiotherapy (Co60 unit with doses not less than 3,000 rads in 3–4 weeks) is given in N0 to the ipsilateral and in N1 to the contralateral submental and cervical lymphatic regions. In N1 and N2 the lymph node bearing areas are given radical radiation therapy. In N3 are irradiated prophylactically also the contralateral submental, cervical and supraclavicular lymphatic regions if clinically free of disease. Endolymphatic radiotherapy is performed only in T1 T2 T3 T4, N3 N4, M–- or M+ cases; otherwise diagnostic lymphangiography is performed and when pathologic nodes are present or suspected they are irradiated with Co60. Chemotherapy is given after the course of radiotherapy in N2 cases only if radical treatment has not been accomplished, while is always administered in combination with radical radiotherapy in N3 cases, and is considered the treatment of choice with palliative radiation therapy in N4 and M+ cases. The drug of choice is methyl-bis-(β-chloro-ethyl)-amine HCl (HN2) 0.4 mg/kg i.v. (single dose) for those patients who did not receive any previous course of chemotherapy. Otherwise, as well as during the course of the disease and in maintenance therapy, other polyfunctional alkylating agents, but chiefly chlorambucil (0.1–0.2 mg/kg/die, p. o.), vinblastine (0.10–0.15 mg/kg/week, i.v.), alone or every two weeks in combination with small daily doses of chlorambucil (5 mg/die, p. o.), methylhydrazine, hydroxyurea, and corticosteroids will be administered according to each clinical situation. Relapses in oropharynx can be treated with intraarterial infusions of amethopterine, vinblastine and cyclophosphamide. Radical surgery followed by a course of radiotherapy is reserved for primary lymphatic involvement only in specially selected patients in Stage I with unifocal lesions. Primary involvement of stomach, small bowel and colon is treated by surgical extirpation and radiotherapy. Splenectomy, lobectomy or pneumonectomy is indicated when these viscus are the only site of involvement. During pregnancy radiation therapy is not administered below the diaphragm and chemotherapy is not given during the first 4 months. The need for one internationally accepted clinical classification for lymphosarcoma and reticulum cell sarcoma is stressed.

Preferential Sites and Mode of Spread of Hodgkin's Disease and Lymphoreticular Sarcomas on the Basis of Clinical Evaluation of 500 Cases

The preferential sites and mode of spread in 500 consecutive untreated patients with malignant lymphomas (200 Hodgkin's diseases, 150 lymphosarcomas and 150 reticulum cell sarcomas) have been studied. After a detailed diagnosis all patients with primary involvement of lymph nodes and spleen were staged according to the international four-stage clinical classification proposed at Rye in 1965. The lymphoreticular sarcomas with primary onset in Waldeyer's ring were staged according to the T.N.M. classification as modified in Milano by the National Cancer Institute in 1965. Patients with involvement of viscera or tissues without apparent disease in the lymph nodes, spleen or pharynx were listed separately. Primary involvement in Hodgkin's disease was confined in 99.5 % to lymph nodes and spleen. In lymphosarcoma and in reticulum cell sarcoma there was a high primary involvement of Waldeyer's ring (20 % and 53 % respectively) and in other extranodal sites (11–12%). Besides the cervical regions the distribution of lymph node involvement in Hodgkin's disease was predominantly in the mediastinum (20%) and in the paraaortic area (20%), while in lymphoreticular sarcomas mainly in the axillary (16%), iliac (23%) and inguinal (17%) regions. In the lymphoreticular sarcomas with primary onset in Waldeyer's ring the disease on first admission was limited to the pharynx and to the neek nodes in 73 % of cases. Study of the mode of spread showed that in untreated Hodgkin's disease the number of cases with contiguous involvement was 66 % while in lymphoreticular sarcomas it was only 35 %. Further, after localized radiation therapy Hodgkin's disease has a higher (72%) tendency to recur in adjacent lymphoid regions than lymphoreticular sarcomas with primary involvement in nodes and spleen (45%). The therapeutic implications of this study are discussed. The most important conclusion is that prophylactic irradiation should be given to localized Hodgkin's disease and not to lymphoreticular sarcomas with the exception of those arising in Waldeyer's ring.

Non-Hodgkin's Lymphomas of Waldeyer's Ring

From 1970 to 1980, 171 consecutive cases with non-Hodgkin's lymphomas (NHL) of Waldeyer's ring were admitted to this Institute. The cases were reviewed to evaluate whether involvement of Waldeyer's ring might represent a distinct clinicopathologic entity. Adequate pathologic staging was performed in 86% of cases. All slides were reviewed, and the histologic diagnosis given according to the Rappaport classification, the Kiel classification, and the recent Working Formulation of NHL for Clinical Usage. Waldeyer's ring alone was involved in 12.3% of the cases at presentation; regional nodes were positive in one-third (35.7%), and distant involvement was detected in half of the patients (52%). The tonsils represented the most frequent site of involvement by NHL within Waldeyer's ring. Treatments employed were heterogeneous, but most of the patients with stage I-II received radiotherapy alone. The present series shows that the association of involvement of Waldeyer's ring and the stomach by NHL occurs in less than 10% of the cases. Treatment results and patterns of recurrence fail to differentiate NHL involving Waldeyer's ring from those of other sites. Prognosis remains related to the classical variables and is independent of the site of onset.

Follow-Up of Pathological Stage I and IIA Supradiaphragmatic Hodgkin's Disease Primarily Treated with Radiotherapy

One hundred and fifty-five consecutive previously untreated adult patients with supradiaphragmatic pathologic stage IA (71) and IIA (84) Hodgkin's disease treated only with radiotherapy (RT) at the Istituto Nazionale Tumori of Milano from 1970 to 1978 were reviewed. Staging procedures included lymphangiography and laparotomy in all cases. Most patients were irradiated with a conventional cobalt machine. Mantle fields were adopted for 36.8% of cases, mainly at stage I, whereas 63.2% received mantle plus paraaortal irradiation. Doses were above 40 Gy for involved sites and 35–40 Gy for prophylactically irradiated nodes. Minimum and median follow-up were 30 months and 6 years, respectively. All patients achieved complete remission at the end of RT. As of June 1981, 89 of 155 patients (57.5%) were alive and free from progression, 60.6% at stage I, and 54.8% at stage II. Relapses occurred in 54 of 155 cases (35%) after a median free interval of 21 months. Marginal recurrences accounted for 5.8%, true recurrences for 9%, nodal extensions for 8.4%, and extranodal extensions for 11.6%. Males older than 40 years and mediastinal involvement were correlated with higher relapse rates. Salvage treatment consisted of RT alone in 8 patients and chemotherapy plus or minus RT in 44, whereas 2 patients died before a new treatment could start. As of June 1981, 38 of 54 relapsed patients (70.4%) were alive and disease free, whereas 2 were alive with evidence of disease. Actuarial overall survival at 6 years was 90.3% for all cases, 97.1% for stage I, and 84.8% for stage II. Treatment toxicity was analyzed, and problems concerning surgical staging procedures, optimal RT and role of chemotherapy as primary or salvage treatment were discussed.

EphrinB2/EphB4 signaling regulates non-sprouting angiogenesis by VEGF

Vascular endothelial growth factor (VEGF) is the master regulator of angiogenesis, whose best-understood mechanism is sprouting. However, therapeutic VEGF delivery to ischemic muscle induces angiogenesis by the alternative process of intussusception, or vascular splitting, whose molecular regulation is essentially unknown. Here, we identify ephrinB2/EphB4 signaling as a key regulator of intussusceptive angiogenesis and its outcome under therapeutically relevant conditions. EphB4 signaling fine-tunes the degree of endothelial proliferation induced by specific VEGF doses during the initial stage of circumferential enlargement of vessels, thereby limiting their size and subsequently enabling successful splitting into normal capillary networks. Mechanistically, EphB4 neither inhibits VEGF-R2 activation by VEGF nor its internalization, but it modulates VEGF-R2 downstream signaling through phospho-ERK1/2. In vivo inhibitor experiments show that ERK1/2 activity is required for EphB4 regulation of VEGF-induced intussusceptive angiogenesis. Lastly, after clinically relevant VEGF gene delivery with adenoviral vectors, pharmacological stimulation of EphB4 normalizes dysfunctional vascular growth in both normoxic and ischemic muscle. These results identify EphB4 as a druggable target to modulate the outcome of VEGF gene delivery and support further investigation of its therapeutic potential.

Myocardial infarction stabilization by cell-based expression of controlled Vascular Endothelial Growth Factor levels

Vascular Endothelial Growth Factor (VEGF) can induce normal or aberrant angiogenesis depending on the amount secreted in the microenvironment around each cell. Towards a possible clinical translation, we developed a Fluorescence Activated Cell Sorting (FACS)-based technique to rapidly purify transduced progenitors that homogeneously express a desired specific VEGF level from heterogeneous primary populations. Here, we sought to induce safe and functional angiogenesis in ischaemic myocardium by cell-based expression of controlled VEGF levels. Human adipose stromal cells (ASC) were transduced with retroviral vectors and FACS purified to generate two populations producing similar total VEGF doses, but with different distributions: one with cells homogeneously producing a specific VEGF level (SPEC), and one with cells heterogeneously producing widespread VEGF levels (ALL), but with an average similar to that of the SPEC population. A total of 70 nude rats underwent myocardial infarction by coronary artery ligation and 2 weeks later VEGF-expressing or control cells, or saline were injected at the infarction border. Four weeks later, ventricular ejection fraction was significantly worsened with all treatments except for SPEC cells. Further, only SPEC cells significantly increased the density of homogeneously normal and mature microvascular networks. This was accompanied by a positive remodelling effect, with significantly reduced fibrosis in the infarcted area. We conclude that controlled homogeneous VEGF delivery by FACS-purified transduced ASC is a promising strategy to achieve safe and functional angiogenesis in myocardial ischaemia.

Scaffold Composition Determines the Angiogenic Outcome of Cell-Based Vascular Endothelial Growth Factor Expression by Modulating Its Microenvironmental Distribution

Delivery of genetically modified cells overexpressing Vascular Endothelial Growth Factor (VEGF) is a promising approach to induce therapeutic angiogenesis in ischemic tissues. The effect of the protein is strictly modulated by its interaction with the components of the extracellular matrix. Its therapeutic potential depends on a sustained but controlled release at the microenvironmental level in order to avoid the formation of abnormal blood vessels. In this study, it is hypothesized that the composition of the scaffold plays a key role in modulating the binding, hence the therapeutic effect, of the VEGF released by 3D-cell constructs. It is found that collagen sponges, which poorly bind VEGF, prevent the formation of localized hot spots of excessive concentration, therefore, precluding the development of aberrant angiogenesis despite uncontrolled expression by a genetically engineered population of adipose tissue-derived stromal cells. On the contrary, after seeding on VEGF-binding egg-white scaffolds, the same cell population caused aberrantly enlarged vascular structures after 14 d. Collagen-based engineered tissues also induced a safe and efficient angiogenesis in both the patch itself and the underlying myocardium in rat models. These findings open new perspectives on the control and the delivery of proangiogenic stimuli, and are fundamental for the vascularization of engineered tissues/organs.

It Takes Two to Tango: Coupling of Angiogenesis and Osteogenesis for Bone Regeneration

Bone regeneration is a complex process requiring highly orchestrated interactions between different cells and signals to form new mineralized tissue. Blood vessels serve as a structural template, around which bone development takes place, and also bring together the key elements for bone homeostasis into the osteogenic microenvironment, including minerals, growth factors and osteogenic progenitor cells. Vascular endothelial growth factor (VEGF) is the master regulator of vascular growth and it is required for effective coupling of angiogenesis and osteogenesis during both skeletal development and postnatal bone repair. Here, we will review the current state of knowledge on the molecular cross-talk between angiogenesis and osteogenesis. In particular, we will focus on the role of VEGF in coupling these two processes and how VEGF dose can control the outcome, addressing in particular: (1) the direct influence of VEGF on osteogenic differentiation of mesenchymal progenitors; (2) the angiocrine functions of endothelium to regulate osteoprogenitors; (3) the role of immune cells, e.g., myeloid cells and osteoclast precursors, recruited by VEGF to the osteogenic microenvironment. Finally, we will discuss emerging strategies, based on the current biological understanding, to ensure rapid vascularization and efficient bone formation in regenerative medicine.

Two-Jet Rate in e^{+}e^{-} at Next-to-Next-to-Leading-Logarithmic Order

We present the first next-to-next-to-leading-logarithmic resummation for the two-jet rate in e^{+}e^{-} annihilation in the Durham and Cambridge algorithms. The results are obtained by extending the ares method to observables involving any global, recursively infrared and collinear safe jet algorithm in e^{+}e^{-} collisions. As opposed to other methods, this approach does not require a factorization theorem for the observables. We present predictions matched to next-to-next-to-leading order and a comparison to LEP data.

Engineered mesenchymal cell-based patches as controlled VEGF delivery systems to induce extrinsic angiogenesis

Therapeutic over-expression of Vascular Endothelial Growth Factor (VEGF) by transduced progenitors is a promising strategy to efficiently induce angiogenesis in ischemic tissues (e.g. limb muscle and myocardium), but tight control over the micro-environmental distribution of the dose is required to avoid induction of angioma-like tumors. Therapeutic VEGF release was achieved by purified transduced adipose mesenchymal stromal cells (ASC) that homogeneously produce specific VEGF levels, inducing only normal angiogenesis after injection in non-ischemic tissues. However, the therapeutic potential of this approach mostly in the cardiac field is limited by the poor cell survival and the restricted area of effect confined to the cell-injection site. The implantation of cells previously organized in vitro in 3D engineered tissues could overcome these issues. Here we hypothesized that collagen sponge-based construct (patch), generated by ASC expressing controlled VEGF levels, can function as delivery device to induce angiogenesis in surrounding areas (extrinsic vascularization). A 7-mm-thick acellular collagen scaffold (empty), sutured beneath the patch, provided a controlled and reproducible model to clearly investigate the ongoing angiogenesis in subcutaneous mice pockets. VEGF-expressing ASC significantly increased the capillary in-growth inside both the patch itself and the empty scaffold compared to naïve cells, leading to significantly improved survival of implanted cells. These data suggest that this strategy confers control (i) on angiogenesis efficacy and safety by means of ASC expressing therapeutic VEGF levels and (ii) over the treated area through the specific localization in an engineered collagen sponge-based patch.

STATEMENT OF SIGNIFICANCE

Development of efficient pro-angiogenic therapies to restore the micro-vascularization in ischemic tissues is still an open issue. Although extensively investigated, the promising approach based on injections of progenitors transduced to over-express Vascular Endothelial Growth Factor (VEGF) has still several limitations: (i) need of a tight control over the microenvironmental VEGF dose to avoid angioma-like tumor growth; (ii) poor implanted cell survival; (iii) effect area restricted mainly to the injection sites. Here, we aimed to overcome these drawbacks by generating a novel cell-based controlled VEGF delivery device. In particular, transduced mesenchymal cells, purified to release a sustained, safe and efficient VEGF dose, were organized in three-dimensional engineered tissues to improve cell survival and provide a uniform vascularization throughout both the mm-thick implanted constructs themselves and the surrounding area.

Spontaneous In Vivo Chondrogenesis of Bone Marrow-Derived Mesenchymal Progenitor Cells by Blocking Vascular Endothelial Growth Factor Signaling

: Chondrogenic differentiation of bone marrow-derived mesenchymal stromal/stem cells (MSCs) can be induced by presenting morphogenetic factors or soluble signals but typically suffers from limited efficiency, reproducibility across primary batches, and maintenance of phenotypic stability. Considering the avascular and hypoxic milieu of articular cartilage, we hypothesized that sole inhibition of angiogenesis can provide physiological cues to direct in vivo differentiation of uncommitted MSCs to stable cartilage formation. Human MSCs were retrovirally transduced to express a decoy soluble vascular endothelial growth factor (VEGF) receptor-2 (sFlk1), which efficiently sequesters endogenous VEGF in vivo, seeded on collagen sponges and immediately implanted ectopically in nude mice. Although naïve cells formed vascularized fibrous tissue, sFlk1-MSCs abolished vascular ingrowth into engineered constructs, which efficiently and reproducibly developed into hyaline cartilage. The generated cartilage was phenotypically stable and showed no sign of hypertrophic evolution up to 12 weeks. In vitro analyses indicated that spontaneous chondrogenic differentiation by blockade of angiogenesis was related to the generation of a hypoxic environment, in turn activating the transforming growth factor-β pathway. These findings suggest that VEGF blockade is a robust strategy to enhance cartilage repair by endogenous or grafted mesenchymal progenitors. This article outlines the general paradigm of controlling the fate of implanted stem/progenitor cells by engineering their ability to establish specific microenvironmental conditions rather than directly providing individual morphogenic cues.

SIGNIFICANCE

Chondrogenic differentiation of mesenchymal stromal/stem cells (MSCs) is typically targeted by morphogen delivery, which is often associated with limited efficiency, stability, and robustness. This article proposes a strategy to engineer MSCs with the capacity to establish specific microenvironmental conditions, supporting their own targeted differentiation program. Sole blockade of angiogenesis mediated by transduction for sFlk-1, without delivery of additional morphogens, is sufficient for inducing MSC chondrogenic differentiation. The findings represent a relevant step forward in the field because the method allowed reducing interdonor variability in MSC differentiation efficiency and, importantly, onset of a stable, nonhypertrophic chondrocyte phenotype.

VEGF dose regulates vascular stabilization through Semaphorin3A and the Neuropilin-1+ monocyte/TGF-β1 paracrine axis

VEGF is widely investigated for therapeutic angiogenesis, but while short-term delivery is desirable for safety, it is insufficient for new vessel persistence, jeopardizing efficacy. Here, we investigated whether and how VEGF dose regulates nascent vessel stabilization, to identify novel therapeutic targets. Monoclonal populations of transduced myoblasts were used to homogeneously express specific VEGF doses in SCID mouse muscles. VEGF was abrogated after 10 and 17 days by Aflibercept treatment. Vascular stabilization was fastest with low VEGF, but delayed or prevented by higher doses, without affecting pericyte coverage. Rather, VEGF dose-dependently inhibited endothelial Semaphorin3A expression, thereby impairing recruitment of Neuropilin-1-expressing monocytes (NEM), TGF-β1 production and endothelial SMAD2/3 activation. TGF-β1 further initiated a feedback loop stimulating endothelial Semaphorin3A expression, thereby amplifying the stabilizing signals. Blocking experiments showed that NEM recruitment required endogenous Semaphorin3A and that TGF-β1 was necessary to start the Semaphorin3A/NEM axis. Conversely, Semaphorin3A treatment promoted NEM recruitment and vessel stabilization despite high VEGF doses or transient adenoviral delivery. Therefore, VEGF inhibits the endothelial Semaphorin3A/NEM/TGF-β1 paracrine axis and Semaphorin3A treatment accelerates stabilization of VEGF-induced angiogenesis.

Rapid and efficient magnetization of mesenchymal stem cells by dendrimer-functionalized magnetic nanoparticles

Aim: Rapid and efficient magnetization of human bone marrow stromal cells (BMSC) through functionalized magnetic nanoparticles (MNP). Methods: MNP were functionalized with poly(epsilon-lysine) dendrons exposing carboxybetaine residue (CB-MNP) to enhance binding to the cellular glycocalix. BMSC were incubated with CB-MNP or non-functionalized PAA-MNP for 5–30 min in suspension. Results: CB-MNP functionalization increased the magnetization efficiency by threefold. Remarkably, 66% of cells were magnetized after only 5 min and the maximum efficiency of >80% was reached by 15 min. BMSC viability, proliferation and differentiation were not impaired: actually, adipogenic and osteogenic differentiation were even improved. Conclusion: Carboxybetaine-dendron functionalization ensured rapid and efficient BMSC magnetization and allowed innovative suspension labeling, with a potential for bypassing adhesion culture of progenitors for regenerative medicine.

Three dimensional multi-cellular muscle-like tissue engineering in perfusion-based bioreactors

Conventional tissue engineering strategies often rely on the use of a single progenitor cell source to engineer in vitro biological models; however, multi-cellular environments can better resemble the complexity of native tissues. Previous described co-culture models used skeletal myoblasts, as parenchymal cell source, and mesenchymal or endothelial cells, as stromal component. Here, we propose instead the use of adipose tissue-derived stromal vascular fraction cells, which include both mesenchymal and endothelial cells, to better resemble the native stroma. Percentage of serum supplementation is one of the crucial parameters to steer skeletal myoblasts toward either proliferation (20%) or differentiation (5%) in two-dimensional culture conditions. On the contrary, three-dimensional (3D) skeletal myoblast culture often simply adopts the serum content used in monolayer, without taking into account the new cell environment. When considering 3D cultures of mm-thick engineered tissues, homogeneous and sufficient oxygen supply is paramount to avoid formation of necrotic cores. Perfusion-based bioreactor culture can significantly improve the oxygen access to the cells, enhancing the viability and the contractility of the engineered tissues. In this study, we first investigated the influence of different serum supplementations on the skeletal myoblast ability to proliferate and differentiate during 3D perfusion-based culture. We tested percentages of serum promoting monolayer skeletal myoblast-proliferation (20%) and differentiation (5%) and suitable for stromal cell culture (10%) with a view to identify the most suitable condition for the subsequent co-culture. The 10% serum medium composition resulted in the highest number of mature myotubes and construct functionality. Co-culture with stromal vascular fraction cells at 10% serum also supported the skeletal myoblast differentiation and maturation, hence providing a functional engineered 3D muscle model that resembles the native multi-cellular environment.

Extracellular matrix and growth factor engineering for controlled angiogenesis in regenerative medicine

Blood vessel growth plays a key role in regenerative medicine, both to restore blood supply to ischemic tissues and to ensure rapid vascularization of clinical-size tissue-engineered grafts. For example, vascular endothelial growth factor (VEGF) is the master regulator of physiological blood vessel growth and is one of the main molecular targets of therapeutic angiogenesis approaches. However, angiogenesis is a complex process and there is a need to develop rational therapeutic strategies based on a firm understanding of basic vascular biology principles, as evidenced by the disappointing results of initial clinical trials of angiogenic factor delivery. In particular, the spatial localization of angiogenic signals in the extracellular matrix (ECM) is crucial to ensure the proper assembly and maturation of new vascular structures. Here, we discuss the therapeutic implications of matrix interactions of angiogenic factors, with a special emphasis on VEGF, as well as provide an overview of current approaches, based on protein and biomaterial engineering that mimic the regulatory functions of ECM to optimize the signaling microenvironment of vascular growth factors.

Macrophage-mediated angiogenic activation of outgrowth endothelial cells in co-culture with primary osteoblasts

The successful vascularisation of complex tissue engineered constructs for bone regeneration is still a major challenge in the field of tissue engineering. In this context, co-culture systems of endothelial cells and osteoblasts represent a promising approach to advance the formation of a stable vasculature as well as an excellent in vitro model to identify factors that positively influence bone healing processes, including angiogenesis. Under physiological conditions, the activation phase of angiogenesis is mainly induced by hypoxia or inflammation. Inflammatory cells such as macrophages secrete proinflammatory cytokines and proangiogenic growth factors, finally leading to the formation of new blood vessels. The aim of this study was to investigate if macrophages might positively influence the formation of microvessel-like structures via inflammatory mechanisms in a co-culture system consisting of human outgrowth endothelial cells (OECs) and primary osteoblasts. Treatment of co-cultures with macrophages (induced from THP-1) resulted in a higher number of microvessel-like structures formed by OECs compared to the co-culture. This change correlated with a significantly higher concentration of the proangiogenic VEGF in cell culture supernatants of triple-cultures and was accompanied by an increase in the expression of different proinflammatory cytokines, such as IL-6, IL-8 and TNFα. In addition, the expression of E-selectin and ICAM-1, adhesion molecules which are strongly involved in the interaction between leukocytes and endothelial cells during the process of inflammation was also found to be higher in triple-cultures compared to the double co-cultures, documenting an ongoing proinflammatory stimulus. These results raise the possibility of actively using pro-inflammatory stimuli in a tissue engineering context to accelerate healing mechanisms.

Non-adherent mesenchymal progenitors from adipose tissue stromal vascular fraction

In primary human bone marrow cultures, the initial adherent cell fraction has been shown to provide a microenvironment for self-renewal of primitive non-adherent mesenchymal progenitors (non-adherent progenitors of bone marrow stroma [BM-NAMP]), with increased differentiation potential compared to adherent colony-forming units-fibroblast (CFU-f). The present study investigates whether NAMP exist also in cultures of stromal vascular fraction (SVF) cells derived from human adipose tissue. Adipose-tissue NAMP (AT-NAMP) were shown to be stably non-adherent and their number correlated with the number of the initial adhering CFU-f. Unlike BM-NAMP, AT-NAMP did not propagate in suspension in serial replating experiments and the number of colonies steadily decreased with each replating step. However, when AT-NAMP were kept on the initially adhering SVF cells, they could significantly expand without loss of clonogenic, proliferation, and differentiation potential. Although AT-NAMP progeny differentiated into mesodermal lineages similar to that of adherent CFU-f, it was enriched in early mesenchymal progenitor populations, characterized by increased expression of SSEA-4 and CD146. Furthermore, FGF-2 supported AT-NAMP survival and could not be replaced by another mitogenic factor, such as platelet derived growth factor BB. In conclusion, these data suggest that the SVF adherent fraction provides niche signals that regulate the expansion of adipose non-adherent mesenchymal progenitors with the maintenance of their potency. The biological differences described between BM- and AT-NAMP further qualify the properties of the stroma from different tissues and will be relevant for the selection of a cell source for specific regeneration strategies.

Induction of aberrant vascular growth, but not of normal angiogenesis, by cell-based expression of different doses of human and mouse VEGF is species-dependent

Therapeutic angiogenesis by vascular endothelial growth factor (VEGF) gene delivery is an attractive approach to treat ischemia. VEGF remains localized around each producing cell in vivo, and overexpression of mouse VEGF(164) (mVEGF(164)) induces normal or aberrant angiogenesis, depending strictly on its dose in the microenvironment in vivo. However, the dose-dependent effects of the clinically relevant factor, human VEGF(165) (hVEGF(165)), are unknown. Here we exploited a highly controlled gene delivery platform, based on clonal populations of transduced myoblasts overexpressing specific VEGF levels, to rigorously compare the in vivo dose-dependent effects of hVEGF(165) and mVEGF(164) in skeletal muscle of severe combined immune deficient (SCID) mice. While low levels of both factors efficiently induced similar amounts of normal angiogenesis, only high levels of mVEGF(164) caused widespread angioma-like structures, whereas equivalent or even higher levels of hVEGF(165) induced exclusively normal and mature capillaries. Expression levels were confirmed both in vitro and in vivo by enzyme-linked immunosorbent assay (ELISA) and quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). However, in vitro experiments showed that hVEGF(165) was significantly more effective in activating VEGF receptor signaling in human endothelial cells than mVEGF(164), while the opposite was true in murine endothelial cells. In conclusion, we found that, even though hVEGF is similarly efficient to the syngenic mVEGF in inducing angiogenesis at lower doses in a widely adopted and convenient mouse preclinical model, species-dependent differences in the relative activation of the respective receptors may specifically mask the toxic effects of high doses of the human factor.

Controlled angiogenesis in the heart by cell-based expression of specific vascular endothelial growth factor levels

Vascular endothelial growth factor (VEGF) can induce normal angiogenesis or the growth of angioma-like vascular tumors depending on the amount secreted by each producing cell because it remains localized in the microenvironment. In order to control the distribution of VEGF expression levels in vivo, we recently developed a high-throughput fluorescence-activated cell sorting (FACS)-based technique to rapidly purify transduced progenitors that homogeneously express a specific VEGF dose from a heterogeneous primary population. Here we tested the hypothesis that cell-based delivery of a controlled VEGF level could induce normal angiogenesis in the heart, while preventing the development of angiomas. Freshly isolated human adipose tissue-derived stem cells (ASC) were transduced with retroviral vectors expressing either rat VEGF linked to a FACS-quantifiable cell-surface marker (a truncated form of CD8) or CD8 alone as control (CTR). VEGF-expressing cells were FACS-purified to generate populations producing either a specific VEGF level (SPEC) or uncontrolled heterogeneous levels (ALL). Fifteen nude rats underwent intramyocardial injection of 10(7) cells. Histology was performed after 4 weeks. Both the SPEC and ALL cells produced a similar total amount of VEGF, and both cell types induced a 50%-60% increase in both total and perfused vessel density compared to CTR cells, despite very limited stable engraftment. However, homogeneous VEGF expression by SPEC cells induced only normal and stable angiogenesis. Conversely, heterogeneous expression of a similar total amount by the ALL cells caused the growth of numerous angioma-like structures. These results suggest that controlled VEGF delivery by FACS-purified ASC may be a promising strategy to achieve safe therapeutic angiogenesis in the heart.

Higgs- and Z-boson production with a jet veto

We derive first next-to-next-to-leading logarithmic resummations for jet-veto efficiencies in Higgs and Z-boson production at hadron colliders. Matching with next-to-next-to-leading order results allows us to provide a range of phenomenological predictions for the LHC, including cross-section results, detailed uncertainty estimates, and comparisons to current widely used tools.

Cell and gene therapy approaches for cardiac vascularization

Despite encouraging preclinical results for therapeutic angiogenesis in ischemia, a suitable approach providing sustained, safe and efficacious vascular growth in the heart is still lacking. Vascular Endothelial Growth Factor (VEGF) is the master regulator of angiogenesis, but it also can easily induce aberrant and dysfunctional vascular growth if its expression is not tightly controlled. Control of the released level in the microenvironment around each cell in vivo and its distribution in tissue are critical to induce stable and functional vessels for therapeutic angiogenesis. The present review discusses the limitations and perspectives of VEGF gene therapy and of different cell-based approaches for the implementation of therapeutic angiogenesis in the treatment of cardiac ischemia.

The effect of controlled expression of VEGF by transduced myoblasts in a cardiac patch on vascularization in a mouse model of myocardial infarction

Key requirements for cardiac tissue engineering include the maintenance of cell viability and function and the establishment of a perfusable vascular network in millimeters thick and compact cardiac constructs upon implantation. We investigated if these requirements can be met by providing an intrinsic vascularization stimulus (via sustained action of VEGF secreted at a controlled rate by transduced myoblasts) to a cardiac patch engineered under conditions of effective oxygen supply (via medium flow through channeled elastomeric scaffolds seeded with neonatal cardiomyocytes). We demonstrate that this combined approach resulted in increased viability, vascularization and functionality of the cardiac patch. After implantation in a mouse model of myocardial infarction, VEGF-expressing patches displayed significantly improved engraftment, survival and differentiation of cardiomyocytes, leading to greatly enhanced contractility as compared to controls not expressing VEGF. Controlled VEGF expression also mediated the formation of mature vascular networks, both within the engineered patches and in the underlying ischemic myocardium. We propose that this combined cell-biomaterial approach can be a promising strategy to engineer cardiac patches with intrinsic and extrinsic vascularization potential.

FACS-purified myoblasts producing controlled VEGF levels induce safe and stable angiogenesis in chronic hind limb ischemia

We recently developed a method to control the in vivo distribution of vascular endothelial growth factor (VEGF) by high throughput Fluorescence-Activated Cell Sorting (FACS) purification of transduced progenitors such that they homogeneously express specific VEGF levels. Here we investigated the long-term safety of this method in chronic hind limb ischemia in nude rats. Primary myoblasts were transduced to co-express rat VEGF-A₁₆₄ (rVEGF) and truncated ratCD8a, the latter serving as a FACS-quantifiable surface marker. Based on the CD8 fluorescence of a reference clonal population, which expressed the desired VEGF level, cells producing similar VEGF levels were sorted from the primary population, which contained cells with very heterogeneous VEGF levels. One week after ischemia induction, 12 × 10⁶ cells were implanted in the thigh muscles. Unsorted myoblasts caused angioma-like structures, whereas purified cells only induced normal capillaries that were stable after 3 months. Vessel density was doubled in engrafted areas, but only approximately 0.1% of muscle volume showed cell engraftment, explaining why no increase in total blood flow was observed. In conclusion, the use of FACS-purified myoblasts granted the cell-by-cell control of VEGF expression levels, which ensured long-term safety in a model of chronic ischemia. Based on these results, the total number of implanted cells required to achieve efficacy will need to be determined before a clinical application.

Therapeutic angiogenesis due to balanced single-vector delivery of VEGF and PDGF-BB

Therapeutic angiogenesis by delivery of vascular growth factors is an attractive strategy for treating debilitating occlusive vascular diseases, yet clinical trials have thus far failed to show efficacy. As a result, limb amputation remains a common outcome for muscle ischemia due to severe atherosclerotic disease, with an overall incidence of 100 per million people in the United States per year. A challenge has been that the angiogenic master regulator vascular endothelial growth factor (VEGF) induces dysfunctional vessels, if expressed outside of a narrow dosage window. We tested the hypothesis that codelivery of platelet-derived growth factor-BB (PDGF-BB), which recruits pericytes, could induce normal angiogenesis in skeletal muscle irrespective of VEGF levels. Coexpression of VEGF and PDGF-BB encoded by separate vectors in different cells or in the same cells only partially corrected aberrant angiogenesis. In marked contrast, coexpression of both factors in every cell at a fixed relative level via a single bicistronic vector led to robust, uniformly normal angiogenesis, even when VEGF expression was high and heterogeneous. Notably, in an ischemic hindlimb model, single-vector expression led to efficient growth of collateral arteries, revascularization, increased blood flow, and reduced tissue damage. Furthermore, these results were confirmed in a clinically applicable gene therapy approach by adenoviral-mediated delivery of the bicistronic vector. We conclude that coordinated expression of VEGF and PDGF-BB via a single vector constitutes a novel strategy for harnessing the potency of VEGF to induce safe and efficacious angiogenesis.