Ischemic wound revascularization by the stromal vascular fraction relies on host-donor hybrid vessels

Nonhealing wounds place a significant burden on both quality of life of affected patients and health systems. Skin substitutes are applied to promote the closure of nonhealing wounds, although their efficacy is limited by inadequate vascularization. The stromal vascular fraction (SVF) from the adipose tissue is a promising therapy to overcome this limitation. Despite a few successful clinical trials, its incorporation in the clinical routine has been hampered by their inconsistent results. All these studies concluded by warranting pre-clinical work aimed at both characterizing the cell types composing the SVF and shedding light on their mechanism of action. Here, we established a model of nonhealing wound, in which we applied the SVF in combination with a clinical-grade skin substitute. We purified the SVF cells from transgenic animals to trace their fate after transplantation and observed that it gave rise to a mature vascular network composed of arteries, capillaries, veins, as well as lymphatics, structurally and functionally connected with the host circulation. Then we moved to a human-in-mouse model and confirmed that SVF-derived endothelial cells formed hybrid human-mouse vessels, that were stabilized by perivascular cells. Mechanistically, SVF-derived endothelial cells engrafted and expanded, directly contributing to the formation of new vessels, while a population of fibro-adipogenic progenitors stimulated the expansion of the host vasculature in a paracrine manner. These data have important clinical implications, as they provide a steppingstone toward the reproducible and effective adoption of the SVF as a standard care for nonhealing wounds.

Effective revascularization of non-healing wounds by the human Stromal Vascular Fraction relies on direct cell integration and paracrine signals

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): PREFER

Introduction

With the increased prevalence of chronic diseases, non-healing wounds place a significant burden on the health system, with a prevalence of 2-5%, similar to the one of heart failure. They are persistent full-thickness skin lesions that affect patients suffering from vascular disorders, such as diabetes and peripheral artery disease. Skin implants and substitutes are currently applied to promote the closure of non-healing wounds. However, both approaches are poorly effective because of lack of appropriate vascularization.

Purpose

To promote the neo-vascularization of non-healing wounds, we use Stromal Vascular Fraction (SVF) as innovative therapeutic opportunity for wound treatment.

Here, we aim to 1) characterize and demonstrate the pro-angiogenic role of SVF cells and 2) provide pre-clinical evidence of the therapeutic efficacy of the human SVF in promoting the neo-vascularization in a new mouse model of ischemic, non-healing wound.

Methods

To assess capacity of SVF-derived cells to improve wound revascularization, we created a new model of non-healing wound generated by wounding an ischemic limb in mice. Human and mouse SVF was purified from adipose tissue and seeded on a clinical-grade skin substitute prior to its implantation on the ischemic wound of a recipient animal. The transplantation of human SVF into NSG immunodeficient mice was verified using species-specific antibodies, while the use of genetically modified mice allowed us to trace the fate of both endothelial and non-endothelial cells upon their transplantation into syngeneic recipient animals. The function of SVF-induced vessels was assessed by systemic injection of biotinylated lectin and by Single Photon Emission Tomography (SPECT) of the treated limb.

Results

At day 7 the implanted mouse SVF gives rise to a widespread vascular network composed by arteries, capillaries, veins, as well as lymphatic vessels. Similarly, human SVF-derived endothelial cells formed hybrid human-mouse vessels that were stabilized by perivascular cells. At both histological and functional analysis, these vessels were connected with the host circulatory system and determined a 2-fold increase in tissue perfusion. The comparison of the activity of human SVF from different donors allowed us to disclose its dual mechanisms of action.

Conclusions

Here we demonstrated the efficacy of the SVF in promoting neo-vascularization of a skin substitute in a mouse model of ischemic, non-healing wounds. Its therapeutic efficacy relies on dual mechanisms of action. On the one hand, SVF-derived ECs engraft and expand, directly forming new vascular units that colonize the scaffold and extend into surrounding tissues. On the other hand, the mesenchymal progenitors stimulate the expansion of the host vasculature, which extends into the scaffold, with the eventual appearance of donor-host hybrid vessels.

Collectively, these data support the use of human SVF as a powerful cell therapy to treat non-healing wounds.

Data on soil physicochemical properties and chemical composition of rainfall and of throughfall and stemflow generated by Turkey oak trees (Quercus cerris L.) in acid and sub-alkaline soils

We report data on the physicochemical properties of soils collected in two adjacent areas, one acid and one sub-alkaline, both developed on sequential beds of Plio-pleistocene marine sediments, and on the chemical composition of ecological solutions (rainfall, throughfall and stemflow) separately collected in the two areas. Throughfall and stemflow were generated by Turkey oak trees (Quercus cerris L.), which was the dominant tree species in both study areas. These data are related to the original article "Soil affects throughfall and stemflow under Turkey oak (Quercus cerris L.)" (Corti et al., 2019) [1].

From rainfall to throughfall in a maritime vineyard

This study deals with the characteristics of throughfall produced by vine (Vitis vinifera L.) in one of the most common pedoclimatic conditions for grape production: a soil derived from marine sediments under a temperate Mediterranean climate, and located rather close to the seacoast. To distinguish the contribution of the plant from that of the atmospheric deposition, the throughfall was collected for more than one year under real and artificial (plastic) vines; for the same period, also the bulk precipitation was collected. The solution collected were analysed for pH, electrical conductivity, and concentration of cations and anions. For each event, the ionic fluxes of bulk precipitation and throughfall were calculated. Results indicated that the chemical composition of the bulk precipitation was strongly influenced by the proximity of the seashore and, to a lesser extent, by local anthropic activities and windblown material coming from distant areas. The chemical composition of the throughfall was affected by the same factors of bulk precipitation, but also by solubilisation of dry deposition trapped by the canopies, agronomic practices, plant, and living-on-the-leaves microorganisms. The comparison of the characteristics of the throughfall of the real with the artificial vines revealed that the vines are a source of Mg and K. During winter season, the reduction of Ca, NH(4) and PO(4) from bulk precipitation to throughfall was ascribed to the formation of biogenic minerals on the plant surface. The presence of these minerals was proved by X-ray diffraction on the powders collected during the winter season on the surface of cordons and fruiting canes. We conclude that an approach to the estimation of the nutritional potentiality of the soil that includes the contribution of the throughfall is functional to the management of the agro-ecosystem.

Mechanisms associated with immunoregulation in human American cutaneous leishmaniasis

Mechanisms possibly involved in the regulation of the immune response were evaluated in 49 patients with American cutaneous leishmaniasis (ACL). The patients were classified on the basis of clinical and histopathological criteria as suffering localized (LCL), mucocutaneous (MCL) or diffuse (DCL) forms of the disease. A significant leishmanial antigen-induced suppression of in vitro mitogen responsiveness was demonstrated in the DCL group, but not in the other two diseases states. Lack of suppressive activity was particularly evident in MCL, this being the group that presented the highest in vivo and in vitro reactivity to the parasite antigens. In fact, a significant inverse correlation was found between the degree of suppression and the antigen-induced lymphocyte proliferative response. In contrast, a mixture of mononuclear cells from MCL patients and normal subjects showed higher that expected responses to mitogen, while this increase was not observed in co-cultures of DCL and normal mononuclear cells. Due to their possible modulatory influences, circulating immune complexes were also evaluated in these patient groups, higher levels being found in MCL and DCL patients than in either LCL or controls. The possible mechanisms involved in the regulation of the immune response to the protozoan in the complex disease spectrum of ACL are discussed in relation to anergy in DCL and hyperresponsiveness in MCL.

Characterization of the cellular immune response in American cutaneous leishmaniasis

The in vitro and in vivo cellular immune reactivity of 49 patients with American cutaneous leishmaniasis (ACL) was evaluated using mitogens and parasite antigens. Patients were examined before treatment and were classified on the basis of clinical and histopathological criteria as suffering localized cutaneous leishmaniasis (LCL, 32 patients) or mucocutaneous leishmaniasis (MCL, 11 patients). A small group (6 patients) of treated diffuse cutaneous leishmaniasis (DCL) patients was also examined. The lymphocyte proliferative responses to PHA were significantly lower than those of controls (87 individuals, from either endemic or nonendemic zones) in LCL, and particularly MCL. Con A responses were, however, effectively normal in these patients. Both in vivo and in vitro cellular immune responses to leishmanial antigens were significantly greater in MCL and LCL patients than in the controls, the intensity of the reactions being by far the greatest in MCL. DCL patients demonstrated a complete absence of specific immune responsiveness both in vivo and in vitro. The significance of these results in the mechanisms leading to the resolution of the infection or production of pathologic lesions is discussed.