Adaptable haemodynamic endothelial cells for organogenesis and tumorigenesis.

Endothelial cells adopt tissue-specific characteristics to instruct organ development and regeneration1,2. This adaptability is lost in cultured adult endothelial cells, which do not vascularize tissues in an organotypic manner. Here, we show that transient reactivation of the embryonic-restricted ETS variant transcription factor 2 (ETV2)3 in mature human endothelial cells cultured in a serum-free three-dimensional matrix composed of a mixture of laminin, entactin and type-IV collagen (LEC matrix) 'resets' these endothelial cells to adaptable, vasculogenic cells, which form perfusable and plastic vascular plexi. Through chromatin remodelling, ETV2 induces tubulogenic pathways, including the activation of RAP1, which promotes the formation of durable lumens4,5. In three-dimensional matrices-which do not have the constraints of bioprinted scaffolds-the 'reset' vascular endothelial cells (R-VECs) self-assemble into stable, multilayered and branching vascular networks within scalable microfluidic chambers, which are capable of transporting human blood. In vivo, R-VECs implanted subcutaneously in mice self-organize into durable pericyte-coated vessels that functionally anastomose to the host circulation and exhibit long-lasting patterning, with no evidence of malformations or angiomas. R-VECs directly interact with cells within three-dimensional co-cultured organoids, removing the need for the restrictive synthetic semipermeable membranes that are required for organ-on-chip systems, therefore providing a physiological platform for vascularization, which we call 'Organ-On-VascularNet'. R-VECs enable perfusion of glucose-responsive insulin-secreting human pancreatic islets, vascularize decellularized rat intestines and arborize healthy or cancerous human colon organoids. Using single-cell RNA sequencing and epigenetic profiling, we demonstrate that R-VECs establish an adaptive vascular niche that differentially adjusts and conforms to organoids and tumoroids in a tissue-specific manner. Our Organ-On-VascularNet model will permit metabolic, immunological and physiochemical studies and screens to decipher the crosstalk between organotypic endothelial cells and parenchymal cells for identification of determinants of endothelial cell heterogeneity, and could lead to advances in therapeutic organ repair and tumour targeting.

Engineering transplantable jejunal mucosal grafts using patient-derived organoids from children with intestinal failure.

Intestinal failure, following extensive anatomical or functional loss of small intestine, has debilitating long-term consequences for children1. The priority of patient care is to increase the length of functional intestine, particularly the jejunum, to promote nutritional independence2. Here we construct autologous jejunal mucosal grafts using biomaterials from pediatric patients and show that patient-derived organoids can be expanded efficiently in vitro. In parallel, we generate decellularized human intestinal matrix with intact nanotopography, which forms biological scaffolds. Proteomic and Raman spectroscopy analyses reveal highly analogous biochemical profiles of human small intestine and colon scaffolds, indicating that they can be used interchangeably as platforms for intestinal engineering. Indeed, seeding of jejunal organoids onto either type of scaffold reliably reconstructs grafts that exhibit several aspects of physiological jejunal function and that survive to form luminal structures after transplantation into the kidney capsule or subcutaneous pockets of mice for up to 2 weeks. Our findings provide proof-of-concept data for engineering patient-specific jejunal grafts for children with intestinal failure, ultimately aiding in the restoration of nutritional autonomy.

In Utero Transplantation of Expanded Autologous Amniotic Fluid Stem Cells Results in Long-Term Hematopoietic Engraftment.

In utero transplantation (IUT) of hematopoietic stem cells (HSCs) has been proposed as a strategy for the prenatal treatment of congenital hematological diseases. However, levels of long-term hematopoietic engraftment achieved in experimental IUT to date are subtherapeutic, likely due to host fetal HSCs outcompeting their bone marrow (BM)-derived donor equivalents for space in the hematopoietic compartment. In the present study, we demonstrate that amniotic fluid stem cells (AFSCs; c-Kit+/Lin-) have hematopoietic characteristics and, thanks to their fetal origin, favorable proliferation kinetics in vitro and in vivo, which are maintained when the cells are expanded. IUT of autologous/congenic freshly isolated or cultured AFSCs resulted in stable multilineage hematopoietic engraftment, far higher to that achieved with BM-HSCs. Intravascular IUT of allogenic AFSCs was not successful as recently reported after intraperitoneal IUT. Herein, we demonstrated that this likely due to a failure of timely homing of donor cells to the host fetal thymus resulted in lack of tolerance induction and rejection. This study reveals that intravascular IUT leads to a remarkable hematopoietic engraftment of AFSCs in the setting of autologous/congenic IUT, and confirms the requirement for induction of central tolerance for allogenic IUT to be successful. Autologous, gene-engineered, and in vitro expanded AFSCs could be used as a stem cell/gene therapy platform for the in utero treatment of inherited disorders of hematopoiesis. Stem Cells 2019;37:1176-1188.

Whole Organ Tissue Vascularization: Engineering the Tree to Develop the Fruits.

Tissue engineering aims to regenerate and recapitulate a tissue or organ that has lost its function. So far successful clinical translation has been limited to hollow organs in which rudimental vascularization can be achieved by inserting the graft into flaps of the omentum or muscle fascia. This technique used to stimulate vascularization of the graft takes advantage of angiogenesis from existing vascular networks. Vascularization of the engineered graft is a fundamental requirement in the process of engineering more complex organs, as it is crucial for the efficient delivery of nutrients and oxygen following in-vivo implantation. To achieve vascularization of the organ many different techniques have been investigated and exploited. The most promising results have been obtained by seeding endothelial cells directly into decellularized scaffolds, taking advantage of the channels remaining from the pre-existing vascular network. Currently, the main hurdle we need to overcome is achieving a fully functional vascular endothelium, stable over a long time period of time, which is engineered using a cell source that is clinically suitable and can generate, in vitro, a yield of cells suitable for the engineering of human sized organs. This review will give an overview of the approaches that have recently been investigated to address the issue of vascularization in the field of tissue engineering of whole organs, and will highlight the current caveats and hurdles that should be addressed in the future.