Heart transplantation improves the prognosis and quality of life in carefully selected patients with advanced heart failure. Outcomes depend on a multitude of donor, operative and recipient factors. There is a high opportunity cost because the number of suitable donor hearts is limited. Many countries regulate their heart transplant programmes, but differences in regulatory systems are not well described. We identified 39 nations that performed >20 transplants annually between 2015-2024. We invited transplant professionals in each nation to complete a survey on regulation in their country. Professionals from 32 nations responded, of which 28 had mandatory outcome reporting to a national registry. Outcome measures included survival (n=26), primary graft dysfunction (n=15) and quality of life (n=5). Only six countries had a pre-specified definition of unacceptable outcomes after heart transplantation. Future studies might investigate the effectiveness of regulatory strategies in heart transplantation.

Collagen IV, encoded by genes COL4A1/COL4A2, is a major component of the basement membrane, a specialised extracellular matrix (ECM) structure. Mutations in these genes cause a genetic form of cerebral small vessel disease (cSVD), a leading cause of stroke and dementia. White matter abnormalities are a hallmark of cSVD and are closely linked to cognitive decline and dementia. While white matter defects occur in patients with COL4A1/2 mutations, they remain understudied and their mechanisms are unclear. To address these knowledge gaps, we combined magnetic resonance diffusion tensor imaging, pathology, ultrastructural investigations, behaviour and proteomic analysis of white matter in an established mouse model of cSVD due to a Col4a1 mutation (Col4a1+/Svc). The studies revealed that Col4a1+/Svc mice have reduced myelinating oligodendrocyte pools, axonal myelination defects, and altered white matter structural integrity as well as cognitive impairments. Proteomic analysis of isolated white matter from Col4a1+/Svc mice identified extensive changes to ECM and basement membrane composition. Furthermore, this provided evidence for altered endoplasmic reticulum (ER) biology including ER stress. To determine if white matter defects can be attenuated by targeting protein folding in the ER by promoting collagen IV secretion, we treated mice with the FDA-approved chemical chaperone 4-phenylbutyric acid. This revealed increased myelinating oligodendrocytes and improved axon-glial integrity in Col4a1+/Svc mice. These data provide novel insight into the pathomolecular mechanisms of collagen IV mutations in white matter abnormalities in cSVD and identify a modifiable pathway as a putative therapeutic target.

Abstract Cerebral small vessel disease (cSVD) is a major contributor to stroke and cognitive decline, ultimately leading to vascular dementia (VaD). Genetic factors play a key role in disease susceptibility and progression, and variants in COL4A1 cause one of the most common forms of genetic cSVD. COL4A1 encodes the α1 chain of collagen type IV which is the major structural component of the basement membrane, a specialised extracellular matrix (ECM) structure, in the vasculature. In addition to this vascular basement membrane (vBM), in the central nervous system (CNS), the neurovascular unit (NVU) also has a unique parenchymal basement membrane (pBM) that is largely produced by astrocytes and forms a critical interface anchoring astrocyte end-feet to vascular cells. Together, these BMs play essential roles in regulating blood-brain barrier (BBB) function. However, the role of the pBM in cSVD has been relatively less investigated compared to the vBM. The lack of relevant human disease models that faithfully recapitulate the pBM, makes it difficult to dissect pBM-related cell-cell and cell-matrix interactions specific to cSVD, hindering the identification of effective therapeutic targets. In this study, we hypothesised that astrocyte-mediated ECM remodelling contributes to BBB dysfunction in COL4A1 -associated cSVD. To investigate this, human induced pluripotent stem cells (iPSCs) derived from a patient carrying the COL4A1 G 755 R variant and its isogenic control line were differentiated into astrocytes and brain microvascular endothelial cells (BMECs). Comparing to isogenic controls, the COL4A1 G 755 R astrocytes significantly reduced the expression of ECM-related genes and increased glutamate uptake. ECM preparations from COL4A1 G 755 R astrocytes significantly damaged the tight junction (TJ) structure formed by control iPSC-BMECs and failed to rescue the TJ integrity in COL4A1 G 755 R BMECs. The secretome from COL4A1 G 755 R astrocytes exacerbated the ECM defects in COL4A1 G 755 R BMECs. Most importantly, COL4A1 G 755 R astrocytes exhibited reduced expression of HTRA1, a serine protease that regulates both ECM turnover and homeostasis, and increased TGF-β signalling. Functional rescue by recombinant human HTRA1 protein rescues TJ defects in COL4A1 G 755 R BMECs, and normalized TGF-β signalling and glutamate uptake in COL4A1 G 755 R astrocytes. Together, these findings define a previously unrecognised astrocyte-driven pBM mechanism in COL4A1 -associated cSVD and highlight HTRA1 in ECM remodelling as a therapeutic target for cSVD.

BACKGROUND:Donation after the circulatory determination of death (DCD) heart transplantation (HT) is becoming more widely adopted across the United States (US) and Europe. OBJECTIVE:This study compared donor and recipient demographics, intraoperative parameters, and outcomes between DCD HT centers in Europe and the US that contributed to the Outcomes after DCD Cardiac Transplantation Database. METHODS:This was a retrospective observational study across 22 HT centers in Belgium, Spain, the United Kingdom (UK), and the US. All patients undergoing DCD HT at participating centers, from the start of each center's DCD program through 01/01/2023, were included with censor date 01/01/2024. The primary outcome was 1-year survival. Secondary outcomes included severe primary graft dysfunction and incidence of acute cellular rejection. RESULTS:Data from 223 patients in Europe and 281 in the US were analyzed. DCD donors in Europe were significantly older (37 years vs 28 years; p < 0.001). Recipients in Europe had inferior 1-year survival (86.6% vs 91.8%; p = 0.043), but 1-month and 3-years survival were similar. 1-year survival in the direct procurement and preservation (DPP) cohort was significantly higher in the US group (91.2% vs 82.6%; p = 0.02). In the thoraco-abdominal normothermic regional perfusion (taNRP) cohort 1-year survival was similar between Europe and the US. Recipients in Europe had higher use of mechanical circulatory assist post-transplant (17.9% vs 11%; p = 0.03). CONCLUSION:This study further confirms the safety and efficacy of DCD HT across centers in the US and Europe, despite important differences in donor and recipient demographics and clinical outcomes. Continued collection of international data may identify opportunities to improve outcomes.

Abstract Single cell genomics has enabled analysis of human prenatal development at unprecedented resolution. However, most studies have relied on dissociated tissues during restricted windows of development, limiting insights into how spatially distributed networks of cells, and multicellular niches emerge and adapt to distinct organ microenvironments in situ. Moreover, existing human developmental atlases have not yet been harmonised, and we thus lack a comprehensive catalogue of known cell types in the developing human body. Here, we introduce the Human Developmental Cell Atlas (HDCA), a unified structural, cellular and molecular resource for prenatal human development. The HDCA integrates published and unpublished single cell/nucleus RNAseq atlases across prenatal organs, and includes a newly generated, spatially resolved, multimodal cell atlas of intact human embryos. Spanning 4-22 post conceptional weeks, capturing embryonic and early to mid fetal stages, the HDCA contains ∼4.6 million cells/nuclei which resolve into ∼450 cell types, explorable with a bespoke web portal. For a global overview of the human embryo’s multicellular communities, we applied unsupervised deep learning to our intact human embryo spatial data, charting 114 tissue niches that are structural and signalling hubs for the cellular interactions of the embryo. Guided by these niches, we profiled cellular networks over space and time, not examinable using single-organ atlases. In so doing, we revealed tissue-specific fibroblast patterning from previously undescribed mesenchyme progenitors, early diversification of organ-specific blood capillaries and lymphatic vasculature, emergence of neural crest cell fates, the formation of placode-and neural crest-derived peripheral sensory neurons, and how tissue niches guide peripheral neuron maturation and axonal migration. The HDCA thus serves as a comprehensive step towards a comprehensive understanding of human prenatal development, and a template towards unravelling the biology of congenital disorders.

Although matrix stiffness is an important determinant of cell behavior, experimentally isolating mechanical cues from the surface chemistry is challenging. Here, intact collagen (Col I) or a constant density of collagen-derived cell-adhesive triple-helical peptides (GFOGER or GLOGEN) was deposited on surfaces with physiologically relevant stiffnesses. Equivalent integrin ligation on each surface decoupled stiffness from collagen-receptor ligation. The cell response was highly cell type-specific. Human dermal fibroblast (HDF) adhesion was largely insensitive to matrix stiffness, while cytoskeletal organization was promoted on stiffer substrates, equivalently for GFOGER and GLOGEN. Human umbilical vein endothelial cells (HUVECs) and human dermal microvascular endothelial cells (HDMECs) adhered and formed PECAM-1-containing cell-cell junctions preferentially on lower-modulus substrates. For HUVECs, this was independent of the coating peptide; however, HDMECs possessed greater PECAM-1-containing cell junctions on GFOGER over GLOGEN. These results offer new insights into the effects of stiffness vs integrin ligation on the cellular response to materials.

Tissue engineering offers great promise for regenerating damaged organs including the heart. Although direct attachment of grafts at the target site is possible during surgery, minimally invasive delivery and suture-free approaches could reduce patient discomfort and allow repeat administration. However, for the therapy to be effective it is essential that the graft is successfully delivered to the epicardium and retained on target.Here, methacrylated alginate-based shape-memory patches labelled with 111InCl3 and loaded with luciferase expressing stem-cells were either injected towards the epicardium under ultrasound guidance or surgically grafted onto mouse hearts. Patch and cell location were serially tracked using SPECT/CT and bioluminescence imaging.Radiolabelling of shape-memory patches permitted serial tracking of graft location for seven days in-vivo, and revealed that injected patches rarely attached on-target whilst surgically implanted patches rapidly detached from the epicardium. In-vivo imaging was then used to evaluate modifications to biomaterial formulation and patch attachment strategies. This ultimately resulted in effective, suture-free surgical attachment of chitosan-coated patches loaded with luciferase-expressing human embryonic stem cell-derived epicardial cells onto the heart, illustrating a model therapeutic.This translational imaging approach facilitates iterative optimization of a novel biomaterial and could have wide-reaching applications for enhancing a range of regenerative therapies.

Biofabricated scaffolds facilitate bona fide cellular interactions, cell type specification, and the formation of three-dimensional tissue architecture from human pluripotent stem cells (hPSCs). However, xenogenic biomaterials are poorly defined, and synthetic biomaterials remain underdeveloped and understudied, hindering regulatory approval for clinical use and preventing the translation of lab-grown therapies. Here, we describe a protein screen-based hydrogel system biofabricated from physiologically relevant human components. We show that ‘Alphagel’, a base hydrogel comprising human embryonic matrices, supports the trilineage differentiation of hPSCs into neural, cardiac, and liver tissue. Alphagel is also shown to be biocompatible and biodegradable in vivo . Further, upon adding select proteins from maturing human foetal liver to Alphagel, we show that the resulting hydrogel (termed ‘Hepatogel’) enhances the differentiation of hPSC-derived hepatocytes (H-iHeps) compared with Matrigel. Importantly, when injected into mice livers, Hepatogel significantly improves the retention of H-iHeps compared to standard aqueous cell injections. Altogether, our results provide proof of concept that customisable, organ-specific hydrogel systems are a valuable tool for developing clinically translatable therapies in regenerative medicine and tissue engineering.

Ex situ heart perfusion (ESHP) was first developed in the 19th century by the German physician Oskar Langendorff. In recent years, ESHP has been critical to the development of donation after circulatory determination of death (DCD) programmes around the globe. ESHP has potential uses that extend far beyond transplantation. Here, we argue that ESHP, and more broadly all ex situ organ perfusion, should be utilised to perform first-in-human studies using turned down donor hearts and explanted recipient hearts from transplantation. This model would enable significantly earlier testing of novel therapeutics in human hearts, with minimal risk to patients. Widespread adoption of this model could streamline drug discovery pipelines, by enabling inefficacious therapeutics to be abandoned earlier in the drug development process. This model is particularly attractive given the high proportion of medicines that fail in stage II and stage III clinical trials due to a lack of efficacy. Development of this model will be dependent on prolonging ex situ perfusion times. Collaboration between industry, academics and clinicians will be needed to ensure successful widespread adoption of this model.

Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional receptor implicated in atherosclerosis, arterial dissection, and vascular disease, with roles in lipid handling, extracellular matrix turnover, growth factor signaling, and vascular homeostasis. Although tissue-specific roles of LRP1 have been described, whether cardiovascular LRP1 expression varies by age, sex, and vascular bed remains unclear. Here, we analyzed publicly available human transcriptomic datasets to define the cardiovascular expression landscape of LRP1 across tissues, demographic strata, and cell populations. Genotype-Tissue Expression-derived data showed that vascular LRP1 expression differed significantly between the aorta, coronary artery, and tibial artery, with the highest expression in the aorta, where levels were 30% higher than coronary artery and 50% higher than tibial artery. In the heart, atrial LRP1 expression was approximately twofold higher than in the left ventricle. Among these five cardiovascular tissues, only the aorta showed sexual dimorphism, with 7.4% higher LRP1 expression in females than males. Tibial artery was the only tissue in which LRP1 expression changed significantly with age, doubling over female adulthood (adjusted P = 0.0019) and increasing 40% in male adulthood (adjusted P = 0.0284). Single-cell analyses of human heart and arterial datasets showed prominent LRP1 expression in adipocytes, fibroblasts, macrophages, and smooth muscle cells, indicating that tissue-level patterns reflect nonuniform expression across vascular and stromal cell populations. Together, these data indicate that cardiovascular LRP1 expression is not static, but can vary by anatomical and demographic context. This work establishes a baseline for interpreting LRP1-related mechanisms in vascular and cardiac disease.NEW & NOTEWORTHY Recent work has highlighted tissue-specific functional roles for Low-density lipoprotein receptor-related protein 1 (LRP1), but its cardiovascular expression landscape has not been systematically defined. Here, we show that human cardiovascular LRP1 expression varies between vascular beds, with sex and age selectively influencing expression, underscoring the importance of anatomical and demographic context in studies of LRP1 biology.

The impact of HLA mismatch and induction therapy in simultaneous pancreas-kidney transplantation on outcomes remains incompletely defined. We conducted a retrospective cohort study of 1705 SPK recipients transplanted in the UK between 2007 and 2019. Using national transplant registry data, we analysed the impact of locus-specific HLA mismatch and induction therapy (Alemtuzumab vs. Basiliximab) on pancreas graft survival primarily. Kidney graft and patient survival were also analysed as secondary outcomes. Multivariable Cox proportional hazards models were adjusted for donor, recipient, and transplant variables. Pancreas graft survival at 1- and 10-year post-transplant was estimated to be 88.6% and 72.7%, respectively. Kidney graft and patient survival at 10 years were 76.7% and 75.3%. In adjusted analyses, donor age, cold ischaemic time, and HLA-DQ mismatch were significantly associated with pancreas graft loss. No significant survival difference was seen between Alemtuzumab and Basiliximab induction therapy. Induction therapy and HLA-mismatch status were not associated with pancreas graft outcome in this large registry study.

Induced pluripotent stem cell (iPSC) derived aortic vascular smooth muscle cells (VSMC) recapitulate key disease features leading to wall failure. We hypothesise iPSC models of thoracic aortic diseases (TAD) can determine causality of genetic variants from the 100,000 Genomes Project. Variants in LOX (122070160 T>TA), MYLK (123401069 ACT>A) and SMAD4 (51076665 C>T) were selected, and genetic editing used to create mutant iPSC lines. The mutant lines were differentiated into VSMCs, analysed with bulk mRNAseq and findings validated in vitro. Mutant VSMCs demonstrated TAD transcriptomic signatures, with common & distinct pathways mediating disease pathogenesis in different variants. EdU incorporation in LOX and SMAD4 mutants confirmed enrichment of pro-proliferative GO terms. An active and basal contraction defect in MYLK and LOX was demonstrated in both 2D and 3D models. LOX mutant showed elevated proteo-/glycosaminoglycans and soluble collagen verifying ECM remodelling GO terms. Increased mitochondrial basal respiration confirmed metabolic defect in SMAD4 and MYLK. Perturbed calcium signalling in MYLK, or an inflammatory phenotype strongly associated with SMAD4 were highlighted. Differential expression of osteochondrogenic/fibroblastic markers in MYLK, and senescent/osteoblast markers in LOX were suggestive of VSMC phenotypic switching. Several targetable signalling pathways were identified. Despite distinct initiators, there is a convergence on abnormal ECM turnover and contractility which in combination are likely the driving factor behind reduced aortic wall integrity. iPSC TAD models offer a precision medicine tool through determining causality of genetic variants, identifying disease mechanisms and providing a blueprint for therapeutic targeting.

The fast-track pancreas scheme (FTS) was brought in to improve pancreas utilisation. It created a scheme for the allocation of pancreas grafts not yet allocated at the time retrieval commenced. There are no previous reports of pancreas allocation using such a scheme. This study compares the outcomes of pancreas grafts allocated via the FTS versus those allocated before retrieval. Data were collected on 1,297 pancreas donors offered through the FTS between 1/12/2010-31/03/2023from the UK Transplant Registry. Donor and recipient characteristics were compared, and graft and patient survival analyses conducted using Kaplan Meier plots. Pancreases offered through the FTS were more likely to be from older, heavier, taller, male, and donation after circulatory death (DCD) donors, with all differences statistically significant (p<0.0001). Recipients of FTS grafts tended to be older (p=0.0074). 166 simultaneous pancreas and kidney transplants were performed from the organs offered. No significant differences were found in graft survival at 1 year (FTS 92.4%, no-FTS 87.6%, p=0.104), 3 years (FTS 83.6%, no-FTS 82.9%, p=0.460), and 5 years (FTS 80.9%, no-FTS 79.4%, p=0.417). Patient survival was comparable between groups at 1 year (FTS 98.3%, no-FTS 95.6%, p=0.185), 3 years (FTS 94.3%, no-FTS 91.5%, p=0.287), and 5 years (FTS 87.7%, no FTS 86.6%, p=0.519). Graft and patient survival rates are similar between those receiving fast-tracked pancreases and those receiving pre-allocated pancreases. This study confirms that despite the perception FTS grafts may be more high risk, pancreas transplant outcomes are comparable with no impact on overall outcomes.

Type 1 diabetes mellitus (T1D) is a chronic disease characterized by the absence of circulating insulin and c-peptide. Exogenous insulin therapy, which is the mainstay of treatment of T1D cannot prevent the microvascular complications or severe hypoglycemia. Beta-cell replacement therapy in the form of whole organ pancreas transplantation or islet cell transplantation helps to maintain endogenous secretion of insulin and other hormones secreted from islet of Langerhans. Over the past 20 years, islet cell transplantation has proven its long-term efficacy in the management of labile diabetes and preventing morbidity. Allogenic islet cell transplantation is a safe therapy for type 1 diabetics with renal failure and nonuremic diabetics with hypoglycemic unawareness. However, access to transplantation is limited by the availability of deceased donor organs and the risks associated with long-term immunosuppression. Cutting edge research in the field of xenotransplantation and stem cells will result in a new source of beta cells in the future. This could potentially eliminate the need for long-term immunosuppression as well. The articles reviewed were identified using PubMed search of relevant key words and Medical Subject Heading terms and after excluding the ones that are beyond the scope of this review.

BACKGROUND:As donation after circulatory determination of death (DCD) heart transplantation (HT) becomes more widely adopted, there is a need to establish the most clinically effective method of organ procurement. OBJECTIVES:This international, multicenter study compares outcomes of DCD HT across Europe and the United States between recipients whose donor hearts were retrieved using thoraco-abdominal normothermic regional perfusion (taNRP) with those whose hearts were recovered using direct procurement and perfusion (DPP). METHODS:This was a retrospective observational study across 22 heart transplant centers in Belgium, Spain, the United Kingdom, and the United States. This study included all patients undergoing DCD HT at participating centers, from the start of each center's DCD program through January 1, 2023. DCD HT with recovery using either taNRP or DPP were compared with one another. Posttransplant outcomes included: 1) survival at 1 year; 2) incidence of severe primary graft dysfunction (PGD); and 3) episodes of treated, biopsy-proven acute-cellular rejection (ACR) in the first year following transplantation. RESULTS:A total of 504 DCD HTs took place in the study period. Survival at 1 year was similar for taNRP and DPP recipients (91% vs 88%; P = 0.100). taNRP recipients had a lower rate of severe PGD (7.6% vs 19.2%; P < 0.001) and fewer episodes of biopsy-proven, ACR requiring treatment in the first year post-transplantation (13% vs 25%; P < 0.001). CONCLUSIONS:In an international study of DCD HT, recipients of hearts retrieved by taNRP technique had lower rates of severe PGD and fewer episodes of biopsy-proven ACR in the first year when compared with those retrieved by using DPP. These results should be further investigated with randomized control trials.

Background Declined donor organs and explanted recipient organs may hold considerable value for biomedical research, particularly in advancing knowledge of disease mechanisms and supporting drug development. However, public perceptions of such use, and preferences for how consent should be obtained, remain underexplored.Methods Four workshops were held across the UK to examine the views of organ donor families and transplant recipients regarding the use of human organs in research, with a focus on myocardial regeneration. Each workshop included three brief presentations on transplantation and cardiac regeneration, followed by facilitated small-group discussions. Observational notes were taken to capture participants’ perspectives on the use of organs unsuitable for transplantation. A follow-up survey generated both quantitative and qualitative data, the latter analysed using thematic analysis.Results Participants expressed strong support for the use of declined donor and explanted recipient organs in research. Transplant recipients frequently cited a desire to give back to the National Health Service (NHS), while donor families viewed research use as a meaningful way to honour their loved ones when transplantation was not possible.Conclusion This exploratory study highlights widespread support for using non-transplantable organs in research among individuals with personal experience of transplantation. The findings suggest a need for further research into how best to support and inform potential donors and families. Participants emphasised the importance of sensitive communication, clear consent processes and transparency regarding the use of donated organs.