Large-Scale Engineering and Cryopreservation of hiPSC-Derived Nephron Sheets

Background The generation of human induced pluripotent stem cells (hiPSCs) has opened a world of opportunities for stem cell-based therapies in regenerative medicine. Currently, several human kidney organoid protocols are available that generate organoids containing kidney structures. However, these kidney organoids are relatively small ranging up to 0.13 cm2 and therefore contain a small number of nephrons compared to an adult kidney, thus defying the exploration of future use for therapy. Method We have developed a scalable, easily accessible, and reproducible to increase the size of the organoid up to a nephron sheet of 2.5 cm2 up to a maximum of 12.6 cm2 containing a magnitude of nephrons. Results Confocal microscopy showed that the subunits of the nephrons remain evenly distributed throughout the entire sheet and that these tissue sheets can attain ~30,000-40,000 glomerular structures. Upon transplantation in immunodeficient mice, such nephron sheets became vascularized and matured. They also show reuptake of injected low-molecular mass dextran molecules in the tubular structures, indicative of glomerular filtration. Furthermore, we developed a protocol for the cryopreservation of intermediate mesoderm cells during the differentiation and demonstrate that these cells can be successfully thawed and recovered to create such tissue sheets. Conclusion The scalability of the procedures, and the ability to cryopreserve the cells during differentiation are important steps forward in the translation of these differentiation protocols to future clinical applications such as transplantable auxiliary kidney tissue.

ATXN10 Is Required for Embryonic Heart Development and Maintenance of Epithelial Cell Phenotypes in the Adult Kidney and Pancreas

Atxn10 is a gene known for its role in cytokinesis and is associated with spinocerebellar ataxia (SCA10), a slowly progressing cerebellar syndrome caused by an intragenic pentanucleotide repeat expansion. Atxn10 is also implicated in the ciliopathy syndromes nephronophthisis (NPHP) and Joubert syndrome (JBTS), which are caused by the disruption of cilia function leading to nephron loss, impaired renal function, and cerebellar hypoplasia. How Atxn10 disruption contributes to these disorders remains unknown. Here, we generated Atxn10 congenital and conditional mutant mouse models. Our data indicate that while ATXN10 protein can be detected around the base of the cilium as well as in the cytosol, its loss does not cause overt changes in cilia formation or morphology. Congenital loss of Atxn10 results in embryonic lethality around E10.5 associated with pericardial effusion and loss of trabeculation. Similarly, tissue-specific loss of ATXN10 in the developing endothelium (Tie2-Cre) and myocardium (cTnT-Cre) also results in embryonic lethality with severe cardiac malformations occurring in the latter. Using an inducible Cagg-CreER to disrupt ATXN10 systemically at postnatal stages, we show that ATXN10 is also required for survival in adult mice. Loss of ATXN10 results in severe pancreatic and renal abnormalities leading to lethality within a few weeks post ATXN10 deletion in adult mice. Evaluation of these phenotypes further identified rapid epithelial-to-mesenchymal transition (EMT) in these tissues. In the pancreas, the phenotype includes signs of both acinar to ductal metaplasia and EMT with aberrant cilia formation and severe defects in glucose homeostasis related to pancreatic insufficiency or defects in feeding or nutrient intake. Collectively, this study identifies ATXN10 as an essential protein for survival.

Smad4 controls proliferation of interstitial cells in the neonatal kidney

Expansion of interstitial cells in the adult kidney is a hallmark of chronic disease, whereas their proliferation during fetal development is necessary for organ formation. An intriguing difference between adult and neonatal kidneys is that the neonatal kidney has the capacity to control interstitial cell proliferation when the target number has been reached. In this study, we define the consequences of inactivating the TGFβ/Smad response in the interstitial cell lineage. We find that pathway inactivation through loss of Smad4 leads to over-proliferation of interstitial cells regionally in the kidney medulla. Analysis of markers for BMP and TGFβ pathway activation reveals that loss of Smad4 primarily reduces TGFβ signaling in the interstitium. While TGFβ signaling is reduced in these cells, marker analysis shows that Wnt/β-catenin signaling is increased. Our analysis supports a model in which Wnt/β-catenin mediated proliferation is attenuated by TGFβ/Smad to ensure that proliferation ceases when the target number of interstitial cells has been reached in the neonatal medulla.

Antithrombotic Management in Adult Kidney Transplantation – A European survey study

In kidney transplantation (KTx), renal graft thrombosis (RGT) is one of the main reasons for early graft loss. Although evidence-based guidance on prevention of RGT is lacking, thromboprophylaxis is widely used. The aim of this survey was to obtain a European view of the different thromboprophylactic strategies applied in KTx. An online 22-question survey, addressed to KTx professionals, was distributed by e-mail and via platforms of the European Society for Organ Transplantation. Seventy-five responses (21 countries, 51 centers) were received: 75% had over 10 years’ clinical experience, 64% were surgeons, 29% nephrologists and 4% urologists. A written antithrombotic management protocol was available in 75% of centers. In 8 (16%) of centers respondents contradicted each other regarding the availability of a written protocol. Thromboprophylaxis is preferred by 78% of respondents, independent of existing antithrombotic management protocols. Ninety-two percent of respondents indicated that an anticipated bleeding risk is the main reason to discontinue chronic antithrombotic therapy preoperatively. Intraoperatively, 32% of respondents administer unfractionated heparin (400 – 10.000 international units with a median of 5000) in selected cases. Despite an overall preference for perioperative thromboprophylaxis in KTx, there is a high variation within Europe regarding type, timing and dosage, most likely due to the paucity of high-quality studies. Further research is warranted in order to develop better guidelines.

Clinical outcomes and temporal trends of immunological and non-immunological rare diseases in adult kidney transplant

Background Rare diseases (RDs) encompass many difficult-to-treat conditions with different characteristics often associated with end-stage renal disease (ESRD). However, data about transplant outcomes in adult patients are still lacking and limited to case reports/case series without differentiation between immunological/non-immunological RDs. Methods Retrospective analysis among all adult kidney transplanted patients (KTs) with RDs (RDsKT group) performed in our high-volume transplantation center between 2005 and 2016. RDs were classified according to the Orphanet code system differentiating between immunological and non-immunological diseases, also comparing clinical outcomes and temporal trends to a control population without RDs (nRDsKT). Results Among 1381 KTs, 350 patients (25.3%) were affected by RDs (RDsKTs). During a f/up > 5 years [median 7.9 years (4.8–11.1)], kidney function and graft/patient survival did not differ from nRDsKTs. Considering all post-transplant complications, RDsKTs (including, by definition, patients with primary glomerulopathy except on IgA nephropathy) have more recurrent and de-novo glomerulonephritis (14.6% vs. 9.6% in nRDsKTs; p = 0.05), similar rates of de-novo cancers, post-transplant diabetes, dysmetabolism, hematologic disorders, urologic/vascular problems, and lower infectious episodes than nRDsKTs (63.7% vs 72.7%; p = 0.013). Additional stratification for immunological and non-immunological RDsKTs or transplantation periods (before/after 2010) showed no differences or temporal trends between groups. Conclusions Kidney transplant centers are deeply involved in RDs management. Despite their high-complex profile, both immunological and non-immunological RDsKTs experienced favorable patients’ and graft survival.

A national cohort study on hemodialysis arteriovenous fistulas after kidney transplantation - long-term patency, use and complications

Objective To describe the long-term hemodialysis arteriovenous fistula (AVF) patency, incidence of AVF use, incidence and nature of AVF complications and surgery in patients after kidney transplantation. Patients and methods We retrospectively analysed the AVF outcome and complications in all adult kidney allograft recipients transplanted between January 1st, 2000 and December 31, 2015 with a functional AVF at the time of transplantation. Follow-up was until December 31, 2019. Results We included 626 patients. Median AVF follow-up was 4.9 years. One month after kidney transplantation estimated AVF patency rate was 90%, at 1 year it was 82%, at 3 years it was 70% and at 5 years it was 61%; median estimated AVF patency was 7.9 years. The main cause of AVF failure was spontaneous thrombosis occurring in 76% of AVF failure cases, whereas 24% of AVFs were ligated or extirpated. In a Cox multivariate model female sex and grafts were independently associated with more frequent AVF thrombosis. AVF was used in about one third of our patients. AVF-related complications occurred in 29% of patients and included: growing aneurysms, complicated thrombosis, high-flow AVF, signs of distal hypoperfusion, venous hypertension, trauma of the AVF arm, or pain in the AVF/arm. Conclusions AVFs remain functional after kidney transplantation in the majority of patients and are often re-used after graft failure. AVF-related complications are common and require proper care.

SLCO1B3 polymorphisms and clinical outcomes in kidney transplant recipients receiving mycophenolate

Aim: Determine the influence of SLCO1B3 polymorphisms on outcomes in kidney transplant recipients. Materials & methods: We retrospectively evaluated 181 adult kidney transplant recipients receiving mycophenolate. Outcomes included treated biopsy-proven acute rejection (tBPAR), de novo donor specific antibody (dnDSA) formation, graft survival, patient survival and mycophenolate-related adverse effects among SLCO1B3 genotypes. Results: The presence of SLCO1B3 variants was not associated with increased risk of tBPAR (HR: 1.45, 95% CI: 0.76–2.74), dnDSA (HR: 0.46, 95% CI: 0.16–1.36) or composite of tBPAR or dnDSA (HR: 1.14, 95% CI: 0.64–2.03). Graft and patient survival were reduced among variant carriers; however, inconsistent findings with the primary analysis suggest these associations were not due to genotype. Adverse effects were similar between groups. Conclusion: Presence of SLCO1B3 polymorphisms were not predictive of rejection or dnDSA in kidney transplant recipients.

Transplant Clinician Opinions on Use of Race in the Estimation of Glomerular Filtration Rate

Background and objectivesCurrent race-based eGFR calculators assign a higher eGFR value to Black patients, which could affect the care of kidney transplant candidates and potential living donors.Design, setting, participants, & measurementsWe conducted a survey of staff at adult kidney transplant centers in the United States (December 17, 2020 to February 28, 2021) to assess opinions on use of race-based eGFR equations for waitlisting and living donor candidate evaluation, availability of serum cystatin C testing and measured GFR, and related practices.ResultsRespondents represented 57% (124 of 218) of adult kidney transplant programs, and the responding centers conducted 70% of recent kidney transplant volume. Most (93%) programs use serum creatinine–based eGFR for listing candidates. However, only 6% of respondents felt that current race-based eGFR calculators are appropriate, with desire for change grounded in concerns for promotion of health care disparities by current equations and inaccuracies in reporting of race. Most respondents (70%) believed that elimination of race would allow more preemptive waitlisting for Black patients, but a majority (79%) also raised concerns that such an approach could incur harms. More than one third of the responding programs lacked or were unsure of availability of testing for cystatin C or measured GFR. At this time, 40% of represented centers did not plan to remove race from eGFR calculators, 46% were planning to remove, and 15% had already done so. There was substantial variability in eGFR reporting and listing of multiracial patients with some Black ancestry. There was no difference in GFR acceptance thresholds for Black versus non-Black living donors.ConclusionsThis national survey highlights a broad consensus that extant approaches to GFR estimation are unsatisfactory, but it also identified a range of current opinions.